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A Sumptuous Feast

Ecologists have studied the role carrion plays in the ecosystem of the Bavarian Forest National Park

Freiburg, Dec 16, 2020

In the photograph you can see a lynx, standing in the depths of the forest, with both forepaws placed possessively on the cadaver of a deer. The picture comes from one of the many photo-traps set up as part of a study by a team headed by Prof. Dr. Marco Heurich. Heurich is the wild animal ecologist for the Bavarian Forest National Park and Professor of Wild Animal Ecology and Nature Conservation Biology at the University of Freiburg. “The aim of the study was to rethink the importance of carrion in the ecosystem,” he says. To reach their result, the researchers analyzed 270,279 photos shot over a total of 15,373 nights spanning roughly six years.

Enjoy your meal! The lynx is a rare predator. Photo: Bavarian Forest National Park 

Previously the Bavarian Forest National Park disposed of or sold the bodies of wildlife that were run over or else hunted in accordance with stock management rules. “Now we leave dead animals be, as it would be in the natural cycle of an ecosystem,” Marco Heurich explains. Things aren’t as natural as all that, however, as the scientists vary the choice of cadavers available. Amongst other things, the team observed whether scavengers preferred eating the meat fresh or thawed, if one time of year was better than another for setting out carrion, and whether large animals like the lynx, which range the national park along with 29 other related species, would rather eat deep in the woods or out in the open.

The photo-traps capture diversity

The photo-traps not only reveal predators such as lynx – which are strictly protected and rare – and foxes – fairly common – but also pine marten, badgers, wild cats, buzzards, red kite and white-tailed eagles, which were also interested in the cadavers. “Three of the seventeen species of vertebrates that frequented the cadavers put out for them are on the Red List of species threatened with extinction,” Heurich states. Two of the birds that were observed are also on the Red List of endangered birds in Bavaria.

In winter carrion plays an important part as an additional source of nutrition. The meat can deteriorate too rapidly in summer, causing difficulties for the animals, the researcher adds. In the warmer months, insects, bacteria and fungi are responsible for decomposition. “If dung beetles and blowflies find the carrion before the large animals do it’s soon gone.” Unique vegetation also develops on the plot of land as a result of the nutrients absorbed at the site of the spoils. “It becomes a hotspot for life,” says Heurich. This hotspot of microbes and fungi is now increasingly interesting the scientists, “The focus of our first study was on vertebrates, but now we’re broadening our focus to include all those involved in this nutrient cycle.”

Carrion is part of the ecosystem

The wild animal researcher is unhappy that scavengers such as vultures or corvids have a bad reputation and that the word ‘Aas’ is an insult in German. “Devouring carrion is an important and completely natural process in an ecosystem,” stresses Heurich. So what was the scavengers’ response to the food set out for them? The animals turned out not to be fussy about the freshness of the meat, whether or not it was thawed. They also weren’t bothered about the timing when the lure was set out.

On the other hand, they were concerned about the choice of location. Birds preferred low-density woodland, while for lynx it was denser areas. Foxes have a clever trick, according to Heurich, “They’re alert to gatherings of corvids, because that is a sign of prey.” So it’s no surprise that foxes were the most frequent visitors to the feeding sites, closely followed by pine marten and the common raven. Best were large cadavers such as red deer with a weight of 70 to 80 kilograms, as they offered enough food to satiate many species, the researcher explains.

Less intervention is better

“In the Bavarian Forest National Park we’re intervening less and less in the processes of the ecosystem, and the lynx is helping us to keep the red deer population in equilibrium,” says Heurich. Roe deer haven’t been hunted for a long time now, however wild boar and red deer are still hunted. This is carried out to protect the managed forests and fields in the vicinity of the national park; to prevent wild boar from digging up gardens, for example.

From the study, the scientists deduce that feeding with carrion in winter in accordance with the latest findings can play an important role in the ecosystem of the national park. This is also worthwhile for the new population of wolves which is being added to the group of major predators, says Heurich. “We’ve already observed a wolf on a cadaver, and we’re delighted that there haven’t yet been any problems with the newcomers.”

Eva Opitz