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

Swallow (Family: Hirundinidae) populations in the Canadian Maritimes have declined since the 1980s. Using mark–recapture data from 2012 to 2019, we determined apparent annual adult survival rates for Barn (Hirundo rustica Linnaeus, 1758), Tree (Tachycineta bicolor (Vieillot, 1808)), Bank (Riparia riparia (Linnaeus, 1758)), and Cliff (Petrochelidon pyrrhonota (Vieillot, 1817)) swallows. For two data-rich species (Barn and Tree swallows), we modelled the relationships between survival and weather (cold snaps, precipitation, temperature, and wind speed), climate (El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO)), Enhanced Vegetation Index (EVI) as a measure of primary productivity during the winter, number of active nests as a measure of site quality, and the Breeding Bird Survey (BBS) annual population index as density-dependent processes. Survival rates for all four species were typically higher (Barn and Tree) or similar to (Cliff and Bank) of estimates from populations that have not undergone severe, long-term declines. Across weather and climate variables, conditions that are typically favourable for high insect availability (e.g., higher precipitation, warmer temperatures, and lower wind speeds) resulted in higher survival. For female Barn and Tree swallows, survival was higher when EVI was lower, and for Barn Swallows, survival was also higher when the BBS index was higher. Collectively our results demonstrate that conditions throughout the annual cycle affect survival, and the relationships with weather and climate variables support the importance of high insect availability.