Feeding habits and trophic niche overlap between sympatric golden jackal (Canis aureus) and red fox (Vulpes vulpes) in the Pannonian ecoregion (Hungary)

1. What they did

Golden jackals died out in Hungary by the early 1900s and have recently come back on their own. Little is known about their role in this new range, or how they share food with red foxes, which until then had been the only wild canid there. The researchers tested two ideas: that the larger jackal would eat more hoofed animals and be more of a generalist than the fox, and that the two species’ diets would overlap less as they divided up food.

• Collecting scats. Every month from December 2000 to November 2004, they walked a standard route (12.8 to 22.7 km) through farmland, forest and shrubs in southwestern Hungary and collected jackal and fox scats.
• Telling jackal from fox. They identified scats by smell, size and shape. Jackals often leave piles of scats within a circle of 1 to 1.5 m; individual scats in these piles were separated by age (if known), visible content and colour. Predator hairs found in the scats were identified under the microscope. The route was kept away from villages to avoid dog scats, and questionable samples (1% to 2%) were left out.
• Analysing diet. In the laboratory, 814 jackal and 894 fox scats were washed and sieved, and the food remains identified with keys and reference collections. They worked out how often each food appeared and estimated how much of the diet each made up by weight.
• Measuring food supply. Small mammals were live-trapped each season from October 2001 to October 2004.
• Comparing the two predators. They compared diets between species, seasons and years, and calculated how broad each diet was (niche breadth) and how much the two overlapped.

2. What they found

What they ate

• Small mammals were the main food of both. They made up about 77% of the jackal’s diet by weight and 68% of the fox’s. The common vole was by far the most important prey, followed by field mice.
• For jackals, wild ungulates (especially wild boar, mainly piglets in spring) were the second most important food. Deer appeared rarely, mostly from remains left by hunters.
• For foxes, plants (mainly fruit) were the second most important food, at about 18% of the diet by weight compared with about 6% for jackals.
• Both scavenged on wild boar and on domestic cattle and pig carcasses from a nearby dump. Brown hare, pheasant, other birds, reptiles, fish and invertebrates were eaten only in small amounts.
• No killing of livestock and no garbage eating were found.
• One jackal scat contained fox remains; whether the fox was killed or scavenged is unknown.

Prey size

• Both mostly ate small prey. Prey of 15 to 50 g appeared more often in jackal scats (76.0%) than in fox scats (64.3%); foxes ate more very small prey (under 15 g) and more prey over 50 g.

Changes over time

• After the severe winter of 2003 and the dry summer that followed, small mammals became scarce. Both predators ate fewer of them.
• Jackals switched mainly to wild boar (piglets and carcasses), domestic carcasses and plants; foxes to other birds and plants.
• Jackals switched earlier and returned to small mammals earlier, in 2004, when small mammals were plentiful again. Foxes kept eating more fruit and other foods through 2003 and 2004.
• Foxes’ diets varied more between seasons and years than jackals’ did.

Niche breadth and overlap

• Both diets were very narrow. Jackals had the narrower diet (standardized breadth 0.06 versus 0.09 for foxes), so they were more of a specialist.
• Diet overlap was high, 73% on average. It was 84% and 81% in 2001 and 2002, and fell to 60% in 2003 and 66% in 2004.
• Overlap rose as foxes ate more small mammals, but showed no clear link with how many small mammals jackals ate.

3. What they concluded

• Contrary to their first prediction, the golden jackal was more carnivorous and more specialized than the red fox, and the differences between the two species’ diets were smaller than expected.
• The high share of small rodents points to both being mainly solitary searching hunters. Jackals may have hunted wild boar piglets or injured ungulates cooperatively or scavenged them, but the paper could not tell how much was hunted and how much scavenged.
• Supporting their second prediction, the two predators reduced their high overlap by turning to different foods when small mammals were scarce. The ability to share food may help them live side by side, as close relatives can when the most important resources are plentiful.
• No evidence of competition between the two in the region has been reported, although the jackal may be the dominant competitor, being about twice the fox’s size.
• The jackal’s particular feeding habits may play an important part in its recent spread into central Europe.

4. How tracking was or was not used

The study rests on scat identification. The researchers collected scats along a fixed route every month for four years and told jackal from fox scats by smell, size and shape, using the jackal’s habit of leaving scats in piles, and confirmed with microscope identification of predator hairs in the scats. They separated individual scats within piles by age, content and colour. Scats per kilometre of route were also used as a measure of how common each species was. No following of tracks was reported.

5. Tracker or observer certification

Not reported. The paper does not say who collected or identified the scats, or how reliable the jackal versus fox identification was, although the whole diet comparison depends on it.

6. Other technologies, skills or innovations

• Laboratory scat analysis: washing through a 0.5 mm sieve, drying, and identifying bones, hair, feathers and plant remains under the microscope with keys and the authors’ own reference collections.
• Converting dry remains into the fresh weight of food eaten, with different factors for each food type and lower digestibility values where scavengers ate bone and skin.
• Live-trapping small mammals with 199 to 299 glass-doored wooden traps per session to track how much prey was available.
• Howling counts and stimulated calling to count jackal family groups (at least three).

7. Implications for conservation (from the paper)

• The spread of the jackal raises conservation and management questions, and its role in its new range is barely known.
• From a wildlife management point of view, the results did not confirm damage by jackals to ungulates or small game.
• Being able to share food resources may help the jackal and fox live together in the region.