Through the winter, a few White-throated Sparrows can be found foraging in the 4th Avenue extension of Green-Wood. Most of the local White-throats who visit us in the winter are found deeper in the cemetery. The 4th Avenue section, which has streets on four sides (there’s a tunnel under 5th Avenue that I bet most Brooklynites don’t know about) is dominated by House Sparrows. House Sparrows aren’t found in large numbers deeper inside the cemetery; they really, really, like the proximity of people (places, food, etc).
Anyway, these White-throats will probably disappear soon as they head north to breed. But this particular one, alas, will not. The body, however, gives us incredible views of the passerine foot.
Backyard and Beyond 
The anisodactyl passerine foot is interesting in that there is a tendon which divide intio three sections as it passes under the foot pad or pes. This tendon closes the three front toes automaticslly as the bird drops down on a perch. This adaptation to arboreal life allows the bird to remain securely attached to the perch without tightening a muscle. This is how these birds can sleep without falling off the perch. There is still some ability to articulate the middle toe, but I can’t get a good explanation for that, so far.
Always sad to see this. Did it run into a glass window or door?
I don’t think so. Quite far from any buildings. Possible a car.
As an added: In New York City we report bird kills, especially those near glass windows, to Audubon’s Project Safe Flight https://www.nycaudubon.org/our-work/conservation/project-safe-flight.