Facultative multiple breeding as a female conditional strategy in Japanese tits: partner's quality affects the initiation of second clutches

Abstract

AbstractMultiple breeding within the same season is a typical reproductive strategy among short‐lived species. Despite the apparent increase in the number of offspring, not all individuals become multiple breeders in most species or populations, known as facultative multiple breeding (FMB). Elucidating the mechanisms producing FMB would be a significant contribution to a better understanding of the complex life histories in wild populations. In the present study, we regarded FMB as a female alternative reproductive tactic (ART) and examined the factors affecting reproductive decisions. ARTs have been investigated mostly in males and male conditions. However, in many bird species both parents raise their offspring and, therefore, a partner's condition may also affect ARTs. We analyzed 6 years of data on multiple breeding in Japanese tits (Parus minor) in northern Japan, where nearly half of breeding pairs reproduce multiple times within breeding seasons. We found that females started breeding early were more likely to breed again in that season. Also, females paired with older males start breeding earlier, suggesting that factors associated with male age, such as territory quality, influence whether a female has multiple broods or not. We found no trade‐off between multiple breeding and female apparent survival. Rather, multiple breeders exhibited a higher apparent survival than single breeders. These results suggested that late‐started females may take an alternative tactic by avoiding the cost of second breeding and concentrating on post‐fledging care of the first broods. We also demonstrated the partner's roles in the decision of conditional strategy.