Carryover effects of long-distance avian migration are weaker than effects of breeding environment in a partially migratory bird

Abstract

Migration may expose individuals to a wide range of increasing anthropogenic threats. In addition to direct mortality effects, this exposure may influence post-migratory reproductive fitness. Partial migration—where a population comprises migrants and residents—represents a powerful opportunity to explore carryover effects of migration. Studies of partial migration in birds typically examine short-distance systems; here we studied an unusual system where residents breed in mixed colonies alongside long-distance trans-Saharan migrants (lesser kestrels (Falco naumanni) in Spain). Combining geolocator data, stable isotope analysis and resighting data, we examined the effects of this stark difference in migratory strategy on body condition, breeding phenology and breeding success. We monitored four colonies in two regions of southern Spain for five consecutive years (2014–2018), yielding 1962 captures, determining migratory strategy for 141 adult bird-years. Despite a 3000-km difference in distance travelled, we find no effect of strategy on breeding parameters. We find weak evidence for a short-term negative carryover effect of migration on body condition, but this was only apparent in the breeding region with lower primary productivity. Our results indicate that carryover effects of even highly divergent migratory strategies may be minimal relative to effects of conditions experienced on breeding grounds.

Carry‐over effects of weather and decision‐making on nest success of a migratory shorebird

“…They use freshwater habitat such as temporary wetlands, flooded fields, and the edges of lakes and reservoirs, in addition to occasional upland habitat, where they feed on primarily on invertebrates (e.g., insects, earthworms; Poole et al, 2020 ). Because habitat availability and distribution for black‐bellied plovers varies with environmental conditions (Skagen & Knopf, 1994 ; Steen et al, 2018 ) and phenology and abundance of invertebrates is linked to site productivity and conditions (Buchan et al, 2021 ; Pettorelli et al, 2005 ), we expected weather and environmental conditions to influence migration decision‐making and reproductive success.…”

“…NDVI indicates net primary productivity, which influences availability of insects (Buchan et al, 2021 ; Sanz et al, 2003 ). Black‐bellied plovers feed on invertebrates; primarily insects during breeding and migration periods when they are away from coastal habitats (Poole et al, 2020 ).…”

Barrier crossings and winds shape daily travel schedules and speeds of a flight generalist

“…We used the ‘dredge’ function in the R package ‘MuMIn’ 61 , which uses Akaike’s information criterion (AIC) to rank all possible subsets of reduced models from each full model. We selected the models if they had ΔAIC ≤ 2 units of the highest ranked-model and we retained the most parsimonious model (with the fewest parameters) because model averaging could not handle models with interaction effects 62 , 63 . We used the Satterthwaite’s method to estimate degrees of freedom and to obtain p -values using the ‘lmerTest’ 64 R package.…”

Spatially explicit risk mapping reveals direct anthropogenic impacts on migratory birds

“…Pronounced declines in long‐distance migrants suggest a substantial influence of conditions during migration or on the non‐breeding grounds, with population trends being sensitive to migratory routes (Hewson et al, 2016; Newton, 2006; Tøttrup et al, 2008), as well as non‐breeding climatic conditions (Ockendon et al, 2012) and habitat change (Adams et al, 2014; Cresswell et al, 2007). However, influential anthropogenic threats may occur throughout the annual cycle (Sergio et al, 2019; Thaxter et al, 2010), and seasonal effects can interact with potential carryover effects from conditions experienced earlier in the annual cycle (Buchan et al, 2021; Morrison et al, 2013). This potential for between‐season cumulative and/or synergistic effects highlights the need for full‐cycle approaches for understanding – and ultimately, targeting – threats to migratory species (Calvert et al, 2009; Marra et al, 2015; Martin et al, 2007; Small‐Lorenz et al, 2013; Zurell et al, 2018).…”