France, Oct. 4 -- Watching vultures feed is an impressive sight. Dozens of birds with wingspans of up to two metres descend simultaneously on to an animal carcass, jostling to get as close as possible.

"It's a real melee, a real scrum. They really go in on each other, they jump on each other's backs. Anything goes," says Robert Straughan, looking down over the edge of a cliff at a clearing 100 metres below, where he has just sent a sheep carcass on a zip line pulley.

Straughan, who is vulture project director for the League for the Protection of Birds (LPO) in the Grands Causses - an area of high limestone plateaus and deep river gorges in France's highland Massif Central region - collects sheep carcasses from farmers three times a week...