Importance of colony size and breeding synchrony on behaviour, reproductive success and paternity in house sparrows Passer domesticus

We examined the effects of breeding density and synchrony on the behaviour, reproductive success and paternity losses in house sparrows. We created nest sites with varying numbers of nest-boxes in order to test the effects of colony size. Our results show that there was an interaction between breeding synchrony and density, namely that breeding synchrony decreased with colony size. Neither colony size nor breeding synchrony seemed to influence brood size at fledging, although birds in larger colonies laid larger clutches. Moreover, mate guarding behaviour was not influenced substantially by these two factors. Only nest guarding was significantly related to colony size and breeding synchrony. Paternity losses were not significantly related to colony size but they appeared to decrease with increasing synchrony. This finding supports the idea that extra-pair fertilisations are under male rather than female control.