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.

Animals are expected to select a breeding habitat using cues that should reflect, directly or not, the fitness outcome of the different habitat options. However, human-induced environmental changes can alter the relationship between habitat characteristics and their fitness consequences, leading to a maladaptive habitat choice. The most severe case of such nonideal habitat selection is the ecological trap, which occurs when individuals prefer to settle in poor-quality habitats while better ones are available. Here we studied the adaptiveness of nest box selection in a tree swallow (Tachycineta bicolor) population breeding over a 10-year period in a network of 400 nest boxes distributed along a gradient of agricultural intensification in southern Québec, Canada. We first examined the effects of multiple environmental and social habitat characteristics on nest box preference to identify potential settlement cues. We then assessed the links between those cues and habitat quality as defined by the reproductive performance of individuals that settled early or late in nest boxes. We found that tree swallows preferred nesting in open habitats with high cover of perennial forage crops, high spring insect biomass, and high density of house sparrows, their main competitors for nest sites. They also preferred nesting where the density of breeders and their mean number of fledglings during the previous year were high. Additionally, we detected mismatches between preference and habitat quality for several environmental variables. The density of competitors and conspecific social information showed severe mismatches, as their relationships to preference and breeding success went in opposite direction under certain circumstances. Spring food availability and agricultural landscape context, while related to preferences, were not related to breeding success. Overall, our study emphasizes the complexity of habitat selection behavior and provides evidence that multiple mechanisms may potentially lead to an ecological trap in farmlands.