Resting metabolic rate in migratory and non-migratory geese following range expansion; go south, go low

21 May 2019

Eichhorn, Götz; Enstipp, Manfred; Georges, Jean-Yves; Hasselquist, Dennis; Nolet, Bart

While many species suffer from human activities, some like geese benefit and may show range expansions. In some cases geese (partially) gave up migration and started breeding at wintering and stopover grounds. Range expansion may be facilitated and accompanied by physiological changes, especially when associated with changes in migratory behaviour. Interspecific comparisons found that migratory tendency is associated with a higher basal or resting metabolic rate (RMR). We compared RMR of individuals belonging to a migratory and a sedentary colony of barnacle geese (Branta leucopsis). The migratory colony is situated in the traditional arctic breeding grounds (Russia), whereas the sedentary colony has recently been established in the now shared wintering area (the Netherlands). We measured RMR by oxygen consumption (V̇O2) during two ontogenetic phases (juvenile growth and adult wing moult). We also investigated juvenile growth rates and adult body mass dynamics.
Mass-independent V̇O2 was 13.6% lower in goslings from the sedentary colony than in goslings from the migratory colony. Similarly, in adult geese, mass-independent V̇O2 was 15.5% lower in sedentary than in migratory conspecifics. Goslings in the Netherlands grew 36.2% slower than goslings in Russia, while we found no differences in body dimensions in adults. Adult geese from both colonies commenced wing moult with similar body stores, but whereas Russian barnacle geese maintained this level throughout moult, body stores in geese from the Netherlands fell, being 8.5% lower half-way through the moult.
We propose that the colony differences in resting metabolic rate, growth rate and body mass dynamics during moult can be explained by environmental and behavioural differences. The less stringent time constraints combined with poorer foraging opportunities allow for a smaller ‘metabolic machinery’ in non-migratory geese. Our analysis suggests that range expansion may be associated with changes in physiology, especially when paired with changes in migratory tendency.