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The relative influence of prey abundance and co-breeders on the reproductive performance of polyandrous Pale Chanting-goshawks
Abstract
This study investigates if
the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax
canorus, is governed by the abundance of dominant rodent-prey species or a
co-breeding male participating fully in prey being delivered to the female and
young. Polyandrous trios in prey-rich habitat, the only habitat where these
trios occurred, failed to produce more offspring than monogamous pairs, but
attempted more second broods in years of high prey abundance. The higher the
prey-delivering rates at the nesting sites by either one monogamous male or two
polyandrous males (combined effort), the higher the proportion of time their
females spent in close proximity to the nest. Since there were no significant
differences between the body masses of nestlings fledged by polyandrous and
monogamous groups, higher delivery rates relieved females from
away-from-the-nest hunting duties and permitted them to feed on prey not fed to
offspring. Although breeding in polyandrous trios held fitness benefits for
females, e.g. to accumulate the necessary body reserves for laying a second
clutch in years of high prey abundance, it is still not clear how males
benefited. The reproductive performance of each group was strongly linked to
the abundance of the dominant, otomyine rodent prey (Otomys unisulcatus
and Parotomys brantsii) and it was therefore prey abundance, and not the
number of males delivering prey to the female and nestlings at each nesting
site, that controlled the reproductive performance of cooperative-breeding Pale
Chanting-goshawks.
Ostrich 2004, 75(1&2): 44–51
the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax
canorus, is governed by the abundance of dominant rodent-prey species or a
co-breeding male participating fully in prey being delivered to the female and
young. Polyandrous trios in prey-rich habitat, the only habitat where these
trios occurred, failed to produce more offspring than monogamous pairs, but
attempted more second broods in years of high prey abundance. The higher the
prey-delivering rates at the nesting sites by either one monogamous male or two
polyandrous males (combined effort), the higher the proportion of time their
females spent in close proximity to the nest. Since there were no significant
differences between the body masses of nestlings fledged by polyandrous and
monogamous groups, higher delivery rates relieved females from
away-from-the-nest hunting duties and permitted them to feed on prey not fed to
offspring. Although breeding in polyandrous trios held fitness benefits for
females, e.g. to accumulate the necessary body reserves for laying a second
clutch in years of high prey abundance, it is still not clear how males
benefited. The reproductive performance of each group was strongly linked to
the abundance of the dominant, otomyine rodent prey (Otomys unisulcatus
and Parotomys brantsii) and it was therefore prey abundance, and not the
number of males delivering prey to the female and nestlings at each nesting
site, that controlled the reproductive performance of cooperative-breeding Pale
Chanting-goshawks.
Ostrich 2004, 75(1&2): 44–51
