Energy Expenditure of Free-Ranging Chicks of the Cape Gannet Morus capensis

AbstractThe Cape gannet Morus capensis, a large fish-eating seabird, is endemic to southern Africa. To study the energetics of nestling growth, we used the doubly labeled water technique to measure field metabolic rate (FMR) of nestlings, from hatchings to large partly feathered chicks (n = 17) at Malgas Island, Saldanha Bay, South Africa. At the same time, the growth rate of a large sample of chicks was measured (n = 338). These data, together with literature values on resting metabolic rate and body composition, were used to construct and partition the nestling energy budget. Nestling FMR (kJ d−1) increased with body mass according to FMR = 1.23m0.923, r2 = 0.944. Mass-specific FMR (FMRratio; kJ d−1 g−3/4) was independent of chick age (r2 = 0.20, P > 0.05); mean mass-specific FMR was 4.11 ± 1.28, n = 17. Peak daily-metabolized energy (DME), which represents the maximum rate at which parents must supply their nestlings, occurred at age 71 d and was 2,141 kJ d−1. Between the ages 51 and 92 d (43% of the f...