Large-scale variation in growth of Black Brant goslings related to food availability

We examined variation in growth of Black Brant (Branta bernicla nigricans) goslings among two colonies on the Yukon-Kuskokwim Delta in southwestern Al aska and the Colville River Delta on Alaska's Arctic coast. We simultaneous ly measured abundance and quality of a key food plant, Carex subspathacea, and grazing pressure on that plant at the three colonies. Our goal was to m easure variation in gosling growth in relation to variation in grazing pres sure and food abundance because growth of goslings is directly linked to fi rst-year survival, and consequently is the principal mechanism for density- dependent population regulation. Goslings grew substantially faster on the arctic coast and were nearly 30% larger than those on the Yukon-Kuskokwim D elta at four to five weeks old. Faster growth on the arctic coast was assoc iated with 2X greater standing crop of C. subspathacea during brood rearing than on the Yukon-Kuskokwim Delta. Dispersal rates are high enough (Lindbe rg et al. 1998) to rule out local adaptation and genetic variation as expla nations for observed variation in growth. Our results are consistent with l ower survival of goslings from the Yukon-Kuskokwim Delta during their first fall migration and stronger density-dependent regulation on the Yukon-Kusk okwim Delta than on the Arctic coast.