Sure looks like a cowbird egg to me.

I observed a similar picture a few days ago. Here is the chipping sparrow being followed by a "baby" cowbird chick to the birdfeeder. The chick follows her everywhere and demands food constantly. I observed this weird couple for several days. It seems like this cowbird was the only surviving chick: This post was edited by green_go on Sun, Aug 24, 14 at 21:28

Sure does! According to the Guide to Boreal Birds: "Parasitism by Brown-headed Cowbirds (Molothrus ater) is rare in this species, probably because cowbirds are rare within its breeding range; however, this may change with changes in land use." I miss the white-throats - they winter over here but migrate north as soon as it's reasonable for them. The cowbirds mostly seem to parasitize Red-winged Blackbirds and Baltimore Orioles here and they seem to be a more suitable choice (at least the rest of the brood survives). It's funny to see a puzzled cowbird chick trying to eat jelly with the rest of its oriole brood (YUCK). Claire

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 ;).