No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Impacts of sudden winter habitat loss on the body condition and survival of Redshank Tringa totanus
Abstract
1. Recent theoretical modelling has provided important insights into how habitat loss may affect local populations through impacts on individual fitness (survival, body condition, fecundity). Despite this, attempts to provide empirical evidence of such impacts on displaced individuals have been limited. Using a before-after-control-impact (BACI) approach, we report how a sudden loss of wintering habitat impacted on the body condition and survival of redshank Tringa totanus. 2. The intertidal mudflats of Cardiff Bay, UK, were inundated with freshwater in November 1999 following impoundment by a barrage, resulting in the displacement of c. 300 redshank to adjacent habitat on the Severn Estuary. Movements and the survival of these birds were monitored through observations of colour-marked individuals. Comparative survival rates were calculated for marked populations at the main recipient site, Rhymney, and a control site. 3. Displaced redshank had difficulty maintaining their mass in the first winter post-barrage closure: adults previously only recorded at Cardiff Bay were significantly lighter than those previously recorded at Rhymney. 4. Survival rates of displaced redshank also declined. The estimated annual survival of adult Cardiff Bay redshank fell from 0·846 in the 2 years pre-barrage closure to 0·778 in the 3 following years because of a significant decline in winter survival (P = 0·0006). In comparison, there was no significant change in the survival of adult Rhymney redshank, and adult survival at the control site was actually greater post-barrage closure than beforehand. The lack of decline in these rates and the similarity between those of Cardiff Bay adults pre-barrage closure and Rhymney adults indicate that the increase in winter mortality of Cardiff Bay birds resulted from their displacement. 5. Synthesis and applications. This study provides the first conclusive empirical evidence that habitat loss can impact individual fitness in a bird population. Adult redshank displaced from Cardiff Bay experienced poor body condition and a 44% increase in mortality rate. Without an increase in the recruitment of first-winter birds, such a change is likely to reduce substantially local population size. The results reported here should help to inform governments, planners and non-governmental organizations (NGOs) seeking to understand how developments might impact on animal populations.
... Reliable estimates of fecundity and survival are fundamental to conservation planning but remain unavailable for many widespread species (Méndez et al., 2018;Piersma et al., 1997;Sandercock, 2003). Baseline information on demographic rates for stable populations are particularly useful for identifying environmental perturbations that are likely to reduce future population viability (Burton et al., 2006;McDuffie et al., 2022;Piersma et al., 2016;Taylor & Dodd, 2013). ...
... Annual estimates of return rates (RR), apparent survival (ϕ), and true survival (S) from population studies of four genera of largebodied shorebirds (Limosa, Numenius, Bartramia, and Tringa Thompson and Hale (1993) Ukraine Breeding RR 0.724 Zhmud (1992) 0.78 following impoundment of an intertidal mudflat with a barrage for flood control (Burton et al., 2006), and apparent survival of wintering Eurasian Curlews dropped from 0.95 to 0.81 during 2 years with mechanized dredging of cockles in a coastal estuary (Taylor & Dodd, 2013). Reductions in apparent survival may be explained by increased mortality rates or by greater displacement from local areas. ...
The Prairie Pothole Region of central Canada supports a diverse community of breeding waterbirds, but many species have declining populations and the demographic mechanisms driving the declines remain unknown. We conducted a 7-year field study during 1995-2001 to investigate the demographic performance of Marbled Godwits (Limosa fedoa) and Willets (Tringa semipalmata) breeding in managed wetlands near Brooks, Alberta. Mark-recapture analyses based on Cormack-Jolly-Seber models revealed that the annual rates of apparent survival for Marbled Godwits ( ϕ ^ = 0.953 ± 0.012SE) and Willets ( ϕ ^ = 0.861 ± 0.015SE) are among the highest rates of survivorship reported for any breeding or nonbreeding population of large-bodied shorebirds. Our estimates of life expectancy for males were comparable to longevity records in godwits (17.3 years ±5.8SE vs. 25-29+ years) and willets (7.7 ± 1.5SE vs. 10+ years). The two species both showed strong breeding site fidelity but differed in rates of mate fidelity. Pairs that reunited and males that switched mates usually nested <300 m from their previous nests, whereas females that switched mates usually moved longer distances >1.1-1.5 km. Returning pairs usually reunited in godwits (85%) but not in willets (28%), possibly because of species differences in adult survival or patterns of migration. Baseline estimates of annual survival for banded-only birds will be useful for evaluating the potential effects of new tracking tags or the environmental changes that have occurred during the past 20 years. Conservation strategies for large-bodied shorebirds should be focused on reduction of exposure to anthropogenic mortality because low rates of natural mortality suggest that losses to collisions at breeding sites or harvest at nonbreeding areas are likely to cause additive mortality.
... There is a need for more research on how birds respond to drones (Mulero-Pázmány et al. 2017) to ensure that if recreational and commercial drone use becomes ubiquitous, effective regulations are in place to mitigate negative impacts. The repeated flushing of non-breeding waterbirds, particularly those species of waders and wildfowl which gather in large flocks in the non-breeding season in the UK (Frost et al. 2018), could increase energetic expenditure and reduce available feeding time, and also lead to effective habitat loss (Burton et al. 2002(Burton et al. , 2006. This study aims to further our knowledge of how non-breeding waterbirds birds could be affected by drone use and investigate whether drones could be a useful aide to monitor non-breeding waterbirds. ...
... It is also important to note that even when birds appear habituated to disturbance they can still show higher levels of stress hormones in more disturbed areas (Formenti et al. 2015). Long-term consequences would also depend on the availability of alternative sites nearby (Gill et al. 2001) as well as interactions between the physiological effects of disturbance and the availability and strength of preference for undisturbed areas (Burton et al. 2006). Distinguishing between these effects is complicated by the fact that the propensity of birds to appear tolerant of higher levels of disturbance (or to promptly return to a site following disturbance) may be driven primarily by an absence of suitable alternative sites nearby (Gill et al. 2001) and the condition of the birds in question (Beale & Monaghan 2004) which in turn will depend on a multitude of other factors. ...
Capsule: Non-breeding waterbirds are more likely to respond to drone approach when in larger flocks, and responses are more likely in arable and coastal habitats than at inland lochs.
Aims: To investigate the extent to which drones are a potential source of disturbance to non-breeding waterbirds.
Methods: Using a commercially available quadcopter drone, we approached waterbird flocks of varying sizes in coastal, freshwater, and arable habitats following a standardized protocol.
Results: Waterbirds at coastal sites and in arable fields were more likely to respond to drone approach than those at inland freshwater bodies. Larger flocks were more likely to respond to drone approach and responded at a greater distance than smaller flocks.
Conclusion: Repeated drone use at coastal and arable sites with large aggregations of feeding or roosting waterbirds could cause energetically costly flight responses, increased stress, and effective loss of available habitat. At such sites, it may be beneficial to regulate recreational and commercial drone use to minimize potential disturbance effects.
... While to date there has been limited work on the long-term effects of disturbance effects on seaducks, grebes and divers on wintering grounds, past work on waders has suggested that frequent disturbance can contribute to reduced survival (Burton et al. 2002(Burton et al. , 2006Armitage 2005, Davidson andRothwell 1993). This may relate to time spent avoiding disturbance (Urfi et al. 1996, Stillman & Goss-Custard 2002 or to displacement from preferred foraging areas making it harder to meet their daily energy requirements (Burton et al. 2006). ...
... While to date there has been limited work on the long-term effects of disturbance effects on seaducks, grebes and divers on wintering grounds, past work on waders has suggested that frequent disturbance can contribute to reduced survival (Burton et al. 2002(Burton et al. , 2006Armitage 2005, Davidson andRothwell 1993). This may relate to time spent avoiding disturbance (Urfi et al. 1996, Stillman & Goss-Custard 2002 or to displacement from preferred foraging areas making it harder to meet their daily energy requirements (Burton et al. 2006). We would also advise caution when interpreting short term behavioural responses of wintering waterbirds to marine activity; birds which appear not to be responding to disturbance may be remaining at a site regardless of negative impacts of disturbance, due to a lack of suitable alternative habitat nearby (Gill et al 2001). ...
SHORT-TERM BEHAVIOURAL RESPONSES OF WINTERING WATERBIRDS TO
MARINE ACTIVITY
... On the contrary, other studies also highlighted a positive role of coastal reclamation in the conservation of endangered birds when ecological compensation could provide food resources or shelters for birds (Huang et al., 2012;Rodríguez & Howe, 2013;Perkins et al., 2015). But these results were limited by focusing on populations of migratory shorebirds using short-term observations aiming at balancing between bird conservation and coastal reclamation management (Evans et al., 1979;Burton et al., 2006). However, an increasing amount of scientific evidence supports the concept that longterm coastal reclamation could affect bird conservation more significantly than short-term reclamation. ...
... However, an increasing amount of scientific evidence supports the concept that longterm coastal reclamation could affect bird conservation more significantly than short-term reclamation. Due to the inherent difficulty of getting the long-term data of both habitat and population of birds (Evans et al., 1979;Burton et al., 2006), empirical evidence supporting bird conservation efforts in remnant natural coastal wetlands is still limited. ...
Exploring how suitable habitat and population size of Red-crowned crane Grus japonensis respond to long-term coastal reclamation plays an important role in species conservation and in related coastal management. Here, we combined field data for suitable habitats and wintering population size of G. japonensis with GIS-based information to elucidate the influence of long-term coastal reclamation on this species and related conservation efforts. During 1975-2013, the intensity and spatial extent of coastal reclamation exhibited a temporal change, increasing dramatically in 1975–2000 and lessening considerably in 2000–2013. Under the pressure of long-term coastal reclamation, the decline of suitable habitat of G. japonensis was affected by increasing levels of human disturbance and decreasing availability of natural habitat. Moreover, the wintering population size of G. japonensis exhibited a decreasing trend during 1975–2013 as a result of the decreasing availability of fish ponds, bare tidal flats and increasing spatial extent of residential areas and P. australis habitat, which were indirectly affected by long-term reclamation. Our results highlight the importance of considering the long-term effects of coastal reclamation on both populations and suitable habitat of G. japonensis, which should be considered in future plans for coastal management and conservation.
... Furthermore, not only can the cumulative impacts from many small-scale disturbances equal or exceed those of large-scale disturbances, even minimal reductions in foraging time may also be meaningful when they accumulate over tidal cycles, weeks or months (West et al. 2002, Goss-Custard et al. 2006. Moreover, disturbances that displace individuals from one site to another might compromise non-displaced individuals at the 'new' site via density-dependent effects (Burton et al. 2006, Rutten et al. 2010. Thus, subtle behavioural changes may have negatively affected Godwits by reducing foraging time due to increased rates of alertness and agitation, which may alter premigratory fuelling and the condition of individuals. ...
Patchily‐distributed resources require individuals to balance risks and rewards associated with foraging sites that vary widely in quality, as determined by factors like food availability, disturbance rates, and predation risk. These trade‐offs may be especially acute for migratory species during the nonbreeding season when they must access high‐quality resources to recover from and prepare for migration. We assessed how density and body condition of nonbreeding Hudsonian Godwits (Limosa haemastica), acting as proxies for foraging site quality, were related to foraging success, availability of intertidal foraging habitat, landscape and bay characteristics, human disturbances, and predation risk at 42 intertidal mudflats in southern Chile. Godwit density and body condition increased with availability of foraging habitat and foraging success, except on mudflats where individuals were more alert and agitated (i.e. higher scanning rates and more displacement flights). In contrast, body condition and density of foraging Godwits were lower at sites with high levels of perceived disturbance. Our findings suggest that the non‐lethal effects of disturbances (i.e. perceived risks) may affect behaviour (e.g. scanning rates and displacement flights) in ways that can compromise refuelling rates, body condition, and performance across seasons. Thus, efforts to reduce disturbances to individuals foraging on tidal mudflats may be important to conserve migratory shorebirds, a guild undergoing severe population declines.
... Compared with 1970, wetland-dependent species, such as waterfowl, are said to be exhibiting a serious decline, with decreases of 81% of inland wetland species and 36% of coastal and marine species. This rapid decrease in waterfowl is reported to be directly affected by changes in their habitats due to land-use change and the lack of food resources due to habitat damage (Burton et al. 2006). ...
This study aimed to analyze the relationship between Cygnus spp. population trends and land-use changes and artificial development activities in the Nakdonggang Estuary for the necessity of management to the buffer area outside the protected area boundary in Korea. Analysis of the 15-year population change revealed a sharp decline in the Cygnus columbianus population in the winter, which could be attributed to the Nakdonggang Estuary becoming unfeasible as their wintering site. In contrast, there was no sharp decline in the Cygnus cygnus population, although a moderate decline was identified. Over the past 30 years, farmland activities decreased by approximately 10% in the areas adjacent to the protected area resulting from the expansion of the urbanized area. The rate of decrease in the water body area was high, attributed to urban development through reclamation. The correlation analysis between the area (ha) of paddy fields and the monthly (Nov.–Feb.) population of C. columbianus indicated that the populations in December (R² = 0.768) and January (R² = 0.743) were more correlated with the change in paddy field areas than those in the early winter (November: R² = 0.457) and at the end of winter (February: R² = 0.582). In the case of C. cygnus, the population tended to increase with increases in the areas of paddy fields, but the statistical explanatory power was low. We identified a distinct difference in that C. columbianus was more sensitive to urbanization than C. cygnus in the Nakdonggang Estuary.
... Soil accretion confers this ecosystem the capacity to adapt to sea-level rise 11 and to maintain all the ecosystem services they provide under future climate change scenarios 12 . At a lower intertidal range compared to saltmarshes, bare tidal (sand or mud) flats also provide important ecosystem services to coastal communities, such as the support of fisheries 13 and biodiversity, being essential habitats for the survival of resident and migratory birds that feed on invertebrates that inhabit these intertidal habitats 14,15 . Due to their lack of vegetation, soil C org stocks by surface area in bare tidal flats are usually lower than in adjacent saltmarsh communities 16 . ...
Intertidal estuarine habitats (e.g., saltmarshes and tidal flats) provide important ecosystem services to society, including coastal protection, food provision and Corg sequestration. Yet, estuaries and estuarine habitats have been subjected to intense human pressure, such as land-use change and artificialization of the shoreline to support economic activities and uses. Construction of engineering infrastructures (e.g., piers, bridges) in these areas alters estuary-wide hydromorphological conditions and thus sedimentation patterns at the estuarine scale, which are key drivers of habitats distribution and ecosystem structure, processes and functions. Most of the research on the impact of civil engineering structures on coastal habitats has focused on the biological communities that colonize them or the bottoms where they are placed, whereas their indirect impacts on adjacent habitats has been largely unexplored. Understanding the influence of man-made infrastructures on the distribution of estuarine habitats and functions is critical, particularly considering that shoreline armoring is expected to increase as a way to protect coastal areas from hazards derived from climate change. Shifts in habitat distribution and functions occur in several years or decades and relating them with the occurrence of past historical events is challenging when no monitoring data is available. By examining historical aerial photographs and different biogeochemical properties along a saltmarsh soil record, this study demonstrates that the construction of an infrastructure (i.e. bridge) caused a rapid transformation (~ 30 years) of a bare sandflat into a high marsh community and to significant changes in sediment biogeochemical properties, including the decrease in sediment accretion rate and Corg burial rates since then. This study contributes to increase the knowledge on the impact that the construction in coastal areas of civil engineering infrastructures can cause in intertidal habitats distribution and the ecological functions they provide for climate change adaption and mitigation.
... The quality, availability, and configuration of habitat at finer scales may reflect population-level patterns and help identify productive and unproductive habitats (Ims et al. 1993;Andreassen et al. 1998). For example, habitat quality influences space use and fitness for mammals (Rode et al. 2012;Bourbonnais et al. 2014) and birds (Burton et al. 2006;Angelier et al. 2011), and poor habitat can limit dispersal (Johnson et al. 2009;Proctor et al. 2012), increase predation (Sievert and Keith 1985;Thompson 1994), and reduce reproductive opportunities (Norris et al. 2003) and prey acquisition (Andruskiw et al. 2008). Ultimately, these factors contribute to population decline and reduced viability (Johnson 2007). ...
The threats that affect a species often vary within its geographic range. Wood turtles (Glyptemys insculpta (Le Conte, 1830), formerly Clemmys insculpta (Le Conte, 1830)) are a species of concern due to widespread decline from anthropogenic threats. We studied two populations of wood turtles from June–September 2019 and 2020 to evaluate how landscape features and vegetative structure influenced space and habitat use and to identify potential risks in the remote, northern parts of its range. We hypothesized that space use would vary due to regional, landscape, and sex-specific differences. Turtles at the conifer-dominated site with higher road density had significantly smaller home ranges than the site with expansive and contiguous floodplains (7.25±1.92 ha and 26.28±6.77 ha, respectively). Females moved farther away from rivers than males (136.00±23.68 m and 69.18±34.81 m, respectively) and made the longest single-event movements. However, movements by males were significantly longer (34.65±1.91 m) than females (23.99±1.03 m) and followed rivers. At finer spatial scales, we found that turtles selected activity areas with complex vegetative structure and a more open canopy. Our study indicates that populations in contiguous forest could be critical to the conservation of wood turtles and we discuss management recommendations to reduce potential mortality risks in the northern part of its range.
... Long-term negative effects of disturbance are driven by the interaction between the (i) energetic costs of disturbance, (ii) the reduction of effective foraging habitat, and (iii) increased stress in response to disturbance (Burton et al. 2006, Stillman & Goss-Custard 2002, Urfi et al. 1996. While flight is thought in most cases to be the most costly mode of locomotion among birds (Nudds & Bryant 2000, Pelletier et al. 2008, the energetic requirements of flight vary by species (Pennycuick 2008), and measuring the energetic costs of diving and swimming is more challenging (Mendel et al 2008, Savard et al. 2017. ...
Capsule
Recording of behavioural responses to ferry traffic for 11 target species showed that Red-throated Diver Gavia stellata, Slavonian Grebe Podiceps auratus, and Black-throated Diver Gavia arctica were most likely to react to passing vessels.
Aim
To provide information on how responses to marine traffic vary between waterbird species to inform marine spatial planning and environmental impact assessments in the near-shore environment.
Methods
We recorded behavioural responses to ferry traffic for 11 target species in near-shore waters: Common Eider Somateria mollissima, Goldeneye Bucephala clangula, Long-tailed Duck Clangula hyemalis, Velvet Scoter Melanitta fusca, Red-breasted Merganser Mergus serrator, Black-throated Diver, Great Northern Diver Gavia immer, Red-throated Diver, European Shag Gulosus aristotelis, Slavonian Grebe and Black Guillemot Cepphus grylle. Responses were analysed using generalized linear models and mixed models.
Results
Red-throated Diver, Black-throated Diver and Slavonian Grebe were the most likely species to exhibit a response to passing vessels. While Red-throated Divers and Slavonian Grebes were highly likely to flush, Black-throated Divers and Great Northern Divers rarely took flight, instead favouring swim or dive responses. In rougher sea conditions birds were more likely to take flight, and the propensity to respond declined across the wintering period.
Conclusions
This research provides comparative evidence on the behavioural responses of waterbirds to marine traffic. The results support previous studies which highlighted the high sensitivity of diver species to disturbance and provide new evidence that Slavonian Grebe may also be a high sensitivity species.
... The shores are covered with small rocks with sporadic reed bed patches. Dice snakes seem to be abundant here, similar to Golem Grad; however further ecological studies are needed to discern population due to its strong associations with reproductive output (Guinet et al. 1998; and survival (Burton et al. 2006;Reading 2007), among other traits. ...
Studies of body condition in snakes are generally lacking and were only done on a few species and with limited sample sizes. Additionally, almost no studies considered how different factors affect body condition. We used a large dataset amassed over a 15 year-long ecological study to make a preliminary screening of body condition index (BCI) variation in a metapopulation of dice snakes (Natrix tessellata) in the region of Lake Prespa. We considered how factors such as sex, food, colour morph, locality and time affect BCI. We demonstrate a positive effect of food (relatively less in males), and lower BCI in females. Importantly, there is a strong seasonal effect, summer months having a positive effect as opposed to spring. The results of our study raise important considerations for future studies on snake BCI, but also conservation of freshwater ecosystems.
... One measure of body condition is an individual's relative amount of energy storage, often quantified as body fat accumulation (Green 2001). Previous work has used such indices to identify the consequences of body condition for reproductive success (Chastel et al. 1995;Testa andAdams 1998) andsurvival (McMahon et al. 2000;Burton et al. 2006). For example, female polar bears (Ursus maritimus) with greater fat stores are able to produce heavier cubs that are more likely to survive (Atkinson and Ramsay 1995). ...
Mass gain is an important fitness correlate for survival in highly seasonal species. Although many physiological, genetic, life history, and environmental factors can influence mass gain, more recent work suggests the specific nature of an individual’s own social relationships also influences mass gain. However, less is known about consequences of social structure for individuals. We studied the association between social structure, quantified via social network analysis, and annual mass gain in yellow-bellied marmots (Marmota flaviventer). Social networks were constructed from 31 738 social interactions between 671 individuals in 125 social groups from 2002 to 2018. Using a refined dataset of 1022 observations across 587 individuals in 81 social groups, we fitted linear mixed models to analyze the relationship between attributes of social structure and individual mass gain. We found that individuals residing in more connected and unbreakable social groups tended to gain proportionally less mass. However, these results were largely age-dependent. Adults, who form the core of marmot social groups, residing in more spread apart networks had greater mass gain than those in tighter networks. Yearlings, involved in a majority of social interactions, and those who resided in socially homogeneous and stable groups had greater mass gain. These results show how the structure of the social group an individual resides in may have consequences for a key fitness correlate. But, importantly, this relationship was age-dependent.
... Whilst this study suggests that oystercatchers may be adaptable during periods of stress, the consequences for their fitness will be dependent on the availability of alternative foraging areas and the levels of intraspecific competition that individuals will face (cf. Burton et al. 2006, Goss-Custard et al. 2006. This study demonstrates an example of site-resilience in a protected area network. ...
With coastal wader populations exhibiting long-term declines globally, understanding how they respond to changes in their preferred prey is important for future predictions, especially given the potential for warming seas to affect invertebrate populations. The cockle Cerastoderma edule population in the Burry Inlet Special Protection Area (SPA) in south Wales, UK, declined from 1997-2004 before an abrupt ‘crash’ in stocks between 2004 and 2010. While there has been some recovery since, stocks of larger cockles are still very low. Using survey data from the UK Wetland Bird Survey and analyses of apparent survival and biometrics from ringing, we investigated how the Burry Inlet SPA’s wintering Eurasian oystercatcher Haematopus ostralegus population responded to this crash. Our analysis showed that both body condition and apparent survival of wintering adult oystercatchers were reduced in the years following the cockle crash but both recovered. The number of birds using the Burry Inlet SPA decreased through the course of the cockle stock decline whilst numbers of birds in the adjacent Carmarthen Bay increased, indicating the importance of adjacent sites for buffering the effects of such changes, i.e. protected secondary habitats can be a vital component of a resilient site network. Our findings are useful in understanding how a predator copes with a serious decline in its preferred food stocks. This study has wide applicability in planning the management of coastal wetlands and shellfisheries as well as the design of resilient protected area networks in the light of environmental change.
... While waterbirds can respond to estuarine habitat loss by emigrating to another estuary (Yang et al., 2011), many of them are site-faithful and, thus, may only move locally in response to a loss of habitat (Burton and Armitage, 2008), which increases local densities and, consequently, competition for resources (Stillman et al., 1997). This may affect individual fitness, i.e., body condition and survival rates (Burton et al., 2006), while effects can also be carried over to impacts on the breeding productivity of birds, with ultimate impacts on population size (Baker et al., 2004;Piersma et al., 2016;Studds et al., 2017). In response to these observations, the creation or restoration of intertidal habitats can help to mitigate the effects of non-breeding habitat loss and the deterioration of intertidal habitats (Atkinson, 2003). ...
Estuaries have historically been subject to considerable habitat loss, and continue to be subjected to such in areas where the natural landward migration of intertidal habitats is constrained by hard coastal defences. Thus, in estuaries where direct (e.g., port development) or indirect (e.g., sea level rise) processes are predicted to threaten intertidal habitats and associated waterbird species, there is a regulatory requirement to produce compensatory intertidal habitats. Managed realignment (MR) is a shoreline management practise that is undertaken to build sustainable coastal defences and create intertidal habitats in estuaries. This nature-based solution brings multiple benefits in the form of carbon storage, increased resilience to flooding, and, potentially, the formation of new habitats, which is the topic of this study. A 75-ha site at the Paull Holme Strays (Humber Estuary, United Kingdom) was monitored over a 10-year period following MR to examine the change in the abundance of waterbirds in the chosen site in response to the physical processes occurring there. Using digital terrain models (DTMs) collected via light detection and ranging (LiDAR), we examined how four compensatory target species responded to changes in elevation after the creation of the site. It was shown that the very rapid accretion of estuarine sediment occurred in the first decade of the new re-created intertidal, which, over time, led to changes in the numbers of benthic foraging birds supported. Furthermore, elevation change was also driven by this sediment accretion, the rate of which depended on the initial bed elevation of the sectors within the site. Ten years after the recreation of the habitat, the spatial heterogeneity in the bed elevation remained high; however, the sectors with the lowest elevations accreted the most over the 10-year period. The foraging number of the four waterbird species that colonised the MR site significantly declined above a certain elevation, with this effect being most pronounced for the Eurasian curlew ( Numenius arquata ). The number of common shelducks ( Tadorna tadorna ), dunlins ( Calidris alpina ), and common redshanks ( Tringa totanus ) declined significantly after initial peaks 5–7 years after the creation of the site, reflecting the ongoing elevation changes. Thus, this study highlighted the need for long-term studies to understand how species respond to large-scale habitat construction. It can also aid in predicting the suitability of an MR site for waterbirds in the medium and long term.
... Oncorhynchus spp.; Magnusson & Hilborn, 2003) and birds (Tringa spp. & Haematopus spp.; Burton et al., 2006;Lambeck, 1990). Reduced body condition (i.e. ...
The deterioration of coastal habitats cascades to the decline of associated fauna by reducing trophic resource availability, shelter from predators and nursery grounds. The decline of biogenic habitat structure, such as in kelp forests, coral reefs, mangroves or seagrass beds, often causes a local increase in water flow velocity and wave exposure. The impact of this change in hydrodynamics on the energy expenditure of animals is largely unknown. Here we demonstrate that loss of seagrass beds increases water current velocity, which impacts associated pipefishes through increased energy expenditure. We correlated ventilation frequency with metabolic rate in four pipefish species, to be able to estimate metabolic rates in free‐swimming fish. Using a hydrodynamic flume, we then experimentally tested the effect of current velocity and substrate (seagrass or sand) on ventilation frequency and behaviour. Ventilation frequency was consistently higher when they swam on sand substratum compared to seagrass substratum for all species, and this was especially noticeable for the species with prehensile tails (i.e. Nerophis ophidion). Seagrass canopies reduced flow velocities by 7‐44%, which increased the overall current exposure that pipefish tolerated. N. ophidion, Syngnathus rostellatus and Syngnathus typhle showed two behavioural responses to currents: holding on to the seagrass canopy, and moving to areas where the current was lower (i.e. bottom) in trials without seagrass. Most of the individuals of all species were unable to maintain position in velocities of 15 – 18 cm s‐1 on sand substratum. In this work, we demonstrate the reliance on seagrass hydrodynamic shelter of four species of pipefish. Among them, N. ophidion showed the highest seagrass shelter dependence and vulnerability, while S. rostellatus and S. typhle are potentially more resilient to vegetation changes. Increased energy expenditure is thus another impact on fishes as seagrass beds and other structural habitats continue to decline in coastal areas.
... Habitat loss is the most frequently implicated cause of population declines (Burton et al. 2006;Sanderson et al. 2006;Moores et al. 2008), yet the evidence of the impact of habitat loss on either individuals or populations of migratory species that move widely throughout the landscape can be hard to establish (Carlisle et al. 2009;Alves et al. 2013). For example, migratory shorebirds travelling through the East Asian-Australasian Flyway are in rapid decline, and there is an urgent need to identify causes of the declines and management interventions to reverse them (Amano et al. 2010;Wilson et al. 2011;Clemens et al. 2016). ...
Many migratory shorebird species using the East Asian–Australasian Flyway are declining rapidly. While the loss of staging habitats in East Asia is considered the primary cause, stressors to fitness often occur throughout the geographic range of declining species, and threats in the non-breeding grounds have been comparatively poorly studied. Three species of migratory shorebird, Curlew Sandpiper (Calidris ferruginea), Sharp-tailed Sandpiper (C. acuminata) and Red-necked Stint (C. ruficollis), use Australia’s dynamic temporary wetland systems opportunistically, yet these large wetland systems have become increasingly degraded, with reduced frequency and extent of flooding. Here, we test whether variables related to wetland availability in Australia’s interior can explain annual variation in apparent survival, abundance or immature to adult ratios at three well-monitored coastal shorebird areas in southern Australia (total area > 1315 km²). We show that coastal annual bird abundance and ratios of immatures at the coast were higher when inland Australia was relatively hot and dry. Also, a small but significant amount of variation in annual apparent survival can be explained by annual variation in inland conditions, with higher survival rates in years when inland conditions were relatively wet and cool. For the endangered Curlew Sandpiper, the impacts of Australian environmental conditions may be exacerbating the impacts of conditions experienced in other parts of its range on fitness and survival. While the effects we document here are relatively weak, they do suggest that management of inland wetlands for these shorebirds may positively affect survival rates of these sharply declining species.
... Human activities are known to affect waterbirds [15,16] by decreasing their foraging success [10,17], reducing breeding success [18], modifying distribution [19], decreasing species richness [20], and also changing community composition [21,22]. Waterbird habitat damage can result in a decline in waterbird numbers [23,24] or cause waterbirds to move to nearby suitable habitats [25]. ...
To design a good conservation strategy for herbivorous Anseriformes wintering in Poyang Lake, knowledge of habitat suitability is essential. Therefore, this study aimed to assess the habitat suitability of herbivorous Anseriformes of China's Poyang Lake. Landsat images with a resolution of 30 m downloaded from the United States Geological Survey, and other ancillary data were used. The ENVI 5.3 software and ArcGIS 10.2 software were used for preprocessing, classifying the satellite image, and mapping habitat suitability. The study reveals that land cover types were divided into vegetation, mudflats, water, and sand. Similarly, the study area's habitats were also divided into unsuitable, fair, good, and best grades. However, the distribution of the habitat suitability for each grade reveals significant spatial variations. For instance, vegetation indicated the areas with the best habitat grade, followed by mudflats, and these areas cover (47.93%, 2015 and 55.78%, 2019) the majority of the study area. The unsuitable grades cover the smallest areas (0.48%) of the lake. Similarly, this study results showed a slight change in habitat suitability areas. Therefore, this study highlighted that Poyang Lake has valuable importance for the conservation of herbivorous Anseriformes. Extending the years of study and including some ecological variables from different stopovers could improve the results.
... Individuals with BCI scores above the mean have above average amounts of metabolizable tissue (fat or protein) relative to their length and vice versa (Schulte-Hostedde et al., 2005). Body condition correlates with fitness metrics such as survival probability and fecundity (Bender et al., 2008;Burton et al., 2006;Carranza & Hidalgo de Trucios, 1993). ...
Anthropogenic land use changes have broad impacts on biological diversity, often resulting in shifts in community composition. While many studies have documented negative impacts on occurrence and abundance of species, less attention has been given to native species that potentially benefit from anthropogenic land use changes. For many species reaching high densities in human‐dominated landscapes, it is unclear whether these environments represent higher quality habitat than more natural environments. We examined the influence of landscape ecological integrity on relative abundance and body condition of two native generalist freshwater turtle species that are prevalent in anthropogenic systems, the painted turtle (Chrysemys picta) and red‐eared slider (Trachemys scripta elegans). Relative abundance was negatively associated with ecological integrity for both species, but the relationship was not strongly supported for painted turtles. Body condition was positively associated with ecological integrity for painted turtles, with no strong association for red‐eared sliders. Our study suggests that both species benefitted at the population level from reduced ecological integrity, but individual‐level habitat quality was reduced for painted turtles. The differing responses between these two habitat generalists could partially explain why red‐eared sliders have become a widespread exotic invasive species, while painted turtles have not.
... It is well known that human activities can affect the health condition of birds (Burton et al., 2006;Johnson et al., 2006;Costantini et al., 2007;Madsen & Riget, 2007). Pollutants, such as heavy metals, oil, synthetic organic contaminants, and plastics, can cause oxidative stress and, consequently, affect seabirds' immune system (Briggs et al., 1996;Thompson & Hamer, 2000;Rainio & Eeva, 2010). ...
Adélie penguins (Pygoscelis adeliae) are seabirds that live exclusively in Antarctica, one of the planet's last pristine areas. However, this remote region is experiencing a continuing expansion of human activities that may affect Antarctic fauna. Trace metals constitute a menace to seabirds because they can adversely affect their health. There is a lack of studies relating to metals' levels in feathers with morphological parameters of seabirds. Trace metal levels were measured in Adélie penguin feathers and their body condition through the relative condition factor (ReCF) in adult individuals from two South Shetland Islands locations and two from Graham Land. Consequently, we determined the levels of some metals in feathers to see any relationship with morphological parameters linked to the bird's health. Our results showed significant differences in metals among locations studied and a significant relationship between ReCF with Cu and Zn in one of the South Shetland Islands. Also, penguins exhibited a significantly lower weight. We found a positive correlation between non-essential with essential metals, indicating that Cu acts as a detoxifying agent for Cr, Cd, and Pb. In contrast, Se could be for V and Pb. Although the relationship between most metals with ReCF was not significant, some site-specific factors may be influencing it, whereas metals may be affecting the organisms at low biological levels. Molecular, biochemical, and genetic studies are required to elucidate this issue.
... In the present paper, we argue that weight and tarsus length similarities connect phylogenetically over-dispersed Nearctic-Neotropical species in heterospecific flocks, which make some similar, commoner, and ecologically flexible species as probable niche-constructing protagonists important to the formation of heterospecific flocks. Over this scenario, urbanization, habitat loss, and climate warming are currently impacts that affect the fitness and survival of shorebirds (Burton et al. 2006;Thomas et al. 2003;Cestari 2015;Rakhimberdiev et al. 2018). Therefore, we do not discard that these relatively recent impacts may also be acting as new selective forces to augment behavioral flexibility and morphological adjustments of long-distance migratory birds (van Gils et al. 2006;Zhang et al. 2019), which also may include reduction of body size (van Gils et al. 2016). ...
Defense, vigilance, and optimal foraging are frequently related to the formation of flocks
in birds. Few studies concerning long-distance migrant shorebirds analyzed whether phylogeny and ecological similarities of species are associated with the formation of heterospecific flocks. Here, we explore (1) the niche conservatism theory, (2) the competition relatedness hypothesis, and (3) the niche construction hypothesis to explain the formation of wintering Nearctic-Neotropical heterospecific shorebird flocks in the southeastern coast of Brazil. In the first, closely-related species keep their ecological traits over time. In the last two hypotheses, ecological dissimilar and distant-related species may coexist due to strong biotic interactions. Our results discard the influence of relatedness between species and/or phylogenetic filtering signals that could act in the formation of heterospecific flocks. Co-participation of species in flocks is explained by similarities in body weight and tarsus length, which invokes the niche construction hypothesis. Probably, some similar-sized and niche-constructing species are relocating in space and changing the environment that they experience to optimize individual capacity to flee from predators. From an ecological perspective, numerous phenotypically similar species with redundant roles could lead to greater resilience of the community under anthropogenic disturbances. From an evolutionary perspective, different species with similar phenotypes may diminish costs of activity matching and augment individual fitness.
... Mud and sand flats are essential habitats for the survival of resident and migratory overwintering shorebirds (Burton et al., 2006), which feed primarily upon infaunal and epifaunal invertebrates (Bowgen et al., 2015). Some small sandpiper species Calidris spp. ...
Ecosystem functioning and services have provided a rationale for conservation over the past decades. Intertidal muddy sediments, and the microphytobenthic biofilms that inhabit them, perform crucial ecosystem functions including erosion protection, nutrient cycling and carbon sequestration. It has been suggested that predation on sediment macrofauna by shorebirds may impact biofilms, and shorebirds are known to consume biofilm, potentially causing significant top-down effects on mudflat ecosystem functioning. We carried out an exclusion experiment on the Colne Estuary, Essex, to examine whether shorebird presence significantly affects sediment erodibility measured with a Cohesive Strength Meter (CSM) and microphytobenthos biomass measured using PAM fluorescence (Fo) and chlorophyll a content. We also tested for treatment effects on sediment-water nutrient fluxes [nitrate, nitrite, ammonia, phosphate and dissolved organic carbon (DOC)] during periods of both dark and light incubation. Excluding shorebirds caused statistically significant changes in regulating and provisioning ecosystem functions, including mudflat erodibility and nutrient fluxes. The presence of shorebirds lowered the sediment critical erosion threshold τcr, reduced nitrate fluxes into the sediment under illumination, lowered nitrate efflux, and reduced phosphate uptake, compared to sediments where birds were excluded. There were no significant differences in macrofauna community composition within the sediment between treatments after 45 days of bird exclusion, suggesting a direct link between shorebird presence or absence and the significant differences in biofilm-related variables. This study introduces previously unknown effects of shorebird presence on ecosystem functions within this system and highlights an area of shorebird science that could aid joint conservation and human provisioning action.
... 국가간 이동하는 철새들은 각기 다양한 번식지와 월동지를 이용하기 때문에 이들의 서식지를 파악하고 특성을 이해하는 것은 종 보호를 위해 매우 중요하다 (Martin and Finch, 1995;Burton et al., 2006;Nebel et al., 2008). 특히 멸종위기종의 번식지와 취식지 등의 정보를 파악하는 것은 종의 보전 및 관리 를 위한 기초자료로서 그 가치가 매우 높다고 할 수 있다 (Ueng et al., 2007;Kang et al., 2016). ...
Migratory birds use a variety of breeding and wintering sites, and it is particularly important to understand more information on breeding and feeding sites for the conservation and management of endangered species. Black-faced spoonbills (Platalea minor) are an international endangered species distributed in East Asia. The
majority of black-faced spoonbills breed on uninhabited islets off the west coast of the Korean Peninsula during the breeding season, and they are distributed in East Asia such as Taiwan, Hong Kong, southern China, Japan, and Jeju island during the winter season. In this study, we used a wild animal location tracking system to analyze and compare home ranges of three black-faced spoonbills spending the post-fledging stage in Gujido islet in Incheon and Chilsando islet in Yeonggwang each in 2015. The tree black-faced spoonbills in Guji islet showed a home range in coastal areas in Hwanghaenam-do and Gangneung-gun. The home range size (mean±SD) was estimated to be 425.49±116.95 km2 using 100% MCP, 43.61±18.51 km2 using KDE 95%, and 7.46±3.68 km2 using KDE 50%. The tree black-faced spoonbills in Chilsando islet showed a home range in the Baeksu tidal
flat and the Buan Saemangeum area with a size of 99.38±55.29 km2 using 100% MCP, 19.87±6.05 km2 using KDE 95%, and 1.16±0.53 km2 using KDE 50%. The figured indicated that the tree black-faced spoonbills breeding in Gujido islet had a wider home range than those breeding in Chilsando islet. During the post-fledging stage, the home ranges of black-faced spoonbills were mostly breeding in mudflats. Therefore, it is necessary to minimize human intervention, such as the construction of roads and structures and the human access, to
protect the habitats during the period.
... One of the most remarkable projects was working with the Centre for Ecology and Hydrology on developing models of how estuary shapes and sediments might change with projected sea-level rise. In addition to producing papers on population estimates for a range of different bird groups, other important studies included an analysis of ringing recoveries to show the optimum spacing for refuges for wintering waders (Rehfisch et al. 1996); how a sudden loss of wintering habitat affects Common Redshank Tringa totanus survival (Burton et al. 2006); the impacts of bird populations on the microbiological quality of bathing waters (Wither et al. 2005); and a number of more general papers on the impacts of climate change on wintering waterbirds (e.g. Austin & Rehfisch 2003, Robinson et al. 2009). ...
... We used indices of individual performance (survival, body condition) as proxies for environmental differences among our study sites because performance consequences ultimately drive adaptive evolution (Arnold 1983). Further, a rich body of work links habitat quality to body condition (e.g., Bearhop et al. 2004, Burton et al. 2006, Maceda-Veiga et al. 2014) and survival (e.g., Paradis 1995, Kindvall 1996, Carvell et al. 2017). However, a drawback of our approach is that it does not reveal proximate drivers of salamander dispersal. ...
Dispersal evolves as an adaptive mechanism to optimize individual fitness across the landscape. Specifically, dispersal represents a mechanism to escape fitness costs resulting from changes in environmental conditions. Decades of empirical work suggest that individuals use local habitat cues to make movement decisions, but theory predicts that dispersal can also evolve as a fixed trait – independent of local conditions – in environments characterized by a history of stochastic spatiotemporal variation. Until now, however, both conditional and fixed models of dispersal evolution have primarily been evaluated using emigration data (stay vs. leave), and not dispersal distances – a more comprehensive measure of dispersal. Our goal was to test whether conditional or fixed models of dispersal evolution predict variation in dispersal distance in the stream salamander Gyrinophilus porphyriticus. We quantified variation in habitat conditions using measures of salamander performance from 4 years of spatially explicit, capture‐mark‐recapture (CMR) data across 3 headwater streams in the Hubbard Brook Experimental Forest in central New Hampshire, USA. We used body condition as an index of local habitat quality that individuals may use to make dispersal decisions, and survival probability estimated from multistate CMR models as an index of mortality risk resulting from the long‐term history of environmental variation. We found that dispersal distances increased with declining survival probability, indicating that salamanders disperse further in risky environments. Dispersal distances were unrelated to spatial variation in body condition, suggesting that salamanders do not base dispersal distance decisions on local habitat quality. Our study provides the first empirical support for fixed models of dispersal evolution which predict that dispersal evolves in response to a history of spatiotemporal environmental variation, rather than as a conditional response to current habitat conditions. More broadly, this study underscores the value of assessing alternative scales of environmental variation to gain a more complete and balanced understanding of dispersal evolution.
... After capture, birds can be subjected to multiple actions that differ greatly in their invasiveness, such as: taking biometric measurements and weighing; marking with alphanumerical, metal, or colour rings; and blood sampling (e.g. Burton et al. 2006;Ręk et al. 2011;Fourcade et al. 2016). These activities are often necessary to discover and explore the biology and ecology of a species. ...
Animals are able to learn, remember, and make use of previous experiences when making decisions in similar situations, which are some of the most fascinating phenomena in behavioural ecology. However, these cognitive abilities can act as impediments for biologists and ecologists when conducting field studies. Experienced animals may significantly modify their behaviour in subsequent interactions, which could lead to incorrect interpretations of the results of experimental or observational studies of such individuals. In this study we examined whether experienced (lured by playback, caught in a mist net, and handled) Chaffinch males (Fringilla coelebs) modified their behaviour during a subsequent playback experiment in comparison with naive males that had not experienced human contact. We examined 46 individuals, and found that, after experiencing capture and playback, Chaffinch males modified their responses during a playback experiment, at least on a short-term basis. Experienced males modified their vocal behaviour during simulated intrusion within their territory, responding predominantly with calls, while control naive males used mostly territorial songs. We suggest that the higher use of calls by experienced males was a result of their previous negative experience and reflected higher levels of anxiety. The differences in response toward playback between experienced and naive males suggest that special attention must be paid to planning, conducting, and analysing studies when performing multiple experiments on the same group of individuals.
... It was reported that the spring peak numbers of Curlew Sandpiper C. ferruginea increased from 3% in 2007 to 23% in 2010 of the flyway population [44]. Fragmentation and loss of waterbird habitat leads to a decline in waterbird numbers [45,46] or to the movement of birds to nearby suitable habitats [47]; the latter can lead to increased densities at other sites and consequently an increase in mortality of the displaced birds, leading to an overall loss of birds [48]. Landscape modification and habitat fragmentation have negative impacts on coastal ecosystems and biodiversity because Bohai Bay is a crucial area for waterbirds to make stopovers or winter here. ...
Landscape change is an important aspect of coastal ecological conservation and has an essential influence on the sustainable development of the coastal economy. With remoting-sensing (RS) images between 2000, 2005, 2010, and 2015, using geographic information system (GIS) technologies, we examined ecosystem spatial changes in the Bohai coastal zone. Results showed that wetlands, mainly constituted by reservoirs/ponds, were the dominant landscape types. The urban ecosystem has the largest area increment and the fastest growth rate from 2000 to 2015. The quantification of landscape metrics revealed that spatial patterns have changed significantly, and the change direction of these ecosystems had moved toward increased heterogeneity and fragmentation. In addition, natural and socio-economic data were used to analyze the major driving forces triggering ecosystem spatial changes through redundancy analysis (RDA). The results revealed that the output of aquatic products (AQ) and population (Pop) were the main factors related to wetland ecosystem change. Pop and gross domestic product per capita (GDPpc) were closely related to the urban ecosystem change. Annual mean temperature (ATm), crop acreage (CA), and grain yield (GY) had positive correlations with the agriculture ecosystem changes.
... Measures of body condition, such as subcutaneous fat deposits and pectoral muscle scoring, have been widely used to assess the health of birds (Labocha & Hayes 2012, Tellería et al. 2013. Links have been found in some species between migratory body condition and survival (Burton et al. 2006, Cresswell 2009) so that, although the physiology of migration is not well documented for many taxa, body condition may offer a reliable way to assess the health of migratory bird populations. Similarly, avian colouration can convey information to conspecifics on individual quality (Andersson 1982) through plumages (Saino et al. 2015), pigmented skin (Velando et al. 2006, Avilés & Parejo 2013, eyes (Newton & Marquiss 1982), and keratinaceous structures (Préault et al. 2005). ...
Capsule: Plumage colour of Northern Saw-whet Owls Aegolius acadicus was strongly associated with body condition and may be used to distinguish the highest quality individuals. Relationships between eye colour and body condition were more complex and deserve further study.
Aims: We explored the association of colouration with body condition of Northern Saw-whet Owls during their autumnal migration across Pennsylvania, USA from 1999 to 2012.
Methods: We used fat and keel scores of female owls to index body condition. Since feathers are laid down during pre-migration moult, we hypothesized that facial white plumage would be more strongly associated with long-term condition (keel scores) whereas eye colour should indicate short-term condition (fat scores).
Results: Facial white plumage and eye colour were largely uncorrelated, but were strongly associated with both fat and keel scores. Contrary to our hypothesis, owls with more facial white plumage had both higher fat and keel scores, indicating that facial white was strongly associated with both short- and long-term condition. This appears to be because facial white was highest in individuals most capable of maintaining good condition in both scores (the highest quality owls). Relationships between condition and eye colour were more complex, since owls with highest fat scores but lowest keel scores had lightest eyes, possibly resulting from trade-offs with pigment function and immunocompetence. Our results also demonstrated environmental forcing (cyclic prey availability) of colouration and body condition, although not the relationship between them which remained consistent between years and for different ages.
Conclusion: Facial white, but not eye colour, was a robust predictor of short- and long-term body condition, permitting detection of individuals in the best and most consistent condition. Further study of colouration and condition are needed to elucidate the extent of genetic control and environmental factors in feather melanization.
... Temporal declines in body condition at a site over successive years can highlight reductions in the ability of individuals to acquire food, for example because food supplies have been lost or disturbance has reduced available feeding time (Mainguy et al. 2002;Brown and Sherry 2006). During years in which available food supplies are reduced, individuals may not be able to gain sufficient body condition to complete migration successfully, which can lead to increased mortality risk and hence reduced population size (Burton et al. 2006;Newton 2006;Morrison et al. 2007). Repeated assessments of body condition at key sites can provide valuable insight into changes in the state of individuals within a population that can help inform species conservation (Armstrong and Perrott 2000;Stevenson and Woods 2006). ...
Assessments of body condition can provide useful information on changes in the state of individuals within a population, which may in turn help to inform conservation efforts. For example, decreases in body condition over time can indicate reduced food resources. Mass and skull length measures recorded for 195 adult and 467 first winter (cygnets) Bewick’s Swans (Cygnus columbianus bewickii) at wintering sites in the UK between winters 1966/1967 and 2017/2018 therefore were analysed to determine whether a ca. 40% decline in numbers in the Northwest European Bewick’s Swan population between 1995 and 2010 corresponded with poorer body condition from the mid-1990s onwards. Parents and siblings were known for all individuals, allowing us to account for shared genetic factors and rearing environment in our analysis. We used linear mixed-effects models and an information-theoretic approach to test different models of temporal variation in scaled body mass index (SBMI). Within our study population, although SBMI values varied both within and between years, we found no evidence of any directional trends in body condition. Of our competing time models of swan SBMI, a model in which age-specific body condition was constant over time received the greatest support in the data. Body condition was greater for adults than cygnets, but did not vary between sexes or wintering sites. Our findings suggest no connection between the recent declines in population size and body condition. Population decline is therefore unlikely to be caused by inadequate food supplies.
... Some very rare species may be especially susceptible to habitat loss on migratory stop-over sites and wintering grounds (e.g. Burton et al. 2006). Year-round studies on habitat preferences are therefore crucial for understanding species' needs, and for proper conservation management (Martin et al. 2007). ...
The Greater Spotted Eagle is an extremely rare species which is strongly associated with wetlands during the breeding period. The winter habitats of this vulnerable species have not been extensively studied so far, although eagles spend over one third of the year there, and these are therefore also crucial for the conservation of the species. We investigated the distribution of Greater Spotted Eagle wintering grounds in the Mediterranean Basin on the basis of telemetry data from individuals caught in breeding grounds, detailed species counts during wintering in Greece, and a literature search. We found that at least 300–400 individuals (c.15% of the European population) winter in the Mediterranean Basin, sometimes numbering a few dozen in particular river valleys. Individuals used on average 89.7 km ² home ranges for wintering. The Maxent model of wintering habitats performed with high reliability, indicating that most of the coastline along the Mediterranean Sea and some parts of the Black Sea are suitable for the wintering of this species. The distribution of coastal marshes was the most informative for the model. Compositional analyses done for home ranges of GPS tracked individuals and wintering sites in Greece showed the highest preference for salines and salt marshes but also a high preference for coastal lagoons and water courses. We link wetland preference with the availability of medium size prey, optimal for this species, and prey specialisation common to breeding sites.
... However, the construction of tidal barrages will reduce the area of the tidal flat by 40% of the current level. The loss of feeding and breeding grounds would be very detrimental to the affected birds, as evidenced by schemes such as the Cardiff docklands redevelopment which inundated 200 ha of mudflats in Cardiff Bay to form a freshwater lake (Burton et al., 2006). Moreover, many wading birds are faithful to a particular site and so may not find new wintering areas. ...
For tidal range power plants to be sustainable, the environmental impacts caused by the implement of various tidal barrage schemes must be assessed before construction. However, several problems exist in the current researches: firstly, evaluation criteria of the tidal barrage schemes environmental impact assessment (EIA) are not adequate; secondly, uncertainty of criteria information fails to be processed properly; thirdly, correlation among criteria is unreasonably measured. Hence the contributions of this paper are as follows: firstly, an evaluation criteria system is established from three dimensions of hydrodynamic, biological and morphological aspects. Secondly, cloud model is applied to describe the uncertainty of criteria information. Thirdly, Choquet integral with respect to λ-fuzzy measure is introduced to measure the correlation among criteria. On the above bases, a multi-criteria decision-making decision framework for tidal barrage scheme EIA is established to select the optimal scheme. Finally, a case study demonstrates the effectiveness of the proposed framework.
... Loss of intertidal mudflat represents a loss of foraging opportunity for waterbirds. Both direct loss of food resources (Baker et al. 2004) and loss of foraging habitats (Burton et al. 2006) are known to cause increased mortality in shorebirds. The population declines of migratory shorebirds in the East Asian-Australasian Flyway are closely correlated with the habitat loss from intertidal land claim in the Yellow Sea region (Amano et al. 2010, Conklin et al. 2016. ...
The Yellow Sea region is of high global importance for waterbird populations, but recent systematic bird count data enabling identification of the most important sites are relatively sparse for some areas. Surveys of waterbirds at three sites on the coast of southern Jiangsu Province, China, in 2014 and 2015 produced peak counts of international importance for 24 species, including seven globally threatened and six Near Threatened species. The area is of particular global importance for the ‘Critically Endangered’ Spoon-billed Sandpiper Calidris pygmaea (peak count across all three study sites: 62 in spring [2015] and 225 in autumn [2014] and ‘Endangered’ Spotted Greenshank Tringa guttifer (peak count across all three study sites: 210 in spring [2014] and 1,110 in autumn [2015]). The southern Jiangsu coast is therefore currently the most important migratory stopover area in the world, in both spring and autumn, for both species. Several serious and acute threats to waterbirds were recorded at these study sites. Paramount is the threat of large-scale land claim which would completely destroy intertidal mudflats of critical importance to waterbirds. Degradation of intertidal mudflat habitats through the spread of invasive Spartina , and mortality of waterbirds by entrapment in nets or deliberate poisoning are also real and present serious threats here. Collisions with, and displacement by, wind turbines and other structures, and industrial chemical pollution may represent additional potential threats. We recommend the rapid establishment of effective protected areas for waterbirds in the study area, maintaining large areas of open intertidal mudflat, and the urgent removal of all serious threats currently faced by waterbirds here.
... As a measure of the relative energy stores of an animal [1], body condition has both theoretical and practical importance because of its strong associations with reproductive capacity [2,3], survivorship [3][4][5], competition [6,7], and disease [8][9][10] condition is generally unfeasible to measure directly because direct measurement requires destruction of the whole specimen [11][12][13][14]. Instead, biologists frequently estimate body condition using a body condition index (BCI) calculated from mass and length variables obtained from non-invasive measurements (reviewed in [14]; see [15] for alternative means to estimate body condition). ...
Body condition is a gauge of the energy stores of an animal, and though it has important implications for fitness, survival, competition, and disease, it is difficult to measure directly. Instead, body condition is frequently estimated as a body condition index (BCI) using length and mass measurements. A desirable BCI should accurately reflect true body condition and be unbiased with respect to size (i.e., mean BCI estimates should not change across different length or mass ranges), and choosing the most-appropriate BCI is not straightforward. We evaluated 11 different BCIs in 248 Burmese pythons (Python bivittatus), organisms that, like other snakes, exhibit simple body plans well characterized by length and mass. We found that the length-mass relationship in Burmese pythons is positively allometric, where mass increases rapidly with respect to length, and this allowed us to explore the effects of allometry on BCI verification. We employed three alternative measures of ‘true’ body condition: percent fat, scaled fat, and residual fat. The latter two measures mostly accommodated allometry in true body condition, but percent fat did not. Our inferences of the best-performing BCIs depended heavily on our measure of true body condition, with most BCIs falling into one of two groups. The first group contained most BCIs based on ratios, and these were associated with percent fat and body length (i.e., were biased). The second group contained the scaled mass index and most of the BCIs based on linear regressions, and these were associated with both scaled and residual fat but not body length (i.e., were unbiased). Our results show that potential differences in measures of true body condition should be explored in BCI verification studies, particularly in organisms undergoing allometric growth. Furthermore, the caveats of each BCI and similarities to other BCIs are important to consider when determining which BCI is appropriate for any particular taxon.
... Thus, Central Valley shorebird populations were likely once much larger, and now may be limited by the availability of suitable foraging habitat (Page and Gill 1994;Shuford et al. 1998). Because the quality and quantity of non-breeding habitat can have important effects on avian body condition, survival, migration timing, and reproductive success (Raveling and Heitmeyer 1989;Sherry and Holmes 1996;Saino et al. 2004;Burton et al. 2006), the quality and quantity of Central Valley wetlands during the non-breeding season can significantly affect shorebird population dynamics and shorebird conservation well beyond the Central Valley. ...
An extensive network of managed wetlands and flooded agriculture provides habitat for migrating and wintering shorebirds in California's Central Valley. Yet with over 90% of historical wetlands in the region lost, Central Valley shorebird populations are likely diminished and limited by available habitat. To identify the timing and magnitude of any habitat limitations during the non-breeding season, we developed a bioenergetics model that examined whether currently available shorebird foraging habitat is sufficient to meet the daily energy requirements of the shorebird community, at either the baseline population size surveyed from 1992 to 1995 or double this size, which we defined as our long-term (100-year) population objectives. Using recent estimates of the extent of managed wetlands and flooded agriculture, satellite imagery of surface water, energy content of benthic invertebrates, and shorebird metabolic rates, we estimated that shorebir foraging habitat in the Central Valley is currently limited during the fall. If the population sizes were doubled, we estimated substantial energy shortfalls in the fall (late July-September) and spring (mid-March-April) totaling 4.02 billion kJ (95% CI: 2.23-5.83) and 7.79 billion kJ (2.00-14.14), respectively. We then estimated long-term habitat objectives as the minimum additional shorebird foraging habitat required to eliminate these energy shortfalls; the corresponding short-term (10-year) habitat objective are to maintain an additional 2,160 ha (5,337 ac) of shallow (<10 cm) open water area in the fall and 4,692 ha (11,594 ac) in the spring. Because the Central Valley is one of the most important regions in the Pacific Flyway for migrating and wintering shorebirds, we expect that achieving these habitat objectives will benefit shorebirds well beyond the Central Valley. Our bioenergetics approach provides a transparent, repeatable process for identifying the timing and magnitude of habitat limitations as well as the most efficient strategies for achieving conservation objectives.
... In addition to the direct effects on habitat availability, roads can reduce the local density of breeding waders in surrounding fields (Reijnen and Foppen 1997, Melman et al. 2008, Fikenscher et al. 2015 leading to population level impacts when a high proportion of a population's breeding range is intersected by roads. Similarly, construction activity, whether associated with coastal development (Burton et al. 2002) or renewable energy (Pearce-Higgins et al. 2012), can have a localised impact on both breeding and non-breeding populations, with displaced birds likely to suffer increased mortality when they settle elsewhere (Burton et al. 2006). Furthermore, these studies suggest that where there is significant overlap between disturbance, habitat loss and habitat conversion, there is the potential for significant population-level impacts to occur. ...
The Numeniini is a tribe of 13 wader species (Scolopacidae, Charadriiformes) of which seven are Near Threatened or globally threatened, including two Critically Endangered. To help inform
conservation management and policy responses, we present the results of an expert assessment of the threats that members of this taxonomic group face across migratory flyways. Most threats are
increasing in intensity, particularly in non-breeding areas, where habitat loss resulting from residential and commercial development, aquaculture, mining, transport, disturbance, problematic
invasive species, pollution and climate change were regarded as having the greatest detrimental impact. Fewer threats (mining, disturbance, problematic native species and climate change) were
identified as widely affecting breeding areas. Numeniini populations face the greatest number of non-breeding threats in the East Asian-Australasian Flyway, especially those associated with coastal reclamation; related threats were also identified across the Central and Atlantic Americas, and East Atlantic flyways. Threats on the breeding grounds were greatest in Central and Atlantic Americas, East Atlantic and West Asian flyways. Three priority actions were associated with monitooring and research: to monitor breeding population trends (which for species breeding in remote areas may best be achieved through surveys at key non-breeding sites), to deploy tracking technologies to identify migratory connectivity, and to monitor land-cover change across breeding and non-breeding areas. Two priority actions were focused on conservation and policy responses: to identify and effectively protect key non-breeding sites across all flyways (particularly in the East Asian-Australasian Flyway), and to implement successful conservation interventions at
a sufficient scale across human-dominated landscapes for species’ recovery to be achieved. If implemented urgently, these measures in combination have the potential to alter the current population declines of many Numeniini species and provide a template for the conservation of other groups of threatened species.
... Because most mortality of waders may occur during the nonbreeding season (Leyrer et al. 2013), deterioration of important staging and wintering sites could have severe repercussions for survival. Such changes may be more common than known because sufficient data on survival are lacking for many species (Baker et al. 2004, Atkinson et al. 2005, Burton et al. 2006, van Gils et al. 2006, Koivula et al. 2008, Conklin et al. 2016. ...
Capsule: Apparent adult survival of the critically endangered Baltic Dunlin Calidris alpina schinzii, showed evidence of a decline between 1990 and 2006 from 0.817 to 0.650.
Aims: In Europe, declines in wet-grassland breeding waders have been attributed to changes in breeding habitat but long-term information on survival is rare. We examined whether adult survival of the Baltic Dunlin declined during a period of strong population decline.
Methods: We modelled apparent survival using Cormack–Jolly–Seber models and long-term capture–recapture data collected from a Danish population. We fitted models that constrained apparent adult survival with linear and quadratic trends, and compared them with constant and time dependent models to test whether survival declined during the study period.
Results: Models including linear and quadratic trends were most supported. However, the trend variables explained only 24–35% of observed temporal variance suggesting that a large portion of variation in survival remained undescribed. Model averaged estimates indicated a decline in adult survival from 0.817 to 0.650 between 1990 and 2006 with increased uncertainty towards the end.
Conclusion: Our results suggest that gradual long-term changes in adult survival may have contributed to the decline of the Baltic Dunlin.
... Some initially used nearby sites, but this proved unsustainable. Only two major studies have been published, both with the same lead author, Niall Burton, of the British Trust for Ornithology (Burton, 2000;Burton et al., 2006), and focused mainly on the Redshank (Tringa tetanus). Although this species has relatively high site-fidelity, there are numerous other species which exhibit site-fidelity but which have not been studied. ...
... Some initially used nearby sites, but this proved unsustainable. Only two major studies have been published, both with the same lead author, Niall Burton, of the British Trust for Ornithology (Burton, 2000;Burton et al., 2006), and focused mainly on the Redshank (Tringa tetanus). Although this species has relatively high site-fidelity, there are numerous other species which exhibit site-fidelity but which have not been studied. ...
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
The Geum River, Republic of Korea, is an important wintering site for waterbirds that migrate along the East-Asian Australasian Flyway. It has recently experienced two major changes in environmental conditions as a result of increased use of bale silage (wrapping and sealing forage crops with plastic bags during harvest) beginning in 2007, and the Four Major Rivers Restoration Project (FMRRP) in 2011 to deepen and widen the major rivers in Republic of Korea. To examine these effects on wintering waterbirds, we monitored changes in wintering waterbird abundance in the downstream and upstream regions of Geum River. Wintering waterbirds in the downstream region were reduced by 67% after use of bale silage compared to before bale silage. The FMRRP changed the habitat structure, deepening and widening the river, followed by a substantial decline in overall wintering waterbirds in both regions (38% in the downstream and 51% in the upstream). Mallard (Anas platyrhynchos) and Spot-billed Duck (A. poecilorhyncha) populations showed the most decrease in numbers. However, Common Mergansers (Mergus merganser), that fish in deep water, increased over the same time. The effects of such changes in habitat conditions are not temporary, elucidating the need for monitoring and conservation programs for wintering waterbirds.
Biodiversity is valuable to society, including through its contribution to cultural benefits: “the non-material benefits people obtain from biodiversity and ecosystem services through spiritual enrichment, cognitive development, reflection, recreation, and aesthetic experiences”. Biodiversity encompasses numerous measures, but the distinct values of these measures have been little studied. We conducted a discrete choice experiment to elicit respondents’ (n = 3000) willingness to pay for increases in four measures of bird diversity in UK coastal ecosystems: number of bird species (species richness), number of individual birds (abundance), probability of seeing rare or unusual bird species, and probability of seeing large flocks of birds (wildlife spectacles). Respondents had a positive willingness to pay (through one-time voluntary donations) for increases in all four measures (mean £3 to £5 per household). However, using latent class analysis we found considerable heterogeneity of preferences, identifying four classes of respondents with strikingly different levels of marginal willingness to pay for the four measures. Income, age, environmental activity, visits to environmental settings, and gender were important determinants of class membership. While focussing on birds, our results demonstrate the importance of a multi-dimensional conceptualisation of biodiversity in broader ecosystem management, rather than focussing on a single aspect such as species richness or abundance. Our findings also highlight the implications of heterogeneous public preferences for biodiversity for conservationists, planners, shoreline managers and developers. These need to be considered in the development of new frameworks for ecosystem services, and when planning and funding conservation actions so that the cultural benefits will accrue across a range of social groups.
Background and goal
The study is conducted to facilitate conservation of migratory wader species along the East Asian-Australasian Flyway, particularly to 1) Identify hotspots of wader species richness along the flyway and effectively map how these might change between breeding, non-breeding and migratory phases; 2) Determine if the existing network of protected areas (PA) is sufficient to effectively conserve wader biodiversity hotspots along the EAAF; 3) Assess how species distribution models can provide complementary distribution estimates to existing BirdLife range maps.
Methods
We use a species distribution modelling (SDM) approach (MaxEnt) to develop temporally explicit individual range maps of 57 migratory wader species across their annual cycle, including breeding, non-breeding and migratory phases, which in turn provide the first biodiversity hotspot map of migratory waders along the EAAF for each of these phases. We assess the protected area coverage during each migration period, and analyse the dominant environmental drivers of distributions for each period. Additionally, we compare model hotspots to those existing range maps of the same species obtained from the BirdLife Internationals’ database.
Results
Our model results indicate an overall higher and a spatially different species richness pattern compared to that derived from a wader biodiversity hotspot map based on BirdLife range maps. Field observation records from the eBird database for our 57 study species confirm many of the hotspots revealed by model outputs (especially within the Yellow Sea coastal region), suggesting that current richness of the EAAF may have been underestimated and certain hotspots overlooked. Less than 10% of the terrestrial zones area (inland and coastal) which support waders are protected and, only 5% of areas with the highest 10% species richness is protected.
Main conclusions
The study results suggest the need for new areas for migratory wader research and conservation priorities including Yellow Sea region and Russian far-East. It also suggests a need to increase the coverage and percentage of current PA network to achieve Aichi Target 11 for Flyway countries, including giving stronger consideration to the temporal dynamics of wader migration.
The north-west European population of Bewick’s Swan Cygnus columbianus bewickii declined by 38% between 1995 and 2010 and is listed as ‘Endangered’ on the European Red List of birds. Here, we combined information on food resources within the landscape with long-term data on swan numbers, habitat use, behaviour and two complementary measures of body condition, to examine whether changes in food type and availability have influenced the Bewick’s Swan’s use of their main wintering site in the UK, the Ouse Washes and surrounding fens. Maximum number of Bewick’s Swans rose from 620 in winter 1958/59 to a high of 7,491 in winter 2004/05, before falling to 1,073 birds in winter 2013/14. Between winters 1958/59 and 2014/15 the Ouse Washes supported between 0.5 and 37.9 % of the total population wintering in north-west Europe (mean ± 95 % CI = 18.1 ± 2.4 %). Swans fed on agricultural crops, shifting from post-harvest remains of root crops (e.g. sugar beet and potatoes) in November and December to winter-sown cereals (e.g. wheat) in January and February. Inter-annual variation in the area cultivated for these crops did not result in changes in the peak numbers of swans occurring on the Ouse Washes. Behavioural and body condition data indicated that food supplies on the Ouse Washes and surrounding fens remain adequate to allow the birds to gain and maintain good body condition throughout winter with no increase in foraging effort. Our findings suggest that the recent decline in numbers of Bewick’s Swans at this internationally important site was not linked to inadequate food resources.
The population of shorebirds in the East Asian–Australasian Flyway (EAAF) has severely declined over the past several decades. One reason for this condition is low survival in stopover sites in the Yellow Sea Ecoregion (YSE) due to habitat degradation. Here, we focused on shorebird habitat quality in the Yellow River Delta (YRD), which is a representative shorebird stopover site in the YSE on the EAAF. We used the InVEST model to assess the past and future shorebird habitat quality changes by considering the effects of anthropogenic threats. The entire duration of the study was 1999–2016, and the modeling was done on 2000 and 2015 data. Our results indicate that the abundance of 11 shorebird species had significant downward trends (70–97% reduction) during 1999–2015. Tidal flats in the nature reserve had higher habitat quality than that in the northwestern (NW) and eastern (E) parts of the YRD because major mariculture occurred in NW and E. The mean habitat qualities in NW and E decreased by 27 and 31% during 2000–2015, respectively. The optimal habitat in the YRD declined from 1433 km² in 2000 to 1154 km² in 2015. The habitat quality decreased significantly in E and Dongying Port parts during 2015–2020.
Individual-based models (IBMs) are a powerful tool in predicting the consequences of environmental change on animal populations and supporting evidence-based decision making for conservation planning. There are increasing proposals for wind farms in UK waters and seabirds are a vulnerable group, which may be at risk from these developments. We developed a spatially explicit IBM to investigate the potential impacts of the installation of wind farms in the English Channel and North Sea on body mass, productivity and mortality of a breeding population of Northern gannets for which we have tracking data. A baseline model with no wind farms accurately represented the status of a sample of tracked gannets at the end of the 90-day chick-rearing period, and the behaviour-time budget was similar to that of tracked gannets. Model simulations in the presence of wind farms indicated that installations should have little impact on the gannet population, when either avoidance behaviour or collision risk scenarios were simulated. Furthermore, wind farms would need to be ten times larger or in more highly used areas in order to have population-level impacts on Alderney's gannets. Synthesis and applications. Our spatially explicit individual-based models (IBM) highlight that it is vital to know the colony-specific foraging grounds of seabirds that may be impacted, when identifying potential wind farm sites, in order to account for cumulative impacts from multiple sites. Avoiding areas highly used for foraging and commuting, and avoiding large-scale developments should be effective in limiting gannet mortality as a result of collision, competition and energy expenditure. Our IBM provides a robust approach which can be adapted for other seabird populations or to predict the impacts from other types of spatial change in the marine environment.
Capsule: Changes in sward height, driven by changes in management, were associated with a large decline in a population of farmland breeding waders.
Aims: To examine the relationship between changes in habitat and numbers of breeding wader on an area of Scottish farmland over the last 25 years.
Methods: Nesting waders in a core survey area of 7.5 km² were monitored annually from 1990 to 2015. An additional 10.3 km² were monitored less frequently. Habitat characteristics of each field were recorded and breeding success by Lapwing determined in a sample of fields.
Results: All species showed large declines over the study period, Oystercatcher Haematopus ostralegus by 95%, Lapwing Vanellus vanellus by 88%, Curlew Numenius arquata by 67% and Redshank Tringa totanus by 87% from peaks of 125, 365, 57 and 53 pairs, respectively. Changes in spring sward height, considered to be due to changes in crop type, were associated with changes in the numbers of breeding waders over time. Productivity by a sample of Lapwings was unchanged through the study period.
Conclusion: Short swards, especially bare till, in spring appear to have been important in contributing to the maintenance of an assemblage of breeding waders in mixed arable-pasture farmland. The decline appeared greater than could be accounted for by losses of preferred habitats alone.
Next generation turbines can be installed to exploit tidal energy resource in estuaries. However, the ecological implications of such deployments remain unknown. Accordingly, this study is focused on the impact of tidal farms on intertidal areas and associated waterbird habitats in estuaries. A numerical model simulates the hydrodynamic conditions of the Solway Firth, comprising one of the most extensive intertidal zones in the UK. The effects of tidal farms with different turbine densities have been evaluated in terms of changes to the areas of habitat for wetland bird species of conservation importance. The results suggest that any habitat loss may be minor and that in some cases there may be an increase (also small) in the area of important habitat. The percentage change in intertidal areas is also considerably lower than that expected to result from tidal barrages of similar capacities, implying the potential for tidal farms to present an alternative solution for exploiting tidal energy in highly protected areas. The changes in the extent of intertidal habitat are not proportional to the energy dissipated by the tidal farm. Therefore a range of tidal farm designs should be evaluated in order to optimise installed capacity while minimising habitat loss. However, the site-dependency of the impacts and the complex responses to change of estuarine ecosystems reinforce the requirement for detailed studies to be undertaken for each specific location and array configuration. The methodology presented here is appropriate for such assessments as it can be applied to different locations and turbine types.
The successful conservation of bird species relies upon our understanding of their habitat use and requirements. In the coming decades the importance of such knowledge will only grow as climate change, the development of new energy sources and the needs of a growing human population intensify the, already significant, pressure on the habitats that birds depend on. Drawing on valuable recent advances in our understanding of bird-habitat relationships, this book provides the first major review of avian habitat selection in over twenty years. It offers a synthesis of concepts, patterns and issues that will interest students, researchers and conservation practitioners. Spatial scales ranging from landscape to habitat patch are covered, and examples of responses to habitat change are examined. European landscapes are the main focus, but the book has far wider significance to similar habitats worldwide, with examples and relevant material also drawn from North America and Australia.
http://jncc.defra.gov.uk/page-1412
This paper presents a modification of the behaviour-based individuals model of Oystercatchers on the Exe
Estuary, England which was adapted to the Seine estuary for three species of waders: Oystercatcher, Curlew and Dunlin. The purpose of this model was to analyze, in the future, the impact of the construction of Port 2000 at le Havre on the mortality and body condition of these species. The aim of the present
paper is to present a modelling approach that may be useful for guiding policy on a wide range of the environmental management issues involving estuarine migratory birds. The present preliminary model predicted quite well the distribution of the three species within the estuary and there was also a good agreement between the predicted numbers of the three species feeding on mudflat 4 (which will disappear with the construction of Port 2000) and the numbers actually observed in the field. Results from this first version of the model suggest that, at the present time, the numbers, mortality and body condition of only the
Dunlin may be density-dependent. The very provisional results therefore suggest that the Dunlin
may be the only one of the three species to be affected by the construction of Port 2000. These
results are not definitive and more field data are required if more reliable evaluations are to be
made of the impact of building the Port and of theefficacy of the proposed mitigation measures.
1. This paper models empirically how habitat loss in winter might affect the size of the European population of oystercatchers Haematopus ostralegus ostralegus. It explores how a density-dependent mortality rate in winter interacts with a density-dependent production rate in summer to determine the total, year-round population size following a loss of winter habitat which itself leads to intensified competition for food and hence increased winter mortality rates. 2. Simulations over a range of probable parameter values show that the density at which winter mortality becomes density-dependent, cW, simply determines the point at which population size is affected as habitat is gradually removed. The population is affected sooner in the more widely fluctuating Continental sub-populations than in the less variable Atlantic subpopulations. 3. Once winter density reaches cW, the consequences depend on the slope, bW, of the density-dependent winter mortality function. In all subpopulations, the reduction in population size increases sharply as bW increases, but only at low values; above a certain level, further increases in bW make less difference. Because of their higher reproductive rate, inland subpopulations are initially less affected by winter habitat loss than coastal subpopulations. These conclusions are robust over a range of assumptions about competition for territories in summer and age difference in mortality in winter. 4. Adding density-dependent fledging success to the basic model reduces the effect of winter habitat loss on population size, but only when low proportions of the habitat are removed. A higher mortality rate in females, whether only in post-fledging young birds or in birds of all ages, makes little additional difference to the population consequences of habitat loss. 5. Field studies on winter habitat loss in migratory bird populations should first test whether density has already reached the critical level, cW; i.e. whether some birds already die of food competition. The parameter bW should then be estimated to determine whether its probable value lies in the range within which predictions are sensitive or insensitive to its precise value. Whether the summer density-dependent functions are linear or curvilinear needs also to be explored, as does the effect of interactions between subpopulations which have different fledgling production rates but share the same winter habitat.
There may be problems concerning the appropriate design of sampling programs to assess the impact upon the abundance of biological populations of, for example, the discharge of effluents into an aquatic ecosystem at a single point. Key to the resolution of these issues is correct identification of the statistical parameter of interest, which is the mean of the underlying probabilistic 'process' that produces the abundance, rather than the actual abundance itself. An appropriate sampling scheme was designed to detect the effect of the discharge upon this underlying mean. Detection of the effect of the discharge is achieved by testing whether the difference between abundances at a control site and an impact site changes once the discharge begins. -from Authors
Long-term mark–recapture data were used to estimate the annual survival rates of Redshank wintering on the Moray Firth in Scotland. Survival modelling required the exclusion of all birds caught during the main passage months (August, March and April), and a highly variable annual catching effort limited the precision of annual survival estimates. Survival rates of juvenile Redshank (between the first and second winters of life) varied markedly from year to year and averaged 43% (se 3.6%). Adult survival rates were less variable between years and were age-dependent, with 67% (se 5.0%) surviving and returning between the second and third winters of life, compared to 74% (se 1.4%) for older birds. Year-to-year variation in adult survival was weakly (and negatively) related to the number of snow days in winter. Year-to-year variation in first-year survival was non-linearly related to winter rainfall, with low survival during dry (and cold) winters, higher survival during winters with average rainfall and lower survival during wet winters. Having accounted for these weather relationships there was no evidence that survival was related to the size of the local wintering Redshank population. Organized annual ringing programmes of wintering waders on British estuaries have the potential to monitor long-term changes in survival rates and productivity. Although constant effort sampling may be difficult to achieve for wintering waders, the utility of mark–recapture data collected on estuaries is likely to depend heavily on careful study design.
Capsule: Serious violations of the model assumptions were seen. Aims: To illustrate the manner in which violations of the mark-recapture model assumptions may occur. Methods: Attempts were made to model annual and seasonal survival of several shorebird species at Teesmouth, northeast England. The database contained 25 years of colour-ring resightings and several suites of models were tested. Results: There was significant heterogeneity in survival and recapture probabilities for all five species of shorebird that had been colour-marked. Various attempts and blocking, stratifying and constraining our survival models, while in many cases providing more parsimonious solutions, had no effect on these heterogeneities. Conclusions: Our problems stem from both the methodology used and lack of information about the status of individuals (e.g. territoriality and variability in the level of site fidelity). We suggest ways in which data more appropriate to survival analyses might be collected in future.
Both British and Icelandic Redshanks may be found in Britain in the nonbreeding season. They are indistinguishable, though their average measurements differ. Samples of breeding Redshanks were caught in Iceland and Britain to collect biometric information to he used to estimate the proportions of Icelandic and British Redshanks in mixed winter populations. Wing, bill and foot were the only structures whose lengths were significantly different between the 2 populations and which could be measured with reasonable precision. Two methods were used to estimate the proportions in mixed samples: discriminant analysis and a maximum likelihood analysis of Mixtures of Normal distributions. A simple graphical method based on the discriminant analysis was devised. The methods resulted in similar estimates of the proportions of Icelandic Redshanks when used on mixed samples. Estimates from captured samples in eastern Scotland indicated that there is an equal mix of Icelandic and British Redshanks in autumn, but that almost the entire winter population is Icelandic. Variability in measurements between and within observers was quantified and is discussed in relation to future work.
The breeding origins and racial composition of Redshank Tringa totanus wintering in the Cardiff area of the Severn Estuary were investigated using information from ring‐recoveries and biometric data. In total, between 1991 and 2000, we received 56 reports from the breeding season of Redshank ringed at Cardiff. These involved 36 different individuals, 31 reported from Britain and five from Iceland. There was a slight bias in records within Britain towards the north and west of the country. The proportion of adult Redshank of the Icelandic race T t robusta present during the non‐breeding seasons varied according to the month of capture and, importantly, between two neighbouring sites within the study area: Cardiff Bay and Rhymney. The latter site held a higher proportion of Icelandic birds throughout the winter. Percentages of Icelandic birds were lowest in October and November (2% and 27% at Cardiff Bay and Rhymney respectively) and highest in February and March (27% and 61% at the two sites respectively). The proportions of British Redshank T t brittanica in the populations at Cardiff were higher than in studies in eastern Scotland, Teesmouth, The Wash, Merseyside and north Wales but less than in north Kent. The apparent partial segregation of Icelandic and British Redshank between Cardiff Bay and Rhymney may have been related to differences in the availability of prey species at the two sites and/or a result of differences in the competitive ability of the two races. The segregation of Redshank between the two sites could potentially have increased the impact of the impoundment of Cardiff Bay in 1999 upon British‐born birds, though lessened the impact for Icelandic‐born birds. The potential for similar segregation occurring elsewhere in other species of migratory birds needs to be considered in determining the impact of any similar environmental change.
Sandercock, B.K. 2003. Estimation of survival rates for wader populations: a review of mark-recapture methods. Wader Study Group Bull. 100: 163–174. Wader life-history traits are comprised of low fecundity, delayed maturity and high annual survival. Robust estimates of annual survival are essential for effective conservation because population growth rates of long-lived vertebrates are often sensitive to variation in survivorship. Estimation of survival rates from individu-ally marked waders requires one of three types of data: live encounters, dead recoveries or known-fate infor-mation from radio-telemetry. Unfortunately, the available methods for estimation of survival rates vary greatly in their assumptions and utility. Maximum longevity, age-ratios and life-table methods require assumptions that are unlikely to be met in field studies. Return rates have been widely reported for waders but can be difficult to interpret because they are comprised of four independent probabilities: true survival (S), site fidelity (F), site propensity (γ*) and detection (p*). Mark-recapture methods based on live encounter data improve on return rates by estimating apparent survival (φ = S × F), corrected for the probability of capture (p = γ* × p*). Fifteen studies have used mark-recapture methods to estimate φ and p for wader populations. Most studies have found that < 1 (95.8%, 23 of 24 estimates), with variation in often due to sex, year and age-class. A majority of available estimates of apparent survival are based on time-dependent models (63.2%, 12 of 19 estimates). The remaining survival analyses (36.8%, 7 of 19) used models that separated apparent survival in the inter-val after banding (φ 1) from subsequent intervals (φ 2). These "age"-structured models control for birds cap-tured on only one occasion and yielded better estimates of survival than time-dependent models. Recovery models have been rarely applied to waders, probably because the proportion of ringed birds that are recov-ered dead is low for nonharvested species (< 0.02). Radio-telemetry can yield accurate estimates of daily and seasonal survival but may have limited value for estimating annual survival because radio battery life is short compared to the average life span of waders. New mark-recapture methods, including the multistate, robust design, temporal symmetry, and joint models, have great potential for estimation of demographic rates but have not yet been applied to waders. I discuss potential applications of these statistical models to investiga-tions of wader demography and conclude with specific recommendations for future studies.
While it has long been known that Pacific salmon use estuarine habitat, it has proven much harder to establish that the loss of estuarine habitat results in reduced survival. We used coded-wire tagging of hatchery fish to estimate the survival from release until maturity and related this survival to several indicators of estuarine condition. We found a significant relationship between the survival of chinook salmon (Oncorhynchus tshawytscha) and the percentage of the estuary that is in pristine condition, but no significant relationship for coho salmon (Oncorhynchus kisutch). This supports field observations that chinook salmon use estuarine habitat much more than coho salmon and confirms that the loss of estuarine habitat results in lower survival of chinook salmon.
The understanding of the dynamics of animal populations and of related ecological and evolutionary issues frequently depends on a direct analysis of life history parameters. For instance, examination of trade-offs between reproduction and survival usually rely on individually marked animals, for which the exact time of death is most often unknown, because marked individuals cannot be followed closely through time. Thus, the quantitative analysis of survival studies and experiments must be based on capture-recapture (or resign ting) models which consider, besides the parameters of primary interest, recapture or resighting rates that are nuisance parameters. Capture-recapture models oriented to estimation of survival rates are the result of a recent change in emphasis from earlier approaches in which population size was the most important parameter, survival rates having been first introduced as nuisance parameters. This emphasis on survival rates in capture-recapture models developed rapidly in the 1980s and used as a basic structure the Cormack-Jolly-Seber survival model applied to an homogeneous group of animals, with various kinds of constraints on the model parameters. These approaches are conditional on first captures; hence they do not attempt to model the initial capture of unmarked animals as functions of population abundance in addition to survival and capture probabilities. This paper synthesizes, using a common framework, these recent developments together with new ones, with an emphasis on flexibility in modeling, model selection, and the analysis of multiple data sets. The effects on survival and capture rates of time, age, and categorical variables characterizing the individuals (e.g., sex) can be considered, as well as interactions between such effects. This "analysis of variance" philosophy emphasizes the structure of the survival and capture process rather than the technical characteristics of any particular model. The flexible array of models encompassed in this synthesis uses a common notation. As a result of the great level of flexibility and relevance achieved, the focus is changed from fitting a particular model to model building and model selection. The following procedure is recommended: (1) start from a global model compatible with the biology of the species studied and with the design of the study, and assess its fit; (2) select a more parsimonious model using Akaike's Information Criterion to limit the number of formal tests; (3) test for the most important biological questions by comparing this model with neighboring ones using likelihood ratio tests; and (4) obtain maximum likelihood estimates of model parameters with estimates of precision. Computer software is critical, as few of the models now available have parameter estimators that are in closed form. A comprehensive table of existing computer software is provided. We used RELEASE for data summary and goodness-of-fit tests and SURGE for iterative model fitting and the computation of likelihood ratio tests. Five increasingly complex examples are given to illustrate the theory. The first, using two data sets on the European Dipper (Cinclus cinclus), tests for sex-specific parameters, explores a model with time-dependent survival rates, and finally uses a priori information to model survival allowing for an environmental variable. The second uses data on two colonies of the Swift (Apus apus), and shows how interaction terms can be modeled and assessed and how survival and recapture rates sometimes partly counterbalance each other. The third shows complex variation in survival rates across sexes and age classes in the roe deer (Capreolus capreolus), with a test of density dependence in annual survival rates. The fourth is an example of experimental density manipulation using the common lizard (Lacerta vivipara). The last example attempts to examine a large and complex data set on the Greater Flamingo (Phoenicopterus ruber), where parameters are age specific, survival is a function of an environmental variable, and an age × year interaction term is important. Heterogeneity seems present in this example and cannot be adequately modeled with existing theory. The discussion presents a summary of the paradigm we recommend and details issues in model selection and design, and foreseeable future developments.
MARK provides parameter estimates from marked animals when they are re-encountered at a later time as dead recoveries, or live recaptures or re-sightings. The time intervals between re-encounters do not have to be equal. More than one attribute group of animals can be modelled. The basic input to MARK is the encounter history for each animal. MARK can also estimate the size of closed populations. Parameters can be constrained to be the same across re-encounter occasions, or by age, or group, using the parameter index matrix. A set of common models for initial screening of data are provided. Time effects, group effects, time x group effects and a null model of none of the above, are provided for each parameter. Besides the logit function to link the design matrix to the parameters of the model, other link functions include the log—log, complimentary log—log, sine, log, and identity. The estimates of model parameters are computed via numerical maximum likelihood techniques. The number of parameters that are estimable in the model are determined numerically and used to compute the quasi-likelihood AIC value for the model. Both the input data, and outputs for various models that the user has built, are stored in the Results database which contains a complete description of the model building process. It is viewed and manipulated in a Results Browser window. Summaries available from this window include viewing and printing model output, deviance residuals from the model, likelihood ratio and analysis of deviance between models, and adjustments for over dispersion. Models can also be retrieved and modified to create additional models. These capabilities are implemented in a Microsoft Windows 95 interface. The online help system has been developed to provide all necessary program documentation.
1. The effect of loss of a spring staging site on dispersal and on the fitness parameters fecundity and survival of Dark-bellied Brent Geese Branta bernicla bernicla was investigated. A group of marked birds from an embanked saltmarsh area was compared with a control group of birds from nearby, non-embanked saltmarshes for a period of 13 years after the embankment.
2. Both displaced and control birds were seen at numerous sites other than their ringing site; long-distance movements were detected more frequently in displaced birds during the first years after the habitat loss.
3. Displaced birds appeared to move more often to less preferred sites that were not filled to capacity than did control birds.
4. Significant differences in subsequent fecundity and survival of displaced and control birds could not be detected; it appears that the majority of displaced birds succeeded in finding good alternative sites. There was, however, a tendency for the displaced birds to have lower breeding success and to survive less well, which suggests that subtle effects of displacement may occur.
5. Even if habitat loss has no significant effects on displaced individuals, loss of a spring staging site increases population pressure on the remaining sites and may reduce fitness parameters of the population as a whole. In addition, invasion of previously unused sites leads to increasing conflict between Brent Geese and agricultural interests.
6. In order to predict impacts of future habitat changes on bird populations, many more empirical data on long-term effects of habitat loss, such as provided in this study, are needed.
Wintering Oystercatchers in The Netherlands are concentrated in the Wadden Sea (c. 200 000), with substantial numbers in the Delta area (c. 90 000). Only 1% of the total wintering population is normally found along the North Sea coast. Cold-rushes under severe winter conditions lead to a reduction of wintering numbers in the Wadden Sea, and to increases in the Delta and along the North Sea coast. The mortality of wintering Oystercatchers in The Netherlands was studied on the basis of beached bird surveys along the coast of the North Sea and Wadden Sea between 1969 and 1996. On the whole, the pattern corresponded well to annual mortality estimates from population studies on the Wadden Sea islands of Schiermonnikoog and Texel. Peak numbers of dead Oystercatchers were found in most severe winters, but also in some moderate winters such as in 1976 and 1991. In mild winters, rather small numbers of dead Oystercatchers were recorded. For 1986-1996, annual mortality along the coast ranged from a c. 500 in the mild winters of 1989 to c. 10 000 individuals in 1987 and 1996. Multiple regression analysis of the number of dead Oystercatchers in winter 1975-1996 on the number of cold days and the biomass of benthic prey revealed an explained variance of 66% (n = 21). Both the number of cold days and prey biomass had a significant effect. The results explained the relatively high mortality among Oystercatchers in the moderate winters of 1976 and 1991 (very low food stock), and the low mortality in the severe winter of 1982 (large food stock). The extremely high mortality in 1987 was due to a combination of low food stock and severe weather. The depletion of Cockles and Mussels in the Wadden Sea in the early 1990s, due to a combination of overfishing and failing reproduction, triggered a southward mass movement of Oystercatchers and substantial mortality in the Delta are in the winter of 1990-1991. The absence of a peak in the mortality among adult breeders in the population studies for that particular winter is the major discrepancy between these population studies and the beached bird surveys. It is an indication that primarily non-local, and therefore probably less dominant, Oystercatchers suffered from the food shortage in the Wadden Sea. The results suggest that for Oystercatchers the scarcity of their principal prey due to over-fishing has taken its toll. Had this season also been a cold winter, the results suggest that the mortality would have been unprecedented.
Understanding numeric changes in wader populations requires knowledge of the demographic parameters underlying such changes, i.e. survival and recruitment. Data from long-term monitoring programmes are crucial for obtaining these parameters. Following discussions held at a workshop on demographic monitoring of wader populations at the 2004 International Wader Study Group meeting, we present guidelines for establishing new programmes to monitor survival and recruitment of waders in non-breeding areas, particularly those species that breed in the Arctic. We provide a general overview of some common issues in the demographic monitoring of waders and then provide detailed methods for measuring both recruitment and survival on the nonbreeding grounds.
This paper presents a modification of the behaviour-based individuals model of Oystercatchers on the Exe Estuary, England which was adapted to the Seine estuary for three species of waders: Eurasian Oystercatcher, Eurasian Curlew and Dunlin. The purpose of this model was to analyse, in the future, the impact of the construction of Port 2000 at le Harvre on the mortality and body condition of these species. The aim of the present paper is to present a modelling approach that may be useful for guiding policy on a wide range of environment management issues involving estuarine migratory birds. The present preliminary model predicted quite well the distribution of the three species within the estuary and there was also good agreement between the predicted numbers of the three species feeding on mudflat 4 (which will disappear with the construction of Port 2000) and the numbers actually recorded during fieldwork. Results from this first version of the model suggest that, at the present time, the numbers, mortality and body condition of only the Dunlin seems to be density-dependent. These very provisional results therefore suggest that Dunlin may be the only one of the three species to be affected by the construction of Port 2000. These results are not definitive and more field data are required if more reliable evaluations are to be made of the impact of building the Port and of the efficiency of the proposed mitigation measures.
A storm surge barrier and secondary dams were built in the Oosterschelde estuary (The Netherlands) resulting in a 30% decrease in intertidal area. If the birds that previously fed behind the secondary dams were able to establish themselves in the intertidal areas outside that remained, their densities should have increased in these areas. To test this, the densities of Oystercatchers, Haematopus ostralegus, were studied in relation to their main prey, Cockles Cerastoderma edule, and Mussels Mytilus edulis, before and after the reduction in tidal area. As the tide ebbed Oystercatchers moved quickly through the higher part of the intertidal area towards the preferred feeding areas below mid tidal level. The distribution of the birds then became related to their food supply. As the number of birds in the whole area increased, the birds gradually spread out from the preferred feeding plots towards the less preferred ones, leading to a sequential pattern of filing of the feeding area. This pattern did not change after the dams were built. After the main loss of intertidal habitat had occurred, densities of Oystercatchers feeding on Cockles were within the range predicted by prey biomass-bird density relationships that had been measured before the environmental changes. On mussel beds, however, densities of Oystercatchers became much higher after 1987/1988 at a given total prey biomass. This was caused by an increase in cockle biomass on the mussel beds due to an abundant spatfall in 1985. It is argued that because the harvestable fraction of Mussels represent only a small proportion of the total mussel population on the bed, whereas large proportion of the cockle population is harvestable, a given combined biomass of Cockles and Mussels supports higher densities of Oystercatcher as the proportion that consists of Cockles increases.
1. In a previous paper (Goss-Custard et al. 1995), a demographic model suggested that different breeding subpopulations of a migrating shorebird, the oystercatcher Haematopus ostralegus, that shared the same wintering area might be affected in different ways by the progressive reduction of their winter habitat. Initially, as winter habitat was removed in simulations, all subpopulations decreased in parallel. However, as habitat loss continued, the subpopulations with lower fledgling production began to be disproportionately affected. This paper explores what caused this difference in response between subpopulations. 2. A simplified version of the model was used in which two or four subpopulations wintered in one area. Two simple density-dependent functions were included, one for breeding territoriality and one for winter mortality, with density dependence starting only above a certain threshold density. Each pair that acquired a breeding territory reared a constant number of hedged young each year. 3. As winter habitat was reduced, the reduction in population size of the subpopulations with lower reproductive rates began to accelerate as soon as the point was reached when all adults were breeding. Before this point, breeding birds that had died in the winter had been replaced by non-breeders. After this point, the subpopulation reproductive output was not sufficient to replace birds dying in the winter. At the same time, winter mortality rates remained high as winter densities were sustained by birds from the other subpopulations. 4. The results suggest that, in order to detect the first effects of winter habitat loss, conservationists should pay special attention to monitoring breeding numbers in local subpopulations with below average rates of reproduction. The results also suggest that the cause of a decline in some local breeding subpopulations, when others remain stable, may need to be sought on the wintering grounds and not in the breeding localities themselves.
(1) The wader populations of the Roggenplaat, a 16.5 km2 intertidal flat in the Oosterschelde estuary (Dutch Delta area), were monitored by a standardized monthly census of their high-water roosts, to evaluate the effect of the loss of 55 km2 of feeding grounds in the adjacent Grevelingen estuary, because of its enclosure in May 1971. (2) A comparison of annual maximum numbers and bird-day totals between 1964-71 and 1971-79 revealed abrupt increases of the oystercatcher (Haematopus ostralegus L.) and the bar-tailed godwit (Limosa lapponica L.), which can unequivocally be attributed to the closure of the Grevelingen. (3) The 'carrying-capacity' of the Roggenplaat (and presumably also of the entire Oosterschelde) was apparently not fully exploited until 1971. (4) Shifts in the average seasonal abundance indicated that upper limits have been reached in oystercatcher and some other species since 1971. (5) This may result in reduced future population numbers, since in 1987 35% of the intertidal areas in the Oosterschelde were lost because of the completion of huge hydraulic engineering projects.
Global climate change may affect the internationally important populations of waders (Charadrii) throughout their annual ranges and in a variety of ways. Within Britain, those waders that winter on estuaries are likely to be affected in two principal manners: increasingly mild winter weather already appears to have affected the distributions of the waders within Britain and rising sea level threatens to alter coastal habitats.Wader densities are largely dependent on the availability of their invertebrate prey, which, in turn depends on the nature of the estuarine sediments, itself a function of estuary morphology. Thus changes in estuary morphology, such as might occur with sea level rise, can affect wader density. Models have thus been developed that allow wader densities to be predicted from readily measured aspects of estuary morphology.The MONARCH project used case studies which employed a Geographical Information System, digital elevation models, coastline management plans and sea level rise predictions to simulate incremental increases in sea level for two estuaries. At each increment, values of morphological measurements required by the models were extracted and wader densities were modelled.In both case studies the densities of wader species favouring muddy sediments decreased under management scenarios that allowed land behind existing sea defences to be reclaimed by the sea.However, the models suggest that where changes in estuary morphology were sufficiently large to bring about a decrease in bird densities, generally as a result of increased estuary width leading to sandier sediments the associated increased area more than compensated for the assumed degradation of habitat such that larger numbers could be accommodated overall.
Recent research on a few populations of sea-birds has revealed a lower mortality rate for adult birds than has been found byLack andBoyd through the evaluation of (chiefly) long distance recoveries. Starting from this fact various methods of evaluating population parameters, i. e. life expectancy e, average age n, and average annual mortality m, are reviewed; it is pointed to their fallacies and to their range of applicability.
By the method ofLack the mortality rate may be determined through sorting out recoveries by age. Obviously, the material upon which such calculations have been based, consisted mainly of long distance recoveries. The procedure may be restricted to the place of banding. Amongst others tear and wear of rings may be a source of error.
All further methods involve the control of populations the individuals of which ought to be known as completely as possible. Colour bands are an important tool in doing this.
In determining the annual mortality from the recovery rate one has to assume that all birds surviving do return to the study area.
In determining the annual mortality from the proportions of birds breeding for the first time banding may be abandoned under certain conditions; however, this does not hold true for the species examined here.
The calculation of the average age from the age class composition of a given population involves a long-term study as far as most coastal birds are concerned. It is suggested as to how long a population should be controlled. Moreover, a nomogramme is presented which allows to predict the final result under certain conditions. The estimation of the life expectancy by means of a long-term population control is possible when populations such as in sea-bird sanctuaries may be checked for several decades; however, this was mostly done rather extensively. Population parameters have been calculated anew for seven species as follows:
A comparison reveals that long distance recoveries always lead to a higher mortality rate than those at the place of banding.
It is proved that a population would not be maintained in several cases if an annual mortality rate would hold true based on long distance recoveries. Consequently, it is concluded that proper age values of birds which are dealt with in this paper can only be obtained by population studies, or by the evaluation of recoveries at the place of banding.
