Feeding ecology and diet

Most members of the dog family receive the majority of their calories from mammalian prey. At particular times and for particular species, fruit, insects, and other invertebrate prey are important. Every canid species observed to date has been seen trying to catch mouse and rat sized prey. While mice may be a supplementary food source for wolves, they are central in the diet of many fox species. Even a species as large as the Ethiopian wolf (C. simensis) at 38-44 lb (17-20 kg) subsists almost exclusively on small rodents. Species specialized for catching rodents have long, pointed jaws with elongated canines to maximize snapping speed and holding power. There is also a specialized behavior, the pounce, for catching rodents. The prey animal is located by sound, a rustle in the grass, and the fox launches itself upwards at an angle close to 45°, dropping down to pin the prey with its forepaws. On open ground rodents may be stalked with a final rush of 33-66 ft (10-20 m). Digging can also be effective,

Red Fox Eating Prey

A red fox (Vulpes vulpes) carries two Arctic ground squirrels (Sper-mophilus parryii) to its den in Denali National Park, Alaska, USA. (Photo by Erwin and Peggy Bauer. Bruce Coleman, Inc. Reproduced by permission.)

Arctic Fox Feeding
An Arctic fox (Alopex lagopus) chases a hare on the snow. (Photo by Tom Brakefield. Bruce Coleman, Inc. Reproduced by permission.)

particularly if a nest of newborn rats or mice is detected. Canids dig quickly and furiously using both front feet.

Rabbits and hares, the lagomorphs, feature in the diet of virtually every canid. Rabbits typically weigh from 1.1-4.4 lb (0.5-2 kg) while hares can weigh up to 10 lb (4.5 kg). In California, the 4.4 lb (2 kg) kit fox feeds primarily on the 4 lb (1.8 kg) black-tailed jackrabbit. Excluding the four or five species of specialized pack hunters, mammalian prey over 11 lb (5 kg) is usually taken only sporadically by members of the dog family. As a general rule, it is weak or young prey that are taken. Coyotes will kill young pronghorn and pairs of jackals cooperate to hunt young gazelles. Unfortunately, the young of domestic animals are sometimes vulnerable to this predation, although many studies show that lambs or calves being eaten by canids were probably stillbirths with embryonic membranes still covering the hooves.

A battle between a wolf pack and a moose weighing up to 1,650 lb (750 kg) and lasting up to several days in the snows of Nearctic winter is one of the grandest predator prey encounters left on the planet. The outcome is far from certain and the hoofs of the great deer can quickly kill an incautious wolf. Of course, it is usually the prey who are already weakened from starvation or disease that succumb. Comparable confrontations between African wild dogs and zebras (genus Equus) in Africa or Asiatic wild dogs or dholes with Sambhar deer (Cervus unicolor) in India, and perhaps the smaller bush dogs with capybara (Hydrochaeris hydrochaeris) in South America, reveal the rare cases in which members of the dog family form groups to hunt large ungulate prey. Popular opinion notwithstanding, there is little evidence that any of the pack hunters use complex hunting techniques such as setting ambushes or even relay running. By far the most common hunting behavior could be called "flush and rush." The pack moves through wooded or scrub habitat and will pursue any prey that breaks cover. These chases will seldom go for more than 1,640 ft (500 m). In open country the approach to prey can seldom be disguised and a pack's only chance is to stampede the prey and look for young or vulnerable animals that fall behind. Zebras in Africa and muskoxen (Ovibos moschatus) in the Artic that resist being stampeded and form a defensive circle will usually avoid predation. African wild dogs, wolves and dholes all have a top speed of about 35 mph (56.3 kph). The limit of the chase is set by the problem of overheating. After 3.5 mi (5.6 km), the effort of running in a wild dog has raised the body temperature to a dangerous 105.8°F (41°C) and only a special circuit of cool blood from the nose keeps the brain from over heating. Canids lack any specialized way to kill their prey (unlike the cats with their specialized throttle bite). Members of the pack will bite any exposed part, often grabbing a hind leg to topple the prey. Once on the ground the animal is usually quickly ripped open and dies quickly. All three of the main pack hunters have been seen to leap up and catch the upper lip of large prey. Once the lip is bitten the struggles of the prey are greatly reduced. (Humans

A dingo (Canis familiaris dingo) adult with pups in Queensland, Australia. (Photo by FRITHFOTO, Bruce Coleman, Inc. Reproduced by permission.)

have also discovered this and will twist a rope around the upper lip of a horse to quiet it.) Hunting is only rarely more efficient when the size of a pack goes above four individuals, but pack sizes in all the pack hunters often reach 20-30 animals. It is the very large prey items that can provide food for all the extra pack members.

Almost all members of the dog family will eat fruits and coyotes have been known to cause damage to commercial melon farms, while Aesop tells a story of the fox and the grapes. Young, dispersing canids often resort to fruit before their hunting skills in new territory are perfected. The maned wolf of South America feeds on fruit from the genus Solanum. Invertebrates are always a component of the diet of foxes. In the foxes of arid lands, where vertebrate prey may be scarce, most species will eat beetles, scorpions and spiders. The red fox of more temperate latitudes often includes substantial quantities of earthworms in its diet. In South America, the crab-eating fox (Cerdocyon thous) depends on its crustacean prey at certain times. Among non-mammalian vertebrates, any canid will pick up and eat the eggs and nestlings of ground nesting birds, and foxes may indeed kill many chickens if they get into the henhouse.

Another topic for this section is the killing of one canid species by another, "dog eat dog." In North America in particular, competition between members of the dog family may result in one species killing or driving off another. If wolves are common, coyotes are usually sparse and wolves have been seen to chase coyotes vigorously and kill them. In turn, coyotes are an important cause of mortality for the kit foxes in California, though the fox carcasses are not always eaten. To make matters worse, the small and endangered kit foxes are also persecuted by the larger, introduced red foxes.

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