Habitat selection by the red fox Vulpes vulpes (L. 1758) in an Alpine area

1. What they did

Very few studies had looked at how red foxes use their ranges in mountains, where habitats change quickly with altitude and the winters are harsh. The authors expected that in the Alps a fox’s range would include a mix of habitats that provide food and shelter all year, that foxes would use these habitats differently through the year, and that the link between resources and habitat would be strongest in the severe cold season.

To test this across the whole of Gran Paradiso National Park in the Italian Alps, they used fox scats as signs of presence:

• Transects. They chose 13 transects, 30 km in total, all on footpaths, crossing the park’s main habitat types and three altitude belts (1000-1500 m, 1500-2000 m and over 2000 m). Footpaths were chosen so that scats would be equally easy to find in every habitat.
• Scat surveys. Every month from August 1996 to August 1997, they walked the transects, mapped every fox scat and then removed it. They collected 922 scats.
• Use versus availability. They compared how many scats were found in each habitat type and altitude belt with what would be expected if foxes used them in proportion to their availability, for the whole year, the cold season (September to February), the warm season (March to August) and each month.
• Attendance in squares. They divided the area into 25 ha squares, close to the average fox home range reported for the park. For each square crossed by a transect they calculated an Attendance Index (scats per km of transect) and measured the share of each habitat and altitude belt, then tested which habitat features set squares with high fox attendance apart from those with low attendance.

2. What they found

Habitats and altitudes used

• Over the whole year, foxes selected dense conifer woods and dense broad-leaved woods, and avoided almost all sparse woods and open habitats such as Alpine prairies, rocky prairies and shrubland.
• The same pattern held in both seasons, except that broad-leaved woods were selected only in the cold season.
• The lowest altitude belt (1000-1500 m) was selected and the highest (over 2000 m) avoided in both seasons. The middle belt was used in proportion to its availability, except in the warm season, when it was avoided.
• Month by month, scats were spread among habitats differently from what availability would predict in every month except November, when few scats were found.
• From September to April the highest belt was almost always avoided; from May to August it was used in proportion to its availability.

Fox attendance in the squares

• Over the year, only dense conifer woods were linked to higher fox attendance. In the cold season, attendance rose with broad-leaved woods and the lowest altitude belt, and fell with the highest belt. In the warm season no habitat feature was linked to attendance.
• Squares with high attendance had more conifer woods and more of the lowest altitude belt; squares with low attendance had more sparse conifer woods and rocky areas.
• The habitat features told high and low attendance squares apart correctly in 75.8% of cases for the whole year, 72.6% in the cold season and 80.6% in the warm season. In the cold season the lowest altitude belt, shrubland and broad-leaved woods mattered most; in the warm season it was rocky areas, sparse conifer woods and conifer woods, and altitude did not matter.

3. What they concluded

• In the cold season, foxes favour low altitudes and forest. The authors link this to ungulate carrion, mainly chamois, which their earlier diet studies showed to be the foxes’ main winter food. Many ibex and chamois die in winter and spring and are found at the bottom of the valleys, while the upper altitudes offer little food then.
• In summer, food is more plentiful and varied and spread across many habitats, so food probably shapes habitat use less, and no clear altitude pattern appeared.
• The steady preference for forest all year cannot be fully explained by food. Forest may also provide resting and denning sites, or better temperatures in both winter and summer.
• Because resources change over short distances along the altitude gradient, foxes may hold “vertical” home ranges that include several habitat types, some of which become key under harsh climate. Earlier radio tracking in one valley of the park recorded such up-and-down movements.
• The authors note limits of the method: scats cannot show activity patterns or individual ranging as radio tracking can, and foxes may use footpaths to travel and mark, which could bias results. They argue that scats suited this study because they allowed a large area and many individuals to be sampled, are not affected by a few individuals’ habits, and can be mapped precisely, whereas radio locations can carry large errors in mountains.

4. How tracking was or was not used

The study rests on signs of presence: fox scats were found, identified and mapped along fixed footpath transects every month for a year, then removed so that each survey counted only fresh scats. The paper does not report following trails or using footprints, and does not describe how scats were told apart from those of other species.

5. Tracker or observer certification

Not reported. The paper does not say who walked the transects or identified the scats, or what experience they had. Park wardens are thanked for their help.

6. Other technologies, skills or innovations

• An Attendance Index (scats per km of transect) for each 25 ha square, used to compare places that foxes visited often with places they visited rarely.
• Habitat mapping from a 1:25000 vegetation map and direct surveys, measured in a Geographic Information System (GIS).