Breeding phenology and performance for four swallows over 57 years: relationships with temperature and precipitation

Abstract

Climate change can drive population declines for many species, often through changes to their food supply. These changes can involve a mis-timing between periods of high food demand and peak food availability, typically from advances in breeding phenology, and/or an overall reduction in food availability. Aerial insectivores, birds that feed on insects caught in flight, are experiencing steep population declines possibly because of shifts in the timing and/or abundance of aerial insects. We determined whether changes in breeding performance over time could account for declines in Bank Riparia riparia, Barn Hirundo rustica, Cliff Petrochelidon pyrrhonota, and Tree Tachycineta bicolor Swallows, and if so, whether changes were related to shifts in breeding phenology and/or climate change. We compared breeding performance and phenology in Maritime Canada before (1962)(1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972) and after (2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016) the onset of steep population declines during the mid-1980s, to determine whether breeding performance was reduced or phenology was advanced. Then, we modeled relationships between temperature, precipitation, breeding phenology, and performance for Barn and Tree Swallows, the only species with sufficient data, from 1960 to 2016, to determine whether phenology and performance were related to climatic conditions. Between the two time periods, we found significantly lower performance in Bank Swallows, higher performance in Barn and Tree Swallows, and unchanged performance in Cliff Swallows. We also found clutch initiation dates advanced by 8-10 d for all species except Bank Swallows. On the breeding grounds, warmer winter temperatures for Tree Swallows and less winter precipitation for Barn and Tree Swallows in a given year were associated with earlier breeding, and for Tree Swallows, changes in nestling survival. Otherwise, Barn and Tree Swallow breeding performance was unaffected by winter temperature and precipitation. Our results suggest that in this region poorer breeding performance could contribute to population declines for Bank Swallows but not for the other three species.

Long-term phenology of two North American secondary cavity-nesters in response to changing climate conditions

“…This contrasts with the results of other studies that have found a seasonal temperature to effect breeding phenology (Vedder 2012;Whitehouse et al 2013). Precipitation levels are also thought to affect the phenology and fitness of insectivorous birds (McKeller et al 2013;Imlay et al 2018). Great tits (Parus major) synchronize their breeding with the abundance of caterpillars to maximize food for their offspring (Visser et al 2006).…”

“…Spring conditions could directly affect the timing of nesting, hatch date, and clutch size, but conditions prior to the breeding season may affect other factors such as food abundance and affect reproductive traits (Nussey et al 2005). Moisture availability, measured as PDSI, may have stronger effects on populations than temperature alone due to ecological interactions such as insect abundance (Fei et al 2017;Imlay et al 2018).…”

Demographic drivers of collapse in an island population of Tree Swallows

“…Kent Island has a shorter breeding period than more southerly sites, so the population may also be limited in its ability to compensate for stochastic weather events (e.g., by renesting). Further, a shorter breeding window could make it more difficult for Kent Island Tree Swallows to shift the timing of breeding in response to long-term climate trends, which may exacerbate phenological mismatches with the availability of insects (Dunn and Winkler 1999, Dunn et al 2011, Imlay et al 2018.…”

“…Populations of many aerial insectivores, including Tree Swallows (Tachycineta bicolor), have been declining in northeastern North America since at least the 1980s . The ecological and demographic mechanisms of ongoing declines are unclear but appear to be species-and region-specific (Nebel et al 2010, Smith et al 2015, Michel et al 2016, Imlay et al 2018. At broad scales, climate change may create a phenological mismatch between breeding and food availability, requiring Tree Swallows to adjust their breeding strategies or suffer population declines (Dunn and Winkler 1999, but see Dunn et al 2011, Imlay et al 2018.…”

“…The ecological and demographic mechanisms of ongoing declines are unclear but appear to be species-and region-specific (Nebel et al 2010, Smith et al 2015, Michel et al 2016, Imlay et al 2018. At broad scales, climate change may create a phenological mismatch between breeding and food availability, requiring Tree Swallows to adjust their breeding strategies or suffer population declines (Dunn and Winkler 1999, but see Dunn et al 2011, Imlay et al 2018. At more local scales, weather conditions may influence adult survival or reproductive success (Weegman et al 2017), and chemical contaminants such as mercury and neonicotinoids can disrupt food availability or reproduction Cristol 2011, Hallmann et al 2014).…”