Comparative spring habitat and food use by two arctic nesting geese

The timing of egg laying is generally constrained by female condition, whic h is partly determined by the food available to her before laying. Although it was generally believed that geese rely exclusively on internal nutrient reserves for egg production, spring feeding is intensive in many populatio ns of geese, significantly adding nutrients necessary for egg production an d incubation. We compared the spring feeding ecology of Greater White-front ed Geese (Anser albifrons frontalis) and Canada Geese (Branta canadensis hu tchinsii) on a shared nesting ground on the Kent Peninsula, NWT (68 degrees N, 108 degrees W), where pairs feed intensively from arrival until incubat ion. Live plant biomass did not significantly increase within specific habi tats during preincubation, bur the total available biomass was greater afte r snow melt because habitats with higher biomass became available. Live pla nt biomass available in pond margins (30-60 g/m(2)) was 4-15 times higher t han in habitats that were available earlier, i.e., mud-flats and hummocks ( 4-8 g/m(2)). Before snow melt, both species shared the 1-20% of the study a rea that was snow free (max, density 600 pairs/km(2)), opportunistically us ed the only two available habitats, mud-flats and hummocks, and primarily a te (50-70%) tillers of Puccinellia spp. During snow melt, pairs dispersed, pair density decreased (max, of 40 pairs/km(2)), and interspecific differen ces in habitat and food use appeared. White-fronted Geese used pond margins and ponds more often than Canada Geese. After snow melt, White-fronted Gee se predominantly fed in ponds on Carex spp, and Dupontia fisheri rhizomes a nd basal stems; Canada Geese continued feeding opportunistically, pecking l eaves in all habitats and grubbing rhizomes in pond margins and ponds. Whit e-fronted Geese used the grubbing technique more often than Canada Geese in all habitats and periods.