African vultures fly long distances and prefer to feed outside of national parks, putting themselves at risk of poisoning from carrion in agricultural areas, a new study has found.

Researchers followed six African white-backed vultures for several months using GPS tracking units strapped to the birds' backs and published the findings in the US journal PLOS ONE on Wednesday.

The researchers found that the vultures range much farther than was previously known, traveling up to 220 kilometers (140 miles) a day and routinely crossing state borders.

The birds shy away from protected national parks because they prefer not to compete with other carnivores -- such as lions -- and are instead drawn to agricultural areas.

But there they often encounter carrion that contains veterinary medicine that is harmful to the birds or carrion that has been deliberately poisoned in order to eliminate predators.

The study also found evidence, however, that the vultures are drawn to carrion set out to attract them for tourists, according to co-lead author Stephen Willis, of Britain's Durham University.

"We found evidence that individual birds were attracted to vulture restaurants' where carrion is regularly put out as an extra source of food for vultures and where tourists can see the birds up close," Willis said.

"As a result, these individuals reduced their ranging behavior. Such restaurants' could be used in (the) future to attract vultures to areas away from sites where they are at high risk of poisoning."

The white-backed vulture is a common but declining species in Africa and is now listed as endangered.

"Modern farming practices mean that vultures face an increasing risk of fatal poisoning," co-lead author Louis Phipps said.

"The provision of an uncontaminated supply of food, research into veterinary practices, and education for farmers could all be part of a future solution, if vulture numbers continue to plummet."