Black vultures used to mainly live in the southeastern U.S. and farther south in Latin and South America, but over the past century they've started to rapidly stretch northward and also west into the desert Southwest, said Andrew Farnsworth, a visiting scientist at Cornell Lab of Ornithology who studies bird migration.

Warmer winters on average, fueled by climate change, are making it easier for the birds to stay in places that used to be too cold for them. What's more, the human footprint in suburban and rural areas is enriching their habitat: development means cars, and cars mean roadkill. Cattle farms can also offer a buffet of vulnerable animals for vultures that learn the seasonal calving schedule.