MULTIPLE BREEDING IN THE GREAT TIT - A TRADE-OFF BETWEEN SUCCESSIVE REPRODUCTIVE ATTEMPTS

1. Multiple breeding (raising more than one batch of young per breedin g season) is a common life-history tactic that has received very littl e attention. A simple static optimization model was developed, applica ble to iteroparous animals with parental care, that predicts: (1) when an animal should be a multiple breeder, (2) the optimal interval betw een successive clutches, and (3) when a clutch should be deserted. 2. More specifically, it was predicted that (I) animals should invest les s in a clutch when it is followed by another clutch in the same season , and (II) as a consequence the contribution of the first clutch to th e parents' fitness will be reduced. 3. These predictions were tested e xperimentally in a population of Great Tits (Parus M. major L.). The e xperiment consisted of the removal of second clutches. When second clu tches were removed, parents tended their first brood fledglings for a longer period than undisturbed control pairs, in agreement with the fi rst prediction. Removal of second clutches did not affect fledgling su rvival, but recruits enjoyed higher reproductive success in their firs t year of breeding when the second clutch of their parents had been re moved, in agreement with the second prediction. 4. It is concluded tha t a trade-off exists between successive reproductive attempts, which w ill affect the optimal rate of reproductive attempts.