Does prey availability affect the reproductive performance of Barn Swallows (Hirundo rustica) breeding in Ontario, Canada?

Abstract

Animal populations are often limited by food availability, particularly during the breeding season. In birds, food limitation can impact several components of the reproductive cycle, including the timing of reproduction and reproductive output. Barn Swallows (Hirundo rustica Linnaeus, 1758) have experienced a population decline over the past 40 years in North America that is thought to be related to changes in prey availability. We monitored Barn Swallow reproductive behaviour and prey availability throughout two breeding seasons at 10 sites in Ontario, Canada, to test the hypothesis that limited prey availability during the breeding season affected reproductive behaviour. We found no relationship between food availability and number of eggs laid or number of young fledged. Neither did we observe higher rates of second brooding or more pairs nesting at breeding sites with higher food availability. Barn Swallows did not time their reproductive effort to maximize prey availability during the nesting period, but any mismatch in phenology of prey and bird reproduction at a breeding site was not associated with lower reproductive success. The results of this study did not support our hypothesis and suggest that Barn Swallow reproductive behaviour was not negatively affected by limited prey availability on the breeding grounds.

Combined influence of food availability and agricultural intensification on a declining aerial insectivore

“…Multiple lines of evidence exist linking changes in specific insect communities, abundance, behavior or phenology to agricultural intensification (Benton et al 2002, Thomas 2004, Pisa et al 2015, Stanton et al 2018, Montgomery et al 2020, Wagner 2020). Yet, the link between agricultural intensification and aerial insectivore declines, through a reduction in the availability of food resources, has so far yielded inconsistent results (Evans et al 2007, Nocera et al 2012, Imlay et al 2017, Stanton et al 2017, McClenaghan et al 2019).…”

“…For example, Bacillus thuringiensis (Bt) insecticides are used to reduce insect abundance and both experimental and observational studies typically report reduced fitness of insectivorous predators following its application (Rodenhouse and Holmes 1992, Nagy and Smith 1997, Marshall et al 2002, Poulin et al 2010. Other studies, conducted under unaltered levels of food availability have reported no link with fitness outcomes of consumers (Dawson and Bortolotti 2000, Imlay et al 2017, McClenaghan et al 2019). Such contrasting results can be explained by food being overly abundant and thus other environmental (e.g.…”

“…For example, Bacillus thuringiensis (Bt) insecticides are used to reduce insect abundance and both experimental and observational studies typically report reduced fitness of insectivorous predators following their application (Rodenhouse and Holmes 1992, Nagy and Smith 1997, Marshall et al 2002, Poulin et al 2010. Other studies, conducted under unaltered levels of food availability have reported no link with fitness outcomes of consumers (Dawson and Bortolotti 2000, Imlay et al 2017, McClenaghan et al 2019). Such contrasting results can be explained by food being overly abundant and thus other environmental (e.g., extreme temperature or elevated precipitation) or endogenous factors (e.g., parental condition, care, and past experience), having a greater influence than food availability in limiting reproductive output and subsequent population growth (Martin 1987, Newton 1998, White 2008, Winkler et al 2013, Quinney 2019.…”

Negative effects of agricultural intensification on the food provisioning rate of a declining aerial insectivore

“…Previous studies have indeed observed that agricultural intensification, including habitats impactful to insect communities and abundances, correlate with changes in dietary composition (Nocera et al 2012, English et al 2017, Bellavance et al 2018, reductions in annual fitness proxies (Benton et al 2002, Ghilain and Bélisle 2008, Garrett et al 2021a, and altered population growth (Stanton et al 2018) of several aerial insectivore species. Studies linking prey availability to aerial insectivore breeding success have, however, often failed to observe such relationships (Dawson and Bortolotti 2000, Dunn et al 2011, Imlay et al 2017, McClenaghan et al 2019. A lack of association between food availability and fitness proxies is potentially explained by breeding individuals compensating for reduced food availability or quality by altering foraging effort (Stephens et al 2007).…”

Regional variability in trajectories of Barn Swallow populations across Canada are not predicted by breeding performance

“…Consistent with this finding, studies conducted at our field sites did not find a link between breeding performance measures and local breeding ground factors in terms of land use. For example, at the southwestern Ontario and British Columbia field sites, farming intensity surrounding the colonies had no effect on breeding performance measures (Boynton 2017, Kusack et al 2020, and no link was found between breeding performance measures and measures of prey availability at the southcentral Ontario field site in (McClenaghan et al 2019 and New Brunswick field site in 2014 and 2015 (Imlay et al 2017). Although we did not find evidence of density dependence, prey availability during the nesting season is important.…”