Abstract
Droughts can affect invertebrate communities in wetlands, which can have bottom-up effects on the condition and survival of top predators. Shorebirds, key predators at coastal wetlands, have experienced widespread population declines and could be negatively affected by droughts. We explored, in detail, the effects of drought on multiple aspects of shorebird stopover and migration ecology by contrasting a year with average wet/dry conditions (2016) with a year with moderate drought (2017) at a major subarctic stopover site on southbound migration. We also examined the effects of drought on shorebird body mass during stopover across 14 years (historical: 1974–1982 and present-day: 2014–2018). For the detailed comparison of two years, in the year with moderate drought we documented lower invertebrate abundance at some sites, higher prey family richness in shorebird faecal samples, lower shorebird refuelling rates, shorter stopover durations for juveniles, and, for most species, a higher probability of making a subsequent stopover in North America after departing the subarctic, compared to the year with average wet/dry conditions. In the 14-year dataset, shorebird body mass tended to be lower in drier years. We show that even short-term, moderate drought conditions can negatively affect shorebird refuelling performance at coastal wetlands, which may carry-over to affect subsequent stopover decisions. Given shorebird population declines and predicted changes in the severity and duration of droughts with climate change, researchers should prioritize a better understanding of how droughts affect shorebird refuelling performance and survival.
Highlights
Droughts can substantially affect ecosystem structure and function
Invertebrate abundance was lower at non-foraging sites across habitats in the drought year (2017: mean ± SE: 1.4 ± 0.4 no. c ore−1) than the year with average wet/dry conditions (2016: 2.7 ± 0.7 no. core−1; z = 2.9, P = 0.004), but there was no difference in invertebrate abundance at foraging sites between the years (Drought, 2017: 2.2 ± 0.6 no. c ore−1; Average wet/dry, 2016: 2.7 ± 0.7 no. core−1; z = 0.9, P = 0.36)
Using DNA metabarcoding, we identified 101 families of prey items in shorebird faecal samples from 29 orders and 13 classes
Summary
Droughts can substantially affect ecosystem structure and function. Reduced ground and surface water volume can change sedimentation and nutrient deposition (Baldwin and Mitchell 2000; Mishra and Singh 2010), reduce primary productivity (Zhao and Running 2010; Huang et al 2016), and alter biological community composition to favour drought tolerant species (Chase 2007; Neto et al 2010). Most studies of drought at marine coastal areas have examined effects at lower trophic levels such as vegetation (McKee et al 2004; Alber et al 2008), zooplankton (Marques et al 2007; Primo et al 2009), meiofauna (Pillay and Perissinotto 2009), and benthic macrofauna (Pillay and Perissinotto 2008; Dittmann et al 2015). These studies reported lower species richness and a dominance of saline tolerant taxa during and after drought (Pillay and Perissinotto 2009; Primo et al 2009; Dittmann et al 2015)
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