Female and male body condition in the Whiskered Tern Chlidonias hybrida , a species with female offspring desertion: a test of the differential parental capacity hypothesis

Offspring desertion by a single parent, mainly the female, occurs in many charadriiform birds. According to the differential parental capacity hypothesis (DPCH), females are more likely to desert, since they may be in poorer body condition than males as a consequence of egg-laying costs. This study investigated the body condition of 122 male and 118 female Whiskered Terns. In this species half of females desert during the chick-rearing period, the remainder during the post-fledging period. Body condition was investigated during the late incubation and early chick-rearing phases during the biparental care period in: (1) females that deserted during the chick-rearing period, (2) females that did not desert during this time, (3) males deserted by females, and (4) males not deserted by females. Among females that stayed, body condition during the pre-hatching period did not vary with relative catching date (clutch/brood age), whereas females that later deserted showed a very poor body condition when caught around seven days prior to hatching. After hatching, body condition was lower in both deserting and non-deserting females caught later. Among males whose females stayed, body condition remained nearly stable, whereas the body condition of males whose females deserted was lower the later they were caught. These results tally only partially with the DPCH: the pattern of parental body condition changes during breeding is apparently more complex than assumed by the DPCH and the cost of egg laying may be lower than suggested. Desertion by Whiskered Tern females is better explained by the sex role differences in parental care. The male’s ability to compensate for the missing female may be playing a role in the evolution of desertion.