Sparrow Interloper

There was a disturbing development in the backyard this morning.  A pair of sparrows perused the nest box.

This is disturbing because sparrows are a threat to bluebirds.  They are known to kill bluebirds and their babies to take over a nest. 

A number of methods are available to discourage sparrows.  As a temporary measure, I am trying this, (photo below) which I've done before.  Unfortunately, it may also discourage the bluebirds from nesting here.  We'll have to see how the bluebirds respond.

I should probably mention that it isn't advisable to post nest boxes on fences because of predators like snakes, cats, and racoons.  Since my birds have had luck nesting here, I've made the decision to leave the box and monitor it carefully.

While I was installing my sparrow deflector, I caught a photo of a brown-headed cowbird in a budding tree.