Extra pair copulation

This time of year is interesting...when a female returns to her nest before her mate, she may engage in copulation outside the pair bond. I have documented quite a lot of this in banded birds. It was previously believed that they "mated for life", but it is actually fairly common for them to engage in extra pair copulation and I believe there may be mixed paternity in a brood. The females who wait for their mate from the previous year to return, do not know if their partner survived migration and the urge to get their eggs fertilized and to breed is a strong one. I have also documented "divorces" ...a term that is anthropomorphic, but explains to people that pairs do split and seek another mate, usually after a failure to breed successfully the prior year. 

My first observation regarding extra pair copulation was many years ago when I was watching a nest that had our oldest male on it. His mate returned and was seen with him on the nest but within a few days of her return, I found her on another nest copulating with another, younger  male for about a week! Then she returned to her nest with the older male to lay her eggs! She had failed to successfully produce chicks with the old guy for several years, so this clearly was her way to improve the odds of producing fertilized eggs! The older male was a good provider, however, which may be why she remained with him.  Interestingly, they produced three chicks that year, but they were predated. The following year she "divorced " the older male and moved in with the younger male.