I have five bluebird houses on fence posts. The eastern bluebirds lay eggs, but then they don't hatch. The eggs aren't broken, and the nests aren't disturbed. Sometimes there are even new eggs on top. What's the problem? ?— Alison Franks, Cullman, Alabama
George: My guess is that the house sparrows or tree swallows in your area are driving the bluebirds away from the houses.
To be sure the eggs are from bluebirds, look at the color. If they are all very pale blue, they definitely belong to bluebirds. If spotted with brown, they are house sparrow eggs.
Sometimes forces of nature interfere with nesting. Keep offering plenty of nesting sites. In turn, hopefully, there will be fledglings in your future.