Food composition and food niche overlap of three kinds of canidae

1. What they did

Wolves, red foxes and raccoon dogs share the grassland of eastern Inner Mongolia, China, and their dens and ranges overlap to some degree. The authors wanted to know what each species eats and how much their diets overlap, as basic information for protecting and managing them.

• Collecting scats. From August to October 2007 and March to July 2008, they followed tracks in snow and sand to find scats beside dens and along trails of footprints in Dalai Lake Natural Reserve. They told the three species apart by scat size (wolf scats are wider and longer) and by where the scats were left (raccoon dogs use fixed latrine sites). In all they collected 59 wolf, 124 red fox and 134 raccoon dog scats.
• Analysing the scats. Scats were oven-dried, then picked apart with tweezers and needles. Hair, feathers, bones, teeth, claws, insect pieces and seeds were separated and weighed. Hair and feathers were examined under a magnifying glass and microscope and compared with reference samples and a hair identification manual. Birds and small rodents were not identified to species.
• Measuring diet. For each species they calculated how often each food type turned up (frequency of occurrence) and its share of the dry weight of remains. They compared the two methods, and calculated how broad each diet was (food niche breadth) and how much each pair of diets overlapped (food niche overlap).

2. What they found

Wolves

• Livestock made up the bulk of the diet: sheep and goats (36.36% of occurrences, nearly half the dry weight), cattle (10.39%) and horses (3.90%), together 50.65%.
• Small rodents (23.38%), birds, hares, plants, insects and garbage made up the rest.
• No remains of wild hoofed animals such as Mongolian gazelle were found.

Red foxes

• Small rodents dominated (76.31% of occurrences, 84% of dry weight).
• They also ate plants, birds, fishes, sheep and goats, hares, insects, shrimps, cattle and garbage, each in small amounts. The authors think the livestock remains came from scavenging dead animals.

Raccoon dogs

• Birds were the most frequent food (39.81%), followed by insects (26.39%) and small rodents (22.69%).
• They also ate plants, fishes, shrimps and mollusks. Eggshell remains near their dens suggest they eat bird eggs too, though none were found in scats.

Diet breadth and overlap

• Wolves had the broadest diet, raccoon dogs the next broadest, and red foxes the narrowest.
• The diets of wolves and red foxes overlapped most (0.4277), then wolves and raccoon dogs (0.4049), then red foxes and raccoon dogs (0.3777).

Comparing methods

• The two methods ranked foods similarly for wolves and raccoon dogs, but not for red foxes, probably because foxes ate so many rodents that the other foods were eaten only now and then.
• Frequency of occurrence can overestimate small foods such as insects; dry weight is affected by how well each food is digested.

3. What they concluded

• The three canids share many food resources, so some competition occurs, but their diets also differ enough to reduce it.
• Wolves prefer large and medium-sized animals while red foxes mostly eat small ones, even though both eat small rodents.
• Red foxes concentrate on rodents while raccoon dogs rely more on birds, insects and plants, which matches findings from Europe.
• Raccoon dogs are dormant in winter when food is scarce, which avoids conflict with red foxes. This may explain how all three species coexist in a rather unproductive grassland.
• The authors suggest wolves eat livestock because wild hoofed animals such as Mongolian gazelle are endangered, because livestock numbers are high and overgrazing has squeezed the wolves’ living space, and because of how livestock are managed.

4. How tracking was or was not used

The researchers used “snowfield tracking and sandy land tracking” to collect scats: they followed tracks in snow and sand and gathered scats beside dens and along lines of footprints. They identified which species left each scat from its size and from where it was found (raccoon dogs use fixed latrines; scats were also found beside dens and with fresh signs). No further detail is given on how the trails were followed or how many scats might have been misidentified.

5. Tracker or observer certification

Not reported. Nothing is said about who followed the tracks or identified the scats in the field, although every result depends on scats being assigned to the right species. In the laboratory, the one person who identified the food remains was blind tested twice (on 60 and 50 samples), with 99.17% and 99.13% accuracy.

6. Other technologies, skills or innovations

• Hair scale impressions viewed under a 200 times microscope, and feathers measured under a 10 times magnifying glass, compared with local reference hair and a hair identification manual.
• Blind testing of the person identifying the food remains.

7. Implications for conservation (from the paper)

• Diet studies give basic information for evaluating habitat, estimating carrying capacity and managing carnivores.
• Wolves here depend heavily on livestock, which the authors link to the loss of wild hoofed animals such as the endangered Mongolian gazelle, to overgrazing and to the way livestock are managed.