INTRASPECIFIC NEST PARASITISM AND ADOPTION OF YOUNG IN THE BARNACLE GOOSE - EFFECTS ON SURVIVAL AND REPRODUCTIVE-PERFORMANCE

DNA fingerprinting was used to determine the proportion of extra-pair young in a population of barnacle geese, Branta leucopsis, breeding in the Baltic area, Sweden. Of 137 analysed fledged young 17% were found to be extra-pair young. One or more extra-pair young were found in 27 % of the 63 analysed families. The proportion of extra-pair young diff ered between years. No case of extra-pair fertilization was detected. All extra-pair young at fledging originated either from intraspecific nest parasitism or from adoptions of foreign hatched young. Broods wit h extra-pair young at fledging were significantly larger than broods w ithout extra-pair young. However, the number of within-pair young did not differ significantly in broods with and without extra-pair young. Body mass, survival or subsequent reproductive performance did not dif fer between parents with and without extra-pair fledged young. Post-fl edging survival and age at first breeding were not significantly diffe rent between the three analysed classes of fledged young, i.e. within- pair young in families without extra-pair young, within-pair young in families with at least one extra-pair young, and extra-pair young. It is concluded that possible costs or benefits associated with caring fo r extra-pair fledged young are small or absent in this population. (C) 1995 The Association for the Study of Animal Behaviour