Colorado State University Study Looks at Reproductive Inhibitorsas Possible Control for Prairie Dogs

Does a sterile prairie dog still act like a prairie dog?

Associate Professor William Andelt hopes to find out in a study that begins this month on Fort Collins open space and neighboring areas where prairie dogs make their homes.

The study, in cooperation with the U.S. Department of Agriculture’s National Wildlife Research Center in Fort Collins, will investigate whether surgically castrated male prairie dogs still fill the designated role as defender of their home territory.

If sterilization does not affect prairie dog behavior–and pilot studies have shown that it does not–Andelt and graduate student Aaron Schwartz believe that special baits or other nonsurgical methods that cause sterility in prairie dogs could be a more acceptable way of controlling the population than with lethal means, such as poison bait or fumigation. "We’re not doing this to see if surgical castration is a viable management tool for prairie dogs, because it would be impractical on a large scale," Andelt said. "We want to find a nonlethal way of controlling prairie dog populations– particularly near urban areas of Colorado and the West, where part of our public objects to poisoning them. That kind of approach is in the best interest of the public and the prairie dogs, because these animals can grow dramatically in number while habitat diminishes."

This month, the researchers will begin marking over 200 male and female prairie dogs. About 40-50 of the males will be trapped and will undergo surgical castration under anesthesia, performed by licensed veterinarians. Each prairie dog will receive an analgesic after surgery, then released the same day to prevent other males from taking over their territory.

During the study, Andelt and Schwartz will monitor the castrated and uncastrated prairie dogs in the wild to see if lower testosterone levels brought on by the surgery changes male behavior. They also will determine if castrating yearling and adult males increases or decreases dispersal of juvenile males from prairie dog towns and if castrated males have a greater or lower tendency to disperse. It is typical for young males to leave home and start a new one in another location. The researchers also plan to monitor the marked females to determine if they are bred by other unsterile males.

Prairie dogs live in colonies commonly referred to as prairie dog towns. Small groups within the prairie dog towns, called coteries, are generally composed of one or two adult males, three adult females and six offspring. It’s the responsibility of adult males to fend off potential invaders–including other male and female prairie dogs–but the adult females and yearlings of both sexes also help.

Andelt and Schwartz do not think sterilization will have much impact on prairie dogs, other than to possibly control their numbers. In a pilot study this summer, five castrated male prairie dogs showed no signs of behavioral changes by continuing to defend their coterie territories, Andelt said. In fact, some of the castrated prairie dogs were seen making territorial calls the same day of surgery–an indication that surgery caused little discomfort and that territorial tendencies were still intact.

Controlling prairie dog populations has been controversial in Colorado and the West because of the three options used: reducing populations by lethal means, relocating problem prairie dogs to new habitat or excluding them with barrier fences, which has not been completely successful.

Currently, an estimated 5 million prairie dogs occupy about 1 million acres of rangeland in Colorado. Rapid development is taking place in areas that once were prime prairie dog habitat, making relocation an even more remote option than it was in the past. Few landowners want to accept relocated prairie dogs because the animals compete with livestock for forage or sometimes transmit plague to pets and humans. As development continues, encounters between humans and prairie dogs also is becoming a public health concern. Prairie dogs, which are hosts for fleas, occasionally carry bubonic plague. Domestic cats can transmit the plague to humans via flea bites or by breath, sometimes causing death.

However, prairie dogs are an important food source for several species, including the endangered black-footed ferret, badgers, coyotes and birds of prey. Their burrows serve as homes for burrowing owls, cottontail rabbits, rattlesnakes and other animals.

Exacerbating the problem is the prairie dogs’ stealth reproductive abilities. Each female usually gives birth to three to five pups each spring, enabling a colony to grow by as much as 30 percent each year.

Andelt hopes that eventual use of reproductive inhibitors will strike a balance between the need to control prairie dogs that are a threat to public health with the need to keep healthy prairie dog populations part of Colorado’s natural environment.

Andelt said other scientists are currently working on reproductive inhibitors that might specifically target prairie dogs. Reproductive inhibitors are being developed for horses and deer, but these have been delivered by injections, darts or biodegradable bullets. A future challenge will be to develop a practical way to administer reproductive inhibitors to prairie dogs, such as through baits.

"We need to treat animals as humanely as possible. We think this approach could really help sustain healthy prairie dog populations in Colorado and still prevent them from being a threat to public health or safety," Andelt explained.