Bird world is a busy place right now
Up and over the short cherry tree, swinging around in a graceful S-curve, it sweeps up to the nest box. It pauses for only a moment as it feeds one of the young and is off again.
The sky is crowded these days. The violet-green swallows in my yard are just the most obvious. They are nesting outside my living-room window tending the brood of five or six rapidly growing young. I enjoy watching the parents dipping and swerving like slalom skiers while harvesting unseen insects out of the air.
Every year, there is a battle on my property. Bird boxes and natural cavities are a valued commodity. Over the years I have hosted oak titmice, black-capped chickadees, white-breasted nuthatches, house wrens, western bluebirds, tree and violet-green swallows, and house sparrows. It is the latter that I take issue with.
House sparrows are bullies and, yes, murderers. If a house sparrow sets its sights on a next box, it simply takes it over regardless of whether it is already occupied. I have watched helplessly as a male house sparrow entered a nest box under vigorous protest of the owners and destroyed the eggs of a tree swallow. Once I even witnessed the end of an intrusion where the house sparrow killed an entire brood of young tree swallows. A friend related another incident where she watched a male house sparrow enter a nest box and kill the young bluebirds nearly old enough to fledge.
I have no love for house sparrows. They were introduced from Europe and do not belong here.
Consequently I work hard to construct nest boxes that house sparrows cannot enter. A box with an entrance precisely 1-1/8" in diameter will permit a house wren or chickadee to enter and leave but proves too tight for the house sparrow. I once watched a house sparrow struggle for nearly a minute trying to extract its head from the entrance of this size before successfully escaping.
As for the swallows, I drill two holes precisely 7/8 of an inch in diameter overlapping side by side and then rasp out the intervening wood, careful not to make the opening more than 7/8 of an inch tall. This produces a horizontal oval about 2 inches wide, just big enough for a large-winged, small-bodied, violet-green swallow to enter and leave. It usually works to exclude house sparrows. However, the entrance is not big enough for a tree swallow. If I make the opening a fraction larger, both tree swallow and house sparrow can enter. I haven't solved this problem. Most commercially available nest boxes have entrances that are too large and end up augmenting the house sparrow population.
As for titmice and nuthatches that require slightly larger entrances than 7/8 of an inch, I put out enough boxes in concealed locations that they find one they can use in relative peace. House sparrows generally prefer boxes in open locations. Also, both the titmouse and nuthatch nest earlier in the year before house sparrows get serious. The other strategy I pursue is to stop feeding between early April and September, avoiding millet (a house-sparrow favorite) at any time of year. This cuts down on the number of sparrows on the property.
Stewart Janes is a biology professor at Southern Oregon University. He can be reached at firstname.lastname@example.org.