Abstract

not-yet-known not-yet-known not-yet-known unknown Avian insectivores have experienced population declines worldwide, with intensification of agricultural practices as a major contributing factor. To understand how species react to such human-driven environmental changes, it is necessary to obtain detailed information on their survival, reproduction and dispersal. This is particularly important for declining species and populations, where immigration contributed by dispersers from neighboring populations can influence local population growth. We used multi-state Capture-Mark-Recapture (CMR) models and 14 years of data (2004-2019) on individually marked Tree Swallows (Tachycineta bicolor) breeding on farmlands in southern Québec, Canada, to quantify the effects of agricultural intensity, local weather, and interspecific competition on the vital rates and population growth. Yearly population growth rates were highly dependent on both immigration and adult return rates. Nest site competition by House sparrows (Passer domesticus), mostly found within intensively cultivated landscapes, had a strong negative effect on reproductive success and adult return rates. Nevertheless, 43% of the variance in lambda was attributed to unexplained differences between farms, suggesting that microhabitat or other unmeasured environmental variables also drive population growth rate. Our results clearly show that the studied population would not persist without immigration, suggesting that intensively cultivated farmlands may act as sinks. Our sampling design may partly explain this result as nest boxes were installed in low quality habitats. Understanding the ecology and demography of declining aerial insectivore species therefore requires studying multiple populations of the same species in a wide range of habitats and geographic locations, as well as several species with contrasting life histories.