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 Sturnus vulgaris pairs during different stages of the breeding cycle and recorded the effect of these removals on male behaviour and on offspring survival in order to assess the possibilities for female mate desertion. Removal of the female during the laying, incubation and early nestling stage (1- to 5-day-old nestlings) invariably resulted in complete failure of the brood. The survival of the nestlings improved slightly if the female was removed during the middle nestling stage (6- to 10-day-old nestlings), but mortality rate of nestlings was still significantly higher than in control two-parent broods. About 80% of the males widowed during the laying/incubation period removed all eggs from the nest, while only 49% of all males widowed during the early and middle nestling stage removed all dead nestlings. Removal of eggs/dead nestlings by a widowed male starling probably functions to increase the chance on a successful re-mating, since replacement clutches were found only in nests whereof the clutch/brood was removed. We recorded one definite and at least nine suspected cases of parental infanticide, the killing of own offspring, by experimentally widowed male starlings. After nestlings reached 10 days of age (late nestling stage), there was no longer a significant difference in nestling mortality rate between male-only and two-parent broods. This crucial point coincides with the 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 successfully is low. Our results thus indicate that after nestlings reach 10 days of age, female starlings may have the opportunity to desert their mate. However, at that time, the benefits of female mate desertion are reduced as opportunities for renesting succesfully are low.