Taking to the Air to Find Foxes that Live Underground

By Jaime Rudd, WIL Scientific Aid

A collared desert kit fox just released after receiving a health exam. Photo courtesy of Deana Clifford.

Working in California’s Colorado Desert can be a challenge, especially during the summer. Daytime temperatures can average over 115°F, and the evenings seldom provide relief from the heat. Another characteristic of this low Sonoran desert is that it typically rains during both winter and summer months. The summer rains are monsoonal in nature, sometimes creating severe flash floods. Luckily, the desert flora and fauna have developed physiological and behavioral adaptations that allow them to tolerate and thrive in such an unforgiving landscape. Because these adaptations are specific to desert living, many of these plants and animals are endemic, meaning they occur only in a certain area and no where else in the world.

One such Colorado Desert dweller we have in California is the desert kit fox (Vulpes macrotis).  Desert kit foxes are equipped with large ears and long limbs for easy heat dissipation and have developed several behavioral adaptations to tolerate desert climates. One adaptation is crepuscular activity during the hot summer months. Crepuscular animals are most active at sunrise and sunset–the coolest parts of the day. Another behavioral adaptation is burrowing and den building and many desert vertebrates and invertebrates are borrow-dwelling animals.

Look at those temps! A remote camera photographs a radio collared fox in California’s Chuckwalla Valley – part of the Colorado Desert. Here, this fox appears to be entering her den to avoid the 107ºF afternoon. Photo courtesy of David Elms from our Region 6 DFG office.

Kit fox burrows, or dens, can be extremely complex with more than 15 openings that wind and turn in various directions and can be more than six feet deep!  Other dens can be simpler and may just consist of one or two entrances. Kit foxes often build multiple den complexes throughout their home ranges, and will occupy them during various portions of the year. Biologists are still trying to understand when and why kit foxes chose certain areas to create dens, but one thing is for certain, kit foxes display fidelity to the sites they choose for den building. That is, they will continuously return to dens in their home range year after year, or at least visit them periodically to make sure no one else has moved in.

Wildlife biologist and veterinarian, Deana Clifford, listens for collared desert kit foxes using a hand-held antenna (also known as a “yagi”). The antenna is connected to a small, receiver that picks up the unique frequencies assigned to each collar transmitter. Photo courtesy of Jaime Rudd.

For the past year, Deana Clifford, the WIL’s wildlife veterinarian for non-game threatened and endangered species, has been investigating an outbreak of canine distemper virus occurring in desert kit foxes along the I-10 corridor of eastern Riverside County. Since the project began in January 2012, biologists have been monitoring the collared foxes using radio telemetry – a sort of biological hide-and-seek. Typically, biologists can find collared individuals by listening to the unique frequency each collar transmits. The collars our kit foxes are wearing have two settings: active and mortality. A mortality pulses at a faster rate than a normal signal if the animal has not moved for many hours. This allows biologists to locate and retrieve the fox carcass and determine the cause of death in a timely manner. In addition to radio-collars, remote cameras have been placed at kit fox dens allowing biologists to monitor their health and physical condition.

Throughout this past summer, thunderstorms surged through the Colorado Desert, resulting in flash flooding. While it is true that this is not atypical of the desert (as mentioned earlier), it can still cause some disruptions to an animal’s regular pattern of activity. Burrowing animals are especially vulnerable because their homes are susceptible to flooding. Moving to higher ground becomes a necessity to avoid being trapped and new burrows need to be established quickly in order to be protected from predators, competitors and the weather.  It was during this time that several of our collared desert kit foxes seemed to have “disappeared.”

When a collared animal goes “off-air” (meaning they cannot be heard via radio telemetry) and seemingly disappears, it is unnerving. As biologists, we have a responsibility to the safety and well-being of a study animal and we do not want the collar to be the reason for any mishap that may occur in the animals daily activities. Additionally, these animals are part of a disease monitoring collaborative and they provide us with very valuable information. Not being able to find the carcasses means information is lost, which undermines the purpose of this effort. After several unsuccessful attempts to locate the animals on foot, it was decided that what we needed was an eye in the sky. We called upon the professionalism of warden-pilot Tom Evans. With his help, we were able to take to the sky and listen for our “missing” foxes. Thanks to Tom and all of his experience in aerial telemetry, we were able to locate and recover our missing foxes. Amazingly, we were also able to clearly see the large den complexes our missing foxes created – from the sky!

A 2-element antenna affixed to the underside of an airplane wing. Often in radio telemetry the transmitter’s signal (in this case a radio collar) often travels upward, not outward. In flat areas, such as the desert, tracking animals can become difficult because gaining enough height to receive the signal is not always permissible. That is why aerial telemetry is an invaluable aid for biologist. Photo courtesy of WIL biological volunteer, Teri Baker.

You can read about what prompted the initial disease surveillance project by following our DFG News Blog. More about recent work can be found by clicking here.

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