title: Energy Expenditure of Free-Ranging Chicks of the Cape Gannet Morus capensis.
abstract: The 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 = 1.23m(0.923), r(2) = 0.944. Mass-specific FMR (FMRratio; kJ d(-1) g(-3/4)) was independent of chick age (r(2) = 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 fledging period), the DME of Cape gannet chicks was equal to or surpassed 90% of adult FMR at the nest. Energy demand during this period of peak DME represented 58% of the total metabolized energy, which was estimated at 150.1 MJ for an average chick during a 97-d period, from hatching to fledging. Sensitivity analysis of the energy budget indicated that the model was robust; the biggest source of error (±15%) was for the mass-FMR equation used in the model.
authors.affiliation: Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa; 2Percy FitzPatrick Institute of African Ornithology, Department of Biological Sciences, University of Cape Town, Rondebosch 7701, South Africa; 3Centre for Isotope Research, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: René A
authors.initials: RA
authors.lastname: Navarro
authors.forename: Ralf H E
authors.initials: RH
authors.lastname: Mullers
authors.forename: Haro A J
authors.initials: HA
authors.lastname: Meijer
authors.forename: Les G
authors.initials: LG
authors.lastname: Underhill
mesh_terms: D000367:Age Factors; D000818:Animals; D001717:Birds / Q000254:growth & development* / Q000378:metabolism*; D001835:Body Weight; D004734:Energy Metabolism; D009425:Nesting Behavior; D013019:South Africa