Does mate-guarding give non-territorial birds the chance to settle?

Abstract

Territory defence has been suggested to serve as a means of preventing extra-pair copulations. This hypothesis predicts that territory size is largest during the fertile period, and hence at this time few new territory settlements are expected. I show that Great Tits Parus major show a peak in new territory settlements in between adjacent territories precisely at the time other pairs start egg-laying. These newly settled individuals were mostly known as floaters in the area, and did not seem to be paired before they settled. This observation is in contrast with the territory defence to prevent EPC’s hypothesis. I hypothesise that males have to trade-off territory defence and mate-guarding, enabling new birds to settle at the time males mate guard.