A (Brood) Parasite in My Backyard

I had heard about it, but I never envisioned contacting it in my own backyard.  Of course I was lucky in a way because I observed it mostly from inside of my house.  But it was still a shock to come face to face with the parasite taking advantage of a favorite Phoenix bird, the Abert's towhee.

Before I make this sound even more dire than I already have, the towhee and I were not in any physical danger.  The invasive creature in my garden was actually just a  juvenile brown-headed cowbird.  This species is sometimes referred to as a brood parasite because it lays its eggs in other birds' nests.  The cowbirds then leave the responsibility of tending the eggs and raising the hatchlings to the nest-building birds, like the Abert's towhee that I found feeding the young cowbird in my backyard.

Unfortunately the baby cowbirds outcompete any other chicks - like the towhees - that also hatch in the nest.  As a result the adult towhee might end up raising an alien species instead of its own offspring.  

Initially I thought the parent in my yard was feeding another towhee, an act I've observed before in that very place.  However even though the birds were a similar tan color, the juvenile looked different, more like a house finch with its streaked patterns.  Indeed it was a cowbird enjoying the largesse of a foster parent. 

Fortunately Abert's towhees thrive in my neighborhood and have multiple broods in a year, so there's a good chance they'll raise their own chicks on the next go around.  Meanwhile there's one more black-headed cowbird well on its way to a healthy maturity.  Eventually it'll flock with other cowbirds in the area, mate, and, if female, lay its many eggs in another bird's nest.

Adult Abert's towhee, left, and juvenile brown-headed cowbird in my Phoenix backyard.

Adult Abert's towhee, left, feeding a juvenile brown-headed towhee in my Phoenix backyard.

Juvenile brown-headed towhee in my Phoenix backyard.

Adult Abert's towhee (left), juvenile brown-headed towhee (center), and house finch (right) in my Phoenix backyard.