Wintering Areas, Migratory Connectivity and Habitat Fidelity of Three Declining Nearctic- Neotropical Migrant Swallows

Abstract

Conservation efforts directed at population declines for migratory animals must consider threats occurring at different stages often separated by vast distances. Furthermore, connectivity between populations and fidelity of individuals to specific habitats during the annual cycle are also important considerations. Avian aerial insectivores are experiencing steep population declines in North America, and those declines may be driven, in part, by conditions on the wintering grounds. Here, using geolocators (2 species; 4 individuals) and stable isotope (δ2H, δ13C and δ15N) measurements of feathers (3 species; 841 individuals), we identified approximate winter areas, and assessed migratory connectivity and among-year winter habitat fidelity for three aerial insectivores (Bank Swallow Riparia riparia, Barn Swallow Hirundo rustica and Cliff Swallow Petrochelidon pyrrhonota) that breed in northeastern North America. All three species of swallows are declining in this region. Our results, largely from the stable isotope analysis, suggest that these species likely winter throughout the Cerrado, La Plata Basin, and the Pampas, in South America. These most likely areas were similar among years (2013-2016) for Bank and Cliff Swallows, but varied for Barn Swallows (2014-2016). We found weak migratory connectivity for all three species, and, with one exception, weak habitat fidelity among years for individuals. For individual Barn Swallows captured in two or more years, we found high repeatability in δ13C values, suggesting some fidelity to similar habitats among years. The most likely wintering areas for these species coincide with large areas of South America experiencing high rates of land-use change.

Geolocators reveal migration routes, stopover sites, and nonbreeding dispersion in a population of Cerulean Warblers

“…Some migratory species use multiple nonbreeding sites throughout the nonbreeding period [e.g. 17,18]. Based on published accounts of the nonbreeding ecology of Cerulean Warblers, we did not expect Cerulean Warblers to use multiple nonbreeding sites during the nonbreeding period [19].…”

Annual adult survival rates for four sympatric breeding swallow species: effects of environmental factors and density-dependence

“…We predicted that ENSO and NAO may affect survival for Tree Swallows from the Maritimes that winter in southeastern USA and Cuba (Knight et al 2018), but was less likely to affect survival for Barn Swallows from the Maritimes wintering in southern Brazil, Bolivia, Paraguay, Uruguay, and northern Argentina (Hobson et al 2015;Imlay et al 2018) (Figure S1) as these areas are less affected by this weather pattern. For NAO, we followed Clark et al ( 2018) and calculated the mean monthly value from December to March.…”

“…To examine primary productivity during the winter, we first determined the winter range of our breeding populations. For Barn Swallows, we obtained a map of the probable winter locations of individuals from the Maritime breeding population (Imlay et al 2018). This map was based on probabilistic assignment of δ 2 H and δ 13 C stable isotopes in feathers molted during the winter.…”

“…The overarching goal of our research was to determine the apparent annual survival rates populations (Nebel et al 2010;Smith et al 2015;Michel et al 2016). We predicted that if apparent annual survival rates were driven by factors during the stationary non-breeding period, then variation in survival rates would be similar across the three species of long-distance migrants (Bank Riparia riparia Linnaeus, 1758, Barn, and Cliff swallows Petrochelidon pyrrhonota Vieillot, 1817) that typically winter throughout southern Brazil, Paraguay, Uraguay, Bolivia, and northern Argentina (Hobson et al 2015;Imlay et al 2018) when compared to the short-distance migrant (Tree Swallow) which winters in southeastern USA and Cuba (Knight et al 2018). Also, for the two species with the most data (Barn and Tree swallows), we determined if apparent annual adult survival rates are correlated with environmental conditions known to influence survival and behaviour for these and similar species (Imlay and Leonard 2019).…”

Distribution and migration phenology of Purple Martins (Progne subis) in Brazil

“…As with other insectivorous migratory birds, Purple Martins have been in a long-term population decline, 37% over the last five decades, although trends differ regionally (Nebel et al 2010;Michel et al 2015;Sauer et al 2017). Suggested causes for these declines include destruction of important stopover and wintering habitats (Rogers et al 2010;Imlay et al 2018;Kardynal et al 2020), detrimental health effects of pesticide and heavy metal contamination (Bernhoft 2012;Nocera et al 2012), and persecution by local human populations (Hill 2004). However, to begin understanding the conservation challenges faced by Purple Martins during the nonbreeding season, it is necessary first to fill existing knowledge gaps about migration timing, distribution, and habitat use in Brazil.…”