usurper prevails

This is a nest which has been occupied every year for the last 20 by a male wren - not necessarily the same one, mind you, but a wren has been there. Now, here is a robin in the nest. Maybe the cold winter has led to a loss in demand for des res from wrens. Maybe the wrens, who usually have more than one nest, have allowed a squatter in for altruistic reasons. Who can quess? Anyway, we are having a great time watching progress!