RESPONSE OF MALE EUROPEAN STARLINGS TO EXPERIMENTAL REMOVAL OF THEIR MATE DURING DIFFERENT STAGES OF THE BREEDING CYCLE

We experimentally removed females from monogamous European starling St urnus vulgaris pairs during different stages of the breeding cycle and recorded the effect of these removals on male behaviour and on offspr ing survival in order to assess the possibilities for female male dese rtion. Removal of the female during the laying, incubation and early n estling stage (1- to 5-day-old nestlings) invariably resulted in compl ete failure of the brood. The survival of the nestlings improved sligh tly if the female was removed during the middle nestling stage (6- to 10-day-old nestlings), but mortality rate of nestlings was still signi ficantly higher than in control two-parent broods. About 80% of the ma les widowed during the laying/incubation period removed all eggs from the nest, while only 49% of all males widowed during the early and mid dle nestling stage removed all dead nestlings. Removal of eggs/dead ne stlings by a widowed male starling probably functions to increase the chance on a successful re-mating, since replacement clutches were foun d only in nests whereof the clutch/brood was removed. We recorded one definite and al least nine suspected cases of parental infanticide, th e killing of own offspring, by experimentally widowed male starlings. After nestlings reached 10 days of age (late nestling stage), there wa s no longer a significant difference in nestling mortality rate betwee n male-only and two-parent broods. This crucial point coincides with t he time when (1) the nestlings are functionally homeothermic, and (2) the exponential growth of the nestlings begins to moderate. Moreover, at this time, late in the season, the only viable option for deserted males is to care for the young because the probability of renesting su ccessfully is low. Our results thus indicate that after nestlings reac h 10 days of age, female starlings may have the opportunity to desert their mate. However, at that time, the benefits of female mate deserti on are reduced as opportunities for renesting succesfully are low.