Dennis Forsyth writes: I have put in a fair amount of work this year re-building some of my nest boxes to facilitate my ongoing Violet-Green Swallow photography project. I was, therefore, faintly horrified to find a House Wren preparing to move into one of them. The problem, as you may know, is that House Wrens are particularly territorial and very much prefer to keep all competition for food sources away. They are cavity nesters and therefore see their competition as anybody with the same real-estate tastes. They discourage Chickadees, Nuthatches, Swallows, etc. first by building rudimentary dummy nests in other cavities (or boxes) in the near vicinity. That often discourages anybody else from trying to inhabit that space. They will also go so far as to enter other cavities after nesting to destroy the eggs laid by other birds. In fact, a couple of active House Wrens may be enough to rid a neighbourhood of all other cavity nesters. What to do?
I am discouraging this first invader right now by faithfully visiting all of my vacant boxes each morning and cleaning out all of the nesting material from the previous day. This Wren is really only trying to work on two boxes at the moment so it isn’t very onerous. I just don’t want House Wrens raising a family here if I can avoid it. Below is a shot of one of my resident pair of Swallows who are just now beginning to court. Dennis
Patrick Fawkes commented: Last year I had the same trouble with House Wrens. In one nest I found a large pile of sticks on top of a Violet green’s nest with five mummified babies; their wing feathers were starting to emerge from quills indicating that they were probably about two weeks old. As I wrote in the August 2016 Flagstone “It is particularly tragic that these young birds’ lives were snuffed out under a dummy nest that hadn’t been used.” I also am checking my nest boxes to discourage the House Wrens.