Benefits of early arrival at breeding grounds vary between males

Abstract

1. It is often assumed that, in migratory birds, males of highest phenotypic quality are the first to arrive at breeding grounds, as only males in good body condition can afford the costs of early arrival. Here it is argued that variation in how much an individual can gain from being early may sometimes override these patterns of condition dependence. Benefits from early arrival will depend on how good the chances of an individual are of successfully occupying and defending a high-quality territory. Other studies have shown that these chances depend on male resource-holding power (RHP) and on value asymmetries (VA), as resulting from prior ownership. 2. Patterns of spring arrival were studied in a polygynous population of the dusky warbler Phylloscopus fuscatus Blyth, a species with high breeding-site tenacity. During the period of postnuptial moult, just before departure to winter quarters, about half of the males preoccupied and vigorously defended high-quality territories. Apparently these males enhanced their success in competition over these territories in the following breeding season by taking advantage of having prior ownership. 3. Males with good chances of obtaining a high-quality territory (i.e. males that had occupied such territories before) were the first to arrive in spring, suggesting that high motivation drives early arrival. In contrast, there was no indication for male quality or body condition to affect arrival patterns. 4. Interestingly, males of small body size, possibly reflecting low RHP, invested more in gaining prior ownership than did large males. 5. The present study suggests that, in some species, individual variation in benefits rather than in costs resulting from early arrival determine which males are the first to arrive.