Having previously studied wolves, coyotes, and red foxes in the wild, I was curious about the small swift fox (Vulpes velox) native to the short-grass prairies of the Great Plains. I hoped to find and photograph them, and eventually observe them as they raised their families. Knowing that the Chico Basin Ranch had swift foxes, I pitched the project to Ranchlands and got their support.
First, in order to find foxes, as with any wildlife, it is important to learn as much as you can about the animal, its identifying field marks, preferred habitat, range, den characteristics, lifecycle, foraging behavior, and other habits. So I researched numerous reports that helped at least answer some of my initial questions.
Swift foxes (along with their closest cousins the kit fox) are the smallest members of the Canidae or wolf/dog family in North America. An adult stands only twelve inches at the shoulder, less than 34 inches long head to tail, and weighing 3 to 7 pounds, about the size of a house cat and half the weight of a red fox.
Swift foxes have a tan-gray fur with rusty-orange highlights on back and sides; tan ears; creamy-white throat, chest, and belly; rusty-tan legs; black-tipped tail or brush; and black on the side of the nose. In the winter, their coat is thicker, softer, and buffy-tan without orange. For contrast, a red fox also has white cheeks, neck, chest, and belly; and black on the sides of their nose. However, they have black legs, black-tipped ears, and their tail has a white tip on the brush.
The most notable characteristic of a swift foxes is their incredible speed; at 30 to 40 miles per hour they can run down a jackrabbit. But swift foxes largely forage on rodents such as prairie dogs, spotted ground squirrels, pocket gophers, kangaroo rats, voles, and mice. They’ll catch the occasional bird, rabbit, or lizard and will scavenge carrion. During the summer, however, much of their diet consists of insects. They also eat berries, prickly pear, and a variety of seeds.
Another key characteristic, one that will make the task of finding foxes difficult, is that they are largely nocturnal for much of the year, hunting after dusk and in pre-dawn hours. The exception is during late spring and summer when they must also hunt during the day to keep their pups fed.
Unlike red foxes, swift foxes live in dens year round for safety and shelter. Last January, I started methodically surveying areas of the ranch looking for fox dens. My method included scouting an area, looking for burrows, logging each potentially active den in my field notebook, and recording the GPS coordinates. If there were signs of recent activity, I would categorize the burrows based on size and shape of the entrance, which indicates the likely occupant – fox, badger, or coyote. Areas with recent or active dens will be the best places to observe and photograph foxes and their families come springtime. I also hoped to learn more about the swift fox’s behavior and habits from how the dens are constructed and from artifacts like tracks, scat, feathers, or bones left outside the dens.
If you want to find swift fox dens, the best places to look are on the outskirts of prairie dog or ground squirrel colonies. They seem to prefer loamy soil or compact sand, with sparse vegetation that is easy to dig. They avoid areas with tall grass, dense sagebrush or cholla, preferring instead areas with an open vista and gentle slopes along a rise, hummock or ridge that affords them good visibility and mobility. In some cases, swift foxes seem to prefer making their dens near roads, possibly because coyotes tend to avoid the roads. Eventually I became pretty good at identifying the best areas to search.
When I am scouting for den sites, I look for such areas and scan for bare dirt excavated in a tailing outside the burrow. You won’t always spot mounded tailings at a den though, as many foxes tend to spread the excavated dirt widely. Entrances are circular or keyhole in shape approximately 7 to 9 inches in diameter. There is often more than one entrance, especially for natal or pup-rearing dens. Single-entrance dens are usually shelter dens used for escaping predators, icy winds, and broiling sun. Foxes will dig their own dens, but will sometimes dig out an old prairie dog or badger burrow.
Most areas are devoid of fox dens, even if the habitat looks good. But in some areas, I would find burrows in sparsely distributed clusters. These areas tend to be associated with a single family group. Swift foxes maintain multiple dens sites in a core area, a territory they will defend against any interloping foxes. A core area ranges from about one-half to one square mile. Depending on the study, their home range or hunting ground is estimated at about 3 square miles to 13 square miles. Home ranges may overlap with other fox families, but not their core area. Within a core area, the maximum span between dens for a given breeding pair is about 500 yards. I realized this was an important clue because all the den sites I find in an area of about a half-square mile will probably belong to the same family. When families move, I had a rough idea of the distance I needed to search to find them again.
With some help from Tim Leppek and Bill Maynard, I identified ten areas on the ranch with potentially active dens, confirmed from fresh digging, scat, dead prey, or tracks in fresh snow. And by back trailing new tracks in the snow I found a couple of new dens. By April I had set up game cameras to confirm the presence of swift foxes. We directly observed foxes in six of those areas, but some were seen only briefly.