Cowbird?

I am wondering if this is a Cowbird. Here is an isolated image and a second image of an adult which has been feeding it in the trees near my feeders. This is near Henderson Inlet outside of Olympia, WA. Taken yesterday. It is nearly twice the size of the adult...

Here is the "baby" being fed...

I believe you are correct. The smaller adult looks to be a sparrow (Fox Sparrow perhaps). Cowbirds are known to lay one egg in the nest of another, usually smaller bird (called parasitism). The Cowbird egg hatches sooner and immediately starts being fed by the unsuspecting parent. By the time the real chicks hatch, they can't compete. The Cowbird chick may literally push them out of the nest, or they may simply starve. In the end, you have a smallish sparrow or vireo feeding a much larger Cowbird. One of the interesting twists in nature and this makes your image a nice record of this behavior. Thanks for posting.

-Jeff

PS: Here's some more explanation on this behavior: http://nationalzoo.si.edu/scbi/migratorybirds/fact_sheets/default.cfm?fxsht=3

Yes, a juvenile Cowbird and probably an adult Song Sparrow feeding it.

Brown-headed Cowbird - the bill is quite distinctive on them (especially where the upper mandible meets the body). Here's one from AZ.