Variation of Insect Assemblages in Fox and Marten Faeces Collected in Southern Poland

1. What they did

Red foxes and martens often live side by side and eat much the same food. Insects turn up often in their scats, but most diet studies lump them together as an “unrecognisable” fraction. Because many insects live only in particular habitats (meadow or forest, for example), the authors asked whether the insects in a carnivore’s scats could show not only what they eat but also where they feed, and how fox and martens differ.

• Collecting scats. In 2003 and 2004 they walked transects along forestry roads in two national parks in southern Poland, twice a month, and collected only fresh scats of red foxes and martens: 200 in Ojców National Park and 150 in Gorce National Park. Pine and stone martens are both common there, and their scats cannot be told apart by how they look, so all marten scats were recorded as “marten”.
• Choosing the sample. To avoid a few individual animals dominating the results, they picked 45 scats at random for analysis.
• Sorting the remains. Scats were frozen, washed through a fine sieve (0.5–1 mm mesh) and sorted into food categories. Insect and other arthropod remains were identified to species using reference collections from each park, and individuals were counted from parts such as heads, the shield behind the head (pronotum), and legs.
• Analysing them. They estimated how many species they might expect to find, grouped the insects by their ecology (meadow, forest, nest-building, carrion feeding and so on), and used ordination methods to see what best explained the differences between scats. They also compared diet breadth, beetle sizes, and how closely the beetles in scats matched the beetles living in the forest.

2. What they found

Insects in the scats

• They identified 30 species of arthropods, mainly beetles and wasps. The species curve was close to levelling off, suggesting most of the species expected in the area had been found.
• Ground beetles of the genera Carabus and Pterostichus were the most often found.
• Earwigs, a nest-building insect, turned up in a quarter of the marten scats from Ojców (39 earwigs in all), and always in large numbers.

What separates fox from marten

• Which predator left the scat (fox or marten) explained most of the variation in the insects found, more than which park it came from.
• Foxes ate more forest insects, larger insects, and carrion feeders such as the carrion beetle Silpha atrata, which the authors take as a sign that foxes eat decaying meat more often.
• Martens ate more meadow insects and nest-building insects, such as earwigs, bumblebees and large grasshoppers or crickets, and smaller insects overall.
• Insects were more abundant and varied in the scats from Ojców.

Diet breadth and choice

• Foxes had a broader insect diet than martens.
• The ground beetles in marten scats closely matched how common each beetle was in the forest. The beetles in fox scats did not. The authors read this as martens eating beetles as they come across them, while foxes pick certain species, not necessarily the most common ones.
• Comparing three beetle size classes (5–15, 15–25 and 25–35 mm), foxes ate significantly more large ground beetles and martens significantly more small ones.

3. What they concluded

• Identifying insects to species in scats is a useful tool for learning about a carnivore’s diet and the habitats where they feed.
• Even a small part of the diet, which some authors consider unimportant, can reveal differences between predators that share an area.
• Fox and martens show clear differences in the insects they eat: martens probably search for insect nests, a rich food source, while foxes choose larger beetles.
• The carrion insects in fox scats point to scavenging, although the authors note there is no method to separate scavenging from hunting, even from stomach contents.
• Few insect species were eaten equally by both predators, which supports the idea that the two differ in their feeding niches.

4. How tracking was or was not used

The study rests on finding and identifying scats. Fresh scats were collected along transects on forestry roads, and each was assigned to red fox or marten. The paper does not say how fox and marten scats were told apart, but notes that pine and stone marten scats cannot be separated by visible features, so they were pooled. No trailing or other tracks and signs were used.

5. Tracker or observer certification

Not reported. The paper does not say who identified the scats or how. Barbara Bober-Sowa is thanked for collecting some of the material. Because every result depends on which predator left each scat, the reliability of scat identification matters to the findings.

6. Other technologies, skills or innovations

• Identifying insects to species from fragments in scats, using reference insect collections from each park.
• Estimating beetle body mass from body length.
• Using the ecology of the insects eaten (meadow, forest, nest-building, carrion feeding) as clues to where and how the predator fed.