Wild Again. David S. Jachowski
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it skimmed quickly across the prairie like a weasel relative. Hammer approached the burrow, and the ferret was still just inside the entrance, peering up from the shadows and chattering at him.
No human could take credit for rediscovering the species—that honor belonged to Shep—but few could have experienced the emotions of Dennie Hammer and Steve Martin. They experienced the career-defining moment of being the first people to see a live black-footed ferret in two years, after the last male died in captivity at Patuxent and the species was widely believed extinct. Perhaps more important, they were the first to hear the chatter of a live ferret in the wild since Mellette County seven years prior. Adrenalin mixed with panic as Dennie put his hat over the burrow while he rushed to get and set a trap. Walking up to the trap eleven hours later and seeing the ferret looking back at him, his thoughts must have been filled with that delicately marked prairie bandit. It was the almost mythical creature for which he had searched hundreds of hours across much of the western United States. This erased the ridicule from other university students who, when he said he wanted to study ferrets for his graduate degree, told Hammer he was trying to study dinosaurs. Then there was the thrill the next day of releasing the ferret that they had nicknamed “620” (after the time it was captured). They watched it scurry down the burrow after it was fitted with a small radio-transmitter collar and hoped it would stay alive so they could monitor its movements. There was so much to learn. Did ferrets here in the shortgrass prairie of Wyoming behave differently than those in Mellette County, South Dakota? Why were they here and nowhere else? And most important, how many were there? Now, finally, ferret research and conservation could begin again in earnest.
• • •
Hammer and Martin, along with telemetry specialist Dean Biggins and a handful of additional federal researchers, intensively monitored the movements of ferret 620 for the next month. They eventually found ten other ferrets in the area. Some of the mysteries of the black-footed ferret had been unlocked in the final days of research in Mellette County, South Dakota. Con Hillman and others had noted that ferrets were typically nocturnal and solitary, mostly visible in early morning or late evening. They found that adult females, on average, produced 3.4 young each year, and that the young typically first venture above ground as early as mid-July. They also learned that ferrets were most readily spotted in early fall when kits dispersed and mothers and their kits played above ground. They learned that ferrets were underground much of the winter, limiting biologists to monitor infrequent movements based on ferret tracks and diggings that could be spotted after a fresh layer of snow had fallen.
But there was still so much to learn. Because only a few ferrets were followed in Mellette County and none was observed to move between prairie dog colonies, it still was not known how and when ferrets moved between colonies. Little was known of their breeding behavior, whether females reared young alone or had help from males, how often they fed their young, or how many prairie dogs were required to sustain them. Were ferrets such efficient predators that they served as a sort of natural control for prairie dog populations, as C. Hart Merriam had predicted in 1902? Given that ferrets vanished from Mellette County, was a particular size and arrangement of prairie dog colonies required to sustain ferrets? There were still the questions of what role prairie dog poisoning had had on ferrets, and how many prairie dogs were required to support a self-sustaining ferret population.
Further, it was possible that ferrets in Meeteetse might behave differently than those in Mellette County because this newly discovered population was on the edge of the ferret’s supposed historical range. The ferrets in Meeteetse persisted on a colony of white-tailed prairie dogs, unlike the ferrets in Mellette County that lived on black-tailed prairie dog colonies. White-tailed prairie dogs were arid-environment specialists, primarily appearing in portions of Montana, Wyoming, Utah, and western Colorado. Lower rainfall meant less vegetation in both summer and winter, resulting in a species that evolved to live in more widely distributed social groups and lower densities. How did ferrets persist on sites having less prey? Did they need to travel farther, were they more competitive, and did they supplement their diet with other rodents or birds?
It was the advent of radio-tracking technology that allowed researchers to begin addressing many of these detailed questions for such a small, cryptic species. By the late 1970s, technology had advanced to the point that small transmitters could be attached with cloth collars to animals. Biologists had already identified the size, design, and weight of a radio collar that the close relative of the black-footed ferret, the Siberian polecat, could tolerate. They knew that ferrets would present a unique issue compared to other animals. Their small weight limited how large a transmitter they could tolerate without the ferret’s ability to move and hunt being hurt. Biologists knew that without a large battery, the transmitter would have limited range and lifetime. They knew that because a ferret spends more than 90 percent of its life below ground, getting a signal would be difficult at best, and it was more likely that they would have to scan continually, often in the middle of the night, for the chance to detect that a ferret had come above ground.
In addition to the technology encased within the plastic-coated transmitter capsule, for a tubular animal the design and tightening of the collar itself was critical. A collar needed to be loose enough to allow breathing and growth of the animal, tight and rugged enough to stay on, and made of cotton that would degrade so the collar would fall off over time as the battery died. This made the stress of placing a collar on a captured and sedated ferret that much more intense. Not only did you have one of the rarest animals in the world in your hands, you had to mount something around its neck that if done improperly could kill it. If it was too loose, you would risk the chance of the ferret slipping the collar, forcing a second stressful capture if you ever even saw the animal again.
For wildlife biologists, tracking an animal is typically a solitary affair conducted by a biologist with a hand-held antenna and receiver tucked under the arm, headphones sending out a hissing sound. The biologist listens for a faint beep as the antenna is panned around, and hikes from waypoint to waypoint, eventually honing in on the location of the animal and taking note of the location. Yet, because ferrets came above ground so infrequently, just detecting them required teamwork. Rather than sending a dozen biologists out onto the prairie throughout the night, three camper trailers, modified so that large directional antennas poked through their roofs, were placed on the highest points surrounding core prairie dog colonies in a triangular design. This required near-constant tracking by a team of biologists who spent hours hunched over within the trailers, rotating the antennas and scanning ferret transmitter frequencies, listening through headsets for faint electronic beeps in the hiss of static signaling a ferret had come above ground. Once a ferret emerged and was detected by one of the biologists, the biologist would relay the approximate location of the ferret to biologists in the other two trailers. When two or more trailers locked on to a ferret signal, they could accurately triangulate the location of the ferret. Over the span of weeks and months, researchers began to define the territories of individual animals, their activity patterns, and their behavioral interactions with other marked ferrets.
As a break from the trailers, researchers would swap their sedentary nightly duties and hit the sagebrush flats to find ferrets by spotlighting, searching for isolated animals on the peripheral colonies that were not already under radio-telemetry study. The researchers would move around on the prairie and capture the remaining few ferrets, recording their measurements and marking them with “passive integrated transponder” implants (PIT tags for short) injected just below the skin. These small, pill-shaped microchips are passive in the sense that they do not rely on a battery to transmit a signal like radio collars do, but instead require an outside scanner to pass within a few inches to relay a reading. With no bulky batteries to worry about, PIT tags last forever and provide a way to permanently identify individual ferrets. By finding and scanning the PIT tags of ferrets over the entire area, biologists were able to get a count of marked individuals. They could learn a minimum population size with which to assess the status of the population and follow the population through time to assess its viability.
With these tools, the small army of researchers learned that it was unlikely to see two or more ferrets together. The solitary ferrets seen above ground in January and February were likely males in search of mates, roaming their territory that overlapped one or more smaller territories of females. Seeing one male trying to maintain access and breeding