TEMPORARY MALE REMOVAL INCREASES EXTRA-PAIR PATERNITY IN EASTERN BLUEBIRDS

The effects of temporary male absence during egg laying on the product ion of extra-pair young by female eastern bluebirds, Sialia sialis, we re examined. Females whose mates were removed for 2 days during egg la ying produced more extra-pair young than did females whose mates were present during egg laying. Replacement males were observed at three of 11 nests from which resident males were temporarily removed, and one of 13 extra-pair young was sired by a replacement male. The increased production of extra-pair young when males were removed during egg layi ng suggests that (1) faced with apparent mate loss, females used copul ations in an attempt to attract replacement males to care for young, ( 2) females were released from the constraints of mate guarding and sou ght extra-pair copulations, or (3) absence during egg laying reduced t he ability of males to devalue rival sperm via supplemental copulation s. (C) 1996 The Association for the Study of Animal Behaviour