Growth and provisioning strategies of Northern Fulmars Fulmarus glacialis

Growth and foraging strategies in procellariiforms show ai great deal of va riation, but the fulmarine petrels are notable in that chicks are fed frequ ently and develop unusually rapidly. This study examined age-related and da ily variation in provisioning of the Northern Fulmar Fulmarus glacialis thr oughout the chick-rearing period at Fair Isle in 1997. In common with many other petrels, meal mass showed an initial rise with age, probably because of a gradual increase in chick gut capacity, but then levelled off. By comp arison, feeding frequency showed little age-specific variation until chicks reached the oldest age-class, when the number of meals declined to less th an a third of the previous level as chicks underwent mass recession prior t o fledging. Compared with the limited day-to-day variation in mean provisio ning rates for the whole sample, food delivery to particular chicks was muc h more variable, suggesting that differences in feeding rates were determin ed by stochastic factors influencing the feeding success of individual pare nts. The caloric density of feeds and their size in relation to adult mass were lower in Northern Fulmars than in most other Procellariiformes. This i mplies that adults are not heavily dependent on stomach oil formation to ra ise the energy content of the payload, but rely on a high feeding frequency to maintain adequate rates of energy transfer to chicks.