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[THREAD] Recently I’ve been fixated on the fledgling brown-headed cowbirds in my yard. Cowbirds, if you’re not familiar with them, are brood parasites—females lay their eggs in the nests of other birds, leaving their young to be incubated and raised by parents of another species.
![[THREAD] Recently I’ve been fixated on the fledgling brown-headed cowbirds in my yard. Cowbirds, if you’re not familiar with them, are brood parasites—females lay their eggs in the nests of other birds, leaving their young to be incubated and raised by parents of another species.](https://pbs.twimg.com/media/EbNQmW3VcAA1u1i.jpg "[THREAD] Recently I’ve been fixated on the fledgling brown-headed cowbirds in my yard. Cowbirds, if you’re not familiar with them, are brood parasites—females lay their eggs in the nests of other birds, leaving their young to be incubated and raised by parents of another species.")
The fostering occurs at the expense of the host’s own chicks, who may get pushed out of the nest or smothered by the young cowbird.
Last month I saw some adult cowbirds, so I knew they were around. But I didn’t know which species they might be parasitizing. Brown-headed cowbirds are widespread in North America and they’ve been observed fledging from the nests of more than 140 species.
Then a couple weeks ago I started seeing a song sparrow w/ a too-big fledgling. I realized the chick must be a cowbird. The chick follows the sparrow around, chittering & fluttering its wings, begging for food. The sparrow dutifully feeds the giant baby. This goes on all day long
Initially I just marveled at how much WORK this is for the poor sparrow (a couple times I’ve seen *2* cowbird fledglings trailing a song sparrow) and how crazy it is that the hosts accept this parasitism.
Now I’m wondering how a cowbird learns to be a cowbird. Youngsters in many species learn species-appropriate behaviors through a process called imprinting, in which they become attached to their parent during a critical development window.
So how does a cowbird learn to eat cowbird foods, sing cowbird songs, and find cowbird mates when it’s raised by a song sparrow (or a goldfinch or a cardinal or…)? HOW???
Falling down the rabbit hole in 3, 2, 1….
(all photos in this thread are my own)
Falling down the rabbit hole in 3, 2, 1….
(all photos in this thread are my own)
Apparently fledgling cowbirds sneak out of the nest at nightfall to explore on their own, which may reduce risk of imprinting on their foster parents & allow them to meet up with other cowbirds at communal roosting sites, where they can learn cowbird ways https://www.sciencedirect.com/science/article/pii/S0003347215003401
Also, there's a PASSWORD?!?!? Young cowbirds are hard-wired to recognize an adult cowbird chatter call. The call works as a password to trigger the youngster to learn the password-giver's other attributes. https://www.researchgate.net/publication/11963519_A_password_for_species_recognition_in_a_brood_parasitic_bird
This study describes the neural basis for the cowbird's password-based species recognition https://jeb.biologists.org/content/220/13/2345
Oh and this one shows that exposure to the chatter call password helps young male cowbirds learn to sing cowbird songs (males) and helps young females recognize those songs. Super interesting! https://www.cell.com/current-biology/pdf/S0960-9822(19)31237-0.pdf
For more on the cowbird, aka my new obsession, check out this review. The discussion of cowbird-host coevolution is fascinating https://link.springer.com/chapter/10.1007/978-3-319-73138-4_9
