Mate guarding in the spotless starling (Sturnus unicolor): Timing and duration pattern in intermediate breeding pairs

Mate guarding behaviour in the spotless starling Sturnus unicolor, acolonially breeding passerine was observed in five focal pairs of anestbox colony in a Spanish `'dehesa'' (extensive pastured helm oakwood) in 1993. Daily observations were performed since the day of pairformation. Escorting behaviour began 4 days prior to laying and declinedsharply between the 2 and 3 days of the laying period. Males followedtheir females more than the reverse, and spent more than 90% of time inthe colony with the female during her fertile period. When escorting thefemales, males actively chased off other males to prevent themappproaching their mate. While males escorted females during fertileperiod up to 100% of times when they left colony, females came back tocolony without their mate nearly 30% of times, showing that femalessucceeded in escaping their mate Vigilance when moving outside thecolony. These results suggest that males guard in aim to keep othermales away from their female, but also to keep females from approachingother males. Most of the observed copulations occurred during theguarding period. No extra-pair copulations (EPC) were witnessed betweenindividuals of breeding pairs during the study time. One attempt of EPCoccurred between a male of focal pair and a female of non-focal unstablepair. Nestbox occupation by unstable pairs and the shortness of timeseparating pair formation and laying in intermediate breeding pairs arediscussed.