Caught in a Dog Fight
Competing with larger canines, the swift fox struggles to survive in its grassland home
The swift fox is the rarest wild dog in North America. Able to streak more than 35 miles an hour over short distances, it is also the swiftest. "At night, when you see one in your headlights running across the road," says biologist Axel Moehrenschlager, "it´s like a sideways flash of lightning." In the dry grasslands of the midwestern plains that it shares with its archenemy, the coyote, speed is the key to its survival. Usually, that is, but not always.
"Swift foxes blend in well with the dry grass where they´re found," says Moehrenschlager, a researcher in Oxford University´s Wildlife Conservation Research Unit who for three years recently studied the species near the U.S.-Canadian border. "If you come close to them, they´ll just sit there with their ears back flat against their head and not move even their eyes." This is obviously not typical canine behavior. "It seems to be especially characteristic of swift foxes," he adds.
As it turns out, the swift fox (Vulpes velox) has a number of traits that set it apart from its larger, more numerous and better-known relatives in the dog family, most notably the red fox and the coyote. These are only now coming to light as biologists and wildlife managers scramble to learn more about the species, which is now a candidate for protection under the Endangered Species Act.
Once plentiful in the midwestern prairies, the swift fox has declined drastically in numbers in this country during the past century and disappeared completely in Canada--a victim of traps and poisons intended for coyotes and wolves as well as the shrinking of short-grass and mid-grass prairies. Today in the United States swift foxes can be found in a narrow north-south ribbon running from Montana to Texas; in Canada, thanks to reintroduction efforts that began in the 1980s, a small but stable population now exists, officially classified as "endangered."
Habitat loss remains the chief threat to the swift fox´s survival. Scientists estimate that as much as 50 percent of the species´ historical range has been converted to cropland. As grasslands, which once covered 40 percent of the United States, disappear, the effects on native wildlife are devastating.
For the swift fox, however, new studies are zeroing in on another threat: the intricate way in which this unaggressive dog fits into the ruthless canine pecking order of the midwestern prairies.
"If through transplantations and reintroductions we put canid species together that can´t coexist, it could be a hopeless cause," says Eileen Dowd Stukel, a South Dakota state wildlife biologist. Dowd Stukel co-chairs the Swift Fox Conservation Team, a 10-state, 2-province group that is spurring the new research. "This is one canid no one seems to have anything against. It would be a shame to let it disappear from the prairie."
For a carnivore, the swift fox causes far fewer problems for humans than do the bigger wild canines, which sometimes prey on livestock. A nocturnal hunter, it feeds on mice, voles, crickets, ground squirrels and other small prey, as well as berries and seeds. An adult weighs only four to six pounds, about half as much as the more common red fox. When its fur is wet, a swift fox looks no bigger than a large house cat.
"Swift foxes seem naive and vulnerable," says Dowd Stukel. "They´re fairly easy to trap and juveniles often end up as road kill." This has led some people to label the creature "dumb fox," but far too little is known about it to justify such a conclusion. In any case, she says, "they´re at times not very shy around people, in contrast to red foxes."
The swift foxes´ relative boldness may be connected to their underground lifestyle. Unlike larger canids, they live in burrows--not only in late spring and summer when their pups are young, but year-round. When a potential threat comes into view, they usually stay near enough to a hole to dive into it. Though they change burrows frequently, swift foxes seem to be loyal to their mates, sticking together year after year, litter after litter.
"The male is extremely important in raising the pups, compared to other carnivores," says Moehrenschlager. "We saw several cases where the female died and the male still raised the pups on his own." In the only known case of polygyny among swift foxes, he adds, "we found the male was actually feeding both litters, which were more than a kilometer apart."
Moehrenschlager is impressed by how sociable the animals seem to be in their own company, even when this includes unrelated males--a highly unusual finding for any canid society. In one case that he and his colleagues observed, two unrelated males whose mates had died pooled their litters. "Both males continued looking after these pups. Somehow they were cooperating, even though theory tells you that genetically it doesn´t make sense to tolerate another male´s pups."
A captive swift fox can live 14 years; in the wild a swift is probably lucky to survive half that long. Though bobcats and golden eagles sometimes pick one off, coyotes are overwhelmingly the swift fox´s number-one predator. Refuting the old adage that we live in a dog-eat-dog world, coyotes do not always eat the swift foxes they kill. "They apparently kill them just to get rid of them," says Moehrenschlager.
Marsha Sovada, a wildlife biologist with the U.S. Geological Survey in North Dakota, has been observing the intricacies of canid competition as they apply to swift foxes. "With canids," she says, "the larger species usually dominate the next-smaller species." Even when food is plentiful for all, gray wolves, for example, at a certain density seem not to tolerate coyotes, coyotes push out red foxes, and red foxes drive away swift foxes.
In a study conducted in Kansas by Sovada and her colleague Christiane Roy, coyotes accounted for 44 percent of the swift fox mortalities in one grassland area. But Sovada suspects that red foxes, which are not known to kill or injure swift foxes, pose a serious threat to their smaller cousins. The reason: Unlike coyotes, which often hunt in groups over a large territory, red foxes are solitary hunters that regularly visit all areas of their smaller territories. As a result, encounters between red foxes and swift foxes tend to be more frequent.
Red foxes are known to harass swifts, pouncing and urinating on the ground outside their burrows. "They may be far more detrimental to swift foxes than coyotes are, even though coyotes kill them," says Sovada. The more time a harassed swift fox spends searching for a new home range, the more likely it is to be hit by a car, go without food, or be nabbed by a predator.
This canine pecking order has an interesting twist: Coyotes in sufficient numbers will drive away red foxes, to the benefit of the more unobtrusive swifts. In the three-year study Moehrenschlager conducted, the coyote population dipped temporarily when local landowners decided to reduce the dog´s numbers one year. "That year was also by far the worst of all three in terms of swift fox survival," he says.
The scientist speculates that with coyote numbers down, the red fox population increased, and that, in turn, was bad news for the swifts. "We know that red foxes can completely take over the range of other foxes, such as the arctic fox," he says. "Coyotes, on the other hand, will kill swift foxes, but there is no evidence that they necessarily eliminate them altogether."
One area in the heart of the swift fox´s historic range that has not hosted one of the animals in decades--despite ideal habitat of short grass, flat ground and plenty of rodents--is North Dakota. "Historically, we had few coyotes here," says Sovada, who is based at the Northern Prairie Wildlife Research Center in Jamestown, North Dakota. "We had even fewer red foxes. Our canid community was wolves and swift foxes." Wolves, even more than coyotes, roam too widely to bother swift foxes on a regular basis. Perhaps, if the little swift fox could institute its own wildlife management plan, it would arrange to invite a new top dog to the neighborhood.
In the wild-canid community in writer Doug Stewart´s Massachusetts town, coyotes rule.