Habitat use and diet of the red fox Vulpes vulpes in an agricultural landscape in Poland

1. What they did

Red foxes have become much more common in western Poland, and they have been moving out of small woods into open fields, often close to villages. The authors studied how many foxes lived in 15 km² of intensively farmed land near Poznań with no woods at all, where they made their dens, and what they ate.

• Counting foxes in two ways. They searched for dens and checked them at least once a month. In 1999 they made extra checks and sorted each den as a breeding den, a permanent den used by a non-breeding fox, or a temporary den, judging by tracks, scats and food remains at the entrances. They assumed two adults per breeding den and one per permanent den. In two winters they also walked 40 random transects (0.5 to 1.5 km) within 24 hours of fresh snow and counted every fox track crossing the line, then converted the track count to a density.
• Den sites. For each den they recorded its location and entrance direction, and measured the distance to the nearest building, major road and other den. They compared these with 103 random points.
• Diet. They collected 163 fox scats and identified bones, teeth, fur and feathers in them, using a microscope for fur and feathers. They also recorded the remains of birds that foxes had eaten (feathers, bones and carcasses) in the study area.

2. What they found

How many foxes

• Snow tracking gave 2.1 foxes per km² in the first winter and 1.79 in the second.
• They found 76 dens over the study. Some were abandoned each year, mostly because people or natural causes destroyed them, and new ones were dug: 32 dens were in use in 1998, 38 in 1999, 44 in 2000 and 27 at the start of 2001.
• In 1999, 5 dens had signs of cubs, 23 were visited very often (permanent), and 10 (26%) were used only as occasional hiding places (temporary). The den count gave 2.2 foxes per km², almost the same as snow tracking that year.

Where foxes dug their dens

• 92% of dens (70) were on slopes: mostly the banks of drainage ditches (39), marsh banks (14) and the strips between fields (9). Eight were in trenches and piles of soil, five were dug in flat maize fields and one in a dry meadow.
• Foxes favoured slopes facing south and dug far fewer dens than expected on west-facing slopes.
• Dens were farther from buildings than the random points were. Dens also tended to be closer to each other than to random points, though this difference was not statistically significant. Distance to roads made no difference.

What foxes ate

• Voles (Microtus), especially the common vole, were the main food (67.5% of scats). Birds were frequent too, mostly medium and large ones: large birds in 22.1% of scats, medium birds in 16.0% and small birds in 9.8%.
• Plants (19.6%), garbage (16.0%) and hares (15.3%) were also common; beetles, fruits, egg fragments and one freshwater snail turned up less often.
• Of 22 bird remains found in the field, most were domestic: 12 feral pigeons, 3 hens and 2 turkeys, plus single wild birds from mute swan to reed bunting.
• Foxes were often seen digging under the fence of the city dump, and in winter their tracks leading to the dump were up to 2 km long.

3. What they concluded

• The fox density here is one of the highest in Poland. The small study area may have led to some overestimate, but two independent methods gave the same answer. The authors think the methods agreed so well because they looked closely at how each den was used.
• Only about 13% of dens were breeding dens, and dens were grouped in clumps, each with one breeding den. The authors read this as foxes living in clans (five, according to the Summary), a social system common where people strongly shape the land.
• With no woods available, foxes adapted fully to open farmland. Steep ditch banks are good for digging and hide den entrances, and the ditches were probably used as corridors that let foxes move unseen. Dens dug in open crop fields, unknown in the 1970s and 1980s, show foxes becoming partly independent of any field-edge habitat.
• Southern slopes probably keep dens warmer through the day, and avoiding west-facing slopes probably reflects the strong westerly winds in the region.
• The diet matches other farmland studies in Central Europe and Britain: mainly rodents and birds, with poultry and garbage as extra food. Taking poultry can bring foxes into conflict with poultry owners, which the authors suggest explains why dens were farther from buildings.
• Hares were a small part of the diet, perhaps because hare numbers fell with European Brown Hare Syndrome (EBHS), or because foxes switched to easier food.
• Farmland foxes are adapting like urban foxes: garbage and poultry make them partly independent of natural food, which probably drove the rapid rise in numbers. The authors also see some evidence that foxes have become less afraid of people and buildings.

4. How tracking was or was not used

Tracking was central to this study:

• Snow track counts. Fox tracks crossing random transects were counted within 24 hours of fresh snow, and the count was turned into a density estimate.
• Reading den use. Tracks, scats and food remains at den entrances were used to decide whether each den was a breeding, permanent or temporary den, which the den-based population estimate depends on.
• Scats and feeding signs. Fox scats were collected for diet analysis, and remains of birds eaten by foxes (feathers, bones, carcasses) were recorded.
• Tracks to the dump. Winter tracks showed foxes travelling up to 2 km to the city dump, and digging under its fence was observed.

5. Tracker or observer certification

Not reported. The paper does not say who searched for dens, read the signs at den entrances or counted tracks, or how experienced they were. This matters because the den-based population estimate depends on classifying dens from tracks, scats and food remains.

7. Implications for conservation (from the paper)

• Fox numbers in western Poland have risen over at least 20 years, which the authors link to oral rabies vaccination, less fox hunting and foxes adapting to human food sources such as garbage.
• Foxes taking poultry in densely populated farmland can cause conflict with poultry owners.
• Where high fox densities are expected, more detailed counts in smaller areas may give more reliable estimates.