Q: When we cleaned out our birdhouses last week, we found a dead female bluebird sitting on her eggs in the bluebird house. Also in cleaning out a birdhouse that the sparrows used we found a dead baby bird. We don't used pesticides on our garden, so we are not sure want happened to them. We have not had any luck with bluebirds this year. Earlier in the year, we think a raccoon pulled out the bluebird sitting on the nest because we found feathers and nesting material on the ground in the morning.
— Carol A.
A: It is always sad to find this, but it does happen and the causes are varied. Sickness, excessive heat, murder. Yes, murder, if that is a proper term in this case; house sparrows (a.k.a. English sparrow) frequently destroy bluebird nests, mother and all. They are competitive and, if human, we would say ruthless.
A season ago, house sparrows destroyed a nest of bluebird eggs in our yard and, another time, killed a female on the nest apparently to eliminate competition, but not in this case, not to use the box. These aliens not only compete for nest boxes, but when too late to claim the box, they will often destroy eggs and place their nest over what instinct tells them is the intruder.
Another small cavity nester is the tree swallow. It will compete, and often win, the battle for dominance, taking the box for its family.
As for feeding, there is no competition as swallows feed in the air, while bluebirds are more likely to feed on the ground or close to it often in shrubs. When this is the case, swallow vs. bluebird, you may consider another box placed about 10 to 20 feet away. In this instance, both species may happily nest in close proximity with each other. And bluebirds may raise two families a season, while the swallows "next door" will raise only one a season (in the north).
House wrens may also compete for a nest box and, like the house sparrow, may kill the bluebird inhabitants by pecking at the female or in the case of this wren, by filling the box with twigs to discourage her. I have seen where they peck holes in the bluebird eggs or kill nestlings and removing them from the nest box.
Titmice, and black-capped chickadees sometimes, although rarely, compete with bluebirds (or more so with each other) for the same nest box, however the bluebirds will frequently win because they are the larger bird.
In the case of a nest box with a larger than ideal size hole (1 1/2 inch) for bluebirds, it may allow the formidable European starling to commandeer a nest box for its own use.
As for the raccoon destroying the nest, it also happens. Information to deter them may be found at www.bbne.org/articles/view/10. These instructions suggest various ways to deter raccoons, including slipping PVC pipe 36 inches over the post; wrapping sheet metal over the pole or post or slipping stove pipe over it, or fashioning a hardware cloth (chicken wire) sleeve over the entrance. It should be folded to be 3 1/2 inches wide and high and extend out 5 1/2 inches from the box. I imagine these tactics will also deter feral cats, as well as energetic house cats.
Thom Smith welcomes your questions and comments. Email him at Naturewatch@live.com or write him care of The Berkshire Eagle, 75 S. Church St., Pittsfield, MA 01201.