Do females of Whiskered Tern Chlidonias hybrida renest after offspring desertion?

Abstract In species with biparental care, one parent may relieve him-/herself of the costs of parental care by deserting and leaving the mate to care for the offspring. Offspring desertion by a single parent, usually the female, occurs in many bird species, especially in Charadriiformes. The reasons for desertion are still being debated, and compelling evidence for the benefits and costs to either sex is not yet handed. The benefits of desertion for the deserter may include renesting with a new mate shortly after desertion. Therefore, desertion may enhance individual lifetime reproductive success. In Whiskered Tern Chlidonias hybrida almost all females desert, about half of females desert during chick-rearing period, the other half during the post-fledging period. Based on intensive fieldwork over a 4-year study, we investigated whether Whiskered Tern females remated and renested after desertion. We assumed that favourable conditions, such as an extended breeding season and food abundance resulting in a high breeding success would prompt most females to renest after desertion. In contrast to this expectation, however, only 5% of females that deserted during chick-rearing period (2 out of 41) remated and renested in the study area. About 50 days elapsed between the initiations of the first and second clutch by these two females. Females also participated in courtship behaviour after desertion (without renesting). We thus estimate that 15% (6 out of 41) of females that deserted during chick-rearing period were subsequently involved in some kind of breeding activity. Therefore, renesting does not seem to be a major direct benefit for deserting Whiskered Tern females. Females of this species probably benefit from desertion in other ways, but these have yet to be discovered.