ABSTRACT. Swallows, along with other aerial insectivores, are experiencing steep population declines. Decreased insect abundance has been implicated as a potential cause of the decline. However, to determine if there is a guild-level effect of reduced insect abundance on swallows, research is needed to examine relationships between insect abundance and breeding success for multiple species. The goal of our study was two-fold. First, we determined if insect abundance during nestling rearing varied with breeding phenology for three species of swallows, Barn (Hirundo rustica), Cliff (Petrochelidon pyrrhonota), and Tree Swallows (Tachycineta bicolor), such that swallows breeding when insects are abundant have greater success. Then we determined if insect abundance was related to nestling survival and mass (as a proxy for postfledgling survival). We collected insects daily at each of three study sites during the breeding season, monitored swallow nests to determine breeding phenology and success, and weighed nestlings at or just prior to the peak of rapid nestling growth to determine mass. We found early hatching Cliff and Tree Swallow nests had higher insect abundance during nestling rearing. However, neither nestling survival nor mass were related to insect abundance. Our results suggest that breeding success in three species of swallows was not related to insect abundance in our study area. We suggest that the role of insect abundance on aerial insectivore declines may vary across their geographic range, and call for broad-scale, multispecies research on aerial insectivore declines. Absence d'effet du nombre d'insectes sur la survie et le poids des oisillons de trois insectivores aériensRÉSUMÉ. Les populations d'hirondelles, tout comme celles d'autres insectivores aériens, affichent des baisses marquées. Pour expliquer celles-ci, la diminution du nombre d'insectes a été soulevée comme cause possible. Toutefois, des études examinant la relation entre la quantité d'insectes et le succès de reproduction de plusieurs espèces sont nécessaires afin de déterminer si la quantité réduite d'insectes a un effet sur l'ensemble des espèces d'hirondelles. La présente étude avait deux objectifs. Le premier était de déterminer si la quantité d'insectes durant l'élevage des oisillons variait en fonction de la phénologie de nidification de trois espèces d'hirondelles, l'Hirondelle rustique (Hirundo rustica), l'Hirondelle à front blanc (Petrochelidon pyrrhonota) et l'Hirondelle bicolore (Tachycineta bicolor), de sorte que les hirondelles qui nichent au moment où les insectes sont nombreux devraient avoir un meilleur succès que celles qui ne le font pas. Le second objectif était de déterminer si la quantité d'insectes était reliée à la survie et au poids des oisillons (comme indicateur de la survie des jeunes ayant pris leur envol). Nous avons récolté quotidiennement des insectes à chacun des trois sites d'étude durant la saison de nidification, suivi des nids d'hirondelles afin de déterminer la phénologie et le succès de nidificatio...

Climate change can drive population declines for many species, often through changes to their food supply. These changes can involve a mis-timing between periods of high food demand and peak food availability, typically from advances in breeding phenology, and/or an overall reduction in food availability. Aerial insectivores, birds that feed on insects caught in flight, are experiencing steep population declines possibly because of shifts in the timing and/or abundance of aerial insects. We determined whether changes in breeding performance over time could account for declines in Bank Riparia riparia, Barn Hirundo rustica, Cliff Petrochelidon pyrrhonota, and Tree Tachycineta bicolor Swallows, and if so, whether changes were related to shifts in breeding phenology and/or climate change. We compared breeding performance and phenology in Maritime Canada before (1962)(1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972) and after (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) the onset of steep population declines during the mid-1980s, to determine whether breeding performance was reduced or phenology was advanced. Then, we modeled relationships between temperature, precipitation, breeding phenology, and performance for Barn and Tree Swallows, the only species with sufficient data, from 1960 to 2016, to determine whether phenology and performance were related to climatic conditions. Between the two time periods, we found significantly lower performance in Bank Swallows, higher performance in Barn and Tree Swallows, and unchanged performance in Cliff Swallows. We also found clutch initiation dates advanced by 8-10 d for all species except Bank Swallows. On the breeding grounds, warmer winter temperatures for Tree Swallows and less winter precipitation for Barn and Tree Swallows in a given year were associated with earlier breeding, and for Tree Swallows, changes in nestling survival. Otherwise, Barn and Tree Swallow breeding performance was unaffected by winter temperature and precipitation. Our results suggest that in this region poorer breeding performance could contribute to population declines for Bank Swallows but not for the other three species.

Research666 the probability that our method missed peaks (spatial: 0.12, temporal: 0.18) or detected false peaks (spatial: 0.11, temporal: 0.37) due to data gaps and showed that our approach remains useful even for sparse and/or sporadic location data. Our study presents a generalizable approach to evaluating migratory connectivity across the full annual cycle that can be used to focus migratory bird conservation towards places and times of the annual cycle where populations are more likely to be limited.

Carry-over effects from one stage of the annual cycle to subsequent stages can have profound effects on individual fitness. In migratory birds, much research has been devoted to examining such effects from the nonbreeding to the breeding period. We investigated potential carry-over effects influencing spring body condition, breeding phenology, and performance for 3 species of sympatric, declining Nearctic–Neotropical migratory swallows: Bank Swallow (Riparia riparia), Barn Swallow (Hirundo rustica), and Cliff Swallow (Petrochelidon pyrrhonota). To examine carry-over effects, we used structural equation modeling and several intrinsic markers, including stable isotope (δ 2H, δ 13C, and δ 15N) and corticosterone (CORTf) values from winter molted-feathers, and changes in telomere length between breeding seasons. We found support for carry-over effects for all 3 species, however, the specific relationships varied between species and sexes. Effects leading to lower breeding performance were only observed in male Bank, female Barn, and female and male Cliff Swallows. In most cases, carry-over effects were attributed to differences in stable isotope values (most commonly with δ 2H) presumably related to differences in winter habitat use, but, for Cliff Swallows, negative carry-over effects were also linked to higher CORTf values and greater rates of telomere shortening. This work provides further support for the potential role of nonbreeding conditions on population declines, and indicates how multiple intrinsic markers can be used to provide information on ecological conditions throughout the annual cycle.

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When an environmental cue that previously signaled a suitable habitat leads an animal to use an unsuitable site, individual fitness can decrease, ultimately leading to population declines. Such “ecological traps” may be particularly likely for birds that use human infrastructure for nesting. Here we tested whether high nest temperatures and the physical properties of barns are associated with lower breeding success for a declining population of Cliff Swallows (Petrochelidon pyrrhonota (Vieillot, 1817)). We monitored nests under barn eaves below wood and metal roofs to determine nestling survival and mass, and recorded temperature under barn eaves, to relate ambient temperature to eave temperature. We found that eave temperature increased with ambient temperatures and was higher at high temperatures and lower at cool temperatures under metal roofs than wood roofs. Nestling survival was lower during periods with higher ambient temperatures, and both survival and mass were lower under metal roofs. Our findings suggest that barn eaves, especially those with metal roofs, may be an ecological trap for Cliff Swallows, where a seemingly suitable nesting site early in the breeding season results in low breeding success. Furthermore, warming temperatures may lead to ecological traps for other bird species, particularly those nesting in man-made structures.