FUELING INCUBATION: DIFFERENTIAL USE OF BODY STORES IN ARCTIC-AND TEMPERATE-BREEDING BARNACLE GEESE (BRANTA LEUCOPSIS)

We compared the use of body stores in breeding Barnacle Geese (Branta leucopsis) in traditional Arctic colonies in the Barents Sea with that in recently established temperate-zone breeding colonies in the Baltic Sea and North Sea by studying female body-mass loss and use of fat and protein stores during incubation. Average daily body-mass loss was almost identical in the 2 temperate-breeding populations (17.0 g and 16.5 g in Baltic Sea and North Sea, respectively), whereas Arctic-breeding females lost significantly less (10.6 g day(-1)). Temperate-breeding females initiated incubation with body mass 1.25 g higher than that of Arctic breeders, but at the end of incubation, body mass was similar among the 3 populations, averaging 1,458 g. Body-mass loss during incubation amounted to 23% (North Sea), 22% (Baltic Sea), and 15% (Barents Sea). Fat mass, as measured by isotope dilution in a subsample of females, was consistently higher in North Sea than in Barents Sea birds, but both Populations showed similar rates of fat-mass loss (94 9 day(-1) on average). By contrast, loss of fat-free mass (assumed to represent wet protein) amounted to 9.3 g day(-1) in North Sea birds but only 1.5 g day(-1) in Barents Sea birds. Energy content of I g utilized body mass was 21.1 kj (North Sea) and 34.9 kj (Barents Sea), which equates to 376 kj day(-1) and 415 kj day'drawn from stored energy, respectively. We suggest that differences in nest-attendance and post-incubation demands are responsible for the differential use of body stores in temperate- and Arctic-breeding Barnacle Geese. Received 1 November 2008, accepted 20 August 2009.