Michael Prinz hunts in his spare time and always has his binoculars with him. In the background, the biologist Pia Anderwald is ready with her GPS device. | Photo: Silas Zindel

The long, dark brown droppings on the hiking trail here in the Swiss National Park look inconspicuous. You might almost think they were from a dog – though hikers are forbidden from bringing dogs with them, because the plants and wild animals here are allowed to thrive undisturbed. What’s more, the droppings contain fine, light-coloured hairs. “It’s fur residue from the animal’s last kill”, says Michael Prinz, who’s assisting researchers here in the National Park this summer as part of his alternative national service. “You won’t find residue like that in dog faeces, because dogs don’t hunt”. The droppings are still fresh. So a wolf was right here, either yesterday or the night before.

For a few months now, the nights in the park have belonged to wolves. This is a new development, as it was only in 2023 that a wolfpack became established there. It was a massive stroke of luck for the researchers, because it meant that they could study how wolves influence other animals in the National Park – not just the red deer and chamois that are their main prey, but also small mammals such as mice and smaller predators like foxes.

Prinz puts on lab gloves, collects the droppings in a plastic bag and places it in his rucksack. The sample will be examined later under a microscope and the wolf from which it came identified by means of DNA analysis. These tests will also reveal what the wolf has been eating in the last few days.

Plants and animals are strictly protected here in the unspoilt Swiss National Park. | Photo: Silas Zindel

Researchers are also active around here. The biologist Pia Anderwald and her assistant Michael Prinz are looking for droppings and checking observation traps. | Photo: Silas Zindel

Tasty treats: Pia Anderwald puts guinea-pig food in traps for small mammals. | Photo: Silas Zindel

Animal’s droppings can reveal how far they have spread out in the National Park, and what they eat. | Photo: Silas Zindel

A track tunnel has been placed on a branch where small mammals will use it instinctively, as it offers welcome protection from predators. | Photo: Silas Zindel

A happy event

The Swiss National Park in the canton of Graubünden had to wait a long time for its wolves. A female wolf had been spotted roaming the area from late 2016 onwards, but remained alone. It was only in 2022 that a second female and a male moved into the area. The following spring, they had a total of eight pups. “It was the first time there’d been young wolves in the National Park, which made us very happy”, says the biologist Pia Anderwald, who is conducting research there. This year, another six pups were born.

A pack has a much bigger influence on its territory than would a single wolf. “We know from other ecosystems that large predators bring about a permanent shift in the interactions among animal species”, says Anderwald.

In Yellowstone National Park, USA, for example, wolves have promoted biodiversity considerably by increasing the food supply available for scavengers, and by controlling the elk population. This has led to less erosion on the plains and along the rivers, which in turn has increased the diversity of the ecosystems in the surrounding landscape.

If foxes be so bold

Prinz sets off again along the hiking trail as it leads gently uphill. It takes him through a forest, then across a stony hollow. When it rains here, he says, it turns into a raging torrent. He seems utterly at home in this rugged landscape with his long, striding gait and walking stick. It’s difficult to grasp that he works in a bank back in his normal life.

Fritz finds more droppings, though much smaller, on a large stone at the edge of the hiking trail. “This is from a fox. They like to leave their droppings a little higher up. It’s how they mark their territory”. He packs up this sample, too, for later analysis in the lab. And he documents his find on paper, with its GPS coordinates.

Today’s hike is part of his fox monitoring duties. Three times each summer, the researchers walk along all the trails here, recording fox droppings in order to ascertain the animal’s precise habitat within the 170 square kilometres of the National Park. “In recent years, we’ve seen them use almost the whole of the Park – both its open spaces and its woodland areas”, says Anderwald. This makes their interactions with the wolves all the more interesting.

Michael Prinz normally works at a bank. For his compulsory community service, he’s helping out in the National Park near Zernez. | Photo: Silas Zindel

When this felt is impregnated with ink, small mammals crawling over it – such as mice – will leave their paw prints on the paper to the right. | Photo: Silas Zindel

Pia Anderwald and her assistant Michael Prinz on their way to set up traps for small mammals. | Photo: Silas Zindel

This fox has been caught in a photo trap. As part of the monitoring programme, some animals are fitted with GPS transmitter collars. | Photo: Swiss National Park

Anderwald sees two possible ways in which the animals might have an impact on each other. Wolves can undoubtedly be dangerous for foxes. “Foxes don’t belong among the typical animals that wolves might prey upon, but if they get too bold in trying to steal prey from a wolf, that can change quickly”. But Anderwald also expects domestic predators to benefit from the presence of the wolf. Faecal analyses in recent years have shown that the foxes in the National Park don’t just feed on small mammals, insects and berries, but also on carrion of deer and chamois. “The wolves probably leave prey remains behind that the foxes can eat. This increases their food supply”.

The mouse traps

The wolfpack probably also has an indirect impact on small mammals such as mice, says Anderwald. While Prinz continues along the hiking trail, she climbs up a forest slope to one of their five trapping areas in the park. It’s quite a slog to get up here because there’s a lot of dead wood lying around in the untouched forest. She has to climb over branches strewn across the ground and weave her way under half-toppled trees. She looks at her GPS device. “Yes, we’re at the right place”. She takes a trap out of her rucksack – it’s a tunnel-like construction made of metal, with a subtle closing mechanism. It contains a tiny rail that the mice have to step on when they crawl through the tunnel to reach the nest box at the end where food is waiting for them.

Anderwald puts some straw and a handful of guinea pig food in the trap, then places it under a mossy branch on the forest floor. The traps will only be activated five days from now for a period of two nights, so that the mice can first get used to seeing them. In this way, Anderwald’s team tries to ensure that they catch as representative as possible a sample of the small mammals living here. Once the traps have been activated, they are checked every eight to ten hours. The animals in them are registered and then released again. This is how the researchers determine their numbers on a periodic basis.

The team has also placed narrow track tunnels at 16 other locations, each of them 90 metres away from the trapping area. These are roughly a metre in length and made of wood. When mice and other small animals crawl through them, they step on a felt mat soaked in a special ink that means they then leave paw prints on strips of paper in the tunnels. This allows the team to record the biodiversity of the fauna living here. “We can assume that most small mammals will use these tunnels because they like to move around where they are safe from predators”, says Anderwald.

“Just 49 more traps to set”, says Anderwald as she strides off for the next location. The summertime is particularly exhausting for her and her team of eight, as the days are long and packed with fieldwork. This last summer and autumn, she has been testing an automated monitoring method that uses cameras to record the animals. But it still isn’t clear whether it will track the composition of species in the area as reliably as the time-consuming method of identifying them with the track tunnels.

More wolves mean fewer deer but more mice

Their exertions are nevertheless worthwhile because this long-term monitoring has enabled the researchers to determine what small mammals live here and in what quantities. They have also come to have a feel for the annual fluctuations in their populations. Forest species are well represented in the National Park, including the bank vole, the alpine field mouse, the common shrew and the garden dormouse. “In contrast, we haven’t yet been able to detect typical meadow species such as the common vole”, says Anderwald.

“This probably has to do with the red deer, which, when they graze, eat the grass down until it’s very short”. This means that there’s no suitable habitat for small mammals that need hiding places. “This is something that’s likely to change with the presence of the wolfpack”, says Anderwald. She believes it unlikely that the deer would now visit the same pastures regularly, and if they did, then they wouldn’t eat so much of the grass.

Park employees have already discovered an indication of this: certain meadow areas this year grew higher than usual. “But this year was also especially good for plant growth overall”, says Anderwald. “We’d have to be able to observe developments over several years in order to get a reliable view of the impact of the wolves”. But it is quite possible that they are already indirectly ensuring that new species are becoming established.