According to Cornell Ornithology (link above), Wood Thrush are
susceptible to Cowbird parasitism.
I noticed one nestling above had a gape of a different color than the others. According to Sialis: A cowbird nestling has a deep pink or cherry red mouth. Apparently an indicator that a nestling has not been fed recently is blood collected around the mouth. After the baby is fed, blood is drawn to the digestive area, and the color of the mouth fades. Thus having a bright red mouth, and the ability (due to earlier hatching and larger size) to reach higher when gaping results in Cowbird nestlings receiving priority for feeding. (www.sialis.org/cowbirds.htm)
In subsequent photos, it's clear that the nestling with the red gape reaches higher than its nest mates and receives first attention. Sadly.
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