A German wildlife rescue project is deploying small aerial drones to find and protect young deer hiding in tall grass from being shredded by combine harvesters cutting hay in spring.

The pilot project has shown great promise in spotting the young animals, about 100,000 of which fall victim in Germany every year to the large agricultural machines, said project spokesman Rolf Stockum on Friday.

In a pilot phase, five small drones -- fitted with combined digital and infrared sensors that can detect colour patterns and body heat -- have been trialed in the southern state of Bavaria to find the animals.

When spotted, the young deer are fitted with beacons that emit radio signals, so that farmers, when they later do the spring mowing, can find and avoid them as they noisily rumble across the grasslands and fields.

Germany's agriculture ministry -- which is backing the project with 2.5 million euros ($3.4 million) -- this month alerted farmers to the threat as mild April weather is ringing in grass-mowing season in much of Germany.

Stockum said "the problem is that deer often hide their fawn in tall fields near the edges of forests" to protect them from natural predators.

"Evolution has created a very effective way to protect the fawns, which do not yet have a sense of smell -- they instinctively stay exactly where they are placed," he told AFP.

This makes it very hard for farmers or even experienced wildlife trackers to spot the animals, leading to horrible accidents, said Stockum.

"Unfortunately, there are many years in which the time when meadows are cut in spring coincides with the time when deer drop their offspring ... and then many animals lose their lives."

Stockum said this is also traumatic for the farmers and machine operators involved and, furthermore, pollutes the cut grass, which is used as livestock feed, with shredded deer remains.

Farmers have in the past made visual inspections of grass areas or used trained dogs, and more recently many have employed hand-held infrared devices, to find the deer, said the spokesman.

However, Stockum said, using drones in coordinated campaigns, with crowds of volunteers, in the weeks before hay-cutting would cover far larger areas with greater accuracy and therefore save many more fawns' lives.