Female Brown-headed Cowbird

Like quite a few birds, this bird is easier to identify when spotted with her significant other; she's a Brown-headed Cowbird. Due to their tendency to be monogamous plus plain old birds-of-a-feather behavior, I usually see them with prominently brown-headed males around, greatly improving my confidence in IDing them.

My understanding is that Brown-headed Cowbirds are the only obligate brood parasites in my area. Obligate brood parasites have essentially lost all their parenting skills, and thus if they were ever unable to fool other birds into raising their young, they would (almost certainly) go extinct [1].

There are, however, other brood parasites in New Jersey. These are called facultative brood parasites, and these birds will usually raise their own offspring, but will also engage in brood parasitism. (Exactly when birds perform facultative brood parasitism seems variable; one source said it occurred when resources were scarce while another said it occurred when resources were abundant. It's possible that different species do this under different conditions.)

The local birds best known for facultative brood parasitism are birds I've yet to photograph: the Yellow-billed Cuckoo and the Black-billed Cuckoo. There are stranger reports though like this one where an American Robin laid a couple eggs in the nest of a Gray Catbird. Generally speaking though, I wouldn't describe American Robins as brood parasites; this was probably a weird one-off rather than normal behavior.

April 18, 2023 at Duke Farms
Photo 272141215, (c) jpviolette, some rights reserved (CC BY-NC)

[1] It seems likely that an extremely effective brood parasite would eventually lead to the extinction of its hosts, and thus its own extinction. This is similar to the problem a predator or disease faces; to survive long-term, they can't be devastatingly effective.