Leapfrog migration and residents: New migratory habits in Swedish Greylag geese

Abstract

Knowledge about intraspecific and individual variation in bird migration behavior is important to predict spatiotemporal distribution, patterns of phenology, breeding success, and interactions with the surrounding environment (e.g., human livelihoods). Such variation is key to adaptive, evolutionary responses, i.e., how individuals respond spatiotemporally to the environment to maximize fitness. In this study we used GPS location data from one to three full annual cycles from 76 Greylag geese (Anser anser) to test the hypothesis that geese originating at five latitudinally separated capture sites in Sweden have different migration strategies. We also assessed individual consistency in movement strategy over consecutive annual cycles. We used the scale‐independent net squared displacement modeling framework to quantify variables of autumn and spring migration for geese from each capture site: distance, timing, and duration. Our results demonstrate a positive correlation between migration distance and latitudinal origin. Geese from the northernmost site on average migrated farther south and about 15 times as far as the short‐moving or resident geese from the two southernmost sites. Movement strategies of individual geese varied considerably both within and among capture sites. Individual consistency in movement strategy from one annual cycle to the consecutive was high in geese from the northern sites moving the farthest, whereas the resident or short‐moving geese from the southernmost sites generally showed lower or no individual consistency. These changes have come about during a time span so short (i.e., ca. 35 years or 8–10 generations) that it can unlikely be explained by classical Darwinian between‐generation adaptation. Consequently, and given that young geese follow their parents during their first migration, we presume an important role of within‐family, inter‐generation change as a driver behind the large‐scale changed migration habits in Swedish Greylag geese.

Southern breeding populations drive declining migration distances in Arctic and subarctic geese

“…For the four species in which we evaluated a latitude effect, populations breeding at higher latitudes remained unchanged, or increased their average migratory distances, in contrast to southern breeding populations which moved north. Latitudinal variation in migratory movements by populations is common in geese and other species, often resulting in a pattern known as leap-frog migration in which northern populations fly farther south than southern populations (Salomonsen 1955, Berthold 2001, Newton 2008, Nilsson et al 2022. Leapfrog migration is a strategy to avoid competition from earlier conspecific arrivals on breeding or wintering grounds (Alerstam and Hedenström 1998).…”

“…We expect to find shortened migration distances, with wintering grounds becoming closer to breeding grounds (Visser et al 2009, Potvin et al 2016, Curley et al 2020). Further, we anticipate that geographic variability in breeding populations will impact temporal changes in migration distances, as in the observed correlation between migration distance and latitude of breeding location in Swedish greylag geese Anser anser (Nilsson et al 2022).…”

“…Shifts in the breeding ranges of migratory species might affect shifts in the non‐breeding ranges, or vice versa, with implications for the annual migration distances and energetics of individuals, as well as for population dynamics and ecological connectivity among regions. Populations of the same species, or even individuals within populations, may display variable migratory behaviors and movements (Chapman et al 2011, Liedvogel et al 2011, Madsen et al 2023), as phenotypic variation in migratory behavior can result from cultural and genetic mechanisms that vary geographically (Pulido and Berthold 2003, Liedvogel et al 2011, Delmore et al 2016, Nilsson et al 2022). Phenotypic plasticity in migratory behavior can be advantageous for adapting to environmental changes and allow individuals and populations to actively respond and seek optimal habitat (Charmantier and Gienapp 2014).…”

Selection of a diversionary field and other habitats by large grazing birds in a landscape managed for agriculture and wetland biodiversity

“…Data available from the Dryad Digital Repository: https://doi.org/10.5061/dryad.hhmgqnkp8 (Nilsson et al., 2024).…”