PT  - JOURNAL ARTICLE
AU  - Daniel R. Garrett
AU  - Fanie Pelletier
AU  - Dany Garant
AU  - Marc Bélisle
TI  - Combined influence of food availability and agricultural intensification on a declining aerial insectivore
AID  - 10.1101/2021.02.02.427782
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.02.427782
4099  - http://biorxiv.org/content/early/2021/02/02/2021.02.02.427782.short
4100  - http://biorxiv.org/content/early/2021/02/02/2021.02.02.427782.full
AB  - Aerial insectivores show worldwide population declines coinciding with shifts in agricultural practices. Increasing reliance on certain agricultural practices, is thought to have led to an overall reduction in insect abundance that negatively effects aerial insectivore fitness. The relationship between prey availability and the fitness of insectivores may thus vary with the extent of agricultural production. It is therefore imperative to quantify the strength and direction of these associations. Here we used data from an 11-year study monitoring the breeding of Tree swallows (Tachycineta bicolor) and the availability of Diptera (their main prey) across a gradient of agricultural intensification in southern Québec, Canada. More specifically, we evaluated the landscape characteristics affecting prey availability, and how this relationship influences the fledging success, the duration of the nestling period, the fledgling body mass and wing length as these variables are known to influence the population dynamics of this species. Diptera availability was greatest within predominately forested landscapes, yet within principally agricultural landscapes, it was greatest within ones dominated by intensive row crops (corn, soybean and wheat), and, counter to our predictions, lowest within those dominated by forage and pasture fields. Of the measured fitness proxies, only fledging success was positively related to prey availability. The impact of prey availability varied across the agricultural gradient as fledging success improved with increasing prey levels within forage landscapes yet declined in more agro-intensive landscapes. Finally, once conditioning on prey availability, fledging success was lowest, nestling periods were the longest, and wing length of fledglings were shortest within more agro-intensive landscapes. Our results highlight the interacting roles that aerial insect availability and agricultural intensification have on the fitness of aerial insectivores, and by extension how food availability may interact with other aspects of breeding habitats to influence the population dynamics of predators.Competing Interest StatementThe authors have declared no competing interest.