SEASONAL-VARIATION IN GROWTH OF GREATER SNOW GOOSE GOSLINGS - THE ROLE OF FOOD-SUPPLY

Even though growth rate is an important fitness component, it is still controversial to what extent parent birds adjust the timing of offspr ing hatch to natural variations in food supply to maximize offspring g rowth. We studied the role of food availability in explaining inter-an d intra-seasonal variation of growth rate in goslings of greater snow geese over 5 years, The peak of hatching generally coincided with the peak of food availability. However, early-hatched goslings usually gre w faster than birds hatched at the peak, which in turn grew faster tha n late-hatched goslings, although. this phenomenon was not observed in all years. There was considerable variation in growth rate among the five years, the smallest goslings produced in the best year (1991) bei ng larger than the largest goslings of the poorest year (1994). We dev eloped three indicts of food availability, based on the cumulative ava ilability of plant biomass and nitrogen content during the growth peri od, and showed that the cumulative exposure to nitrogen biomass explai ned up to 43% of variation (intra-and inter-annual) in body size just before fledging. In years with good feeding conditions, early-hatched goslings had access to more nitrogen during their growing period than those hatching on or after the peak and they grew faster, In years of lower food availability: early-hatched goslings had no detectable adva ntage over peak-or late-hatched birds for access to protein-rich food and no seasonal decline in growth rate was observed. These results con firm the critical role of food supply in the seasonal variation of gro wth rate in Arctic-nesting geese.