Effect of felling on red fox (Vulpes vulpes) and pine marten (Martes martes) diets in transitional mixed forest in Belarus

1. What they did

Since the late 1990s, logging in Belarus has increased sharply, and clearcuts now cover a large part of many woodlands. Grass grows up in these clearcuts and rodents become more numerous there. Red foxes and pine martens are both common forest predators with flexible diets, so the authors asked how heavier felling changed what the two species eat, and whether it changed how much their diets overlap.

They worked in two forests in Belarus with very different soils:

• A “clay” area in central Belarus, with rich soils and many rodents. Heavy felling began in autumn 1998 after spruce trees died off following a bark beetle outbreak.
• A “sandy” area in northern Belarus, with poor pine forest and few rodents. Heavy felling began in 2000.

From 1995 to 2005 they collected 1904 red fox scats and 1624 pine marten scats, mostly along the animals’ tracks and near dens. They chose years that covered both peaks and lows of Microtus vole numbers, before and after heavy logging. In the laboratory they washed the scats and identified prey by hair under the microscope, and by feathers, bones, scales and insect remains. They calculated how often each food appeared and how much of the diet’s biomass it made up, separately for the warm and cold seasons. They then measured how broad each diet was and how much the two predators’ diets overlapped. For pine martens in the clay area after heavy logging, they used diet data from another study (Shamovich 2004).

2. What they found

Red foxes

• Before heavy logging, red foxes ate mostly mammals. Bank voles were their main rodent prey, and hares (and, in the clay area, hedgehogs) were also important. In the cold season they ate much more carrion, and in the sandy area they ate many fruits in the warm season.
• After heavy logging, in both areas and both seasons, red foxes ate far more Microtus voles (4 to 18 times more, depending on area, season and measure) and fewer bank voles. Microtus voles became their main rodent prey.
• Eating more voles meant eating less of other foods: carrion, hares and hedgehogs in the clay area; bank voles, fruits, birds, reptiles and carrion in the sandy area.
• Seasonal differences in the fox diet almost disappeared after heavy logging.
• In the rich clay area the fox diet became narrower; in the poor sandy area it became broader.

Pine martens

• Before heavy logging, pine martens in the clay area ate mostly mammals, especially bank voles, and many small birds. In the sandy area they relied on fruits, bank voles, beetles and birds in the warm season, and mostly on carrion of wild ungulates in the cold season.
• After heavy logging they ate more Microtus voles and more Apodemus mice, but kept eating bank voles at about the same level.
• In the clay area, birds and medium-sized mammals almost disappeared from the warm-season diet. In the sandy area, they ate fewer fruits.
• In the clay area the warm-season diet became narrower; in the sandy area it became more diverse (by frequency of occurrence).

Diet overlap

• Before heavy logging, the two predators’ diets overlapped strongly in both areas and seasons (Morisita’s index 0.83 to 0.89 by occurrence, 0.50 to 0.88 by biomass).
• After heavy logging, the overlap dropped (0.53 to 0.76 by occurrence, 0.40 to 0.51 by biomass). The main reason was that they took different rodents: foxes switched from bank voles to Microtus voles, while martens kept taking bank voles and added Apodemus mice.

3. What they concluded

• In both forests, heavier felling shifted red fox and pine marten diets towards rodents, especially Microtus voles. This matched the rise in vole and rodent numbers in clearcuts recorded in their earlier work.
• Red foxes may be drawn to clearcuts both by more rodents and by Microtus voles, which the authors describe as easier to catch than mice and bank voles.
• Pine martens may forage less in clearcuts because they are more exposed there to larger predators such as red foxes and birds of prey (in forest they can escape up trees), and because the deeper, harder-crusted snow in clearcuts makes it harder to catch rodents under the snow.
• The two predators’ diets, which had been very similar, drew apart once logging became heavy.
• The authors expect these changes to be short-term (perhaps 10 to 15 years): as clearcuts grow into young forest, rodents seem to decline sharply, and the predators’ diets would shift again. They also suggest that the response could be very different in broadleaf forests, where logging may reduce food for rodents.

4. How tracking was or was not used

Tracking was used to collect samples. The authors say most scats were collected “on tracks and nearby dens”, but they do not explain how scats were found or how they were assigned to red fox or pine marten. The dietary analysis itself was laboratory work on scat contents, identifying prey from hair, feathers, bones, scales and insect remains.

5. Tracker or observer certification

Not reported. The paper does not say who collected the scats or how scats of the two species were told apart. This matters because the whole study rests on red fox and pine marten scats being correctly identified in the field.

6. Other technologies, skills or innovations

• Microscopic identification of prey hair in washed scats, using published hair keys.
• Telling young ungulates (up to about two months old) from older ones by their hair: roe deer fawn hair in scats is shorter, more wiry and carroty-coloured, while older roe deer hair is longer, fragile and almost colourless. Hooves of young ungulates in scats also helped.
• Biomass estimates using digestibility coefficients, to correct for small prey being over-represented when only counting occurrences.

7. Implications for conservation (from the paper)

• Logging changes the prey available to forest predators and, through that, what they eat. Changes in predator diets could shift their predation pressure on prey populations and their interactions with other predators.
• Heavy clear cutting can create heavier predation risk for pine martens in open clearcuts and make winter foraging harder for them.
• The effects of felling on rodents and their predators may be short-lived as clearcuts regrow, and may differ in broadleaf forests.