Sex, age, experience and condition as factors affecting arrival date in prospecting common terns, Sterna hirundo

Several studies have shown that seabird colonies consist to a large extent of young nonbreeders (prospectors). These individuals appear at the colony later in the season than established breeders. The reasons for this late arrival have remained unclear in most cases, mainly because of technical difficulties in collecting sufficient data from nonbreeding individuals. We used a novel transponder system to identify remotely the members of a common tern colony, including nonbreeders, during eight breeding seasons and we combined the system with automatic balances. Ninety-two per cent of prospectors returned for the first time when 2 years old and 88.9% of recruits to the breeding population had spent at least one previous season at the colony as prospectors. In both sexes, most individuals prospected for one season, but more males than females prospected for more than one season, although a higher proportion of females started breeding without a previous prospecting phase. Terns arrived earlier in the season the older they were and the more experience of the colony they had, but experience proved to be more important than age. Prospectors gained about 3 weeks with a previous prospecting season whereas an additional year of age allowed birds to arrive only about 6 days earlier. Prospectors returning later in the season arrived with lower body masses. Males on average arrived earlier at the colony than females. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.