Chick Energy Requirements And Adult Energy Expenditures Of Dovekies (Alle Alle)

Abstract

-We constructed an energy budget for Dovekie (Alle alle) chicks in West Spitsbergen by measuring energy metabolism, rate of accumulation of energy in growing tissues, and body water turnover rate, the last serving as the basis for energy-consumption calculations. The energy budget of a typical was calculated for chicks measured in 1986 and 1987. Mass-specific resting metabolic rate in Dovekie chicks peaked at days 7 to 10 and then declined considerably. Thermal conductance decreased by 60% between hatching and fledging. Energy deposition in growing tissues, resting metabolic rate, and energy consumption reached maximum values midway through the fledging period. Chicks examined in 1984 had 11% lower growth rate than 1986 and 1987 chicks, and their energy deposited in tissues between hatching and the age of peak body mass before fledging was 17% lower. Energy requirements of Dovekie chicks were much higher than those of other seabird chicks of similar body mass. We attribute this to the arctic nesting of Dovekies. We compared energy demands of Dovekie chicks with those of adults reported in another study. Despite high chick energy demands, energy delivered to the chick by one parent was only 15% of the total energy gathered by the parent (to meet both its own and the chick's needs). We suggest that this reflects a high cost of foraging in adult Dovekies. Additionally, high energy demands of chicks may contribute to the high energy expenditures of adults. This may be a major contribution to the restriction of a Dovekie brood to one chick and to the low chick body mass at fledging. Received 6 January 1992, accepted 27 May 1992. THE ABILITY of parents to provide food for offspring is generally considered a major factor shaping reproductive strategies of birds with nidicolous young. Parents should raise the greatest possible number of young permitted by food availability (Lack 1968) and optimized with respect to the trade-off between investment in a given brood and probability for future reproductive success (Williams 1966, Charnov and Krebs 1974). Brood-size reduction is the primary means of matching reproductive effort to declines in parental foraging capacity. Depression of chick growth rate is a means of fine tuning the adjustment. The latter is especially 3Current address: Department of Physiology, University of California Medical School, Los Angeles, California 90024, USA. 4Current address: Alaska Cooperative Fish and Wildlife Research Unit, 209 Irving Building, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA. 5Current address: Norwegian Institute for Nature Research, University of Tromso, c/ o Tromso Museum, N-9000 Tromso, Norway. important in birds that lay small clutches, where the integer steps of adjusting clutch size become too crude (Ricklefs 1968). The adaptive value of growth rate adjustment is based on the assumption that change in growth rate results in substantial change in chick energy requirements, but this assumption has not been consistently supported (for a recent discussion see Klaassen et al. 1992). Seabirds have much lower reproductive rates than most terrestrial birds (Lack 1968). In many seabird species, adults lay one-egg clutches, forage at long distances from their breeding colonies, and feed their chicks infrequently. Presumably, the severely limited ability of adult birds to deliver food requires that reproductive effort be adjusted to a minimum anticipated level, resulting in slow chick growth in most seabird species (Ricklefs 1983). Among seabirds, alcids (family Alcidae) offer a good opportunity for comparative studies of growth patterns and factors leading to clutch reduction. Alcids exhibit three patterns of posthatching development: precocial, semiprecocial, and intermediate. Chicks of intermediate