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 a
nestbox colony in a Spanish `'dehesa'' (extensive pastured helm oak
wood) in 1993. Daily observations were performed since the day of pair
formation. Escorting behaviour began 4 days prior to laying and declined
sharply between the 2 and 3 days of the laying period. Males followed
their females more than the reverse, and spent more than 90% of time in
the colony with the female during her fertile period. When escorting the
females, males actively chased off other males to prevent them
appproaching their mate. While males escorted females during fertile
period up to 100% of times when they left colony, females came back to
colony without their mate nearly 30% of times, showing that females
succeeded in escaping their mate Vigilance when moving outside the
colony. These results suggest that males guard in aim to keep other
males away from their female, but also to keep females from approaching
other males. Most of the observed copulations occurred during the
guarding period. No extra-pair copulations (EPC) were witnessed between
individuals of breeding pairs during the study time. One attempt of EPC
occurred between a male of focal pair and a female of non-focal unstable
pair. Nestbox occupation by unstable pairs and the shortness of time
separating pair formation and laying in intermediate breeding pairs are
discussed.