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Late arrival on the breeding grounds has been associated with reduced fitness in migratory birds. Because migratory stopover accounts for the majority of time spent on migration, how individuals respond to both exogenous and endogenous factors associated with stopover will influence the pace of migration and arrival timing on the breeding grounds. Among the most important endogenous factors, body condition (i.e. fat stores) is expected to influence both movement behavior and departure decisions of individual migrants during stopover. In a novel experiment, we manipulated the condition of after-second-year (adult) male American Redstarts (Setophaga ruticilla) captured during spring migratory stopover and radio-tracked all individuals after release using a passive automated telemetry array and conventional hand tracking. After accounting for the positive effect of tailwind and capture date on departure probability, we demonstrated that body condition influenced both the movement behavior of individ...

The Red-headed Woodpecker (Melanerpes erythrocephalus) has experienced strong population declines during the past 3 decades. Using North American Breeding Bird Survey (BBS) and Audubon Christmas Bird Count (CBC) data, we investigated 4 hypotheses that may explain this decline, including: (1) interspecific competition with native Red-bellied Woodpeckers (Melanerpes carolinus) and nonnative European Starlings (Sturnus vulgaris); (2) predation by Cooper's Hawks (Accipiter cooperii) and Sharp-shinned Hawks (Accipiter striatus); (3) climate change; and (4) changes in forested area within their range. In analyses of both the breeding and overwintering periods, our results indicated a role of increased accipiter populations in driving Red-headed Woodpecker declines through increased predation. We also found evidence for significant effects of warmer winter temperatures and increased forest cover, both directly and indirectly through their effects on enhancing accipiter populations. In contrast, our resu...

Billions of migratory passerines encounter ecological barriers during migration that are risky in time, energy, and safety. Migrants are thought to behave differently prior to crossing to minimize these risks. We demonstrate that departure from stopover is influenced by both wind conditions and energy stores. However, this behavior did not differ pre- or post-crossing of a migratory barrier. We conclude that barriers of varying sizes are likely to have different effects on stopover departure behavior. Twitter: @BryantDossman

Long-distance migratory animals typically stop-over between migratory movements to rest and refuel. In species lacking stopover site fidelity, including most songbirds, timely arrival to breeding areas with sufficient energy stores for reproduction requires that migrants rapidly locate suitable stopover habitat in unfamiliar landscapes. Few studies have examined movement ecology in such species during stopover, and even fewer have addressed how these migrants adjust movement behaviors in response to encountering preferred or non-preferred habitats. We experimentally translocated spring transient Northern Waterthrushes (Parkesia noveboracensis) to preferred (bottomland) and non-preferred (upland) forest habitats and characterized subsequent fine-scale movements and stopover duration using radiotelemetry. Minimum stopover duration averaged 4.1 days and was 1.5 days longer in bottomland-released birds than in upland-released birds. Minimum stopover duration decreased by 1.4 days per week over the spring migratory period. For upland-released and bottomland-released birds, respectively, maximum distance moved from the release point was 635 ± 58 m and 326 ± 51 m on the day of the release and 773 ± 109 m and 504 ± 83 m on the following day. Upland-released individuals traveled nearly twice as far from the release point on day 1 as bottomland-released birds. Upon reaching bottomland habitats within 2.0 ± 0.3 h of release, subsequent distance moved on day 1 by upland-released birds was similar to that of bottomland-released birds. Cumulatively, these results indicate that initial exploratory movements were facultative and habitat dependent and that waterthrushes can successfully locate suitable stopover habitats in a heterogeneous landscape at the spatial scales we investigated.

Aim Demand for quantitative conservation targets has yielded a search for generalities in habitat thresholds, particular amounts of habitat at which extinction probabilities change strongly. These thresholds are thought to vary across regions, but investigation of this variability has been limited. We tested whether thresholds (of forest separating extinction from persistence) increased as either average forest cover in landscapes decreased or the degree of fragmentation increased. Location Massachusetts, Michigan, New York, Ohio, Pennsylvania and Vermont. Methods We used segmented logistic regressions to estimate thresholds in the relationship between extinction probability and forest cover for 25 forest-breeding birds, comparing estimated thresholds across states. We also selected landscapes from our entire study area in which landscape-level forest cover and degree of fragmentation varied independently and compared thresholds. Results We found that thresholds in extinction probability varied widely among species (7–90% forest cover) and within species across states [e.g. 12–90% for white-throated sparrow (Zonotrichia albicollis)]. Additional analyses showed no indications that thresholds correlated with the degree of fragmentation or forest cover across the landscape; we found considerable variability in thresholds across landscapes, species and even landscapes in which (average) fragmentation and forest cover were similar. Main conclusions Extinction threshold estimates varied tremendously across species and landscapes. Thus, habitat thresholds are difficult to generalize as they depend on many factors beyond landscape fragmentation and habitat availability (e.g. landscape characteristics such as matrix quality). Our findings highlight the need to avoid oversimplification and generalization of habitat thresholds, especially as they might prove counterproductive to conservation efforts. Instead, we propose that we evaluate thresholds for individual species – preferably using species-centred habitat definitions in threshold modelling – to derive generalities for ecological and conservation applications.

Nocturnal roosting at locations disjunct from daytime foraging areas (hereafter disjunct nocturnal roosting) is a common avian behavior on both the breeding and wintering grounds but to our knowledge has not been documented in arboreal passerines during migratory stopover. We report observations of a spring migrant Yellow-rumped Warbler (Setophaga coronata) commuting to a nocturnal roost site 2.6–3.2 km north from its 5.1–9.0 ha daytime home ranges on two consecutive stopover days. We discuss the potential significance of this behavior in terms of roost habitat type, predator avoidance, and thermoregulation. We encourage those conducting telemetry studies on stopover migrants to examine existing data and, when possible, to use tracking methods that advance understanding of the behavioral ecology of nocturnal roosting and the prevalence of and causes for disjunct roosting.

Birds require additional resources for raising young, and the breeding currency hypothesis predicts that insectivorous species exploit large soft-bodied prey during the breeding season, but shift to small, likely hard-bodied, prey during the non-breeding season. To test this hypothesis, we examined prey use by Cerulean Warblers (Setophaga cerulea), foliage-gleaning Nearctic-Neotropical migrants, during the breeding and non-breeding seasons. We collected data on foraging behavior during the breeding season (including observations of prey items fed to young) in upland mixed-oak forest in southeastern Ohio in 2009 and 2010 and, during the non-breeding season, in shade coffee in the Cordillera de Merida, Venezuela, in 2008–2009. Cerulean Warblers captured 7% more large prey (visible prey extending beyond the bill) during the breeding than the non-breeding season, but foraged at similar rates during both seasons. Large, soft-bodied prey appeared to be especially important for feeding young. We found that adults delivered large prey on >50% of provisioning visits to nests and 69% of identifiable large prey fed to nestlings were greenish larvae (likely Lepidoptera or caterpillars) that camouflage against leaves where they would tend to be captured by foliage-gleaning birds. Availability of specific taxa appeared to influence tree species foraging preferences. As reported by other researchers, we found that Cerulean Warblers selected trees in the genus Carya for foraging and our examination of caterpillar counts from the central Appalachian Mountains (Butler and Strazanac 2000) showed that caterpillars with greenish coloration, especially Baileya larvae, may be almost twice as abundant on Carya than Quercus. Our results provide evidence for the breeding currency hypothesis, and highlight the importance of caterpillars to a foliage-gleaning migrant warbler of conservation concern. RESUMEN Comportamiento forrajero del Chipe Ceruleo durante la temporada reproductiva y no reproductiva: evidencia de la hipotesis de divisa de crianza Las aves requieren recursos adicionales a fin de criar a los pichones, y la hipotesis de divisa de crianza predice que las especies insectivoras explotan presas grandes de cuerpo blando durante la temporada reproductiva, pero que cambian a presas pequenas de cuerpo duro en la temporada no reproductiva. A fin de poner a prueba esta hipotesis, examinamos el uso de presas por parte del Chipe Ceruleo (Setophaga cerulea), forrajeadores de follaje y migrantes Neartico-Neotropico, durante la temporada reproductiva y no reproductiva. Colectamos datos del comportamiento forrajero durante la temporada reproductiva (incluyendo observaciones de presas entregadas a los pichones) en un bosque de tierras altas compuesto de varias especies de roble en el sur este de Ohio en 2009 y 2010 y, durante la temporada no reproductiva, en una plantacion sombreada de cafe en la Cordillera de Merida, Venezuela, en 2008–2009. Los Chipes Ceruleos capturaron presas un 7% mas grandes (presa visible extendiendose mas alla del pico) durante la temporada reproductiva que durante la temporada no reproductiva, pero forrajearon a igual tasa durante ambas temporadas. Las presas grandes y de cuerpo blando parecian ser especialmente importantes para alimentar a los pichones. Encontramos que los adultos entregaban presas en mas del 50% de las visitas de entrega de presas al nido y el 69% de las presas identificables entregadas a los pichones era larvas verduzcas (probablemente Lepidoptera u orugas) que se camuflaban contra las hojas donde tendian a ser capturadas por aves forrajeadoras de follaje. La disponibilidad de taxas especificos parece influenciar las preferencias en el forrajeo arboreo. Como ha sido reportado por otros investigadores, encontramos que los Chipes Ceruleos seleccionaron arboles dentro de genero Carya para el forrajeo y nuestro conteo de orugas del centro de las Montanas Apalaches (Butler and Strazanac 2000) mostraron que las orugas con coloracion verduzcas, especialmente las larvas de Baileya, deben ser al menos el doble de abundantes en Carya que en Quercus. Nuestros resultados proveen evidencia a la hipotesis de divisa de crianza, y resaltan la importancia de las orugas en un chipe forrajeador de follaje y migrante con problemas de conservacion.

Shade coffee has been identified as an important habitat for Nearctic-Neotropical migrants during the non-breeding season, including species of conservation concern such as Cerulean Warblers (Setophaga cerulea). To better understand habitat features important for migrants in shade coffee, we studied the foraging behavior of migrants in mixed-species flocks at six shade-coffee farms in the Cordillera de Merida, Venezuela, in 2008–2009 and the El Nino drought year of 2009–2010. We examined interspecific differences in foraging behavior and tree species selection of three foliage-gleaning migrants, Blackburnian (Setophaga fusca), Cerulean, and Tennessee (Oreothlypis peregrina) warblers, and aerial-foraging American Redstarts (Setophaga ruticilla). For morphologically similar Blackburnian and Cerulean warblers, we also examined factors influencing foraging rates (attack and movement rates), capture of large prey, and maneuver/substrate type. We found that aerial-foraging American Redstarts foraged lower, used more aerial maneuvers, showed no tree species selection, and were less likely to forage in flocks than foliage-gleaners. Although foraging rates were similar for Blackburnian and Cerulean warblers, the three foliage-gleaners differed in foraging height and use of maneuvers. Cerulean Warblers foraged lower than the other two species, whereas Blackburnian Warblers used the greatest proportion of woody gleans. All three foliage-gleaners selected Inga spp. (a commonly planted shade tree in shade-coffee farms) for foraging, and Blackburnian and Cerulean warblers captured a greater proportion of large prey in Inga spp. than in other tree species. During the drought year, Blackburnian and Cerulean warblers captured half as many large prey and used a greater proportion of woody-gleans. We found that interactions among behavioral, floristic, and environmental drivers influenced the foraging behavior of migrants wintering in shade coffee. Our results support those of previous studies suggesting that migrants partition resources behaviorally during the non-breeding season, that foliage-gleaners may benefit from the presence of shade trees, especially Inga spp., in agroforestry systems, and that drought may influence the foraging behavior of foliage-gleaning migrants, presumably due to reduced prey availability. RESUMEN Comportamiento de forrajeo de reinitas migrantes en bandadas mixtas en cafe bajo sombra en Venezuela: diferencias inter-especificas, seleccion de especies de arboles y efectos de sequias El cafe bajo sombra ha sido identificado como un habitat importante para especies migratorias neartico-neotropicales durante la epoca no reproductiva, incluyendo especies con importancia para la conservacion como Setophaga cerulea. Con el fin de obtener un mejor entendimiento de las caracteristicas del habitat importantes para las especies migratorias en los cafes bajo sombra, estudiamos el comportamiento de forrajeo de migrantes en bandadas mixtas de especies, en seis fincas con cafe bajo sombra en la Cordillera de Merida, Venezuela, en 2008–2009 y durante los anos de sequia por El Nino en 2009–2010. Examinamos diferencias inter-especificas en los comportamientos de forrajeo y seleccion de especies de arboles en tres especies “buscadoras de follaje/foliage gleaners”, Setophaga fusca, Setophaga cerulea y Oreothlypis peregrina, ademas de una especie con comportamiento de “forrajeo aereo/aerial foraging”, Setophaga ruticilla. Para especies que son similares morfologicamente como Setophaga fusca y cerulea, examinamos tambien los factores que influencian las tasas de forrajeo (tasas de ataque y movimiento), captura de presas grandes y tipo de maniobra/substrato. Encontramos que Setophaga ruticilla forrajea mas bajo y utiliza mas maniobras aereas, no mostro ningun patron en la seleccion de especies de arboles y fue menos propensa a forrajear en bandadas mixtas que las buscadoras de follaje. A pesar que las tasas de forrajeo fueron similares en S. fusca y S. cerulea, las tres especies “buscadoras de follaje” difieren en la altura de forrajeo y uso de maniobras. S. cerulea forrajea mas bajo que las otras dos especies, mientras que S. fusca usa una mayor proporcion de estrategias de“busqueda en madera/woody-gleans”. Las tres especies buscadoras de follaje seleccionaron activamente Inga spp. (una especie de arbol utilizada comunmente como sobra en fincas de cafe bajo sombra) para forrajeo y S. fusca y S. cerulea capturaron una mayor proporcion de presas grandes en Inga spp. que las otras tres especies. Durante el ano de sequia, S. fusca y S. cerulea capturaron la mitad de presas grandes en comparacion con anos anteriores y utilizaron en una mayor proporcion estrategias de busqueda en madera. Nuestros resultados sugieren que interacciones entre caracteristicas de forrajeo, floristicas y del ambiente influencian el comportamiento de forrajeo de especies migratorias durante la epoca de invierno en cafe bajo sombra, y soportan los resultados de estudios previos que indican que las especies migratorias reparten los recursos mediante diferencias en el comportamiento durante las epocas no reproductivas. Nuestros resultados sugieren tambien que las especies buscadoras de follaje se pueden beneficiar de la presencia de arboles de sombrio, especialmente Inga spp., en sistemas agroforestales, y que la sequia puede, probablemente debido a la reduccion en la abundancia de presas, influenciar el comportamiento de forrajeo de especies migratorias buscadoras de follaje.

We report the first well-documented hybrid between Field Spizella pusilla and Clay-coloured Sparrows S. pallida. This hybrid combination has previously been suggested from field observations in eastern North America, but not confirmed. We encountered an individual in Lorain County, Ohio, USA, during surveys for the state's second breeding bird atlas. It was a territorial male, singing a buzzy but accelerating trilled song with characteristics of both parents. It responded vigorously to playback of both Field and Clay-coloured Sparrows. In the hand, the bird showed plumage characteristics of both species and intermediate measurements. Using molecular data, we were able to confirm Clay-coloured Sparrow as the mother of the individual, with support for Field Sparrow as the father. This and other recent field observations of this hybrid pairing have been reported at the eastern boundary of the expanding breeding range of Clay-coloured Sparrow, suggesting that this hybrid combination can be expected elsewhere in the Great Lakes region and in New England, where these species are increasingly syntopic.

Competition theory predicts that local communities should consist of species that are more dissimilar than expected by chance. We find a strikingly different pattern in a multicontinent data set (55 presence-absence matrices from 24 locations) on the composition of mixed-species bird flocks, which are important subunits of local bird communities the world over. By using null models and randomization tests followed by meta-analysis, we find the association strengths of species in flocks to be strongly related to similarity in body size and foraging behavior and higher for congeneric compared with noncongeneric species pairs. Given the local spatial scales of our individual analyses, differences in the habitat preferences of species are unlikely to have caused these association patterns; the patterns observed are most likely the outcome of species interactions. Extending group-living and social-information-use theory to a heterospecific context, we discuss potential behavioral mechanisms that lead to positive interactions among similar species in flocks, as well as ways in which competition costs are reduced. Our findings highlight the need to consider positive interactions along with competition when seeking to explain community assembly.