Blue Tits fighting in nestbox

On 6th May 2010, with the aid of a camera mounted in a nestbox in my garden, I witnessed a savage fight between the female Blue Tit Cyanistes caeruleus that had built the nest and another Blue Tit. At the time of the fight, four eggs had been laid, and earlier in the day I had observed a Blue Tit removing one of these from the nest; it was dropped to the floor under the box. In mid afternoon, I sw...