Nov 292011

For several days I had noticed a pair of House Finches flying to and from a holly near my front porch. Typically, just standing next to the bush for longer than a few seconds would cause a bird to bolt from deep within the leaves near the top.

I suspected the finches had constructed a nest, and I retrieved a step ladder in order to have a better look. I was surprised by what I found

The House Finches were indeed nesting in the bush off my front porch, and when I examined the nest more carefully I made an interesting discovery. The nest contained three light blue House Finch eggs, but unexpectedly, it also held a fourth and different kind of egg. This one was white with brown speckles and slightly larger than the others.

Clearly this fourth egg did not belong with the other three, and a little research revealed that this egg belonged to a different species of bird altogether, the Brown-headed Cowbird.

The cowbird is a what is known as a parasitic species. It lays its eggs in the nest of other, smaller birds. The host species (in this case the House Finch) then incubates the cowbirds eggs along with its own, and when the eggs hatch, the larger cowbird juvenile is frequently able to out-compete the host bird’s young for parental care, due to its larger size.

County Denton
Center map
City Carrollton
Date May 11, 2008 – Jun 3, 2008
Time of Day Various
Temperature Various
Weather Various
Habitat Residential-Single Family
Type of Behavior Care of Young, Nesting
Gender Mixed
Maturity Mixed
Observer Chris Jackson
Main Article House Finch Observation Location

  6 Responses to “House Finch – Parasite Foiled”

  1. Pretty cool.

  2. I discovered this bit of information on wikipedia this afternoon. If true, it would explain what happened to the cowbird nestling in this observation:

    Some species, such as the House Finch feed their young a vegetarian diet. This is unsuitable for young Brown-headed Cowbirds, meaning almost none survive to fledge

  3. Chris, I keep discovering gems in your blog. This is a great series of photographs. Thanks again for doing the blog.

  4. You said parasite foiled? Did you remove it? The Cornell Ornithology Lab requests that Cowbird eggs not be removed. Cowbirds are native and the behavior is natural. This is the only way they can reproduce themselves. Please don’t take sides.

    • The story is explained in the captions under each picture and in these comments… House Finches feed their young primarily vegetable matter. Cowbirds juveniles need to be fed insects, or else they will die. That is what happened in this case. The Cowbird juvenile hatched first and died a few days later. The adult House Finches removed the carcass from the nest. The mother Cowbird made a bad choice in this case.

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