I came across an interesting sight at the Ballona Freshwater Marsh. The bird on the right was going around following and begging the little bird on the left for food. And that bird on the left, a male Common Yellowthroat, was dashing frantically all over, finding morsels to put in its mouth. Now, it should be obvious from the size mismatch that they are completely different species! Turns out the brown bird is an immature brown-headed cowbird (see also the second picture below), one of the most notorious brood parasites. It has grown up in the Yellowthroat's nest this year, where its mother dropped off the egg (while getting rid of one of the host's original eggs). It's not good to anthropomorphize birds too much perhaps, but I found the close relationship between these two sad and sweet at the same time.
An article titled "Brown-headed Cowbirds in California: Historical Perspectives and Management Opportunities in Riparian Habitats", by S. A. Laymon documents the steady increase of brown-headed cowbirds in California over the past century, and their devastating impact on host populations of small birds; As a remedy, it advocates trapping and killing them, a possibly necessary act of intervention, but one that I nevertheless find rather troubling. This growth in cowbirds has been linked to human activities such as deforestation.
There is also some interesting information about this at the Griffith Wildlife Biology's page about Cowbird control: "when a cowbird parasitizes a small species like the vireo, flycatcher, or gnatcatcher, these smaller hosts are able to raise only the cowbird and none of their own young – a short route to extinction." Sigh.
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