Energetics of nestling growth and parental effort in Antarctic fulmarine petrels.

Antarctic fulmarine petrels breed in some of the coldest conditions encountered by any bird and their young grow twice as fast as predicted allometrically. To examine the energetic consequences of fast growth in a cold environment, we used the doubly labeled water technique to measure field metabolic rates of adults (three species) and different-aged nestlings (four species) of Antarctic fulmarine petrels in the Rauer Islands, East Antarctica: Antarctic fulmar Fulmarus glacialoides, Antarctic petrel Thalassoica antarctica, Cape petrel Daption capense and snow petrel Pagodroma nivea. We used our data to assess parental effort and, together with literature values on nestling growth and resting metabolic rate, to construct and partition nestling energy budgets. Nestling total energy expenditure and peak daily metabolic rate were significantly higher than predicted allometrically (33-73% and 17-66% higher, respectively), and the relative cost of growth in nestling petrels was among the highest reported for birds (54-72 kJ g(-1)). Parental effort during the nestling-feeding period was identical in adult Cape and Antarctic petrels (3.5 times basal metabolic rate, BMR), and was somewhat (but not significantly) higher in snow petrels (4.6 times BMR). These values are comparable to those of other high-latitude procellariiform birds. Thus, despite the constraints of a compressed breeding season, cold temperatures and fast-growing nestlings, adult Antarctic fulmarine petrels do not work harder than procellariid adults whose chicks grow much more slowly. Our findings suggest that obtaining sufficient food is generally not a constraint for adult fulmarine petrels and that factors operating at the tissue level limit nestling growth rate.