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

Abstract

Swallow (Family: Hirundinidae) populations in the Canadian Maritimes have declined since the 1980s. Using mark-recapture data from 2012–2019, 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 swallows Petrochelidon pyrrhonota Vieillot, 1817. 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

Ecology and conservation of avian aerial insectivores

“…Drivers of aerial insectivore declines are likely occur throughout the annual cycle (Imlay and Leonard 2019;Spiller and Dettmers 2019) and two papers in this Special collection focus on identifying limiting factors throughout the annual cycle and identifying important non-breeding locations. Imlay et al (2022) investigated the adult apparent annual survival of four sympatric swallow species breeding in Atlantic Canada relative to conditions on the breeding and non-breeding grounds using an 8-year mark-recapture data set. They show species-and sex-specific differences in survival for multiple environmental variables across the annual cycle, highlighting that factors on the breeding and non-breeding grounds may be important in influencing swallow survival.…”