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Ecology and conservation of avian insectivores of the rainforest understory: A pantropical perspective

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... The fragmentation of forest habitats adversely impacts forest-dependent understory species, as well as forest interior species (Askins et al., 1990;Newmark, 1991;Stouffer et al., 2009). This impact is particularly notable on understory insectivorous birds (Powell, Cordeiro, & Stratford, 2015;Powell, Wolfe, et al., 2015;Stratford & Stouffer, 1999. The scarce mobility and limited seasonal territoriality of understory birds restrict their movement between forest fragments (Develey & Stouffer, 2001;Laurance, 2004;Moore et al., 2008), making them vulnerable to local extinction in fragmented habitats (Lens et al., 2002;Powell, 2013). ...
... Many studies have shown that the horizontal, vertical, or temporal distribution patterns of diversity between local species communities were common in understory birds (Montaño-Centellas et al., 2020;Sayer et al., 2017;Sun et al., 2022;Zhang et al., 2020). Additionally, the α diversity of understory birds has previously been associated with temperature, microclimate, and precipitation (Meng et al., 2021;Neate-Clegg et al., 2021;Powell, Cordeiro, & Stratford, 2015;Powell, Wolfe, et al., 2015;Visco et al., 2015). Spatial variation in bird assemblage structure was also significantly correlated with environmental and topographic variables but not strongly related to spatial variables (Menger et al., 2017). ...
... This discrepancy may reflect the characteristics of avian community compositions in the two zoological regions, as their biological habitat is the primary determinant of the richness and abundance of understory bird communities (Young et al., 1998). In the Neotropics, suboscine songbirds of the Antbird (Thamnophilidae), Ovenbird (Furnariidae), Antthrush (Formicariidae), and Tyrant Flycatcher (Tyrannidae) families dominate understory insectivores (Powell, Cordeiro, & Stratford, 2015;Powell, Wolfe, et al., 2015). Common understory birds in northeast Tanzania include Broadbills, Greenbuls, Flycatchers, and Sunbirds (Mkongewa et al., 2013). ...
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Understory bird communities, especially those comprising insectivores, are highly sensitive to forest loss and fragmentation. Currently, there is little knowledge regarding the large‐scale diversity patterns of understory bird communities, particularly in Eastern Asia. Consequently, we aimed to identify the distribution patterns of understory birds in southern China and the factors underlying these patterns. We analysed the diversity distribution patterns of taxonomic and functional α and β diversity for understory Passeriformes birds in southern China utilising cluster and ordination analyses. Subsequently, we analysed the effects of geographic distance, annual mean temperature, annual temperature range, annual mean precipitation, and annual precipitation range on diversity distribution patterns. In total, 9282 individuals belonging to 11 orders, 48 families, and 297 species were captured over 98,544 net hours, with Alcippeidae being the most abundant family in southern China. The understory bird communities of the 25 sites were categorised into six sub‐regions of the Oriental Realm (Indo‐Malayan Realm). The pattern in the distribution of taxonomic and functional β‐diversity of understory birds in southern China was consistent with zoogeographical regionalisation. Three distinct geographical groups were identified: Group 1 was located in the Min‐Guang Coast and Hainan sub‐regions; Group 2 was located in the East Hilly Plain, Southwest Mountains, and Western Mountains and Plateaus sub‐regions; and Group 3 was located in the Southern Yunnan Mountain subregion. The most critical factors related to the distribution patterns of β‐diversity were geographical distance, annual mean temperature, and annual temperature range. Our results showed that the understory bird communities of the Southwest Mountain, East Hilly Plain, and Western Mountains, and Plateaus sub‐regions were similar, as were those of the Min‐Guang Coast and Hainan sub‐regions. Our results underscore the joint roles of distance, temperature, and historical evolution in understory bird communities.
... Forest fragmentation has particularly negative effects on tropical biodiversity, which declines with decreasing fragment area and increasing isolation (Fletcher et al. 2018;Betts et al. 2019). One ongoing conservation challenge in tropical fragmented landscapes, however, is understanding the mechanisms underlying sensitivity to patch area, even for well-studied taxa such as birds (Stratford and Robinson 2005;Sodhi et al. 2008;Robinson and Sherry 2012;Powell et al. 2015;Sherry 2021). Bird species respond differently to fragmentation, with some functional groups showing greater sensitivity than others (Bregman et al. 2014;Keinath et al. 2017). ...
... Bird species respond differently to fragmentation, with some functional groups showing greater sensitivity than others (Bregman et al. 2014;Keinath et al. 2017). Insectivores, a group that makes up ~60% of both all tropical forest (Şekercioğlu 2012) and all Neotropical (Sherry et al. 2020) bird species, are particularly sensitive to fragmentation (Şekercioğlu et al. 2002;Bregman et al. 2014;Pavlacky et al. 2015;Powell et al. 2015;Sherry 2021). Therefore, mechanisms explaining area sensitivity are particularly needed for this diet guild. ...
... Alternative hypotheses, however, abound. Fragment edges, for example, may alter the normally stable abiotic conditions of the forest understory, including light intensity, temperature, and humidity (Stratford and Robinson 2005;Robinson and Sherry 2012;Powell et al. 2015). Of these, light intensity may be most important because tropical forest birds are restricted to specific light microenvironments linked to their foraging stratum Walther 2002b), and light intensity is more affected by edge effects than temperature or humidity (Patten and Smith-Patten 2012). ...
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The fragmentation of tropical forests remains a major driver of avian biodiversity loss, particularly for insectivores, yet the mechanisms underlying area sensitivity remain poorly understood. Studies in lowland systems suggest that loss of food resources, changes to light microenvironments, increased nest predation, and dispersal limitation are possible mechanisms , but these are untested for montane tropical bird communities. In this study, we related avian functional traits to area sensitivity (quantified using beta estimates from a multi-species occupancy model) to test the above four hypotheses for a cloud forest bird community (both resident species and just resident insectivores) in the Colombian Western Andes. We found that species with more specialized diets and those that use the canopy and subcanopy (loss of food hypothesis), larger relative eye sizes (light microhabitat hypothesis), and larger clutch sizes (nest predation hypothesis) were significantly more area sensitive. By contrast, there was no support for the dispersal limitation hypothesis; instead, we found that insectivores with more pointed wing shapes, and more aerial lifestyles , were significantly more fragmentation sensitive. These results suggest that reduced vegetation structure, loss of late-successional plant species, and loss of epiphytic plants may reduce food availability in fragments. Similarly, the ability to tolerate higher light intensity near fragment edges, or when traversing matrix habitat, may be important for persistence in fragments and suggests that habitat configuration may be of special importance in fragmented Andean landscapes. Overall, a lack of information on foraging, movement, and breeding ecology complicates avian conservation in the Andes.
... They are associated with forest interiors due to the relative abundance of herbivorous insects as their preferred food resource, which makes them highly susceptible to deforestation. Hence, forest degradation and fragmentation are the main threats to these groups of birds (Powell et al., 2015). Despite knowledge on responses of insectivorous avian species to habitat degradation in the tropics, Powell et al. (2015) pointed out the scarcity of these studies in Africa and suggested a wider geographic coverage. ...
... Hence, forest degradation and fragmentation are the main threats to these groups of birds (Powell et al., 2015). Despite knowledge on responses of insectivorous avian species to habitat degradation in the tropics, Powell et al. (2015) pointed out the scarcity of these studies in Africa and suggested a wider geographic coverage. ...
... In conclusion, our study has provided insights into responses of bird feeding guilds to disturbance at local landscape scale of a hitherto unknown West African dry forest, and adds to the existing knowledge on the adverse effect of disturbance on bird communities in Africa as suggested by Powell et al. (2015). Our result showed that continuous disturbance in the woodland will provide suitable habitat for the granivores but shrink habitat suitable for the insectivorous woodland specialist (Coppedge et al., 2001). ...
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West African birds have been declining due to intensive deforestation, yet how bird communities respond to such habitat modification remains understudied in this region. We used point transects to survey bird species in the undisturbed and disturbed edges of Tula Mountains Woodland (TMW), in order to examine responses of bird feeding guilds to disturbance. We found significantly more species in the disturbed than in the undisturbed sites. Number of insectivores was significantly higher than other feeding guilds, followed by the granivores, while nectarivores were the fewest. The lack of variation in mean species richness of bird feeding guilds per timed count between habitats indicates that members of all feeding guilds were widespread across the two habitats. However, the higher species numbers of the carnivores and granivores in the disturbed habitat, and the insectivores in the undisturbed habitat suggest their potential affinities for these habitat scenarios. On the other hand, one‐third of the frugivores and nectarivores utilised the two habitat types, indicating generalist behaviour. Our results suggest that disturbance was not as intensive as to cause significant changes in composition of bird feeding guilds at TMW, but increase in disturbance can potentially have adverse effects on the insectivores, as evidenced in their decreased number of species in the disturbed edges.
... Understory insectivorous birds are an ecologically heterogeneous group, but closely associated with vegetation near the floor of tropical forests. These species are very sensitive to vegetation changes (Powell et al. 2015). They can belong to several families, particularly those within the Passeriformes order (Powell et al., 2015, Stratford andŞekercioğlu, 2015). ...
... These species are very sensitive to vegetation changes (Powell et al. 2015). They can belong to several families, particularly those within the Passeriformes order (Powell et al., 2015, Stratford andŞekercioğlu, 2015). Although they are considered insectivores, the diet of many species may be partly composed of other items, including fruits, seeds, small vertebrates and other invertebrates, such as spiders, earthworms and snails (Wilman et al. 2014;Anjos et al., 2015;Sherry et al. 2020). ...
... The great variety of niches of these species, a reflection of high specialization in foraging tactics and substrates, may be an explanation for their sensitivity to environmental disturbance; placing understory insectivores as important ecological indicators (Powell et al., 2015, Stratford andStouffer, 2015;Sherry et al. 2020). In addition to foraging specialization, other factors have been pointed out to explain the high sensitivity of this group to fragmented and/or degraded forest landscapes. ...
Article
Understory insectivorous Passeriformes are known for their vulnerability to forest loss and degradation. Here we investigated whether the proportion of groups of understory insectivorous Passeriformes with different levels of specialization increase with forest cover in the Atlantic Forest, Brazil. We hypothesized that Tyrannides, a very large clade of the order Passeriformes which are closely associated with forest habitat, would be more associated to forest loss than Passeri. We evaluated whether the abundance of single species is associated to forest cover. Published databases were used to select 34 locations and to classify bird species into 3 groups according to degree of specialization in diet and the use of understory for foraging. The percentage of forest cover in 500 meters radii around the locations was calculated and its relationship with the proportion of species was evaluated using binomial models. A total of 86 species of forest Passeriformes was classified as understory insectivores (68 Tyrannides and 18 Passeri). Forest cover was positively associated to the proportion of Passeriformes overall. But while forest cover was also positively associated to the proportion of two more specialized understory insectivores, it had no relation with the group of generalists. Tyrannides were also similarly associated to forest cover. Only some of the most common insectivores Passeriformes had a positive association of their abundance with the forest cover. Higher percentage of understory insectivores in bird communities of Atlantic Forest could be considered indication of higher forest cover.
... Selective logging also alters the structural and functional composition of bird communities (Burivalova et al., 2015). Amongst tropical birds, insectivorous species (whose diets are dominated by arthropods) are especially sensitive to land-use change (Bregman et al., 2014;Srinivasan et al., 2015;Powell et al,. 2015). Across the tropics, studies have repeatedly found that terrestrial insectivorous are the most vulnerable to changes in forest structure, and are often the first dietary guild to disappear from disturbed forest (Stratford & Stouffer, 1999;Canaday & Rivadeneyra, 2001;Peh et al., 2005;Pavlacky et al., 2015;Rutt et al., 2019;Stouffer et al ...
... 2015). Across the tropics, studies have repeatedly found that terrestrial insectivorous are the most vulnerable to changes in forest structure, and are often the first dietary guild to disappear from disturbed forest (Stratford & Stouffer, 1999;Canaday & Rivadeneyra, 2001;Peh et al., 2005;Pavlacky et al., 2015;Rutt et al., 2019;Stouffer et al., 2021) and the last to return after forests regenerate (Powell et al., 2013(Powell et al., , 2015. ...
... ;https://doi.org/10.1101https://doi.org/10. /2022 also affect foraging by insectivorous birds indirectly by altering resource availability and diversity (Powell et al., 2015). ...
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1. Selective logging—the practice of removing a subset of commercially important trees from a forest—is a globally pervasive form of forest degradation. Selective logging alters both the structure and function of forests and the composition of ecological communities. 2. Tropical insectivorous birds are highly vulnerable to microhabitat alterations in logged forest. Such altered microhabitats might affect the foraging of forest birds by altering (a) resource availability, and (b) foraging behaviour. 3. We investigated the effect of selective logging on microclimates, prey availability, foraging behaviour and the foraging success of eastern Himalayan birds in the breeding season. 4. Selective logging alters temperature-humidity microclimates and the composition of arthropod communities, both of which are likely to then collectively alter foraging behaviour by birds. We show that birds spent a lower proportion of their time foraging in primary compared with logged forest. Further, selective logging interacts with species traits such as body mass, preferred foraging stratum (understorey, midstorey or canopy) and foraging manoeuvre to influence foraging success. Gleaners generally foraged more successfully in primary forest and salliers in logged forest, although these patterns were modified by body mass and foraging stratum. 5. Synthesis and applications: Our study shows how altered microclimates in anthropogenically modified habitats can influence resource availability and have downstream impacts on the behaviour of species at higher trophic levels.
... Rampant deforestation in the region has motivated research on the consequences of clearing and fragmentation for rainforest biota, including the avifauna (Bierregaard and Gascon 2001, Peres et al. 2010, Stouffer 2020. Tropical insectivorous birds are consistently identified as highly vulnerable to anthropogenic disturbance (Powell et al. 2015, Sherry 2021, with ground-foraging species among the most sensitive to landscape alteration. For example, experimental forest isolation led to loss of terrestrial insectivores from fragments in central Amazonia, with extinctions inversely proportional to fragment size Bierregaard 1995, Stratford andStouffer 1999). ...
... Similar patterns materialized in Ecuador (Canaday 1996, Canaday andRivadeneyra 2001). Outside of Amazonia, declines of understory insectivores following disturbance were documented particularly in Costa Rica and Panama (Sekercioglu et al. 2002, Sigel et al. 2006, Visco et al. 2015, but this phenomenon is not restricted to the Neotropics (Powell et al. 2015, Sherry 2021. Strong sensitivity to forest disturbance thus makes terrestrial insectivores indicators of rainforest health. ...
... Results from studies in disturbed landscapes offer a place to start. Hypothesized explanations range from vulnerability to changing forest structure (Laurance et al. 2002, Stratford andStouffer 2015), reduction in forest patch area (Stouffer 2007) and several other factors (Powell et al. 2015, Visco et al. 2015, Sherry 2021. Notably, the 'microclimate hypothesis' posits that non-forest areas and forest edges harbor altered microclimates (sensu Chen et al. 1999) that are unsuitable for terrestrial insectivores, which are associated with shaded, cool and wet conditions within forest interior. ...
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Rainforest loss threatens terrestrial insectivorous birds throughout the world's tropics. Recent evidence suggests these birds are declining in undisturbed Amazonian rainforest, possibly due to climate change. Here, we first asked whether Amazonian terrestrial insectivorous birds were exposed to increasingly extreme ambient conditions using 38 years of climate data. We found long‐term trends in temperature and precipitation at our study site, especially in the dry season, which was ~1.3°C hotter and 21% drier in 2019 than in 1981. Second, to test whether birds actively avoided hot and dry conditions, we used field sensors to identify periodic intervals of ambient extremes and prospective microclimate refugia within undisturbed rainforest from 2017 to 2019. Simultaneously, we examined how tagged black‐faced antthrushes Formicarius analis used this space. We collected > 1.3 million field measurements quantifying ambient conditions in the forest understory, including along elevation gradients. For 11 birds, we obtained GPS data to test whether birds adjusted their cover usage using variation in GPS fix success (n = 2724) as a proxy and elevation using successful locations (n = 640) across seasonal and daily cycles. For four additional birds, we collected > 180 000 light and temperature readings to assess exposure. Field measurements in the modern landscape revealed that temperature was higher in the dry season and highest on plateaus. Thus, low‐lying areas were relatively buffered, providing microclimate refugia during hot afternoons in the dry season. At those times, birds apparently entered cover and shifted downslope. Because climate change intensifies the hot, dry conditions that antthrushes seemingly avoid, our results are consistent with the hypothesis that climate change decreases habitat quality for this species. If other terrestrial insectivores are similarly sensitive, climate‐induced changes to otherwise intact rainforest may be related to their recent declines.
... canopy, mid-levels, understorey etc (Asner et al., 2004;Kalko & Handley, 2001); as well as the intensity of timber harvesting (Asner et al., 2004;Burivalova et al., 2014). Some studies addressing bird responses to selective logging found that insectivorous birds experienced a greater decline after logging compared to other bird feeding guilds (Gray et al., 2007;Owiunji & Plumptre, 1998;Powell et al., 2015), whereas others have reported the opposite (Cleary et al., 2007;Edwards et al., 2012). Similar studies have found that canopy species may be most sensitive after RIL due to breaks in the canopy from logging (Felton et al., 2008), with frugivorous species being the most affected (Chaves et al., 2017). ...
... F.analis (black-faced Antthrush) (Stouffer et al., 2021), two of which increased in abundance as timeframe increased in logged sites. Terrestrial insectivores are deemed most sensitive to habitat change (Powell et al., 2015;Stratford & Stouffer, 1999), but it has also been proposed that a small number of terrestrial insectivores may persist from low-impact disturbances (Boyle & Sigel, 2015;Stratford & Stouffer, 2015). Additionally, terrestrial insectivores have narrow microhabitat preferences (Bicknell & Peres, 2010;Borges, 2013;Cintra & Naka, 2011) that are often associated with shallow leaf litter and a greater density of canopy cover (Stratford & Stouffer, 2013). ...
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Selective logging is the most widespread driver of land‐use change in biodiverse and carbon‐rich tropical forests. However, the effects of selective logging on biodiversity are less than those associated with other drivers of forest degradation. A suite of recent research has shown that reduced‐impact logging (RIL) results in few or no changes to biological assemblages. But because this logging technique is relatively new, most studies have only considered short‐term impacts. We address this research gap by quantifying changes in biodiversity assemblage as a result of RIL over the longer term. We comprehensively sampled bird and bat assemblages pre‐logged, 1 year after, and 10 years after RIL in Guyana, using a before‐after control‐impact (BACI) sampling design. We compared bird and bat assemblages in each timeframe, and additionally appraised the impact of time since logging, and the number of trees harvested across the suite of species which we further divided between different feeding guilds, disturbance sensitivity and vertical stratification of forest use. We found that 1 year after logging only minor changes could be detected, but 10 years later richness had slightly declined in some groups, while others had shown complete recovery. Nectivorous and insectivorous birds, and carnivorous bats declined in richness, while carnivorous birds, showed a clear recovery to a state akin to pre‐logging. This indicates that for some niches a subtle, but long‐term relaxation effect may be occurring, whereby extinction debts are realized long after the initial disturbance, while other groups have either recovered or not changed after logging. Assemblage changes were also predicted by vertical stratification of forest use, with avian species using the understorey and mid–upper levels of the forest being most affected. Synthesis and applications : Our study demonstrates how best practice forestry and logging can maintain healthy vertebrate populations over the long term. Forestry concessions that adopt techniques of low‐harvest RIL and are managed for their long‐term timber provision through extension of regeneration times beyond 10 years after harvest, are likely to benefit from the ecosystem services provided by biodiversity, while also making a valuable contribution to the global conservation estate.
... Despite these studies, the diversity, status, and feeding guilds of birds in some forest ranges of lesser Himalayas are poorly studied or not recorded systematically yet (Kukreti and Bhatt 2014). For temperate regions of worlds like Europe, Australia and North American bird species foraging guild have been well documented (Adamik and Kornan 2004, Kornan et al 2013 but there are few studies from the tropical region of Asia and Africa (Powell et al 2015). Thus, there is a gap of knowledge about avifaunal ecological studies especially in tropical forest types of lower Himalayan ranges. ...
... The understory insectivores are threatened in tropics because of frequent fires and fragmentation of forests with other immediate threats such as deforestation, agricultural expansion, urbanization, and logging. The decline in the population of birds in its turn may result in outbursts of insect pests in tropical forests and adjoining agricultural areas (Powell et al 2015). ...
Article
This study examined avifaunal assemblage patterns and feeding guild structure in the forest habitat of a part of Garhwal Himalayas foothills. Field studies were conducted from January 2015 to December 2016. Birds were surveyed by standardized Verner's line transects method. A total of 201 species belonging to 44 families were recorded in the area. The family Muscicapidae (14.92%) was dominant followed by Corvidae (13.43%). The estimated Bird Species Richness (BSR) and diversity (BSD) were greater in a low elevation forest sites in comparison to mid and high elevation sites. Analysis of trophic guild structure showed high insectivory (55.22%) in the area. The foraging behavior study showed a high arboreal pattern (42.78%) than other foraging strategies viz., understory, and terrestrial. This study area harbors five threatened species and hence requires the attention of the conservation biologist for protection of the habitat. Regular monitoring of avian community structure in the Himalayas is also required with preference to lower foothills which are more prone to human disturbances.
... Biodiversity conservation in these coffee landscapes is paramount because the tropical Andes is a global hotspot of species diversity and endemism, including many poorly known species threatened by habitat loss (Schipper et al., 2008;Karger et al., 2021). We focused on ground-dwelling birds, a group sensitive to habitat degradation and indicators of habitat quality (Powell, Cordeiro, & Stratford, 2015;Kupsch et al., 2019), and medium and large mammals, which play key functional roles in tropical ecosystems (Laurance, Vasconcelos, & Lovejoy, 2000;Lino et al., 2019). Throughout the tropics, these species are highly vulnerable to extinction in human modified landscapes (Rovero et al., 2020;Soto-Saravia et al., 2021). ...
... At our site, responses of ground-dwelling birds and mammals were distinct, both in terms of how biodiversity was lost, and which species remained in shade coffee. Differences in bird communities in coffee and forest represented species turnover driven by loss of insectivorous, forest-restricted ground and understory species, a group particularly sensitive to disturbance of vegetation structure and loss of foraging microhabitats (Philpott & Bichier, 2012;Powell, Cordeiro, & Stratford, 2015;Stratford & Stouffer, 2015). Grounddwelling birds in coffee plantations primarily comprised disturbance-adapted woodland or shrubland specialists that were not found in continuous forest or fragments (e.g., Leptotila doves, Turdus and Catharus thrushes). ...
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Shade coffee is among the most widespread and economically important crops in montane tropical regions and is considered more hospitable to wildlife than non‐shaded crops. Questions remain regarding the value of shade coffee as habitat for wildlife, however, given the historical research focus on small‐bodied and canopy species. Simultaneously, climate‐driven upslope migration of coffee crops represents an emerging threat to well‐conserved tropical montane forest at higher elevations. This study examined ground‐dwelling birds and medium‐large mammals in a shade coffee landscape of the Western Andes of Colombia. We asked the following questions: (1) How do bird and mammal occupancy, richness, and community composition change from continuous forest at higher elevations to middle‐elevation forest fragments and shade coffee? (2) Do birds and mammals differ in their response to shade coffee? (3) Do high‐elevation forests contribute to maintaining biodiversity in mid‐elevation shade coffee? We sampled birds and mammals with camera traps in middle‐elevation shade coffee plantations and forest fragments and in continuous forest further upslope. We then used a multi‐species occupancy model to correct for imperfect detection and to estimate occupancy, richness, and community composition. Shade coffee lacked ~50% of the bird and mammal species found in continuous forest, primarily large‐bodied and insectivorous birds and forest‐specialist and large‐bodied mammals. Forest fragment richness was closer to shade coffee than to continuous forest, but species composition significantly differed between coffee and both forest types. Birds in coffee plantations were generally a unique subset of disturbance‐adapted specialists, whereas mammals in coffee were mostly generalists. Distance from continuous forest was the most important landscape‐level predictor of occupancy for both taxa, suggesting that this forest plays a key role in maintaining biodiversity across the coffee landscape. Biodiversity conservation in shade coffee landscapes, therefore, will be ineffective unless linked to landscape‐level initiatives that conserve higher elevation tropical montane forest.
... Our direct comparison between Cocha Cashu and other similar sites in the Neotropics show that overall changes in abundance are smaller at Cocha Cashu. Given extensive documentation of the sensitivity to change of insectivores (Powell et al., 2015), it is surprising that a group showing declines in other undisturbed (Blake & Loiselle, 2015;Stouffer et al., 2020) and fragmented forest sites (Bregman et al., 2014;Powell et al., 2015) shows little variation at Cocha Cashu ( Figure 4). ...
... Our direct comparison between Cocha Cashu and other similar sites in the Neotropics show that overall changes in abundance are smaller at Cocha Cashu. Given extensive documentation of the sensitivity to change of insectivores (Powell et al., 2015), it is surprising that a group showing declines in other undisturbed (Blake & Loiselle, 2015;Stouffer et al., 2020) and fragmented forest sites (Bregman et al., 2014;Powell et al., 2015) shows little variation at Cocha Cashu ( Figure 4). ...
Preprint
Documenting patterns of spatio-temporal change in hyper-diverse communities remains a challenge for tropical ecology, yet is increasingly urgent as some long-term studies have shown major declines in bird communities even in relatively undisturbed sites. In 1982, Terborgh et al. quantified the structure and organization of the bird community in a 97-ha. plot in southeastern Peru. We revisited the same plot in 2018 and repeated the same intense combination of methodologies as the original study in order to evaluate community-wide changes. Contrary to the results from studies elsewhere, we found little change in bird distribution and abundance within the plot, although there were some declines related to loss of mixed-species flocks with a high level of species interdependence. This apparent stability suggests that large-scale forest reserves such as Manu National Park may provide the conditions necessary for establishing refugia from at least some of the effects of global change on birds.
... Our direct comparison between Cocha Cashu and other similar sites in the Neotropics show that overall changes in abundance are smaller at Cocha Cashu. Given extensive documentation of the sensitivity to change of insectivores (Powell et al., 2015), it is surprising that a group showing declines in other undisturbed (Blake & Loiselle, 2015;Stouffer et al., 2020) and fragmented forest sites (Bregman et al., 2014;Powell et al., 2015) shows little variation at Cocha Cashu ( Figure 4). ...
... Our direct comparison between Cocha Cashu and other similar sites in the Neotropics show that overall changes in abundance are smaller at Cocha Cashu. Given extensive documentation of the sensitivity to change of insectivores (Powell et al., 2015), it is surprising that a group showing declines in other undisturbed (Blake & Loiselle, 2015;Stouffer et al., 2020) and fragmented forest sites (Bregman et al., 2014;Powell et al., 2015) shows little variation at Cocha Cashu ( Figure 4). ...
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Documenting patterns of spatiotemporal change in hyper‐diverse communities remains a challenge for tropical ecology yet is increasingly urgent as some long‐term studies have shown major declines in bird communities in undisturbed sites. In 1982, Terborgh et al. quantified the structure and organisation of the bird community in a 97‐ha. plot in southeastern Peru. We revisited the same plot in 2018 using the same methodologies as the original study to evaluate community‐wide changes. Contrary to longitudinal studies of other neotropical bird communities (Tiputini, Manaus, and Panama), we found little change in community structure and organisation, with increases in 5, decreases in 2 and no change in 7 foraging guilds. This apparent stability suggests that large forest reserves such as the Manu National Park, possibly due to regional topographical influences on precipitation, still provide the conditions for establishing refugia from at least some of the effects of global change on bird communities.
... En poblaciones de fragmentos forestales, la extinción es inevitable si es que las aves no pueden dispersarse por todo el paisaje (Hanski, 1994(Hanski, , 1998, impidiendo la recolonización de fragmentos aislados incluso si tiene el hábitat adecuado (Powell et al., 2015). Muchos insectívoros del sotobosque son residentes sedentarios con alas proporcionalmente cortas, capacidad de vuelo relativamente pobre (Moore et al., 2008) y distancias de dispersión relativamente cortas. ...
... Las aves insectívoras del sotobosque son buenas indicadoras de la calidad ambiental de los bosques húmedos ya que son particularmente sensibles a los cambios causados por la deforestación, por el reemplazo del bosque original por bosques secundarios y la fragmentación (Aleixo, 1999;Stratford y Stouffer, 2013;Stratford y Stouffer, 2015). Estos insectívoros especializados están fuertemente influenciados por la estructura de la vegetación y evitan las selvas muy alteradas si es que los elementos estructurales claves para su subsistencia están ausentes (Powell et al., 2015). La pérdida de insectívoros del sotobosque ha sido relacionada también con el aumento de la deforestación (Thiollay, 1997). ...
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SOBRE LA CAPACIDAD DE DISPERSIÓN DE Syndactila rufosuperciliata oleaginea (AVES. FURNARIIDAE) EN EL BOSQUE HÚMEDO DE YUNGAS On the dispersion capacity of Syndactyla rufosuperciliata oleaginea (Aves: Furnariidae) in the Yungas Moist Forest 59
... The Eastern Himalayas is among the world's most biodiverse regions (Grenyer et al. 2006;Pandit et al. 2014), and presently faces the twin threats of selective logging and climatic warming. Furthermore, Eastern Himalayan bird species, especially the understorey insectivores, are adapted to narrow thermal ranges and microhabitats, potentially making them extremely vulnerable to anthropogenic change (Jetz et al. 2007;Powell et al. 2015;Srinivasan et al. 2018). ...
... The direct impact of climatic niche parameters on the long-term survival of species has seldom been tested in the field. Previous studies on tropical rainforest species show that vulnerability is strongly predicted by ecological specialisation (Sekercioglu 2011), and that understory insectivores are in particular peril due to anthropogenic change because of their limited dispersal ability (Moore et al. 2008;Powell et al. 2015) and sensitivity to the opening up of the canopy (Patten and Smith-Patten 2012;Pollock et al. 2015). ...
Preprint
The synergistic impacts of climate change and habitat degradation threaten tropical species worldwide. However, how species′ abiotic niches affect their demographic vital rates and phenotypic changes under anthropogenic change remains poorly understood. Using an 11-year mark-recapture dataset from primary and selectively logged forest in the Eastern Himalayas, we investigated how temperature-humidity niche characteristics predicted body mass and survival trends in understorey insectivorous birds over time in each habitat. Our results show that logged forest is hotter and drier than primary forest, and the arthropod community shows dramatic shifts in composition upon selective logging. In understorey insectivores, the degree of dissimilarity between species-specific primary and logged forest niches was strongly and negatively correlated with survival and body mass trends in logged forest. Here, we show that temperature-humidity niche shifts in response to anthropogenic habitat modification can impact demographic vital rates and body condition crucial for population persistence. This work has the potential to inform prompt, targeted conservation efforts toward species that are the most threatened in a warmer and more degraded world.
... We predicted that avian diversity would be highest in undisturbed forest sites and would decrease with disturbance intensity. Additionally, we expected that responses to disturbance intensity would differ among bird dietary guilds [12,32] and that ant-followers and other insectivores would be the most negatively affected by past forest disturbance [23,33,34]. ...
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As tropical forests are frequently impacted by human disturbance, forests in various stages of disturbance recovery are increasingly important for maintaining biodiversity. However, much remains unclear regarding the impacts of prior disturbance intensity on wildlife in regenerating forests. Here, we used mist net capture data to compare bird communities in three tropical forest habitats representing various disturbance intensities: undisturbed primary forest, selectively logged forest (low disturbance), and secondary forest regenerating on abandoned agricultural fields (high disturbance). We found that after a 19-year recovery period, low-disturbance sites contained similar bird communities to undisturbed sites. High-disturbance sites, however, had lower species richness and distinct bird communities, with fewer insectivores and more nectarivores than other sites. Structural equation models revealed that the impacts of disturbance intensity on bird communities were partially explained by changes in vegetation structure: ant-following insectivore abundance declined with disturbance intensity as ground cover vegetation increased, and nectarivore abundance increased with disturbance intensity as tree density decreased. Our results suggest that selectively logged forests can regain pre-disturbance bird diversity and vegetation structure within two decades, provided that they are protected from further disturbance and located near source species pools. Increasing tree density and decreasing ground-level vegetation in secondary forests may improve these areas as habitats for forest-interior birds.
... For instance, 423 hylia showed a likely negative effect of shade on growth rate, yet the population settled at 424 similar biomass in shady farms compared to sunny ones, indicating a response to other taxa in 425 the community. In contrast, forest birds show an intrinsic positive response to shade cover, 426 reflecting perhaps habitat and microclimate requirements for breeding or foraging (Jirinec et 427 al., 2022;Powell et al., 2015). Our findings suggest that widespread intensification and 428 expansion of cocoa agriculture, as seen for instance in much of Côte d'Ivoire, will likely 429 result in a landscape dominated by generalist bird taxa, and devoid of forest birds and other 430 sensitive insectivores (Kupsch et al., 2019). ...
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Balancing biodiversity conservation and agricultural productivity is commonly regarded as a trade-off, but such analyses overlook ecosystem services that functional biodiverse communities provide in agroecosystems, and the possibility that win-win strategies may exist. We developed a dynamic mechanistic community model of the bird-insect food web associated with African cocoa agroforestry, structurally informed by metabarcoding data on bird diets, and fitted to trapping data on species abundances. We used the model to predict equilibrium community composition under varying intensities of shade management and pesticide use. Our results indicate that low-intensity farming favours forest bird species, and potential pollinator abundance, with no increase in pest biomass. Furthermore, using simulations of pesticide application, we found that pesticides do not effectively reduce pest biomass, and result in forest bird extinction. Our mechanistic framework combines the influence of management and the direct and indirect effects of species' interactions, and demonstrates that low intensity agriculture may provide a win-win for biodiversity and ecosystem services.
... In the dry forest landscape, the percentage of insects in birds diets remained high along the gradient of distance to forest, likely due to the higher offer of resources for insects in irrigated agroecosystems . In contrast, it is likely that in the subtropical rainforest specialized insectivores relying on, for example, complex understory vegetation fail to find an adequate microhabitat in agroforestry areas (e.g., Ocampo-Ariza et al., 2019;Powell et al., 2015). Considering that biocontrol services by insectivorous birds are known to contribute significantly to cacao yield in Peru and elsewhere in the tropics, (Ferreira et al., 2023;Maas et al., 2013;Vansynghel et al., 2022), cacao agroforestry in subtropical forest landscapes should prioritize enhancing microhabitat conditions for insectivores to maintain their benefits for cacao productivity. ...
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Diversity and functionality of bird communities in tropical agroforests are shaped by their surrounding landscape, particularly the extent and type of natural forest. However, most evidence comes from tropical rainforest landscapes, whereas the bearing of such trends in other forest types remains understudied. We compared functional and beta diversity of bird communities in 23 cacao agroforests embedded in landscapes of two contrasting Peruvian regions: seasonally‐dry tropical forests and subtropical rainforests from the Andean foothills. Strong climatic seasonality affects both landscapes, but forest vegetation structure and complexity differ. We found higher bird species richness (n = 179 spp) and higher species turnover in the subtropical forest than in the dry forest landscape (n = 64 spp). Only in the dry forest landscape, distance from forest increased dissimilarity driven by species loss, that is, the nestedness component of beta diversity. This points to the importance of conserving dry tropical forests within the broader landscape matrix, with known benefits for pest control and cacao yield. Functional diversity indices were not influenced by forest distance in either landscape, but the proportion of insects in birds' diet decreased by 27% along a 1 km distance gradient from forest in the subtropical forest landscape. In the dry forest landscape, however, it decreased by only 3% across the same distance gradient. Far from forest (≥1 km), forest specialization decreased by ~33% and 20% in the subtropical and dry forest landscapes, respectively. These differences indicate that regionally‐adapted agroforest management is paramount for conserving bird diversity and ecosystem services as pest control. Procuring high‐canopy shade trees and adequate microhabitats for insectivorous species is essential to maintain biocontrol services in the subtropical forest. Conversely, in the dry forest enhancing low‐canopy vegetation with a focus on frugivores and ensuring forest closeness to agroforests may maximize bird diversity and their ecosystem services. A complete version of this article is translated to Spanish in the supplements.
... I analyzed more than three million measurements representing local weather and its effects on nine species of terrestrial insectivores -rainforest specialists thought to be sensitive to microclimate variation (Powell et al. 2015, Ausprey et al. 2021, Sherry 2021, Jirinec et al. 2022a. Comparing the thermal flux representing avian and ambient sensors revealed a striking consistency in responses to ambient changes as well as endogenous behavior. ...
Article
Understanding the capacity for thermoregulation is critical for predicting organismal vulnerability to climate change, especially in lowland tropical rainforests, where warming conditions combine with high humidity and limited elevational or latitudinal refugia. Here, I focused on nine species of ground‐foraging insectivorous birds in the genus Myrmoderus , Myrmornis , Hylopezus , Myrmothera , Formicarius and Sclerurus – sensitive forest specialists characterized by recently documented population declines in both disturbed and undisturbed forests. Using high‐resolution data from loggers deployed on birds and their environment, I examined whether and how birds used thermoregulation and whether ambient water provided cooling opportunities. Variation in the rate of temperature change over the diel cycle suggested that all species employed behavioral and physiological thermoregulation, but some patterns differed by species' phylogenetic relatedness. All species warmed hours before their environment at sunrise, then experienced lower temperature increases at midday relative to the ambient thermal flux. These morning warming periods peaked around sunrise for all but Sclerurus rufigularis and constituted the diel temperature change maxima for five of the nine species. Six species exhibited pronounced oscillations in temperature change consistent with regular bathing around sunset, possibly for thermoregulatory or other purposes. This oscillation was the most prominent feature in the diel thermal flux for all three Sclerurus species and, to a lesser extent, for Myrmoderus ferrugineus , Myrmornis torquata and Myrmothera campanisona . Local rainfall reduced ambient temperatures, and birds experienced stronger cooling in the wet season and with higher rainfall intensity. However, rain‐induced cooling events were markedly absent in all three Sclerurus spp. These results highlight the fundamental role of water in avian thermoregulation and suggest that terrestrial insectivores attempt to maintain thermal homeostasis throughout the diel cycle. The observed thermoregulatory behaviors highlight a potentially critical aspect of their vulnerability – thermal regimes are profoundly altered by forest disturbance, climate change, and their combination.
... Insectivorous birds, with their specialised foraging strata and behaviour, drastically respond to habitat complexity structures, making them particularly susceptible to habitat disturbance especially in tropical regions (Castaño-Villa et al., 2019). Considering their sensitivity to disturbance, they often become the first group to disappear in modified and fragmented habitats as they have a high habitat specificity and relatively low range and mobility compared to other species (Şekercioḡlu et al., 2002;Powell et al., 2015). Terrestrial insectivores were also found to respond negatively to anthropogenic disturbance, which reflects the limited ability of this group to cross open areas and move between more suitable forest habitats (Pabico et al., 2021). ...
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The establishment of Protected Areas is deemed of critical importance in global conservation initiatives, particularly in biodiverse regions and global biodiversity hotspots, such as the Philippines. However, the crucial role played by smaller Protected Areas in biodiversity conservation is frequently overlooked, making this a particular area of research interest. The Initao-Libertad Protected Landscape and Seascape (hereinafter-ILPLS) is one of the last remaining karst forests with natural vegetation and refuge for wildlife conservation on the island of Mindanao, the Philippines. However, the landscape component of this Protected Area is very small (ca. 506 000 m 2), bisected by a road, and heavily disturbed by illegal logging and frequent tourist visits. From 2014 to 2018, we assessed the community structure and revealed patterns of bird diversity in ILPLS. We recorded a total of 814 individuals of birds from 36 species and nine feeding guilds from a total sampling effort of 558 230.40 mist-net hours in the Protected Areas' two management zones, namely the Special Protection Zone (SPZ) and Tourism Zone (TZ). ILPLS has a high level of endemism at 33% (12 species), including nine Philippine endemics and three Mindanao Island endemics. We also recorded Gorsachius goisagi, a globally threatened species categorised by IUCN as Vulnerable. Species richness was higher in the SPZ than in the TZ (p = 0.012), whereas no significant differences were observed in the Shannon index values (p = 0.101) and mean capture rates (p = 0.378) between the two management zones. Species and feeding guild assemblages did not differ between the two management zones (p = 0.939) but varied between vertical strata (p = 0.001). Here, we show how this small, protected landscape harbours a comparatively diverse bird community, including restricted-range species and species with high conservation priority. This suggests that forest fragments, even of this size, are important habitats for bird conservation efforts and should not be undervalued. We recommend extending such studies to other fragments, especially those that are still not protected, to improve our biodiversity database, further our understanding of biodiversity and fragment dynamics, and make a case for the protection of other forest fragment habitats.
... Many previous studies have documented declines in abundance and/or changes in distribution patterns of tropical birds but most have been related to effects of anthropogenic activitiese.g., deforestation, fragmentation (Robinson, 1999, 2001, Stouffer et al., 2011Sigel et al., 2006;Shaw et al., 2013). Understory insectivores are particularly sensitive to forest fragmentation and degradation (Powell et al., 2015). Yet, even in protected reserves, factors extrinsic to the reserve can impact populations within the reserve, particularly if the reserve is not sufficiently large (Sigel et al., 2006;Latta et al., 2011). ...
... Herbivory is a crucial ecological process that contributes to the individual adaptation of species (Janzen, 1971). Environmental variables such as temperature fluctuations, humidity, and sunlight also can also impact forest recovery, affecting various trophic levels (Kuprewicz, 2013;Powell et al., 2015;Yong et al., 2011). ...
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Introduction: Evidence suggests that herbivores, such as peccaries, shape vegetation structure and diversity through predation, trampling, dispersal, and rooting behavior. Objective: To evaluate the impact of peccaries (Dycotiles tajacu) on the understory vegetation of the tropical rainforest in the Nogal-La Selva Local Biological Corridor, Costa Rica, comparing a site with the absence of pec-caries to another with the presence of these animals. Methodology: From June to November 2021, 20 experimental exclusions and 20 free access plots, each measuring 2 m 2 were used to quantify herbivory, the number of leaf blades, damaged leaves, healthy leaves, sapling height, and fallen biomass at both sites. Results: A higher sapling density was found in the Nogal Reserve, but a lower sapling diversity, while in La Selva there was a higher sapling diversity, but a lower density of seedlings. Herbivory and sapling height in La Selva exceeded those in Nogal. The exclusion of peccaries reduced seedling damage but did not affect the dynamics of fallen biomass. Conclusion: For the design, implementation, and evaluation of the effectiveness of biological corridors, it is crucial to consider plant-animal interactions to enhance the flow of ecological processes through functional and structural connectivity, analyzed from interactions such as those presented in this paper.
... Two possible explanations may account for these positive responses: (1) The resources were habitat-specific, concentrated in certain vegetation types Packett and Dunning 2009); and (2) Due to a higher plant resource variability in edges, as a result of vegetation structure and plant diversity, which may attract insects (Wiącek et al. 2015). Resource availability may attract some invertivore species, leading to the replacement of species that are able to tolerate forest edges (Powell et al. 2015), as occurs with many bird species in some families (e.g. Tyrannidae, Phylloscopidae, Picidae). ...
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Context Although local studies comparing species abundance between forest edges and interiors are common, general patterns in the response of different species to edges are still to be determined. There is little consensus on the impacts of forest edge effects on the abundance of individual bird species, probably because the species traits affecting edge responses have rarely been synthesized. Objective We aimed to identify how different species’ traits, as well as extrinsic (environmental) factors, mediate the responses of birds to forest edges globally. Methods We collected global information from bibliographic databases from 59 studies with 63 different datasets that compared bird abundance between forest edges and interiors. For each species, we compiled six traits (diet, habitat preference, territoriality, body mass, hand-wing index, and foraging stratum). Using Linear Mixed-effects Models, we evaluated how species traits, latitude, edge contrast, and sampling method affected bird responses to edges. Results Based on 2981 responses of 1414 bird species, we found that plant/seedeaters birds responded positively to edges. The strength of habitat preferences on edge responses was also mediated by latitude. Open-area species from tropics exhibited a positive response, diminishing as latitude increases. Conversely, forest species tend to exhibit a somewhat more negative response in tropical zones. Edge effects were more negative for soft (low-contrast) edges. Conclusions Species traits, in particular diet and habitat preferences interacting with latitude, mediate the impacts of edge effects on different bird species. These species traits and latitudinal gradients must be explicitly considered in models attempting to explain variability in edge responses among species, as well as in conservation actions in fragmented landscapes.
... A broader understanding of habitat affinities, summarised here, may provide a basis for improving our understanding of the effects of anthropogenic disturbance by emphasizing impacts that may occur at the scale of bird communities (e.g., Botzat et al. 2013, Grass et al. 2013, 2014, Barros et al. 2020a, Tinoco et al. 2021. While this study does not include a formal protocol for habitat sampling, it presents habitat affinities based on field observations which have proven to be very good indicators for exploring diversity patterns in many tropical systems (Laurance 2004, Grass et al. 2014, Powell et al. 2015, Willrich et al. 2019). In addition, several studies have shown the effects of habitat loss and landscape fragmentation on bird habitat guilds at a regional scale (e.g., Astudillo 2014, 2020, Barros et al. 2020a). ...
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The páramo ecosystem is a significant centre of Andean bird diversity with high concentrations of threatened species. The Macizo del Cajas Biosphere Reserve’s páramos are a district of the biogeographic páramo province of northern Andes and are therefore considered a conservation hotspot with representative bird diversity. To enhance regional conservation efforts, comprehensive inventories of bird species that occupy this páramo are required. We present an updated bird inventory for the páramos of Macizo del Cajas and included validated records from eBird and GBIF databases along with records from continuous monitoring across this páramo landscape for five years. We also provide notes on habitat affinity and important new, rare, restricted range, and threatened birds. We report 112 bird species within the reserve, including five endemics, and three globally and 12 nationally threatened species. Finally, we discuss the use of habitat affinities as indicators of biodiversity patterns in páramo to improve conservation tools for key habitats.
... Our study provides the first direct test of the "microclimate hypothesis," an influential explanation for the disproportionate sensitivity of tropical understory birds to environmental change. The hypothesis posits that narrow thermal tolerances and limited physiological flexibility in this group induce high susceptibility to environmental perturbations such as forest fragmentation and climate change (Powell et al., 2015;Şekercioḡlu et al., 2002;Stratford & Robinson, 2005). We found no evidence to support the microclimate hypothesis-understory forest species presented TNZs and HTLs similar to those of canopy and open-habitat species, both of which experience more variable and extreme temperatures (Figure 1). ...
Article
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The climate variability hypothesis posits that an organism's exposure to temperature variability determines the breadth of its thermal tolerance and has become an important framework for understanding variation in species' susceptibilities to climate change. For example, ectotherms from more thermally stable environments tend to have narrower thermal tolerances and greater sensitivity to projected climate warming. Among endotherms, however, the relationship between climate variability and thermal physiology is less clear, particularly with regard to microclimate variation—small‐scale differences within or between habitats. To address this gap, we explored associations between two sources of temperature variation (habitat type and vertical forest stratum) and (1) thermal physiological traits and (2) temperature sensitivity metrics within a diverse assemblage of Neotropical birds (n = 89 species). We used long‐term temperature data to establish that daily temperature regimes in open habitats and forest canopy were both hotter and more variable than those in the forest interior and forest understory, respectively. Despite these differences in temperature regime, however, we found little evidence that species' thermal physiological traits or temperature sensitivity varied in association with either habitat type or vertical stratum. Our findings provide two novel and important insights. First, and in contrast to the supporting empirical evidence from ectotherms, the thermal physiology of birds at our study site appears to be largely decoupled from local temperature variation, providing equivocal support for the climate variability hypothesis in endotherms. Second, we found no evidence that the thermal physiology of understory forest birds differed from that of canopy or open‐habitat species—an oft‐invoked, yet previously untested, mechanism for why these species are so vulnerable to environmental change.
... In forest habitats, we observed an alarming trend of biodiversity loss: Nearly 65% more species were decreasing than increasing over the 18 y across Costa Rica. The steepest declines were observed in forest-specialized invertivores, a group known to be particularly sensitive to the effects of deforestation and fragmentation (14,29), and matching findings from other Neotropical forests (14,28). A recent global analysis of avian population declines found that severe population fragmentation was the best predictor for declines in nonmigratory birds in South America (30). ...
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While some agricultural landscapes can support wildlife in the short term, it is uncertain how well they can truly sustain wildlife populations. To compare population trends in different production systems, we sampled birds along 48 transects in mature forests, diversified farms, and intensive farms across Costa Rica from 2000 to 2017. To assess how land use influenced population trends in the 349 resident and 80 migratory species with sufficient data, we developed population models. We found, first, that 23% of species were stable in all three land use types, with the rest almost evenly split between increasing and decreasing populations. Second, in forest habitats, a slightly higher fraction was declining: 62% of the 164 species undergoing long-term population changes; nearly half of these declines occurred in forest-affiliated invertivores. Third, in diversified farms, 49% of the 230 species with population changes were declining, with 60% of these declines occurring in agriculture-affiliated species. In contrast, 51% of the species with population changes on diversified farms showed increases, primarily in forest-affiliated invertivores and frugivores. In intensive farms, 153 species showed population changes, also with similar proportions of species increasing (50%) and decreasing (50%). Declines were concentrated in agriculture-affiliated invertivores and forest-affiliated frugivores; increases occurred in many large, omnivorous species. Our findings paint a complex picture but clearly indicate that diversified farming helps sustain populations of diverse, forest-affiliated species. Despite not fully offsetting losses in forest habitats, diversified farming practices help sustain wildlife in a critical time, before possible transformation to nature-positive policies and practices.
... Birds respond strongly to vegetation structure, especially the understory insectivores (see Powell et al. 2015). Mature Araucaria forests have dense canopies that limit light availability in the lower stratum (Polisel et al. 2014), which will result in an understory dominated by shade-tolerant, slow-growth species, such as the fern Dicksonia sellowiana. ...
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Disturbed forests are increasingly common in tropical regions. Although the conservation value of these habitats has been highlighted, few studies have considered their potential in retaining biodiversity and ecosystem services. Therefore, in this study, we address how different levels of disturbance in Araucaria forests affect bird functional diversity. We used Rapid Ecological Assessment as a method to determine a disturbance gradient in Araucaria forest sites and evaluated how biotic integrity of vegetation was associated with alpha functional diversity (functional richness and functional dispersion). We recorded a total of 112 bird species in the eight Araucaria forest sites. Biotic integrity of vegetation ranged from 33.3 to 51.3. No association was found between functional richness and biotic integrity of vegetation. However, we found a negative association between biotic integrity of vegetation and functional dispersion, which indicates that bird communities in less disturbed forests sites are more functionally redundant than those communities in highly disturbed habitats. Overall, the studied disturbed Araucaria forest sites have great biodiversity value and should be considered in conservation strategies to guarantee bird taxonomic and functional diversity.
... In addition to the loss and fragmentation of habitat for forest-dependent taxa, degradation of the remaining indigenous forest may jeopardize long-term survival of habitat specialized species (Barlow et al. 2016;FAO 2020). For example, insectivorous birds of the tropical rainforest understorey are particularly vulnerable to forest fragmentation and degradation (Powell et al. 2015) as they often show limited dispersal (Lens et al. 2002), and depend on a distinct vegetation structure for foraging and breeding . The persistence of forest species may not only be a direct function of the availability of vegetation structure attributes that provide shelter, breeding sites and protection from predators (Atikah et al. 2021;Melin et al. 2019), but also the availability of sufficient food such as arthropods (Ferger et al. 2014;Peter et al. 2015). ...
Article
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Land-use change remains the main threat to tropical forests and their dependent fauna and flora, and degradation of existing forest remnants will further accelerate species loss. Forest degradation may result directly from human forest use or through spatial effects of land-use change. Understanding the drivers of forest degradation and its effects on biodiversity is pivotal for formulating impactful forest management and monitoring protocols, but such knowledge is lacking for many biodiversity hotspots, such as the Taita Hills in southeast Kenya. Here we first quantify effects of social factors (human activity and presence) at plot and landscape level, forest management (gazetted vs. non-gazetted) and spatial factors (fragment size and distance to forest edge) on the vegetation structure of indigenous Taita forest fragments. Next, we quantify effects of degraded vegetation structure on arthropod abundance and diversity. We show that human presence and activity at both the plot and landscape level explain variation in vegetation structure. We particularly provide evidence that despite a national ban on cutting of indigenous trees, poaching of pole-sized trees for subsistence use may be simplifying vegetation structure, with the strongest effects in edge-dominated, small forest fragments. Furthermore, we found support for a positive effect of vegetation structure on arthropod abundance, although the effect of daily maximum temperature and yearly variation was more pronounced. Maintenance of multi-layered forest vegetation in addition to reforestation maybe a key to conservation of the endangered and endemic fauna of the Taita Hills.
... Our results also point to the sensitivity of species with insectivorous diets, as has been reported at regional scales in the Andes, including in our work in Peru (Jones et al., 2021;Kattan et al., 1994;Renjifo, 1999). Major hypotheses for why insectivores in the Neotropics appear particularly sensitive to anthropogenic disturbance include poor dispersal ability, highly specialized trophic niches, sensitivity to subtle changes in habitat microclimate, and increased prevalence of agricultural pesticides that may reduce prey availability (Jirinec et al., 2022;Powell, Cordeiro, et al., 2015;Sherry, 2021). ...
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Tropical montane bird communities are hypothesized to be highly sensitive to anthropogenic disturbance because species are adapted to a narrow range of environmental conditions and display high rates of endemism. We assessed avian sensitivity at regional and continental scales for a global epicenter of montane bird biodiversity, the tropical Andes. Using data from an intensive field study of cloud forest bird communities across 7 landscapes undergoing agricultural conversion in northern Peru (1800–3100 m, 2016–2017) and a pan‐Andean synthesis of forest bird sensitivity, we developed management strategies for maintaining avian biodiversity in tropical countrysides and examined how environmental specialization predicts species‐specific sensitivity to disturbance. In Peru, bird communities occupying countryside habitats contained 29–93% fewer species compared with those in forests and were compositionally distinct due to high levels of species turnover. Fragments of mature forest acted as reservoirs for forest bird diversity, especially when large or surrounded by mixed successional vegetation. In high‐intensity agricultural plots, an addition of 10 silvopasture trees or 10% more fencerows per hectare increased species richness by 18–20%. Insectivores and frugivores were most sensitive to disturbance: abundance of 40–70% of species declined in early successional vegetation and silvopasture. These results were supported by our synthesis of 816 montane bird species studied across the Andes. At least 25% of the species declined due to all forms of disturbance, and the percentage rose to 60% in agricultural landscapes. The most sensitive species were those with narrow elevational ranges and small global range sizes, insectivores and carnivores, and species with specialized trophic niches. We recommend protecting forest fragments, especially large ones, and increasing connectivity through the maintenance of early successional vegetation and silvopastoral trees that increase avian diversity in pastures. We provide lists of species‐specific sensitivities to anthropogenic disturbance to inform conservation status assessments of Andean birds.
... In the Neotropics, the guild of understory insectivores is of interest to conservation practitioners Stouffer 2013, Powell et al. 2015). These birds are often unwilling to engage in long flights and are reluctant to cross open areas, favoring the isolation of small populations in fragments of habitats and the consequent exposure to inbreeding and to the demographic impacts of isolation (Moore et al. 2008, Oliveira, Jr., et al. 2011, de Camargo et al. 2015, Powell et al. 2015. Although they are not game birds and are not targets of illegal trapping, two of the three bird species from the PEC that were recently uplisted as globally extinct, the Cryptic Treehunter and the Alagoas Foliagegleaner, were forest insectivore passerines, and of the 14 other endangered taxa, six are forest understory insectivores (Pereira et al. 2014, ICMBio 2018. ...
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The Pernambuco Endemism Center (PEC) is the most fragmented and degraded tract of the Atlantic Forest, considered to be a hotspot within a hotspot. Recent bird extinctions and the high number of endangered taxa have called the attention of conservation practitioners all over the world to this area. Among the most vulnerable groups of birds are the insectivorous passerines of the forest understory, yet empirical information on demography and habitat requirements are unavailable for these taxa. Here, we provide population density estimates and microhabitat selection information for two endangered insectivorous passerines endemic to the PEC, the Pernambuco Fire-eye, Pyriglena pernambucensis, and the Black-cheeked Gnateater, Conopophaga melanops nigrifrons. Distance-sampling estimates resulted in population densities of 0.15 and 0.35 individuals/ha, respectively, in an Atlantic Forest fragment of approximately 1000 ha. Extrapolations of population densities to 39 fragments where the occurrence of these taxa was confirmed resulted in population estimates of 4936 individuals for the Pernambuco Fire-eye and 12,679 individuals for the Black-cheeked Gnateater, but these may be underestimates because other fragments where they could potentially occur were never surveyed. Although extrapolating data from only one fragment to other areas is problematic, these are the first rough minimum population size estimates for birds from the PEC. Microhabitat preference analyses revealed that both species selected sites with denser forest understory vegetation, which is associated with areas in regeneration. This is evidence that these taxa can tolerate certain levels of habitat disturbance and that their limited distributions and habitat loss may be more important causes of threat than habitat requirements. In the face of ongoing PEC fragmentation, our data will serve to parameterize other studies and may contribute to practical conservation policies.
... Moreover, organisms vary in their response to environmental change. For instance, selective logging may negatively impact understorey insectivorous birds, which are among the most disturbance-intolerant guilds (Powell, Cordeiro and Stratford, 2015). However, the same intervention may benefit species that browse on understorey plants (e.g. ...
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Forests harbour a large proportion of the Earth’s terrestrial biodiversity, which continues to be lost at an alarming rate. Deforestation is the single most important driver of forest biodiversity loss with 10 million ha of forest converted every year to other land uses, primarily for agriculture. Up to 30 percent of tree species are now threatened with extinction. As a consequence of overexploitation, wildlife populations have also been depleted across vast areas of forest, threatening the survival of many species. Protected areas, which are considered the cornerstone of biodiversity conservation, cover 18 percent of the world’s forests while a much larger 30 percent are designated primarily for the production of timber and non-wood forest products. These and other forests managed for various productive benefits play a critical role in biodiversity conservation and also provide essential ecosystem services, such as securing water supplies, providing recreational space, underpinning human well-being, ameliorating local climate and mitigating climate change. Therefore, the sustainable management of all forests is crucial for biodiversity conservation, and nations have committed to biodiversity mainstreaming under the Convention on Biological Diversity (CBD). Mainstreaming biodiversity in forestry requires prioritizing forest policies, plans, programmes, projects and investments that have a positive impact on biodiversity at the ecosystem, species and genetic levels. In practical terms, this involves the integration of biodiversity concerns into everyday forest management practice, as well as in long-term forest management plans, at various scales. It is a search for optimal outcomes across social, economic and environmental dimensions of sustainable development. This study is a collaboration between FAO and the Center for International Forestry Research (CIFOR), lead centre of the CGIAR research programme on Forests, Trees and Agroforestry (FTA). Illustrated by eight country case-studies, the report reviews progress and outlines the technical and policy tools available for countries and stakeholders, as well as the steps needed, to effectively mainstream biodiversity in forestry.
... Then, criteria related to habitat conservation and distribution, such as former and current habitat extension, reduction tendencies, and levels of fragmentation have been the most frequent parameters used for the categorization of many species (see ICMBio 2018, Santini et al. 2019. Although these criteria have been sufficient to include a relevant number of taxa in red lists, knowledge on demographic aspects is important for at least three main reasons: first, species vary naturally in population densities within target habitats (Gottschalk & Huettmann 2011), in such a way that in a same geographic region different species can have highly divergent population sizes; second, species sharing the same endangered habitats may respond differently to the effects of habitat disturbances, meaning that their risks of extinction are not uniform (Powell et al. 2015), and third, the determinants of the demographic parameters of many taxa may not be related only to habitat amount and quality, but also to other anthropogenic effects such as poaching and trapping (Bernardo et al. 2011, Alves et al. 2017. Then, censuses are essential to address the relative risks of extinction of endangered taxa, and their publications in the form of scientific articles, with detailed methodological descriptions, permit their reproducibility and the monitoring of future population tendencies (Alves et al. 2017, Tonetti & Pizo 2016. ...
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Determining the relative risks of extinction of declining taxa is important to delineate conservation priorities and to guide the investments in conservation. Brazil concentrates the greatest number of endangered avian taxa on Earth, yet demographic information is lacking for most of them. Here we present distance-sampling population density estimates for three endangered bird taxa endemic to the Pernambuco Endemism Center (PEC), the most critically disturbed Atlantic Forest region. The analyzed taxa were the White-shouldered Antshrike Thamnophilus aetiops distans (Endangered), the Brown-winged Mourner Schiffornis turdina intermedia (Vulnerable), and the White-bellied Tody-tyrant Hemitriccus griseipectus naumburgae (Vulnerable). The estimated numbers of individuals/ha in an approximately 1,000 ha forest fragment were 0.21, 0.14, and 0.73, respectively. Our findings corroborated the premise that even taxa classified in similar threat categories based on habitat characteristics alone can have different population densities and consequently, divergent risks of extinction. Although population densities can vary among fragments, the extrapolation of our data to the whole PEC confirmed the Vulnerable status of the Brown-winged Mourner, and indicated the Vulnerable and Least Concern categories for the White-shouldered Antshrike and for the White-bellied Tody-tyrant, suggesting that for the two later taxa, the current classifications (Endangered and Vulnerable) based on their Areas of Occupancy must prevail.
... Discussing why understorey insectivores are especially vulnerable to forest fragmentation and disturbance, Powell et al. (2015) remarked that MSFs in Africa seem less rigidly organised than in the Neotropics, with the caveat that they are also less studied. Species studies are important, as Zou et al. (2018) argued that anthropogenic disturbance seriously disrupts MSFs, and they proposed that nuclear species should be assigned special conservation value. ...
Article
Mixed-species flocks of foraging insectivorous birds are found worldwide and have been best studied in the Neotropical region. A survey of the published literature reveals that mixed-species flocks (often termed ‘bird parties’) comprised of 2–30 species and sometimes >70 individual birds are regularly encountered in forest and woodland habitats throughout the Afrotropical region. On mainland Africa, >600 species representing 59 bird families have been reported in such flocks, and for at least 300 species foraging in such flocks may constitute an important part of their feeding activity. In Madagascar, >60 species of 19 families have been recorded in mixed-species flocks, with more than 40 species frequent participants. These foraging parties are dominated by gleaning and sallying insectivorous birds, with other feeding guilds represented by fewer species and individuals. The main hypotheses to explain why birds participate in such flocks emphasise protection from predators while searching for food, and increased foraging efficiency through the disturbance of insects caused by the different foraging activities of flock members. Certain key species may be responsible for the initial formation of the flock. Mixed-species flocks are regarded as particularly vulnerable to disruption by anthropogenic habitat changes, especially to forests, and are thus of special conservation concern. In the Afrotropics, these proposals remain working hypotheses since we currently lack data for a full assessment of the ecological role of mixed-species flocks and their importance in the life history of the participating species.
... While a recent discussion of the conservation implications of mixed-species flocks explicitly excluded ant-following birds from the analysis (Zou et al. 2018), the conservation of ant-followers was one of five research areas highlighted by Martinez et al. (2021). This review of Neotropical antfollowing birds reveals the many gaps in our knowledge of this system in the Afrotropical region; earlier Powell et al. (2015) had noted that the importance of ant swarms to birds is much less well understood in the Afrotropics. Some key areas for future research in Africa will be: ...
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Ant-following birds have been studied extensively in the Neotropics, but much less information is currently available for the Afrotropics. There are published records of 168 African bird species from 37 families foraging in association with driver ants (Dorylus, sub-family Dorylinae). However, of 52 bird species assessed as regular ant-followers, 38 belong to three families, which are disproportionately represented compared to other large Afrotropical bird families: Muscicapidae (18 spp.), Pycnonotidae (13 spp.) and Turdidae (7 spp.). The extent to which these birds are dependent on ants through their annual cycle is not known. African driver ants forage primarily under shaded, humid conditions by day, and may spend a month or longer underground. Conservation assessments of African forest habitats suggest that both driver ants and ant-following birds may be especially sensitive to the loss of forest cover.
... Nevertheless, a handful of studies have provided insight into how resident tropical bird populations have fared in recent decades and helped identify ecological traits underlying population trends. For example, certain guilds, such as understory or terrestrial insectivores, appear to be consistently declining in both intact (25,26) and fragmented tropical forests (reviewed in ref. 27). Body size has also been implicated, with both small- (28) and large-bodied species (29) exhibiting declines or even extirpation following fragmentation. ...
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Significance We leveraged a 44-y population study of Neotropical understory birds from a protected forest reserve in central Panama to document widespread and severe declines in bird abundance. Our findings provide evidence that tropical bird populations may be undergoing systematic declines, even in relatively intact forests. The implications of these findings are that biodiversity baselines may be shifting over time, and large tracts of tropical forest may not be sufficient for maintaining stable bird populations. Our study highlights the importance of long-term monitoring for detecting cryptic losses in biodiversity and motivates the need for future work drilling down to the underlying mechanisms to understand and mitigate future declines.
... Globally, many aerial insectivores have declined in abundance since the mid-1980s, with steep declines documented for many insectivorous birds (Bowler et al., 2019;Nebel et al., 2011Nebel et al., , 2020Powell et al., 2015). Declining insect prey has been proposed as a primary driver of the concomitant decline of several avian aerial insectivores (Cox et al., 2019;Spiller & Dettmers, 2019), but the evidence is equivocal and declines are likely to be multifactorial, with the relative impact of specific factors varying among species (Michel et al., 2016). ...
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Reduced food availability is implicated in declines in avian aerial insectivores, but the effect of nutritional stress on mammalian aerial insectivores is unclear. Unlike birds, insectivorous bats provision their young through lactation, which might protect nursing juveniles when prey availability is low but could increase the energetic burden on lactating females. We analyzed a 15‐year capture–mark–recapture data set from 5312 individual little brown myotis (Myotis lucifugus) captured at 11 maternity colonies in northwestern Canada, to test the hypothesis that nutritional stress is impacting these mammalian aerial insectivores. We used long‐bone (forearm [FA]) length as a proxy for relative access to nutrition during development, and body mass as a proxy for access to nutrition prior to capture. Average FA length and body mass both decreased significantly over the study period in adult females and juveniles, suggesting decreased access to nutrition. Effect sizes were very small, similar to those reported for declining body size in avian aerial insectivores. Declines in juvenile body mass were only observed in individuals captured in late summer when they were foraging independently, supporting our hypothesis that lactation provides some protection to nursing young during periods of nutritional stress. Potential drivers of the decline in bat size include one or both of (1) declining insect (prey) abundance, and (2) declining prey availability. Echolocating insectivorous bats cannot forage effectively during rainfall, which is increasing in our study area. The body mass of captured adult females and juveniles in our study was lower, on average, after periods of high rainfall, and higher after warmer‐than‐average periods. Finally, survival models revealed a positive association between FA length and survival, suggesting a fitness consequence to declines in body size. Our study area has not yet been impacted by bat white‐nose syndrome (WNS), but research elsewhere has suggested that fatter bats are more likely to survive infection. We found evidence for WNS‐independent shifts in the body size of little brown myotis, which can inform studies investigating population responses to WNS. More broadly, the cumulative effects of multiple stressors (e.g., disease, nutritional stress, climate change, and other pressures) on mammalian aerial insectivores require urgent attention.
... Avian insectivores consume arthropods as their main diet source; they are very common and are diverse in species which makes them essential to any ecosystem (Powell et al. 2015). Bewick's Wren (Thryomanes bewickii), Yellow-billed Cuckoo (Coccyzus americanus), Golden-fronted Woodpecker (Melanerpes aurifrons), Ladderbacked Woodpecker (Picoides scalaris), Whiteeyed Vireo (Vireo griseus), and Verdin (Auriparus flaviceps) are resident insectivores based on foraging guilds described by Graaf et al. (1985). ...
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Bewick's Wren (Thryomanes bewickii), Yellow-billed Cuckoo (Coccyzus americanus), Golden-fronted Woodpecker (Melanerpes aurifrons), Ladder-backed Woodpecker (Picoides scalaris), White-eyed Vireo (Vireo griseus), and Verdin (Auriparus flaviceps) are all residents of the South Texas landscape. While the species are unique in appearance, they share the diet of arthropods with each of these species categorized as an insectivore during the breeding season. During this time, they need more nutrients to keep up with the pressures of finding a suitable mate and maintaining their young. The objective of this study was to investigate the influence of brush cover and arthropods on avian insectivores in native rangelands of South Texas. It is important to look at relationships because it can help determine what is impacting bird abundance if populations are low. We established 600 m x 100 m line transects in two levels of brush cover (high [.50%] and low [,50%]). We placed pitfall traps at every 100 m along transects to capture arthropods utilizing ground habitat. We also used beatsheets and branch clippings at each pitfall site to sample arthropods living in shrubs and trees. Bird surveys were conducted once a week on transects and the focal bird species were recorded by visual and auditory means. Our results showed that there was a significant effect of brush cover level (high and low) and arthropod diversity on the relative abundance of avian insectivores. We observed a higher relative abundance of birds as arthropod diversity increased in high brush, and a lower relative abundance of birds as arthropod diversity increased in low brush. There were no significant effects of brush cover level and arthropod metrics on avian richness or diversity. Having a mosaic habitat with different canopy heights and diverse vegetation communities can positively influence animal populations and is important when considering land management strategies.
... The Neotropics are a hotspot of avian diversity, with Amazonia holding the world's highest richness of suboscine passerines (Harvey et al., 2020). These birds largely comprise understory insectivores, a group highly sensitive to disturbance and therefore useful as indicators of change in rainforest ecosystems (Bregman et al., 2014;Powell et al., 2015a;Sherry, 2021). Approximately 20% of the Amazon rainforest had been removed by 2018 (Artaxo, 2019;da Cruz et al., 2021), but the footprint of disturbance is even greater as clearing degrades habitat beyond deforested areas (Bregman et al., 2014). ...
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Insectivores of the tropical rainforest floor are consistently among the most vulnerable birds to forest clearing and fragmentation. Several hypotheses attempt to explain this pattern, including sensitivity to extreme microclimates found near forest borders, particularly brighter and warmer conditions. Importantly, this “microclimate hypothesis” has additional implications for intact forest under global climate change that could be evaluated through direct assessment of the light and temperature environment of terrestrial insectivores. In this study, we harness novel technology to directly quantify the light and thermal niches of 10 species of terrestrial insectivores in undisturbed Amazonian rainforest. Loggers placed on birds (N = 33) and their environment (N = 9) recorded nearly continuous microclimate data from 2017 to 2019, amassing >5 million measurements. We found that midday light intensity in tree fall gaps (~39,000 lux) was >40 times higher than at the ground level of forest interior (950 lux). Light intensity registered by sensors placed on birds averaged 17.4 (range 3.9–41.5) lux, with species using only 4.3% (0.9%–10.4%) of available light on the forest floor. Birds therefore selected very dark microhabitats—the light environment was >2200 times brighter in tree fall gaps. Bird thermal niche was a function of ambient temperature as well as body temperature, which averaged >40.5°C but varied among species. Forest floor temperature peaked daily at 27.0°C, whereas bird loggers averaged 35.1°C (34.5–35.7°C) at midday. The antpitta Myrmothera campanisona and the antthrush Formicarius colma used thermal conditions closest to their body temperatures, whereas leaftossers (Sclerurus spp.) and Myrmornis torquata occupied relatively cool microclimates. We found no general link between abundance trends and variation in species‐specific light and thermal niches. However, all species occupied markedly dim and cool microclimates. Because such conditions are rare outside the interior of primary forest, these results support the microclimate hypothesis in disturbed landscapes. Moreover, strong avoidance of conditions that are becoming more common under climate change highlights the vulnerability of terrestrial insectivores even in the absence of disturbance and may be the reason for enigmatic declines in Amazonia and elsewhere.
... Indeed, not all animal groups respond in the same way to land-use change and there are often contrasting patterns among groups with different functional traits, such as feeding or habitat preferences. Among flying vertebrates, insectivorous birds are notably sensitive to land-use change and deforestation (Powell et al., 2015;Ş ekercioĝlu, 2012), especially those relying on understory vegetation for foraging (e.g. Kupsch et al., 2019;Maas et al., 2009). ...
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Agricultural expansion and intensification increasingly threaten birds and bats, especially insectivorous species from the tropics. Cacao agroforests in tropical rainforest areas have been shown to support higher bird and bat biodiversity than other land-use systems, but their suitability for tropical dry forest biodiversity remains unclear. We present the first assessment of bird and bat diversity patterns in cacao agroforests inside tropical dry forest landscapes. We investigated the response of bird and bat species richness and abundance to forest distance and season across 12 smallholder, organic cacao agroforests and adjacent tropical dry forests in the Peruvian lowlands of Piura. We found that insectivorous bird abundance and species richness increased with forest distance in the dry but not in the rainy season, indicating the value of cacao agroforests for these birds when resources are scarce in forests. In the case of bats, we observed more species in agroforests with increasing forest distance independent of season, and the abundance of insectivorous species increased along the gradient. Other dietary groups and forest specialists of both taxa did not vary notably across the forest distance gradient. Our findings point to the relevance of cacao agroforests as alternative habitats for insectivorous birds and bats in tropical dry forest landscapes, especially during the dry season. We suggest that the maintenance of wildlife friendly cacao agroforests, parallel to dry forest conservation and restoration, creates win-win situations for both the conservation of tropical dry forest fauna and the maintenance of related ecosystem services from which cacao smallholders may benefit.
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Current and near future climate policy will fundamentally influence the integrity of ecological systems. The Neotropics is a region where biodiversity is notably high and precipitation regimes largely determine the ecology of most organisms. We modeled possible changes in the severity of seasonal aridity by 2100 throughout the Neotropics and used birds to illustrate the implications of contrasting climate scenarios for the region's biodiversity. Under SSP‐8.5, a pessimistic and hopefully unlikely scenario, longer dry seasons (> 5%), and increased moisture stress are projected for about 75% of extant lowland forests throughout the entire region with impacts on 66% of the region's lowland forest avifauna, which comprises over 3000 species and about 30% of all bird species globally. Longer dry seasons are predicted to be especially significant in the Caribbean, Upper South America, and Amazonia. In contrast, under SSP‐2.6—a scenario with significant climate mitigation—only about 10% of the entire region's forest area and 3% of its avifauna will be exposed to longer dry seasons. The extent of current forest cover that may plausibly function as precipitation‐based climate refugia (i.e., < 5% change in length of dry periods) for constituent biodiversity is over 4 times greater under SSP‐2.6 than with SSP‐8.5. Moreover, the proportion of currently protected areas that overlap putative refugia areas is nearly 4 times greater under SSP‐2.6. Taken together, our results illustrate that climate policy will have profound outcomes for biodiversity throughout the Neotropics—even in areas where deforestation and other immediate threats are not currently in play.
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Choosing effective methods to restore habitat for the diverse faunal assemblages of tropical forests is hampered by lack of long-term data comparing multiple restoration treatments. We conducted area counts of bird assemblages over 12 years (∼5–17 years since restoration) in a blocked experiment with two active planted treatments (tree plantations and applied nucleation) and a passive restoration treatment (natural regeneration) replicated at 11 sites in Costa Rica. We also surveyed six pastures and five remnant forest sites to assess recovery of avian species richness, composition, forest specialists, and range-restricted species in restoration plots relative to degraded and reference systems. Restoration treatments showed increased resemblance of avian assemblages to remnant forest over time. Applied nucleation proved equally effective as plantation, despite a reduced planted area, whereas natural regeneration recovered more slowly. Assemblage-level trends in avian species richness and compositional similarity to reference forest are underpinned by reductions in use by pasture birds and by gradual increases in richness of forest-affiliated species. Because forest-affiliated species tend to have narrower distributions than the open-country species they replace, forest restoration can reduce biotic homogenization at the local scale. Restoration practitioners should consider applied nucleation as an alternative to standard plantations if seeking rapid recovery of bird assemblages. However, the ecological return on investment from natural regeneration increases over a couple of decades. Managers should monitor trends in forest-affiliated and range-restricted species to track the recovery of the full avian assemblages, since coarse metrics like species richness and overall compositional similarity may plateau relatively quickly.
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El habia ceniza (Habia gutturalis) y el torito capiblanco (Capito hypoleucus) son aves amenazadas y endémicas de Colombia. Ambas especies tienen rangos geográficos y tamaños poblacionales pequeños posiblemente como resultado de la destrucción y fragmentación de sus hábitats. Con el fin de obtener estimados cuantitativos de los efectos de características del paisaje sobre la ocupación de ambas especies, muestreamos una variedad de configuraciones del paisaje al interior de las zonas de amortiguamiento de dos hidroeléctricas en la cordillera Central de los Andes de Colombia y empleamos modelos de ocupación para estimar la proporción del área ocupada en función de estas covariables. Realizamos 35 puntos de conteo en cada zona de amortiguamiento entre junio y julio del 2014 y 2015. Utilizamos modelos de ocupación de una sola temporada para estimar la ocupación reconociendo la detección imperfecta. Los promedios de ocupación para ambas especies en el área de estudio fueron similares (0.61 SD=0.33 para el habia ceniza y 0.63 SD=0.25 para el torito capiblanco). Sin embargo, la distribución de la ocupación al interior del área de estudio fue muy diferente entre ellas. El mejor modelo para la habia ceniza propone que su ocupación disminuye con la elevación, mientras que el mejor modelo para la ocupación del torito capiblanco propone un aumento en la ocupación con la distancia a quebradas. Las probabilidades de detección fueron similares para ambas especies (<0.4) y declinaron significativamente durante el segundo año. Nuestros resultados proveen lineamientos cuantitativos para evaluar y monitorear el estado de estas poblaciones a corto y largo plazo.
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The shifts of bird song frequencies in urbanized areas provide a unique system to understand avian acoustic responses to urbanization. Using passive acoustic monitoring and automatic bird sound recognition technology, we explored the frequency variations of six common urban bird species and their associations with habitat structures. Our results demonstrated that bird song frequencies in urban areas were significantly higher than those in peri-urban and rural areas. Anthropogenic noise and habitat structure were identified as crucial factors shaping the acoustic space for birds. We found that noise, urbanization, and open understory spaces are factors contributing to the increase in the dominant frequency of bird sounds. However, habitat variables such as vegetation density and tree height can potentially slow down this upward trend. These findings offer essential insights into the behavioral response of birds in a variety of urban forest habitats, with implications for urban ecosystem management and habitat restoration.
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Animals respond to habitat alteration with changes in their behavior and physiology. These changes determine individual performance and thus precede changes in population size. They are therefore hypothesized to provide important insights into how animals cope with environmental change. Here, we investigated physiological and behavioral responses of a cooperatively breeding bird, the placid greenbul (Phyllastrephus placidus), in a severely fragmented tropical biodiversity hotspot and combined these data with remotely sensed (LiDAR) environmental data. We found that individuals had increased glucocorticoid hormone levels when breeding in territories with low native canopy cover or located within small fragments. However, when breeding with the help of subordinates, breeders in low quality territories had similar glucocorticoid levels as those in higher quality territories. Our study shows that sociality may impact how well animals cope with environmental change and contributes to our understanding of the role of glucocorticoid physiology and behavior in response to anthropogenic change.
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The synergistic impacts of climate change and habitat degradation threaten tropical species worldwide. However, how species’ microclimatic niches affect their demographic and phenotypic responses to anthropogenic change remains poorly understood. Using an 11-year mark-recapture dataset from primary and selectively logged forest in the Eastern Himalaya, we investigated how species-specific microclimatic niches predicted body mass and survival trends in understorey insectivorous birds in each habitat. Overall, logged forest is hotter and drier than primary forest, and the arthropod prey community shows shifts in composition upon selective logging. For understorey insectivorous birds, the degree of dissimilarity between species-specific primary and logged forest microclimatic niches was strongly and negatively correlated with survival and less strongly with body mass trends in logged forest. Microclimatic niche shifts in response to anthropogenic habitat modification can impact both demographic rates and body condition, crucial for population persistence. Our results can inform prompt, targeted conservation efforts toward the most threatened species in a warmer and more degraded world.
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Environmental mercury (Hg) contamination of the global tropics outpaces our understanding of its consequences for biodiversity. Knowledge gaps of pollution exposure could obscure conservation threats in the Neotropics: a region that supports over half of the world's species, but faces ongoing land-use change and Hg emission via artisanal and small-scale gold mining (ASGM). Due to their global distribution and sensitivity to pollution, birds provide a valuable opportunity as bioindicators to assess how accelerating Hg emissions impact an ecosystem's ability to support biodiversity, and ultimately, global health. We present the largest database on Neotropical bird Hg concentrations (n = 2316) and establish exposure baselines for 322 bird species spanning nine countries across Central America, South America, and the West Indies. Patterns of avian Hg exposure in the Neotropics broadly align with those in temperate regions: consistent bioaccumulation across functional groups and high spatiotemporal variation. Bird species occupying higher trophic positions and aquatic habitats exhibited elevated Hg concentrations that have been previously associated with reductions in reproductive success. Notably, bird Hg concentrations were over four times higher at sites impacted by ASGM activities and differed by season for certain trophic niches. We developed this synthesis via a collaborative research network, the Tropical Research for Avian Conservation and Ecotoxicology (TRACE) Initiative, which exemplifies inclusive, equitable, and international data-sharing. While our findings signal an urgent need to assess sampling biases, mechanisms, and consequences of Hg exposure to tropical avian communities, the TRACE Initiative provides a meaningful framework to achieve such goals. Ultimately, our collective efforts support and inform local, scientific, and government entities, including Parties of the United Nations Minamata Convention on Mercury, as we continue working together to understand how Hg pollution impacts biodiversity conservation, ecosystem function, and public health in the tropics. Resúmen La contaminación ambiental por mercurio (Hg) en los trópicos supera nuestra comprensión de sus consecuencias para la biodiversidad. Los vacíos de conocimiento que existen sobre la exposición a la contaminación podrían ocultar las amenazas para la conservación en el Neotrópico: una región que alberga a más de la mitad de las especies del mundo, pero que enfrenta una continua intensificación de las emisiones de Hg y del cambio de uso del suelo por el avance de la minería de oro artesanal y de pequeña escala (MAPE). Debido a su distribución global y su sensibilidad a la contaminación, las aves brindan una oportunidad valiosa como bioindicadores para evaluar cómo las emisiones de Hg afectan la capacidad de un ecosistema para sustentar la biodiversidad y, en última instancia, la salud global. Presentamos la más grande base de datos sobre concentraciones de Hg en aves Neotropicales (n = 2,316) para establecer una línea base para los niveles de exposición a Hg en 322 especies de aves de nueve países de América Central, América del Sur, y el Caribe. Encontramos patrones de las concentraciones de Hg en aves de los trópicos que se asemejan a los de las regiones templadas: mostrando una bioacumulación consistente a través de grupos funcionales y una alta variación espaciotemporal. Las especies de aves que ocupan posiciones más altas en la cadena trófica y en hábitats acuáticos registraron concentraciones elevadas de Hg que podrían tener efectos negativos en su éxito reproductivo. Es importante resaltar que las concentraciones de Hg en las aves de los sitios afectados por la MAPE fueron cuatro veces más altas que las de los sitios control y además difirió por temporada para ciertos nichos tróficos. Desarrollamos esta síntesis a través de una red de investigación colaborativa, la Iniciativa de Investigación Tropical para la Conservación y Ecotoxicología Aviar (TRACE), que ejemplifica un intercambio de datos inclusivo, equitativo e internacional. Si bien nuestros hallazgos sugieren una necesidad urgente de evaluar los sesgos en el muestreo, los mecanismos, y las consecuencias de la exposición al Hg en las comunidades de aves tropicales, la Iniciativa TRACE proporciona un marco para abordar estos objetivos. Nuestro esfuerzo colectivo tiene como propósito respaldar y brindar información a las entidades locales, científicas, y gubernamentales, incluyendo las Partes de la Convención de Minamata de las Naciones Unidas sobre el Mercurio, mientras continuamos trabajando juntos para comprender cómo la contaminación por Hg en los trópicos puede afectar la salud pública, el funcionamiento de los ecosistemas, y la conservación de la biodiversidad.
Article
Selective logging—the practice of removing a subset of commercially important trees from a forest—is a globally pervasive form of forest degradation. Selective logging alters both the structure and function of forests and the composition of ecological communities. Tropical insectivorous birds are highly vulnerable to microhabitat alterations in logged forest. Such altered microhabitats might affect the foraging of forest birds by altering (a) resource availability, and (b) foraging behaviour. We investigated the effect of selective logging on microclimates, prey availability, foraging behaviour and the foraging success of eastern Himalayan birds in the breeding season. Selective logging alters temperature-humidity microclimates and the composition of arthropod communities, both of which are likely to then collectively alter foraging behaviour by birds. We show that birds spent a lower proportion of their time foraging in primary compared with logged forest. Further, selective logging interacts with species traits such as body mass, preferred foraging stratum (understorey, midstorey or canopy) and foraging manoeuvre to influence foraging success. Gleaners generally foraged more successfully in primary forest and salliers in logged forest, although these patterns were modified by body mass and foraging stratum. Synthesis and applications: Our study shows how altered microclimates in anthropogenically modified habitats can influence resource availability and have downstream impacts on the behaviour of species at higher trophic levels.
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Context: Shade coffee plantations are purported to maintain forest biodiversity in agricultural landscapes. Understanding their conservation importance is hindered, however, by the limited taxa studied and failure to account for the landscape context of plantations and quality of reference sites. Objectives/Research questions: (1) how occupancy of mammals and birds changed from continuous forest to fragmented forest and coffee plantations while statistically controlling for landscape context, and (2) whether mammal and bird communities responded differently to shade coffee with regard to richness and composition. Methods: We used camera traps to sample ground-dwelling birds and medium- and large-bodied mammals (31 and 29 species, respectively) in shade coffee plantations and two types of reference forest (fragmented and continuous) in Colombia’s Western Andes. We used a multi-species occupancy model to correct for detection and to estimate occupancy, richness, and community composition. Results Shade coffee lacked ~50% of the species found in continuous forest, primarily forest-specialist insectivorous birds and forest-specialist and large-bodied mammals, resulting in different species composition between coffee and forest assemblages. Coffee plantation birds were generally a unique subset of disturbance-adapted specialists, whereas mammals in coffee were mostly generalists encountered across land uses. Forest fragments had species richness more similar to shade coffee than to continuous forest. Species sensitive to shade coffee responded negatively to isolation and disturbance at the landscape scale. Conclusions: Studies comparing coffee with relictual forest fragments may overestimate the conservation value of shade coffee. Conservation of biodiversity in shade coffee landscapes will be ineffective unless these efforts are linked to larger landscape-level conservation initiatives.
Article
Coffee, one of the major traded commodities in the world, has economic value for rural livelihood and potentially as habitat for forest wildlife. Previous work in Central Kenya has demonstrated that when cultivated with shade trees, coffee farms can host high levels of bird diversity. However, questions of how the African bird communities in shade coffee farms compares to those in natural forest remained unanswered. Using three visits to each of 160-point count locations in natural forest (80) and shade coffee sites (80) in Central Kenya, we estimated bird abundance and species richness in natural forest and shade coffee. Specifically, we tested hypotheses that the abundance and diversity of birds in shade-coffee and natural forests varies by feeding guilds and forest-association status. We found that, compared to natural forest, shade coffee had higher bird abundance and species richness of carnivores, granivores, omnivores, and insectivores, including understory forest insectivores specifically. Frugivores and nectivores had similar abundance in forest and coffee, but were more species rich in forest and coffee, respectively. The abundance and species richness of forest specialists and forest visitors were higher in natural forest than in shade coffee, whereas forest generalists and birds with no forest association status were more abundant and species rich in shade coffee. Our study confirms the value of remnant native trees within coffee plantations for the persistence and conservation of avian communities, while also clarifying that some groups of birds are reliant on natural forests and unlikely to be conserved in shade coffee farms.
Article
Forest fragmentation is a major driver of tropical bird endangerment, yet the mechanisms underlying species losses in fragmented landscapes remain poorly known. Loss of foraging microhabitats and food diversity in fragmented landscapes are potential mechanisms explaining fragmentation sensitivity. We therefore measured the body condition (i.e., body mass adjusted for individual size) of 20 tropical understory birds as a proxy for food availability across gradients of fragment patch size and silvicultural histories in the Western Andes of Colombia. Specifically, we asked (1) if body condition correlates with patch size, edge effects, or selective logging disturbance; and (2) if species responses were driven by the same explanatory variables or varied idiosyncratically. We documented significant variation in body condition with covariates in 11 of 20 (55%) understory bird species, and 55% of significant correlations were with fragmentation and selective-logging associated variables. Species responses were idiosyncratic and contrasting, with at least 1 significant response to each fragmentation-related covariate. Most effects, however, were driven by logging-induced changes to vegetation structure including loss of large-diameter trees, reduction in foliage height diversity and canopy cover, and loss of understory vegetation. The body condition of frugivores and nectarivores increased with logging-induced shifts in vegetation structure, with canopy gaps potentially favoring early-successional fruiting and flowering plants. By contrast, some insectivores suffered lower body condition with loss of vegetation structure (reduced foliage height diversity). Overall, our data support the hypothesis that fragmentation and selective logging change food resources available to birds and that some widespread nectarivores, frugivores, and omnivores may benefit from increasing edge density and logging-driven vegetation disturbance. We also documented significant positive effects of breeding condition on body condition, however, highlighting the need to control for this factor. Body condition may therefore be a useful index of habitat suitability when paired with analyses of abundance and demographic changes.
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Amazonian forest bird communities are among the richest in the world. Even so, relatively little is known about the organization of the entire avian community at local scales or about differences across Amazonia. These are fundamental data not only for understanding the processes generating and maintaining tropical diversity, but also as a baseline for evaluating anthropogenic changes to Amazonian forests. Here we provide a description of the entire bird community for a 100 ha plot of terra firme forest at the Biological Dynamics of Forest Fragments Project, near Manaus, Brazil, based on spot-map and mist net surveys augmented by additional field and analytical techniques. Although our results are from a single plot surveyed in a single year, our methods and interpretation reflect nearly 30 years of ornithological research at the site. We found 228 species on the plot, of which 207 were considered part of the core regional avifauna. Median density was five individuals/100 ha. Only 13 species (6% of the core species) had densities ≥ 20 individuals on the plot, although 55 species (27%) had ≤ 2 individuals. No species had territories smaller than 3 ha; median territory size was 11 ha for the 103 species for which we could make reasonable estimates. Measured by numbers of species or individuals, the plot was dominated by insectivores (54% of species, 62% of individuals). Biomass, however, was dominated by frugivores and granivores (59%). Compared to available data from other Amazonian forests, our site appears to have comparable richness of a similar set of species, but lower density and greater patchiness. Our results suggest that the area required to support populations of many species will be even greater in central Amazonia than in western Amazonia.
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Local abiotic conditions (microclimates) vary spatially and selection of favorable microclimates within a habitat can influence an animal’s energy budgets, behavior, and ultimately, fitness. Insectivorous birds that inhabit the understory of tropical forests may be especially sensitive to environmental variation and may select habitat based on microclimatic (e.g. temperature, humidity, light) conditions. Sensitivity to microclimate could contribute to the population declines of understory insectivores in response to forest fragmentation or degradation, which changes the physical structure of the forest, thereby increasing light intensity and temperature and decreasing humidity. To understand the role of microclimates in the habitat selection of understory insectivores, we characterized the microclimatic associations of nine species of understory insectivores at three sites along a precipitation gradient and across seasons in central Panama. We compared the distributions of microclimates selected by birds with microclimates at randomly chosen points within their home ranges to test for microclimate selectivity. We predicted that: (1) birds would select microclimates that are more humid, cooler, and less bright than random microclimates, (2) selectivity would be greater in hotter, drier habitats and (3) selectivity would be greatest in the dry season. We found no evidence of selectivity for the nine species we sampled on a seasonal or spatial basis. Microclimate variation was minimal in the forest understory at all sites, particularly in the wet season. Understory insectivores did not use microhabitats characterized by high light intensity, and may be sensitive to light, though the mechanism remains unclear. The lack of microclimate variation in the understory of tropical forests may have serious fitness consequences for understory insectivores due to increasing temperatures associated with climate change coupled with a lack of thermal refugia.
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Laboratory and field experiments were conducted on the island of Hawaii from 1977-1980 in an effort to determine the impact of avian malaria on the forest birds. At 16 study sites from sea level to tree line in mesic and xeric habitat, birds were captured and bled to determine the host and altitudinal distribution of blood parasites. In the laboratory, six bird species were challenged with malarial parasites to measure host susceptibility. Distributions, activity cycles, and transmission potentials of malarial parasite vectors were also analyzed. One species of Plasmodium was present from sea level to tree line, concentrated in the mid-elevational ranges in the ecotonal area where vectors and native birds had the greatest overlap. Native forest birds were: (a) more susceptible to malaria than were introduced species; (b) most likely to have malaria during the nonbreeding, wet season; (c) found ranging lower in xeric than in mesic forests; and (d) found to have a lower prevalence of malaria in xeric forests. Temporal as well as elevational differences in prevalence and parasitemia levels of wild birds were apparent throughout the annual cycle, a result of differing host and parasite responses to biotic and abiotic factors. Avian malaria probably did not reach epizootic proportions on Hawaii until after @?1920. However, since that time it has had a negative impact on the population dynamics of the native forest birds and is today a major limiting factor, restricting both abundance and distribution of these species on the island. In response, a number of native bird species have developed immunogenetic and behavioral responses that reduce the impact of the parasite on host populations.
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Two of the five bird species (D. merula and M. fortis) displayed resource selectivity among antswarms by foraging significantly more with one of the two ant species. The woodcreeper D. merula further segregated from the four antbirds in its utilization of white-lipped peccary (Tayassu peccari) herds as a foraging resource; the peccaries act as "beaters'' of arthropod prey in a manner similar to that of the army ants. The three antbirds that did not prefer one army ant species over the other (P. nigromaculata, R. melanosticta, and G. salvini) segregated by body mass, which may allow differential use of space along the width of an antswarm front. That size difference would permit a smaller, more subordinate species to "fit" along the front of a swarm that was already "full" to a different bird species. Population dynamics of the birds were not stable over five years of data collection, and total population of obligate ant-followers declined by almost half over the course of the study. It is suggested that periodic population fluctuations are a normal occurrence in guilds of obligate ant-followers and may be exacerbated by the lack of territoriality exhibited by most of these species. Lower population density correlated with decreased interference competition among individuals. Population fluctuations may increase the ability of the subordinate species R. melanosticta to coexist with the larger, dominant P. nigromaculata in floodplain forest. Nest-site selection may contribute to niche breadth among the obligate ant-followers. I provide descriptions of the nests, eggs, and nestlings of P. nigromaculata, R. melanosticta, and G. salvini, which were undescribed at the start of the present study. Received 22 November 2003, accepted 3 February 2004. /// Se estudiaron cinco especies de aves que siguen hormigas arrieras—Phlegopsis nigromaculata, Myrmeciza fortis, Rhegmatorhina melanosticta y Gymnopithys salvini (Thamnophilidae) y Dendrocincla merula (Dendrocolaptidae)—y dos especies de estas hormigas (Eciton burchelli y Labidus praedator) en la Amazonía peruana durante cinco años. En este trabajo se exploran aspectos de la coexistencia de estas cinco especies ecológicamente similares por medio de análisis de su ecología poblacional, uso de recursos, comportamiento y patrones espaciales de movimiento. El tamaño promedio del rango de hogar de cada especie de Thamnophilidae fue reducido por su dependencia en las impredecibles pero abundantes oportunidades de forrajear que brindan los ejércitos de L. praedator. Esta especie de hormiga jugó un papel determinante para expandir los recursos disponibles para las aves, lo que permitió un incremento en la densidad poblacional de éstas más allá de los niveles que podrían mantenerse únicamente con las hormigas de la especie E. burchelli. Dos de las cinco especies de aves (D. merula y M. fortis) exhibieron selectividad de recursos entre legiones de hormigas, forrajeando signficativamente más junto a una de las dos especies de hormigas. Además, el trepatronco D. merula se segregó ecológicamente de las otras cuatro especies de aves en términos de su utilización de manadas de huanganas (Tayassu peccari) como recurso de forrajeo; estos animales espantan artrópodos que pueden ser depredados por las aves en una forma similar a como lo hacen las hormigas arrieras. Las tres especies que no prefirieron una especie de hormiga sobre la otra (P. nigromaculata, R. melanosticta y G. salvini) se segregaron en términos de su peso corporal, lo que podría permitir un uso diferencial del espacio en el frente de avance de los ejércitos de hormigas. Las diferencias de tamaño podrían permitir que las especies más pequeñas y subordinadas puedan acomodarse en el frente de un ejército que ya estaría lleno para individuos de otra especie. Las dinámicas poblacionales de las aves no fueron estables a través de los cinco años de toma de datos, y el total de la población de aves seguidoras de hormigas declinó a casi la mitad durante el curso del estudio. Se sugiere que las fluctuaciones poblacionales periódicas son eventos normales en los gremios de aves que siguen hormigas obligatoriamente, y que éstas podrían ser acentuadas por la falta de territorialidad exhibida por la mayoria de las especies. Los tamaños poblacionales menores se correlacionaron con una competencia por interferencia reducida entre individuos. Las fluctuaciones poblacionales podrían incrementar la habilidad de la especie subordinada R. melanosticta para coexistir en el bosque del plano de inundación con P. nigromaculata, que es más grande y dominante. La selectión de sitios de nidificación podría contribuir a la amplitud del nicho entre las aves seguidoras de hormigas. Aquí proveo descripciones de los nidos, huevos y pichones de P. nigromaculata, R. melanosticta y G. salvini, los cuales no habían sido descritos al comienzo de este estudio.
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A 1960-71 study of populations of color-banded ant-following antbirds of three species on a tropical-forested lowland reserve, Barro Colorado Island, showed that the small species (Spotted Antbird, Hylophylax naevioides) remained stable at about 20 pairs/km^2. A medium-sized species, the Bicolored Antbird (Gymnopithys bicolor), decreased from about 3 pairs to 1.5 pairs/km^2. A large species, the Ocellated Antbird (Phaenostictus mcleannani), declined from 1.5 pairs/km^2 to near extinction--only one female remained in early 1971. Two of three other species that regularly follow army ants showed relatively stable populations, but a third large species (Barred Woodcreeper, Dendrocolaptes certhia) declined from two pairs to local extinction. Prior to 1960 a very large ground-cuckoo that follows ants had already become extinct there. Thus, the three largest of the seven original species that regularly followed ants were gone or nearly gone by 1970. The decrease in numbers of regular ant-following birds was not made up by increases in occasional followers. Detailed studies of antbirds showed no clear reasons for declines, except that annual mortalities of adults were high in Ocellated Antbirds (about 30%) compared to Spotted Antbirds (15%-17%) and nest losses perhaps higher in the former (96% compared to 91%). Nest mortalities were slightly lower (88%) and adult mortalities intermediate (about 25%) in Bicolored Antbirds. Female Ocellated Antbirds had higher mortalities than males. The antbirds renest repeatedly during long nesting seasons, up to 14 times per year for Ocellated Antbirds. However, to replace females of this species under Barro Colorado conditions 19 nestings per year would be needed. Concurrent listing of all birds of the island showed that 45 species of breeding birds, 22% of the avifauna present when the island was made a reserve, had disappeared by 1970. No new species replaced them. Of the lost species 13 are forest birds, in danger if forests are cut elsewhere. The other species, second-growth and forest-edge birds, have been crowded out by growth of the forest. Loss of species from this tropical reserve, especially the part apparently caused by the small size and isolation of the reserve, poses problems for conservation and ecological studies of tropical biotas. It is suggested that large future reserves have corridor zones to each other, that is, that intensive human use not preempt too much area nor interrupt immigration of animals or plants from one refuge to another.
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Recovery from infection is not always complete, and mild chronic infection may persist. Although the direct costs of such infections are apparently small, the potential for any long-term effects on Darwinian fitness is poorly understood. In a wild population of great reed warblers, we found that low-level chronic malaria infection reduced life span as well as the lifetime number and quality of offspring. These delayed fitness effects of malaria appear to be mediated by telomere degradation, a result supported by controlled infection experiments on birds in captivity. The results of this study imply that chronic infection may be causing a series of small adverse effects that accumulate and eventually impair phenotypic quality and Darwinian fitness. Copyright © 2015, American Association for the Advancement of Science.
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Amazonia now contains vast areas of secondary forest because of widespread regeneration following timber harvests, yet the value of secondary forest to wildlife remains poorly understood. Secondary forest becomes structurally similar to primary forest after abandonment, and therefore we predicted that avian movement across the interface of primary and secondary forest (hereafter "the interface") would gradually increase with time since abandonment until recovery to pre-isolation levels. From 1992 to 2011, we captured 2,773 understory birds of 10 foraging guilds along the interface of primary forest fragments and zero- to 30-year-old secondary forest at the Biological Dynamics of Forest Fragments Project near Manaus, Brazil. Our objectives were to understand the differences in land-use history that affect cross-interface movement and to determine how long it takes each guild to recover to pre-isolation capture rates. Across guilds, age of secondary forest within 100 m of the interface was the most important explanatory variable affecting capture rates; rates increased with age of secondary forest for all guilds except non-forest species. Mean recovery to pre-isolation was 26 years (asymmetric SE = 13 years below and 16 years above estimate) after secondary forest abandonment and 9 of 10 guilds recovered within 13 to 34 years. In the slowest guild to recover, terrestrial insectivores, 6 of 12 species were never caught along the interface, and we projected that this guild would recover in 60 years. Our recovery estimates quantify the dynamic permeability of the interface and contribute to a better understanding of the value of secondary forests as corridors among primary forest fragments. Received 26 October 2012, accepted 19 May 2013.
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The first edition of Tropical Rain Forests: an Ecological and Biogeographical Comparison exploded the myth of 'the rain forest' as a single, uniform entity. In reality, the major tropical rain forest regions, in tropical America, Africa, Southeast Asia, Madagascar, and New Guinea, have as many differences as similarities, as a result of their isolation from each other during the evolution of their floras and faunas. This new edition reinforces this message with new examples from recent and on-going research. After an introduction to the environments and geological histories of the major rain forest regions, subsequent chapters focus on plants, primates, carnivores and plant-eaters, birds, fruit bats and gliding animals, and insects, with an emphasis on the ecological and biogeographical differences between regions. This is followed by a new chapter on the unique tropical rain forests of oceanic islands. The final chapter, which has been completely rewritten, deals with the impacts of people on tropical rain forests and discusses possible conservation strategies that take into account the differences highlighted in the previous chapters. This exciting and very readable book, illustrated throughout with color photographs, will be invaluable reading for undergraduate students in a wide range of courses as well as an authoritative reference for graduate and professional ecologists, conservationists, and interested amateurs.
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Multi-species flocking behavior in birds as-sumes a wide range of forms. At one ex-treme are casual feeding aggregations such as those of herons and seabirds (Sealy 1973, Baltz 1977, Kushlan 1977). Showing some-what more social and temporal cohesive-ness are the restless flocks of blackbirds or sandpipers that form and dissolve on a daily basis (Recher 1966, Recher and Recher 1969, Goss-Custard 1970, Page and Whit-acre 1975, Burtt and Giltz 1977). Winter for-aging groups of chickadees (Parus sp.) and their consorts represent a further step to-wards continuity and organization (Morse 1970, Austin and Smith 1972, Glase 1973, Smith 1976, Hogstad 1978). These flocks form daily during the non-breeding season and may include many of the same indi-viduals. Tropical mixed-species foraging flocks are even more constant, existing vir-tually year-. We describe here a syndrome of flock be-havior that appears to represent the end-point of this series. It occurs in the mixed parties of small insectivorous birds that glean the understory foliage of Amazon ba-sin forests. These flocks are an important part of the bird life of the forest. They form daily in the hour following dawn and persist until late afternoon. This pattern is followed throughout the year, regardless of the amount of current breeding activity. Many species join these flocks, though under a variety of circumstances, detailed later. By means of color-banding and observa-tion we have discovered that these flocks possess the following properties. First, the core membership of the main study flock at our site in southeastern Peru consisted of 12 species whose territories coincided ex-actly. Observations on four neighboring flocks revealed that not all of the "core" species in the main study flock are present in every flock (Tables 1 and 2). Second, membership in these flocks appeared to be limited to one family of each species (i.e., a mated pair with perhaps one or two ju-veniles). This means that the core species possessed nearly identical population den-sities over large areas. If this pattern is com-mon, it helps to account for the unusually high equitability of netted bird samples from the Amazonian lowlands (Terborgh and Weske 1975). Third, territorial defense was communal. Boundary disputes arose in-frequently when neighboring flocks hap-pened to meet. When this occurred, a pro-longed confrontation might ensue, marked by vigorous vocal activity on both sides. Otherwise, territorial songs rarely were giv-en by most of the species. Fourth, nesting of flock members took place within the jointly-held flock territory. Young birds re-mained closely associated with their par-ents in the flock for at least several months and perhaps for as much as a year after fledging. In addition to documenting these find-ings, we present data on the ecological sort-ing of flock members, and propose a new interpretation of the status of so-called "oc-casional" flock members.
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Individual variation in natal dispersal behaviors has extensive ecological and evolutionary consequences. Traits such as offspring sex, age, and body condition may influence dispersal, resulting in a potentially complex suite of associations in traits that can affect fitness. Conceivably, individuals with particular phenotypes may breed in different habitats, thus potentiating the develop-ment of geographic variation. Moreover, studies typically underestimate dispersal distance owing to sampling issues and rarely consider the direction of movement, limiting understanding of this important life history stage. I examined the influence of phenotypic and social traits on dispersal distance and direction in a family living bird, the western slaty antshrike (Thamnophilus atrinucha). When accounting for detection probability, juveniles dispersed 1–14 territories and 46–1268 m.The age at dispersal and body mass upon leaving the nest influenced dispersal distance and direction. Older and heavier individuals dispersed shorter distances. Younger individuals dispersed towards comparatively younger forest with a higher density of antshrike territories. Older and heavier offspring may be more competitive and/or have increased experience with the local habitat, increasing their prob-ability of acquiring nearby territories. Contrary to other studies, sex-biased dispersal distance was not observed. Instead, the sexes dispersed in different directions, potentially to reduce the risk of inbreeding. This study revealed the importance of age at dis-persal and body mass on variation in dispersal behaviors and highlighted the need to investigate sex biases in dispersal direction.
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Long-term bird-banding programs provide knowledge of the demographic rates of avian populations, but we currently lack information on demographic rates of most bird populations in species-rich tropical ecosystems. Banding in tropical regions is typically conducted with protracted or irregular sampling occasions that make the choice of the proper capture–mark–recapture (CMR) model difficult. Here, we address common challenges related to collecting and analyzing data to estimate survival rates of resident Neotropical birds using 20 years of banding efforts in Mexico as a case study. We applied Cormack-Jolly-Seber and Barker models to estimate apparent survival and recapture probabilities of species with sufficient data for survival analyses. We were able to analyze 6 resident species of 136 total species; apparent survival probabilities ranged from 0.30 to 0.77, and recapture probabilities from 0.11 to 0.52. For monitoring programs with existing data collected at continuous, uneven, or irregular intervals, we recommend the application of the Barker model over other models because it was more efficient in the use of available banding data and less often violated CMR assumptions. We recommend that monitoring programs last >10 years and provide additional protocol suggestions for primary and secondary sampling occasions, as well as the number of nets, potential net configurations, and the extent of the spatial scale. These baseline recommendations are likely to foster an increase in our knowledge of avian survival rates in tropical ecosystems, which is imperative for managing tropical bird populations under changing environmental conditions.
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Long-term bird-banding programs provide knowledge of the demographic rates of avian populations, but we currently lack information on demographic rates of most bird populations in species-rich tropical ecosystems. Banding in tropical regions is typically conducted with protracted or irregular sampling occasions that make the choice of the proper capture–mark–recapture (CMR) model difficult. Here, we address common challenges related to collecting and analyzing data to estimate survival rates of resident Neotropical birds using 20 years of banding efforts in Mexico as a case study. We applied Cormack-Jolly-Seber and Barker models to estimate apparent survival and recapture probabilities of species with sufficient data for survival analyses. We were able to analyze 6 resident species of 136 total species; apparent survival probabilities ranged from 0.30 to 0.77, and recapture probabilities from 0.11 to 0.52. For monitoring programs with existing data collected at continuous, uneven, or irregular intervals, we recommend the application of the Barker model over other models because it was more efficient in the use of available banding data and less often violated CMR assumptions. We recommend that monitoring programs last >10 years and provide additional protocol suggestions for primary and secondary sampling occasions, as well as the number of nets, potential net configurations, and the extent of the spatial scale. These baseline recommendations are likely to foster an increase in our knowledge of avian survival rates in tropical ecosystems, which is imperative for managing tropical bird populations under changing environmental conditions.
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Many contemporary ecosystems are likely to be affected by multiple environmental drivers, complicating efforts to predict future changes in those ecosystems. We studied long-term changes (1980-2012) in forest dynamics and liana (woody vine) abundance and biomass in fragmented and intact forests of the central Amazon. We did so by contrasting trends in 33 permanent 1-ha plots near forest edges (plot center <100 m from the nearest edge) with those in 36 1-ha plots in intact-forest interiors (150-3300 m from nearest edge). In fragmented and edge-affected forests, rates of tree ( {greater than or equal to} 10 cm diameter-at-breast height) mortality and recruitment were often sharply elevated, especially in the first 10-15 years after fragmentation. Lianas ( {greater than or equal to} 2 cm stem diameter) also increased markedly in abundance (mean±SD=1.78±1.23% yr-1) and biomass (1.30±1.39% yr-1) over time, especially in plots with high edge-related tree mortality. However, plots in undisturbed forest interiors, which were originally established as experimental controls, also experienced long-term changes. In these plots, tree mortality and recruitment rose significantly over time, as did liana abundance (1.00±0.88% yr-1) and biomass (0.32±1.37% yr-1). These changes were smaller in magnitude than those in fragments but were nonetheless concerted in nature and highly statistically significant. The causes of these changes in forest interiors are unknown, but are broadly consistent with those expected from rising atmospheric CO2 or regional climate drivers that influence forest dynamics. Hence, the dynamics of Amazonian forest fragments cannot be understood simply as a consequence of forest fragmentation. Rather, the changes we observed appear to arise from an interaction of fragmentation with one or more global- or regional-scale drivers affecting forest dynamics. Both sets of phenomena are evidently increasing forest dynamics and liana abundances in fragmented forests-changes that could reduce carbon storage and alter many aspects of forest ecology.
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Birds are ubiquitous and highly interactive members of forest communities. As insect predators, birds influence tree growth by reducing the effect of folivorous arthropods. Coffee plantations, for example, benefit from insectivorous birds and have increased productivity as a result of bird control of insect pests. As frugivores that can move large distances, birds are the most important seed dispersers in tropical forests. Many crows and jays play critical roles as nut dispersers in temperate forests. Large vertebrate predators, such as hawks, may affect seedling establishment by preying on scatter-hoarding mammals or affecting their behavior. Pollination by birds is an important element in influencing the genetic structure of tree populations. Many of these ecosystem functions vary by latitude and by season. In return, forests provide food, nesting sites, and, in some cases, thermal refugia for birds. Forest structure, particularly in tropical sites, is closely tied to avian species richness on local and regional scales. Major threats to forest birds include deforestation, forest fragmentation, and urbanization. Invasive predators on nests and adults are also an important threat to island birds and climate-related changes.
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This book had its origin when, about five years ago, an ecologist (MacArthur) and a taxonomist and zoogeographer (Wilson) began a dialogue about common interests in biogeography. The ideas and the language of the two specialties seemed initially so different as to cast doubt on the usefulness of the endeavor. But we had faith in the ultimate unity of population biology, and this book is the result. Now we both call ourselves biogeographers and are unable to see any real distinction between biogeography and ecology.
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This chapter presents the author’s reflections about Norman Podhoretz. Like many leftists, Podhoretz is Jewish and has relied on verbal braininess as his chief means of getting on in the world. He purports to be, among other things, an intellectual. Yet despite his occupation and his manifest engagement with ideas, the author suggests that Podhoretz is far more visceral than cerebral. The power of his writing to anger or, conversely, to evoke the superior eyeroll depends largely on its subtext. On some level Podhoretz is usually raising a basic question: is real freedom desirable, or even possible? For the past decade his answer has been an aggressive and passionate no. Since his message often comes packaged in frenetic exaggeration and dubious logic, he is an easy target. But because radicals are not nearly so sure of their own answer as they pretend, he makes them nervous.
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