Thanks guys, I followed your advice and removed the egg. I made a home-made hole reducer out of a piece of cardboard and taped it inside the box to the front of the box. It's been taped to the hole from all angles. Hoping it will hold up. It is a 1 1/4" or as close as I could get eyeballing it. The chickadees accepted it after a few minutes. Cardboard was the only thing I could think of that is flexible yet sturdy since I have gilbertson boxes. Crossing my fingers for no cowbird attacks. Never had a cowbird egg in 13 years of backyard birding, but now my 1st year at my new house and 1st nest of chickadees ever, I get one.

They are certainly not one of my favorites. They're also notorious for parasitic brooding. We've had them for a month now, and they'll move on in another month or so.

Thanks guys! Perhaps someone will see the cowbirds in context, their association with bison, and maybe realize they aren't just a nuisance preying on unsuspecting parent's to be. To be fair however, the brown headed cowbird is a "homegrown" introduced species. They have expanded their range outwards from the central plains significantly since the days of American westward expansion. While once confined to the prairies, this adaptive bird now occupies almost all of North America. Such is the case with a number of bird species, though. Before the 20th century blue jays were found pretty much exclusively east of the Mississippi, but now can be found all the way to the Rockies. Similarly, northern cardinals have begun to hopscotch their way west, following man-made urban forests and waterways that, prior to human mitigation, flooded too regularly for the forests that now grow along their banks to establish. They show up on eBird lists around Denver with increasing regularity. In a less fortunate instance this is one of the ways that it is suspected that barred owls have found their way to the Pacific Northwest where they out-compete and contribute to the decline of their cousins, spotted owls. It seems I'm going off on a tangent here... As far as ticks go, Claire, I can't imagine that bird would pass up a meal. However, I have never found ticks to be a big problem here on the Front Range, we are after all a relatively "bug-free" region when compared to hotter and more humid climates. Perhaps there is simply no one who has ever asked the question of whether cowbirds eat ticks. It would be interesting. I do know possums (another critter that has started to migrate into Colorado) have a voracious appetite for ticks, and folks who can stand to keep a flock of screaming guinea fowl report that they do a fantastic job as well. Catherine, I consider myself to be among the luckiest people on earth to have to opportunity to do what I do every day. My only complaint would be that I would prefer a more "rural" location than right outside downtown Denver, but, it sure beats sitting in an office all day ;).

It's my understanding that they always lay in other birds' nests. As I mentioned in the other cow bird thread, maybe their behavior might change, since there aren't many buffalo herds to follow anymore. I had never thought about that.......will their behavior change in this changing world? I wonder if they even know how to make a nest?