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Male red-winged blackbirds (Agelaius phoeniceus) provisioned 50%(118/235) of available broods over an 8-year period. In most cases, each male provisioned only the oldest brood on his territory, but in 21 cases, the male fed a younger brood after first feeding an older one. In 10 of these cases the switch to the younger brood followed predation of the older brood, but in the remaining 11 cases the cause of the switch was unknown. To determine whether male red-winged blackbirds adjust their provisioning when the demands of their broods change, we exchanged broods between pairs of nests on 10 territories. Before each exchange, each male had been feeding nestlings of only one of the two broods. In response to the exchanges, male (and female) red-winged blackbirds immediately adjusted their rates of provisioning to the increased or decreased demands of the broods. In addition, most males switched their provisioning within a day after the exchange so that they fed the same broods as before the exchanges. Our results show that male red-winged blackbirds adjust their provisioning when the demands of their broods change and suggest that males have enough information about other nesting attempts on their territories to shift to a more profitable brood when the expected benefits of provisioning change. Male red-winged blackbirds do not appear to follow an investment strategy based on prior investments (i.e., they do not commit the “Concorde fallacy”). |
