Abstract
Arctic breeding songbirds migrate early in the spring and can face winter environments requiring cold endurance throughout their journey. One such species, the snow bunting (Plectrophenax nivalis), is known for its significant thermogenic capacity. Empirical studies suggest that buntings can indeed maintain winter cold acclimatization into the migratory and breeding phenotypes when kept captive on their wintering grounds. This capacity could be advantageous not only for migrating in a cold environment, but also for facing unpredictable Arctic weather on arrival and during preparation for breeding. However, migration also typically leads to declines in the sizes of several body components linked to metabolic performance. As such, buntings could also experience some loss of cold endurance as they migrate. Here, we aimed to determine whether free-living snow buntings maintain a cold acclimatized phenotype during spring migration. Using a multi-year dataset, we compared body composition (body mass, fat stores, and pectoralis muscle thickness), oxygen carrying capacity (hematocrit) and metabolic performance (thermogenic capacity – Msum and maintenance energy expenditure – BMR) of birds captured on their wintering grounds (January–February, Rimouski, QC, 48°N) and during pre-breeding (April–May) in the Arctic (Alert, NU, 82°). Our results show that body mass, fat stores and Msum were similar between the two stages, while hematocrit and pectoralis muscle thickness were lower in pre-breeding birds than in wintering individuals. These results suggest that although tissue degradation during migration may affect flight muscle size, buntings are able to maintain cold endurance (i.e., Msum) up to their Arctic breeding grounds. However, BMR was higher during pre-breeding than during winter, suggesting higher maintenance costs in the Arctic.
Highlights
Arctic breeding birds typically migrate early in the spring to maximize the chances of successful reproduction during a relatively short summer (Love et al, 2010; Reneerkens et al, 2016; van Gils et al, 2016; Ramenofsky and Wingfield, 2017; Rakhimberdiev et al, 2018)
Such early arrival implies migrating through cold winter conditions and, upon arrival on Arctic breeding grounds, birds are often faced with substantial snow accumulation, subzero temperatures and unpredictable weather that can persist for several weeks (e.g., Meltofte, 1983; Walsh et al, 2005; see Morrison et al, 2007; Wingfield et al, 2011)
Snell et al (2018) tracked snow buntings breeding at Svalbard and reported a mean temperature on their wintering range (i.e., Siberian steppes) of −10.9◦C to −3.6◦C, which encompasses the mean temperature on the wintering ground for this study (−8.9◦C in February, Table 2)
Summary
Arctic breeding birds typically migrate early in the spring to maximize the chances of successful reproduction during a relatively short summer (Love et al, 2010; Reneerkens et al, 2016; van Gils et al, 2016; Ramenofsky and Wingfield, 2017; Rakhimberdiev et al, 2018) For these species, early arrival allows for securing the best breeding territories and partners, and for breeding as soon as conditions become suitable (Drent et al, 2003; Ramenofsky and Wingfield, 2006), which can improve reproductive success (Lepage et al, 2000; Guindre-Parker et al, 2013). Birds migrating early in the spring could profit from a carryover of their winter phenotype to benefit migration in the cold
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