THE EFFECT OF MALE REMOVAL ON FEMALE PARENTAL CARE IN THE ORANGE-TUFTED SUNBIRD

The importance of male care and the nature of facultative adjustments in female care were assessed by experimentally removing males in pairs of orange-tufted sunbirds, Nectarinia osea, feeding broods of two or three chicks. The predation of all three-chick broods with female-only care suggested that male nest guarding is critical, especially becaus e males also deter infanticidal floater males. Comparison of provision ing and nest guarding behaviour in male-removed and control nests was therefore limited to two-chick broods. As expected, lone females provi sioned at a greater rate, but compensated incompletely for the lack of male provisioning effort. Surprisingly, even when provisioning at hig h rates, lone females still performed the usual levels of nest guardin g and nest sanitation. Lower rates of chick mass gain in the nest, and subsequent premature disappearance of fledglings from male-removed br oods, confirmed that reduced provisioning to broods of lone females ha d detrimental effects upon chick fitness. Sunbirds exhibit sex-specifi c roles in parental care. Female provisioning appears flexible, ensuri ng adequate care for young in the nest. Nest guarding is incompatible with high foraging effort, but it may be compatible with male non-pare ntal activities such as territorial defence and extra-pair mating. The se results concur with recent data concerning male responses to experi mentally reduced female care in this species, and are discussed in ter ms of evolutionary strategies for stable biparental cooperation. (C) 1 996 The Association for the Study of Animal Behaviour