Postnatal growth rate varies with latitude in range‐expanding geese: The role of plasticity and day length

Abstract

1. The postnatal growth period is a crucial life stage, with potential lifelong effects on an animal's fitness. How fast animals grow depends on their life-history strategy and rearing environment, and interspecific comparisons generally show higher growth rates at higher latitudes. However, to elucidate the mechanisms behind this gradient in growth rate, intraspecific comparisons are needed. Recently, barnacle geese expanded their Arctic breeding range from the RussianBarents Sea coast southwards, and now also breed along the Baltic and North Sea coasts. Baltic breeders shortened their migration, while barnacle geese breeding along the North Sea stopped migrating entirely.3. We collected cross-sectional data on gosling tarsus length, head length and body mass, and constructed population-specific growth curves to compare growth rates among three populations (Barents Sea, Baltic Sea and North Sea) spanning 17° in latitude. 4. Growth rate was faster at higher latitudes, and the gradient resembled the latitudinal gradient previously observed in an interspecific comparison of precocial species. Differences in day length among the three breeding regions could largely explain the observed differences in growth rate. In the Baltic, and especially in the Arctic population, growth rate was slower later in the season, most likely because of the stronger seasonal decline in food quality. 5. Our results suggest that differences in postnatal growth rate between the Arctic and temperate populations are mainly a plastic response to local environmental conditions. This plasticity can increase the individuals' ability to cope with annual variation in local conditions, but can also increase the potential to redistribute and adapt to new breeding environments.

Earlier springs increase goose breeding propensity and nesting success at Arctic but not at temperate latitudes

“…The geese used this period to forage locally and allocated more local resources in their eggs. This comes at the cost of nesting later relative to the onset of spring, which might compromise gosling growth (Boom et al., 2022; Doiron et al., 2015; Nolet et al., 2020) and gosling survival through a trophic mismatch (Lameris, van der Jeugd, et al., 2018).…”

“…This more stable food supply might facilitate the high breeding propensity at temperate latitudes, which is also indicated by laying dates which are late relative to the onset of spring and less synchronized than in Arctic‐breeding geese (van der Jeugd et al., 2009). Furthermore, the breeding season in the temperate region is longer than in the Arctic, allowing temperate goslings enough time to reach fledging size despite growing slower than goslings in the Arctic, where daylight no longer restricts feeding time due to the 24 h polar day (Boom et al., 2022). Post‐fledging survival was also found to decrease rapidly in the Arctic with hatch date, but remained high in temperate breeding geese (van der Jeugd et al., 2009).…”

“…However, while many studies on birds have focussed on the hatching, growing and fledging stages of the breeding cycle (e.g. Boom et al., 2022; Dickey et al., 2008; Lameris et al., 2019), breeding propensity is one of the least known demographic parameters, because it is difficult to estimate (Etterson et al., 2011; Sedinger et al., 2008; Souchay et al., 2014). Compared to breeding individuals, non‐breeding birds are usually less conspicuous in behaviour and therefore often overlooked (Reed et al., 2004; Sedinger et al., 2008), or can be absent from breeding colonies (Chastel, 1995; Tavera et al., 2020).…”

“…Furthermore, the breeding season in the temperate region is longer than in the Arctic, allowing temperate goslings enough time to reach fledging size despite growing slower than goslings in the Arctic, where daylight no longer restricts feeding time due to the 24 h polar day(Boom et al, 2022). Post-fledging survival was also found to decrease rapidly in the Arctic with hatch date, but remained high in temperate breeding geese(van der Jeugd et al, 2009).…”

Biogeographical variation in migratory patterns of palearctic breeding Greater White‐fronted Geese

“…Eurasia is an excellent region to study environmental effects on migration patterns, where several species have almost continuous breeding distributions across the Eurasian Arctic, adapting to contrasting environments in eastern and western Eurasia (Boom et al., 2022). In particular, western Eurasian routes between breeding areas in the continental Russian Arctic and wintering areas in lowland western Europe are dominated by low altitude, open plains presenting little impediment to avian migration.…”