I have a love-hate relationship with House Wrens. On the good hand, they are easy to photography as they allow me to get fairly close to their nest boxes. On the other hand, they have a habit of taking over multiple boxes in their zone – but only use one to raise their chicks. It reminds me of the people who would shovel a parking spot on a Chicago city street during winter, plunk a couple of lawn chairs in the spot, and assume that nobody should take their parking space so that it would be available when they returned home from work in the evening.
The House wrens fill their “finders – keepers” boxes with very large twigs, but will make a nice, soft grassy nest in the one for their young. I have also observed them break the eggs or kill the very young chicks of Bluebirds or Tree Swallows in order to take over their nests. But, they are a native species that belongs in the natural realm of “there’s no morality in Nature” scheme of things. Last week I observed a Bluebird couple building a nest in the box that this House Wren pair now seems to occupy. I felt sad for the Bluebirds, but it’s not up to me to judge Mother Nature.
While I see these birds routinely, I have actually never captured both the male and feamle on a box at the same time. Since they are not sexually dimorphic (which means that the male and female are different in appearance), I never knew what bird was building the nest. But, I am guessing that it’s the male that I film singing, and the female that takes grass (rather than large twigs) into the box. I have read that the males start the nest by creating a base of large twigs, and the female finishes it with the more fin, soft grasses. The “finders – keepers” boxes that I often encounter are typically filled to the brim – in fact over flowing – with very large twigs.