EFFECTS OF MALE REMOVAL ON PARENTAL CARE OF FEMALE WHITE-THROATED SPARROWS, ZONOTRICHIA-ALBICOLLIS

The white-throated sparrow occurs in two genetically based colour morphs and exhibits negative assortative mating. Previous work has shown that birds of each morph differ in the amount of care given to nestlings. It was suggested that the ability of females of the white-striped and tan-striped morphs to compensate for the loss of male assistance in raising young may differ. To test this hypothesis, male whitethroated sparrows were removed from their territories when their young were 6 days old. After male removal, both tan-striped and white-striped females compensated for the loss of their mates by increasing their feeding rates, rather than changing the number of prey items brought per trip. Correspondingly, these females decreased their brooding time. After male removal, new birds often came into the territory and followed the resident female but did not feed the young. The young from experimental nests weighed less at fledging than control young. However, young fledged from all experimental nests. Therefore, contrary to the expectation, both white-striped and tan-striped females compensated for the loss of male help. In the present study, differences in the level of parental care between white-striped and tan-striped birds were not as distinct as previously found. Polygyny is rare in this species, and a number of factors are suggested that may be important in selecting for monogamy. © 1990 The Association for the Study of Animal Behaviour.