Breeding phenology and performance for four swallows over 57 years: relationships with temperature and precipitation 1, 2 1 TARA L. IMLAY , JOANNA MILLS FLEMMING, SARAH SALDANHA, 3 1 NATHANIEL T. WHEELWRIGHT, AND MARTY L. LEONARD 1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4R2 Canada 2Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 4R2 Canada 3Department of Biology, Bowdoin College, Brunswick, Maine 04011 USA Citation: Imlay, T. L., J. Mills Flemming, S. Saldanha, N. T. Wheelwright, and M. L. Leonard. 2018. Breeding phenology and performance for four swallows over 57 yr: relationships with temperature and precipitation. Ecosphere 9(3):e02166. 10.1002/ecs2.2166 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 availabil- ity. Aerial insectivores, birds that feed on insects caught in flight, are experiencing steep population decli- nes 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 (1962–1972) and after (2006–2016) 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 Swal- low 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. Key words: citizen science; climate change; Hirundo rustica; historical ecology; insect availability; Petrochelidon pyrrhonota; reproductive success; Riparia riparia; Tachycineta bicolor. Received 15 February 2018; accepted 20 February 2018. Corresponding Editor: Debra P. C. Peters. Copyright: © 2018 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. E-mail: [email protected] INTRODUCTION temperature and precipitation extremes that result in worsening droughts, heavier rainfall, reduced Climate change has altered weather patterns snow cover, and more frequent and intense storms across the planet, from gradual warming trends (Easterling et al. 2000, Hayhoe et al. 2007, Levin- (Hayhoe et al. 2007, Hartmann et al. 2013) to son and Bromirski 2007, Hartmann et al. 2013). ❖ www.esajournals.org 1 March 2018 ❖ Volume 9(3) ❖ Article e02166 IMLAY ET AL. Changes to weather patterns have wide-reaching mid-1970s) began in close proximity to popula- impacts on the population dynamics and persis- tion declines (Hansen et al. 2006, National tence of many taxa. These effects can include Research Council 2007). Given their common changes in species distributions, predator–prey food source, one way that climate change might interactions, demography, and phenology (re- drive declines is by shifting the timing or abun- viewed in McCarty 2001, Walther et al. 2002, dance of aerial insects (Shutler et al. 2012). Crick 2004, Parmesan 2006, Selwood et al. 2015). Warmer temperatures are linked to both earlier One well-documented effect of warmer spring first emergence and timing of peak abundance for temperatures is a change in avian breeding phe- a variety of insects (Visser et al. 2006, Bartomeus nology (i.e., the timing of breeding). Birds of a et al. 2011, Brooks et al. 2014, Kharouba et al. variety of species are arriving on the breeding 2014). In addition, changes in winter temperature grounds and nesting earlier than in the past and precipitation also affect the annual abun- (Dunn and Winkler 1999, Butler 2003, Sanz 2003, dance and diversity of insects (Finn and Poff 2008, Donnelly et al. 2009, Townsend et al. 2013), Templer et al. 2012). In turn, reductions in insect which in turn can affect breeding performance availability during breeding have been repeatedly (Dunn and Møller 2014). For some species, early associated with lower reproductive performance breeding results in more young fledged (Møller in the Tree Swallow, as measured by decreased 2008, Vatka et al. 2011), higher nestling mass clutch sizes, fewer fledglings, and reduced nest- (Vatka et al. 2011), and increased rates of double- ling body condition (Quinney et al. 1986, Hussell brooding (i.e., raising two or more broods each and Quinney 1987, McCarty and Winkler 1999, year, Townsend et al. 2013). In most species, how- Nooker et al. 2005). ever, early breeding results in poor nestling body Although decreased breeding performance can condition, lower nestling survival, and reduced contribute to population declines in aerial insecti- rates of double-brooding (Visser et al. 2006, Both vores (Ambrosini et al. 2011), there is little infor- et al. 2009, Husby et al. 2009). The effects of early mation on whether breeding performance has breeding are often mediated through a shift in declined during the period of population declines. food availability, especially for species that largely While earlier breeding appears related to warmer exploit a single prey item during breeding (Visser spring temperatures (Dunn and Winkler 1999, But- et al. 2006, Both et al. 2009, Husby et al. 2009, ler 2003, Sparks and Tryjanowski 2007, Møller Vatka et al. 2011). Specifically, reduced food sup- 2008, 2011, but see Hussell 2003), it is not clear ply during breeding, from a mismatch between whether early breeding could negatively affect per- peak food abundance and peak food demand or formance. It is also unclear whether these patterns an overall reduction in food abundance, results in are consistent across species, suggesting a common lower performance and in turn drives population driver of decline. Thus, research investigating declines and increased risk of extinction (Both changes in breeding performance before and after et al. 2006, Møller et al. 2008). the onset of steep population declines is needed to Aerial insectivores, including swallows (Hirun- determine whether the declines result from dinidae), swifts (Apodidae), nightjars (Capri- reduced breeding performance, and if so, whether mulgidae), and tyrant flycatchers (Tyrannidae), changes in breeding phenology and climatic condi- experienced severe and widespread population tions could contribute to changes in performance. declines beginning in the mid-1980s in North Here we take a comparative, multi-species America, particularly so in the northeast (Nebel approach to determine whether changes in breed- et al. 2010, Shutler et al. 2012, Smith et al. 2015, ing phenology and performance (i.e., clutch size, but see Michel et al. 2016). Although the causes brood size, and nestling survival) over time could of the declines are unknown, like many other account for declines in Bank Riparia riparia,Barn species, aerial insectivores face a variety of Hirundo rustica,CliffPetrochelidon pyrrhonota, and shared threats, including habitat loss, pesticides, Tree Swallows Tachycineta bicolor in the Maritime pollution, road mortality, and climate change provinces of Canada, an area where aerial insecti- (Nebel et al. 2010). The latter threat, in particular, vores have experienced steep declines (Sauer et al. is a likely driver of these declines, because the 2014). The climate in this region has changed rapid warming trend in North America (e.g., since the mid-1900s, with increases in annual ❖ www.esajournals.org 2 March 2018 ❖ Volume 9(3) ❖ Article e02166 IMLAY ET AL. temperature, particularly during the winter, and initiation and hatching dates) and five variables rainfall, and decreases in snowfall and snow depth that represent different components of breeding (Mekis and Vincent 2011, Vincent et al. 2012, performance (clutch size, brood size, hatching 2015), and thus could be implicated in the success [whether or not at least one egg hatched], observed population declines. To determine nestling survival [the number of surviving nest- whether there have been changes in breeding phe- lings], and nest success [whether or not at least nology and performance over time, we used his- one young survived]). We applied several deci- torical data to compare each before (1962–1972) sion rules to ensure that these