Black vultures attacking and killing newborn or sick calves is a problem faced by many livestock farmers and one that may grow worse as the scavenging birds’ range expands northward, in part due to climate change.

Lobbying groups have been pushing for legislation that would allow landowners to kill more of these birds, which are protected under the Migratory Bird Treaty Act. But some experts say more research is needed to better understand the impact on livestock. They also caution that removing these scavengers from the ecosystem could have lasting negative consequences.

Allan Bryant, a livestock producer in northern Kentucky, has lost calves to these vultures and says he frequently sees them after the birth of calves in the spring and fall.

In some of his fields, he erects a scarecrow of sorts — a dead black vulture — aimed at scaring off the birds. It's a requirement of his depredation permit through the Kentucky Farm Bureau, which allows him to shoot a few birds a year. The dead bird keeps the live birds away for about a week, but they eventually come back, he said.

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.

Although black vultures are protected by the Migratory Bird Treaty Act, they aren't really a migratory species, he said. Instead, they breed, and some disperse to new areas and settle there.

In March, lawmakers in Congress introduced a bill that would let farmers capture or kill any black vulture "in order to prevent death, injury, or destruction to livestock.” Many farmers and others in the cattle industry have supported the move, and the National Cattlemen's Beef Association in July commended the House Natural Resources Committee for advancing the bill.

Farnsworth, of the Cornell lab, said it's not necessarily a good thing to make it easier to kill black vultures, which he said fill "a super important role" in cleaning up "dead stuff.”

Simply killing the birds, Farnsworth said, may make room for more bothersome predators or scavengers. He said though black vultures can leave behind gory damage, current research doesn't show that they account for an outsize proportion of livestock deaths.

But many farmers are unwilling to do nothing.

(AP Video by Joshua A. Bickel and Mary Conlon, produced by Joshua A. Bickel)