Comparative spring habitat and food use by two arctic nesting geese

-The timing of egg laying is generally constrained by female condition, which 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 populations of geese, significantly adding nutrients necessary for egg production and incubation. We compared the spring feeding ecology of Greater White-fronted Geese (Anser albifronsfrontalis) and Canada Geese (Branta canadensis hutchinsii) on a shared nesting ground on the Kent Peninsula, NWT (680 N, 108? W), where pairs feed intensively from arrival until incubation. Live plant biomass did not significantly increase within specific habitats during preincubation, but the total available biomass was greater after snow melt because habitats with higher biomass became available. Live plant biomass available in pond margins (30-60 g/m2) was 4-15 times higher than in habitats that were available earlier, i.e., mud-flats and hummocks (4-8 g/m2). Before snow melt, both species shared the 1-20% of the study area that was snow free (max. density 600 pairs/km2), opportunistically used the only two available habitats, mud-flats and hummocks, and primarily ate (50-70%) tillers of Puccinellia spp. During snow melt, pairs dispersed, pair density decreased (max. of 40 pairs/km2), and interspecific differences in habitat and food use appeared. White-fronted Geese used pond margins and ponds more often than Canada Geese. After snow melt, White-fronted Geese predominantly fed in ponds on Carex spp. and Dupontia fisheri rhizomes and basal stems; Canada Geese continued feeding opportunistically, pecking leaves in all habitats and grubbing rhizomes in pond margins and ponds. White-fronted Geese used the grubbing technique more often than Canada Geese in all habitats and periods. Received 13 Feb. 1998, accepted 17 Nov. 1998. Energy investment by females in reproduction is highest during the period of egg formation in birds with precocial young, such as geese (King 1973). Clutch size and timing of laying are potentially constrained by female condition, which is partly determined by the amount of energy and nutrients available to her before egg formation (Drent and Daan 1980, Winkler and Walters 1983). Early nesting is critical for Arctic nesting geese because of the short summer and the rapid seasonal decline in components of reproductive success such as gosling growth and probability of producing recruits (Barry 1962, Cooke et al. 1984, Cooch et al. 1991, Sedinger and Flint 1991, Lindholm et al. 1994). One strategy to facilitate early nesting is to carry nutrient reserves accumulated during migration to the breeding grounds (Ankney and MacInnes 1978, Wypkema and Ankney 1979, Ankney 1984, Budeau et al. 1991, Bromley and Jarvis 1993, Choiniere and Gauthier 1995). There is, however, an upper limit to the amount of reserves that can be economically carried during migration (Lindstrom and Alerstam 1992). In migratory birds, the timing of rapid follicular development (RFD) initiation with respect to spring migration may affect the relative contribution to egg production of nutrients acquired en route versus those acquired on nesting grounds. Timing of RFD initiation directly determines laying date of the first egg (reviewed by Rohwer 1992). Because some female geese in some locations typically nest soon (3-6 days) after their arrival on the nesting ground (Anser rossii: Ryder 1970; Anser caerulescens caerulescens: Ankney 1977, Ankney and Maclnnes 1978; Anser canagica: Thompson and Raveling 1987; Branta bernicla bernicla: Spaans et al. 1993), RFD is initiated before arrival, hence the date of nest initiation is independent of food availability on the nesting ground (Raveling 1978, Ankney 1984, Newton 1977; but see Prop and de Vries 1993). 1 Dept. de Biologie et Centre d'Etudes Nordiques, Univ. Laval, Quebec, QC, GlK 7P4, Canada. 2 Present address: Wildlife and Fisheries Division, Dept. of Resources, Wildlife, and Economic Development, Government of the Northwest Territories, 600 5102-50 Avenue, Yellowknife, NT XIA 3S8, Canada. I Wildlife and Fisheries Division, Dept. of Resources, Wildlife, and Economic Development, Government of the Northwest Territories, 600 5102-50 Avenue, Yellowknife, NT XIA 3S8, Canada. 4 Present address: Box 1177, Yellowknife, NT XI A