Age-related improvement of reproductive success in Bluethroats Luscinia svecica

Capsule Young birds are less likely to have high reproductive success compared with older ones because of a lack of several skills influencing breeding performance. Aims To test the 'constraint' hypothesis by investigating the effect of male and female age on reproductive performance of a Bluethroat Luscinia svecica population. Methods We compared two age-classes (yearling versus old), breeding for the first time at Guerande salt-pans, France, by evaluating arrival dates on breeding site, territory quality, laying dates, clutch size and egg size, delay before re-nesting, breeding performance, feeding rate at two different nestling periods (on days 4-5 and 10-11 after hatching) and nestling body condition. Results Our results clearly demonstrated an age effect on reproductive performance for both males and females: young breeders were less likely to fledge young. In older males, improvement of reproductive success was related to feeding rate during the first nestling period. For females, timing of breeding (laying date) and reproductive investment (such as clutch size, feeding rate in the whole nestling period, brood condition) were the main determinants. The presence of a yearling in a pair strongly decreased the number of young produced per breeding season. Conclusion Bluethroat supported the 'constraint' hypothesis, i.e. that behavioural and physiological maturation is needed for young breeders to enhance reproductive performance.