Casualties of migration

Found this American redstart yesterday in a Massachusetts parking lot. No trees in site. Since there are no signs of injury (although what is that thing in it's cloacal region?!) I'm guessing it landed exhausted after a night of migration and just keeled over from lack of food? But it could have just fallen off of somebody's grill. 

In a previous May, I found an ovenbird dead outside of a convenience store in an urban area. These two observations lead me to conclude that migration is: 1) difficult and 2) messy, with a certain percentage just dropping dead along the way...a percentage that is certainly higher (and rising) in this age of parking lots and convenience stores.