Reproductive effort of urban Little Ravens: the nest attendance regime
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|| Alan Lill
Parental care is a major component of reproductive effort in altricial birds, but the time allocated to it is patchily documented for Corvus species, including Little Ravens Corvus mellori. Nest attendance by Little Ravens was documented in urban Melbourne to: (a) assess its extent and potential to entail costs sufficient to significantly reduce its obvious fitness benefits, and (b) compare it with that of congeners, as reported in the literature. Both sexes built the nest and, on average, six 2-minute nest visits/hour were made during intensive nest building. Incubation was probably conducted exclusively or largely by the female, which was fed at the nest once an hour by her mate, whose visits lasted ~1 minute. Mean diurnal incubation attentiveness was 83% and there was a mean of 1.8 incubation bouts and 1.2 incubation recesses/hour. Both sexes brooded and fed the nestlings, although one sex (probably the female) appeared to do much more of the brooding after the first two weeks of nestling life. Mean diurnal brooding attentiveness considered over the nestling period in toto averaged ~20%, but it was as high as 75-90% early in development, before declining to close to zero. Provisioning of the brooding individual and/or nestlings occurred ~5.5 times/hour. When both nestlings and fledglings were present at the nest site around fledging time, they received an average of 7 provisioning visits/hour from parents. Nest attendance broadly resembled that of congeners, and overall was probably at a sufficiently high level to potentially have short- and long-term costs (as well as benefits) for parents.
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