Tree Swallow eggs destroyed by a House Wren. They are usually found directly below the entrance hole of the raided nestbox.
I heard a House Wren in this area on 5/11 and installed a wren guard. On 5/14/08, I found the entire clutch of bluebird eggs on the ground below the nestbox. The developing embryos are visible inside the broken eggs. These eggs were within a day or two of hatching. If they had not been so badly damaged and dried up, I could have tried putting them back in the box (covering a tiny peck hole with nail polish sometimes works) to see if they would hatch - one monitor did have a titmouse egg hatch after an attack when she returned it to the box.
The box already had a sparrow spooker on it, so I do not suspect House Sparrows, as spookers are more effective at preventing House Sparrow attacks than wren guards are at deterring House Wrens. (Sparrow spookers do not deter House Wrens.) Also, a few days later a couple of sticks showed up in the box.
See related video showing a House Wren removing one-day old bluebird nestlings from a box.
House Wrens are the biggest problem on my trail other than paper wasps. (House Sparrows are regularly controlled via passive and active methods and no longer pose a serious problem.)
May 29, 2008 - Take Your Pick (parents feeding fledgling)
June 10, 2008 - That Look Belongs in a Holster (female MOBL)
You cannot begin to preserve any species of animal unless you preserve the habitat in which it dwells. Disturb or destroy that habitat and you will exterminate the species as surely as if you had shot it. So conservation means that you have to preserve forest and grassland, river and lake, even the sea itself. This is vital not only for the preservation of animal life generally, but for the future existence of man himself—a point that seems to escape many people.
-Gerald Durrell, The Nature Conservancy
