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Least Bittern (Ixobrychus exilis)
... Ixobrychus exilis Gmelin (Least Bittern) is a small, secretive, wetland-dependent heron of conservation concern (Gibbs et al. 1992). It is commonly assumed that detections of this species will increase with the use of call-broadcasts (Conway and Gibbs 2005). ...
... At the beginning of each survey, the MMP bird call-broadcast (Crewe et al. 2006) was played with a cassette recorder (Radio Shack Optimus Intertan portable AM/FM cassette recorder, CTR-110, Model #14-733) from 1 m above the substrate, with 80-dB maximum sound pressure measured with a sound-level meter (Radio Shack, Model #33-2050) 1 m from the source. The call-broadcast contained approximately 30 seconds of calls of each of 5 species (original recordings from: Monte Brigham, Lang Elliot, and the Cornell Library of Natural Sounds; Crewe et al. 2006) separated by 30 seconds of silence, in the following order (call type in quotes): Virginia Rail ("grunt;" Conway 1995), Sora ("whinny;" Melvin and Gibbs 1996), Least Bittern ("cooing;" Gibbs et al. 1992), Fulica americana Gmelin (American Coot) ("grunt, croak, squawk, etc." Bent 1926), and Podilymbus podiceps (L.) (Pied-billed Grebe) ("song;" Muller and Storer 1999). The entire area of each half-circle was systematically searched for Least Bittern nests between 1 May and 1 August 2001. ...
... The entire area of each half-circle was systematically searched for Least Bittern nests between 1 May and 1 August 2001. To relate timing of Least Bittern detections with nesting chronology, we estimated the dates of egg and nestling stages for each nest following Manolis et al. (2000), based on a 19-day incubation and a 14-day nestling period (Fragnier 1996, Gibbs et al. 1992. Each nest was visited every 3-5 days to determine status until the nest failed or all of the nestlings fledged. ...
We conducted 11 call-broadcast surveys at one location in each of four wetlands, and detected an Ixobrychus exilis (Least Bittern) on only 9 of the 44 (20%) surveys, while the observer was located on average 50.1 m ± 19.7 SD (range = 25–75 m, n = 11 nests) from at least one active bittern nest during each survey. For 8 of 9 (89%) detections, at least one bittern was already vocalizing at the beginning of the survey, before the Least Bittern call was played. We show that it is possible for this species to remain undetected with the use of call-broadcasts that are less than 30 seconds, even though the species may be nesting as close as 25 m to the location from which the calls are broadcasted. We suggest that systematic nest searches are more reliable than call-broadcast surveys for detecting nesting Least Bitterns.
... All of our focal species are believed to have at least two broods in a season (Poole et. al. 2009, Bannor and Kiviat 2002, West and Hess 2002, especially in the southern United States where the growing season is longer (Pickens and Meanley 2015). Distinguishing between second broods and renests after failed attempts is difficult given our limited dataset, but the timing of later nests in relation to fledged young from earlier nest a ...
... Least Bitterns typically prefer taller emergent marsh vegetation (Poole et al. 2009), and our data corroborate this since the average total substrate height above water was the greatest among all species at 250 cm (Table 1). Average water depth and nest height above water were similar among Common and Purple Gallinules. ...
... Least bittern is designated threatened in Canada and is considered at-risk in 36 US states (NatureServe, 2012). Wetland types identified as habitat for wetland birds were emergent marsh or shrub thicket swamp (i.e., wetland types 2 or 3; Sub section 2.1) (Bannor and Kiviat, 2002;Eddleman et al., 1988;Gibbs et al., 2009;Mowbray, 1997). We excluded wetland patches <0.4 ha (Gibbs et al., 2009). ...
... Wetland types identified as habitat for wetland birds were emergent marsh or shrub thicket swamp (i.e., wetland types 2 or 3; Sub section 2.1) (Bannor and Kiviat, 2002;Eddleman et al., 1988;Gibbs et al., 2009;Mowbray, 1997). We excluded wetland patches <0.4 ha (Gibbs et al., 2009). ...
... What may be a driver for the evolution of functional precociality of the hind limbs in smaller species of herons, subsequently displayed in typical foraging modes in adults? In general, small species with accelerated foot prehensility, e.g., Green Heron, are mostly solitary or loosely colonial nesters ( Davis and Kushlan 2020 ), and/or nest close to the ground or just above water (e.g., Least Bittern nests in emergent vegetation only 15-76 cm above the water's surface: Poole et al. 2020 ; Zigzag Heron, of which there is little known, is also a solitary nester, as is the American Bittern: HeronConservation 2020 ). Thus, nestlings of these species are more vulnerable to predators (e.g., lack "safety in numbers") compared with densely colonial species and/or those that nest higher in trees; they also typically have smaller body sizes and consequently Evolutionary dynamics in herons 13 Fig. 4 Relationship between the de viation of f emur length from isometry with leg length and behavioral mode without ( A ) and with ( B ) phylogenetic corrections. ...
Synopsis
The ultimate form an organism attains is based, in part, on the rate and timing of developmental trajectories and on compensatory relationships between morphological traits. For example, there is often an inverse correlation between the relative size of an organism's head and the length of its legs. Avian examples with a disproportionately small head and long legs include ostriches (Struthionidae), flamingos (Phoenicopteridae), cranes (Gruidae), and stilts (Recurvirostridae). To determine whether a possible compensatory relationship exists between relative head size and hind-limb length in a typically long-legged family of birds—the Ardeidae—we measured and analyzed skull dimensions (length, width, and height of cranium, and bill length) and skeletal hind-limb dimensions (femur, tibiotarsus, and tarsometatarsus) of the 12 North American species (north of Mexico) and of 12 additional taxa, including the morphologically divergent Agamia and Cochlearius. We found that Ardea species exhibit the smallest relative head sizes associated with the longest legs, while Butorides, Nycticorax, Nyctanassa, and Cochlearius have among the largest heads relative to hind-limb length. Furthermore, both positive and negative allometries occur in paired comparisons between the three hind-limb bones, expressed in tall morphotypes having disproportionately short femurs while short-legged morphotypes exhibit disproportionately long femurs; we show that this relationship has implications for foraging behavior. Moreover, the nestlings of short-legged herons exhibit functional precociality of the hind limbs through an early onset of prehensile ability of the feet to grasp branches, which is later expressed in adult foraging mode. This developmentally accelerated prehensile function in small-bodied species may be attributed, in part, to selection for predator avoidance in the early nestling stage.
... Marsh birds (rallids, bitterns and grebes) are a group of wetland-dependent migratory birds associated with emergent vegetation communities (i.e., persistent and non-persistent emergent vegetation) and often characterized by their elusive nature. Most marsh bird species in North America have experienced population declines primarily due to wetland loss and degradation [7,[9][10][11][12]. In response to population declines, several species of marsh birds have been listed as species of conservation concern at the state, provincial and regional levels [13,14]. ...
Marsh birds (rallids, bitterns, and grebes) depend on emergent wetlands, and habitat loss and degradation are the primary suspected causes for population declines among many marsh bird species. We evaluated the effect of natural wetland characteristics, wetland management practices, and surrounding landscape characteristics on marsh bird occupancy in Illinois during late spring and early summer 2015–2017. We conducted call-back surveys following the North American Standardized Marsh Bird Survey Protocol three times annually at all sites (2015 n = 49, 2016 n = 57, 2017 n = 55). Across all species and groups, detection probability declined 7.1% ± 2.1 each week during the marsh bird survey period. Wetlands managed for waterfowl (ducks, geese, and swans) had greater occupancy than reference wetlands. Marsh bird occupancy increased with greater wetland complexity, intermediate levels of waterfowl management intensity, greater proportions of surface water inundation, and greater proportions of persistent emergent vegetation cover. Wetland management practices that retain surface water during the growing season, encourage perennial emergent plants (e.g., Typha sp.), and increase wetland complexity could be used to provide habitat suitable for waterfowl and marsh birds.
... The Least Bittern breeding range extends from southeastern Canada through the Atlantic Coast, the Caribbean, and parts of South America (Poole et al. 2009). ...
Ixobrychus exillis (Least Bittern) is listed as a species of high concern in the North American Waterbird Conservation Plan and is a US Fish and Wildlife Service migratory bird species of conservation concern in the Northeast. Little is known about the population of Least Bitterns in the Northeast because of their low population density, tendency to nest in dense wetland vegetation, and secretive behavior. Urban and agricultural development is expected to encroach on and degrade suitable wetland habitat; however, we cannot predict the effects on Least Bittern populations without more accurate information on their abundance and distribution. We conducted surveys of wetlands in Vermont to assess the efficacy of a monitoring protocol and to establish baseline Least Bittern abundance and distribution data at a sample of 29 wetland sites. Surveys yielded detections of 31 individuals at 15 of 29 sites across 3 biophysical regions and at 5 sites where occupancy had not been previously reported. Probability of occupancy was positively related to wetland size and number of patches, though the relationships were not strong enough to conclude if these were true determinants of occupancy. Call-response broadcast surveys yielded 30 detections, while passive surveys yielded 13. Call-response broadcasts (P = 0.897) increased the rate of detection by 55% compared to passive surveys (P = 0.577). Our results suggest that call-response broadcast surveys are an effective means of assessing Least Bittern occupancy and may reduce bias in long-term monitoring programs.
... In terms of traits, species that rely on stalking or dabbling for foraging and nest on the ground were more strongly associated with meadow marsh, cattail marsh and open-water habitat than with P. australis (ESM Fig. S3). This includes the marsh-nesting species Virginia rail, sora, and least bittern, who forage for food by probing, ground foraging and stalking, respectively, and preferentially build ground nests using cattail vegetation or sedges (Conway, 1995;Melvin and Gibbs, 2012;Poole et al., 2009). American bittern, a species observed only in cattail marsh and open-water, is also a ground nesting bird who forages via stalking and has been reported to avoid dense, even-aged stands of vegetation when hunting ). ...
On the North shore of Lake Erie, Long Point provides habitat to many thousands of breeding and migrating birds, including marsh-nesting species that are in decline across the Great Lakes. Invasive Phragmites australis threatens the ecological integrity of these marshes. Early concerns prompted a study into the effects of invasion on bird use in 2001–2002 that concluded P. australis was not a major bird conservation issue. We evaluate breeding season bird occupancy in these wetlands after over a decade of P. australis expansion, comparing bird diversity and abundance in P. australis with diversity and abundance in the vegetation communities that P. australis is displacing: cattail, meadow, and open-water marsh. We also examine community composition and functional traits to better capture the effects of P. australis invasion. In 2015, total bird abundance was lower in P. australis than cattail marsh (ANOVA p < 0.001), with little difference in bird species richness among vegetation types (ANOVA p = 0.272). Bird community composition was distinct among the vegetation types (MRPP p < 0.001), such that P. australis supported a subset of bird species found within cattail and meadow marsh habitat, rather than novel species. Phragmites australis habitat excludes many marsh-nesting species and provides habitat for shrub-nesting, ground and foliage gleaners instead. Marsh-nesters of conservation concern are restricted to remaining cattail, meadow marsh, and open-water habitat. The full effects of P. australis invasion may exhibit a lag time, and community composition and functional traits should be considered when evaluating the effects of biological invasions.
... This protocol consists of a 5-min passive listening period followed by 1-min periods of 30 sec of playback and 30 sec of listening for each focal species. We broadcast calls of Black Rail (Laterallus jamaicencusis), Least Bittern, King Rail (Ralus elegans), Purple Gallinule and Limpkin as suggested by the Standardized North American Marsh Bird Monitoring Protocol and because these species have been recorded breeding in the area (Bryan 2002;West and Hess 2002;Poole et al. 2009). Recordings of calls were obtained from the National Marsh Bird Survey Coordinator (Conway 2011). ...
Wetland loss has led to population declines of many species of North American marsh birds. However, due to the secretive nature of many of these species, there is uncertainty about their population status and habitat requirements. Recently developed techniques, such as the Standardized North American Marsh Bird Monitoring Protocol and analytical methods that account for variable detection probabilities, can be used to improve both the quality and quantity of information about secretive marsh birds. In 2009 and 2010, point counts were conducted using the marsh bird monitoring protocol to count Least Bittern (Ixobrychus exilis), Purple Gallinule (Porphyrio martinica) and Limpkin (Aramus guarauna) in the Kissimmee Chain of Lakes, Florida. Habitat factors thought to influence abundance were compared using competing hierarchical mixture models. Abundance of Least Bittern had a positive relationship with amounts of emergent vegetative cover and interspersion (i.e., vegetation to water edge). Purple Gallinule abundance was positively related to percentage of area cover by floating-leaved vegetation, interspersion and diversity of vegetation type. Limpkin abundance was non-linearly related to vegetation cover in both years. In 2009, Limpkin abundance was positively related to vegetation to water edge and vegetation type diversity, and negatively related to vegetation edge in 2010. Results demonstrate that marsh habitats with greater amounts of vegetative cover, interspersion, and vegetation diversity will support the greatest abundance of this suite of marsh birds.
... For this species water depth may be more important as they prefer shallow water (<30 cm) and mud flats for foraging (Conway, 1995), but since we did not measure water depth at each site it is difficult infer a relationship. The Least Bittern is limited by distribution because the northern limit of its breeding range is southern Georgian Bay, and in addition, it prefers tall, dense, emergent vegetation for nesting and the vegetation in Georgian Bay was shorter than that of Lake Ontario (Poole et al., 2009). This is not the first time that the applicability of indicators on a basin-wide scale has been called into question. ...
Ecological indicators have gained increasing attention within the scientific community over the past 40 years. Several taxonomic groups have been used successfully as indicators including most prominently fish, invertebrates, plants, and birds because of their ability to indicate environmental changes. In the Laurentian Great Lakes region, there has been recent concern over the applicability of using indicators on a basin-wide scale due to species range restrictions and lake-based differences. The objective of this study was to determine the ability of the Index of Marsh Bird Community Integrity (IMBCI) to indicate land use disturbance surrounding coastal marshes of Georgian Bay and Lake Ontario. To meet this objective, we surveyed birds and vegetation at 14 marshes in Georgian Bay (low land use disturbance) and Lake Ontario (high land use disturbance). Even though Lake Ontario marshes were surrounded by significantly more altered land than Georgian Bay marshes, and had poorer water quality, we found significantly fewer birds in Georgian Bay marshes (mean=8.2) compared to Lake Ontario (mean=13.7) and no significant difference in IMBCI scores. This inconsistency could be due to vegetation differences affecting the strength of the index, because Georgian Bay wetlands had significantly more bulrush (Schoenoplectus spp.) and floating vegetation, while Lake Ontario wetland vegetation was taller and cattail-dominated (Typha spp.). These findings suggest that the IMBCI may not be useful on a basin-wide scale in the Great Lakes region in detecting human disturbance surrounding wetlands.
Marsh birds have decrease their populations in the neotropic; among the main causes are the lost and degradation of wetlands. With the objective of providing information about marsh bird´s populations and their habitats, we analyze bird’s abundance and its relationship with some environmental and structural features of marshes from a portion of Lake Chapala. We study 14 marshes during 2018 breading season; we measure two groups of variables (biotic and abiotic), water pH, relative humidity and water and atmospheric temperature. The other group of variables includes vegetation: species richness, coverage and stratification. To detected birds, we follow the North American Marsh Bird Monitoring Protocol using calls from eight species with previous records in the area. Five sampling visits are required to detect, at least once, all species. Fulica americana y Gallinula galeata were the most abundant and Rallus tenuirostris, Butorides virescens and Porphyrio martinica were the least abundant. The use of calls positively increase the number of responses of birds. Lake Chapala marshes have considerable plant species richness, high similarity in composition and are dominated by Typha domingensis. The variables that best explain variation in bird abundance are time since sunrise, coverage and plant species richness.
ESPAÑOL:
Las poblaciones de aves de ciénagas han decrecido en el neotrópico; entre las principales causas se consideran la pérdida y degradación de los humedales. Con el fin de proveer información sobre las poblaciones de aves de ciénagas y sus hábitats, se analizó la abundancia de las aves y su relación con algunas características ambientales y estructurales de las ciénagas de una porción del Lago de Chapala. Se estudiaron 14 tulares durante la temporada reproductiva de las aves en el año 2018, y se midieron dos conjuntos de variables. 1) Las variables físicas: pH, humedad relativa y temperatura atmosférica y del agua, y 2) las variables de la vegetación: riqueza de especies, cobertura y estratificación. Las ciénagas del lago tienen una considerable riqueza de plantas, alta similitud en su composición y están dominadas por Typha domingensis. Para la detección de las aves se siguió el protocolo norteamericano estandarizado de monitoreo de aves de ciénagas, en el cual se utilizaron llamados de ocho especies con registro en el área de estudio. Fulica americana y Gallinula galeata mostraron mayor abundancia, y Rallus tenuirostris, Butorides virescens y Porphyrio martinica fueron las de menor abundancia. El uso de llamados incrementó significativamente el número de respuestas de aves. Las variables que mejor explican la variación en la abundancia de aves son: el tiempo transcurrido desde el amanecer, la cobertura y la riqueza de especies vegetales.
The capuchinos, a subset of the genus Sporophila, represent a radiation of seedeaters characterized by little genetic differentiation, virtually no change in bill and body shape, marked plumage differences on a common theme, and notable differentiation in vocalizations and habitat use. We describe a distinctive variant that would have been considered a species by the traditional strictly phenotypical criteria for classification of species in the genus. This variant resembles the Tawny-bellied Seedeater (S. hypoxantha) but has a tawny, not gray, nape and back. It is also identical in pattern to the Chestnut Seedeater (S. cinnamomea) but has a tawny rather than chestnut body. We tested four hypotheses to assess the status of the variant: that it represents a new species, a hybrid S. hypoxantha x S. cinnamomea, a color morph of S. cinnamomea, or a color morph of S. hypoxantha. The variant is identical to S. hypoxantha in vocalizations and habitat use, varying geographically in parallel. Both forms breed syntopically, and the tawny variant is recorded only within the range of S. hypoxantha, with many records from areas where S. hypoxantha is the only breeding representative of the ruficollis group. We consider the tawny variant to be a color morph of S. hypoxantha. Two nontrivial evolutionary paths can constitute precursors to speciation in the capuchinos: (1) differentiation in vocalizations and habitat use arises with little plumage change in more or less geographically isolated populations, and (2) differentiation in plumage proceeds without change in vocalizations and habitat use within some populations.
The Least Bittern (Ixobrychus exilis) is at risk in several regions of North America and the effectiveness of multi-species marsh bird surveys to detect this secretive species has been questioned. A species-specific standardized survey protocol for Least Bitterns was developed to increase detection, quantify detection probability and improve knowledge of the species' distribution, abundance and habitat use. The protocol is a modification of the Standardized North American Marsh Bird Monitoring Protocol (Conway 2009), whereby only the Least Bittern call is broadcast repeatedly at fixed point count survey stations, and a second passive listening period is added after the broadcast period to increase detection. Vocalizations and behavior are noted on a minute-by-minute basis for each individual Least Bittern, along with estimated distance at first detection. The protocol has been implemented in Canada since 2006 and has resulted in Least Bitterns being detected in more sites and larger numbers than previously suspected. Adoption of the proposed protocol is recommended across the Least Bittern range when Least Bittern detection is the focus of a survey or monitoring program; therefore allowing direct comparisons of relative abundance and detection probabilities amongst sites.
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