Energetic Requirements for Growth and Maintenance of the Cape Gannet (Aves; Sulidae)
Energetic requirements for growth and maintenance of the Cape gannet (Sula capensis) were studied by hand-rearing captive chicks and keeping juveniles in captivity at constant mass. Daily gain in mass was linear until 60 days of age; after 82 days the chicks lost mass prior to attaining fledging age (97 days). Daily relative growth decreased with age. Food intake increased to 70 days and thereafter decreased. Guano production increased to SO days. Relative food intake decreased with age. Energy content of guano and assimilation efficiency showed no clear changes with age. Mass recession prior to fledging may be related to the lack of post-parental care. Hand-reared gannets grew at an optimum rate when compared with field growth rates from the literature. Juvenile birds were maintained on a diet forming 12,4% of body mass at an assimilation efficiency of 74,2%. Aviary-existence maintenance was 2,4 times standard metabolic rate. The cost of free living in an adult gannet is roughly estimated to be 4,5 X SMR, corresponding to a food intake of 20% of body mass.