Apr 28 2015
Last week in Schenley Park I watched a house wren claiming a nest box at the golf course. While the wren sang near the box, a Carolina chickadee peered out of the hole. One of them was going to win the box. My bet is on the house wren.
Good nest locations are highly contested both within and between species. Chickadees, house wrens, bluebirds, tree swallows and house sparrows all compete for the same nest boxes. The winners are determined by timing, temperament, and weaponry.
Chickadees are brave but small. They usually lose.
Eastern bluebirds and tree swallows are well matched and can share the same territory if two nest boxes are placed next to each other. The bluebirds begin nesting earlier and pick a box. The swallows arrive later and pick the other. But it can go either way.
House wrens don’t need to nest in boxes but when they’ve picked one they are persistent, quick builders and will remove the eggs and very young nestlings of other birds. They trump the other three.
By law you can’t interfere with these native species but you can put up more boxes. The wider the selection, the less they’ll compete.
House sparrows are another story, though.
Aggressive and well armed, house sparrows always win. They claim several boxes even though they use just one. They kill the nestlings and even the adult bluebirds incubating eggs. The only way to protect bluebirds is to trap and kill the house sparrows. You can to do this because house sparrows aren’t protected by law. They’re “listed” as an invasive species. (Click here to read more at the bluebird website, sialis.org.)
In the city there’s cruel justice for house sparrows. When another invasive species wants their nest they’re out of luck. The starlings win.