The place is lousy with birds

Several commenters mentioned the large number of vultures in the area shown above (from Park Avenue to Ridge Avenue, between 10th and 11th Streets).
I saw dozens of them swarming around the trees in this area at about 4:30 on Tuesday afternoon.

I estimated well over a hundred in the area shown on the map at the top of this post.
There are over 70 in this shot alone.
I wonder what’s drawing them to this particular spot.  They seem to prefer roosting in large pine trees, which provide protection, but is there enough carrion in the area to sustain this many birds?  Yes, they fly to other nearby areas to find meals, but are there that many animals dying in town each day to supply these birds with enough food?  Apparently so.
Supposedly, they are some of the cleanest birds around, but you wouldn’t know it from looking at them.