Bluebirds: Parasitism in bluebird nestboxes with properly sized holes is not common. Cowbirds occasionally parasitize nests in nestboxes. The female is capable of squeezing through 1.5″ hole, however they probably prefer a larger hole (1.75″ or maybe a Peterson hole). Keith Kridler has found Cowbird eggs right beneath a bluebird nestbox entrance hole, and wonders whether the tight squeeze will sometimes “pop” an egg out of the female as she enters the box.
Cowbirds are tricky…detailed information on them can be found on the Sialis website.
The Cowbirds are still around, whenever I see them I turn the garden hose on them hoping that they will move on. We have 5 eggs in the nest and hatching date is around the 27th. I have an additional curious observation….it seems like one of the males from last year’s fledglings is still hanging with the parents. I finally looked at him through my binoculars today and after doing some research he appears to be a second year. I know from reading past posts that this is unusual, however the three of them seem to be getting along just fine. I always appreciate your comments! Susan