Track Plates Baited with Scent Attractants as a Method to Survey for Black-Footed Ferrets: A Pilot Study

1. What they did

Black-footed ferrets were thought extinct in the mid-1970s until a small population was found in Wyoming in 1981. Ferrets were reintroduced into the Aubrey Valley Experimental Population Area in north-central Arizona from March 1996, and by 2001, 144 ferrets had been released there and 7 wild-born kits found. The Arizona Game and Fish Department (AGFD) monitored them with yearly night spotlighting surveys and occasionally telemetry, but ferrets are elusive, rarely seen at night, and the area is large. The authors ran a pilot study to see whether baited track stations could detect ferrets.

• The track station. Each station was a tube of ultraviolet (UV) resistant plastic (PVC) pipe, 76.2 cm long and 15.24 cm across, set on short wooden legs, meant to look like a tunnel or burrow. Inside sat an aluminium plate painted with blue carpenter’s chalk mixed with ethanol. A sheet of white contact paper, sticky side up, lay across the middle, so an animal walking through picked up chalk and left a blue print on the paper.
• The baits. Three baits, none tested before, were tried in turn: urine-soaked bedding from non-breeding captive ferrets at The Phoenix Zoo; bedding from breeding ferrets (females in estrus and males in breeding condition); and prairie dog parts, which are used to trap wild ferrets in Aubrey Valley. Bedding was held in a nylon stocking under the plate and dampened with water to refresh the scent.
• The layout. Twelve stations were placed 200 m apart in a grid in the area where spotlighting had found the most ferrets, alternating “male” and “female” scent stations. Each was covered with burlap, staked down and marked with a flag, and its Global Positioning System (GPS) location recorded.
• Checking and identifying. Stations ran for 155 nights (January to July 2002) and were checked in the daytime, at least weekly and often every other day. Prints were covered with clear contact paper, labelled and saved. To help identification, reference prints were collected from captive male and female ferrets and a Gunnison’s prairie dog, prints were measured, and a field guide (Murie 1982) was used. All field biologists agreed on any questionable tracks.

2. What they found

• No definite ferret tracks were recorded with any of the three baits.
• Prints were collected 69 times in all: Peromyscus mice 38, unidentified animals 20, cottontails 7 and Gunnison’s prairie dogs 4.

Bait

Peromyscus

Cottontail

Prairie dog

Unknown

Total

Non-breeding urine (72 nights)

13

2

0

6

21

Breeding urine (77 nights)

18

5

2

9

34

Prairie dog parts (6 nights)

7

0

2

5

14

• One possible ferret track was seen on a plate in February, but it had not transferred to the contact paper, was smudged, and could not be saved or confirmed. It was not repeated.
• Twice, with the first (non-breeding) bait, plates had been pushed out of the tube, with large smudges that looked like nose prints, probably from an animal trying to reach the bait. Some unknown prints looked like rabbit tracks.
• Once a young cottontail ran out of a tube where they had been sheltering. With the prairie dog bait, the contact paper was chewed three times and scratched once.
• Ferrets were seen on 17 occasions during spotlighting surveys on the edge of or inside the track plate area, some within 5 m of a plate.
• Captive ferrets at The Phoenix Zoo readily ran through the same station design and left prints.
• The prairie dog bait lasted only about 3 nights before attracting flies; the bedding kept its scent for about 2 to 4 months.

3. What they concluded

• This track plate design collects good prints from many animals, but the approach is not suitable for wild ferrets: the stations did not attract them.
• The chalk medium was probably not the cause, because damp conditions, which spoil chalk prints, are rare in Aubrey Valley.
• Site selection was probably not the cause, since ferrets were seen near the plates.
• Survey length was probably not the cause: it was longer than the 11 to 22 days suggested in earlier work. Ferrets may be harder to attract in summer, as martens are.
• Station design may be the reason. Wild ferrets may not explore unfamiliar objects, even with a round opening and attractive scent. Burying the tubes so that only the entrance and exit show might mimic a burrow better.

4. How tracking was or was not used

Tracking was the survey method. Animals were identified from footprints left on chalked plates and contact paper. The team compared field prints with reference prints made by captive ferrets and a prairie dog, measured print width and length, and used a tracks field guide. They note, citing Luce and others (2000), that prints look different on track plates than in mud, sand or snow. No trailing was done.

5. Tracker or observer certification

Not reported. The plates were checked and interpreted by different field personnel, and all field biologists agreed on any questionable tracks, but no tracking qualification or test is described. This matters here because a single smudged, possibly ferret print and 20 unidentified prints could not be confirmed.

6. Other technologies, skills or innovations

• A tubular track station adapted from a rainproof design used for squirrels (Drennan and others 1997), with a removable aluminium plate held in place by wooden supports.
• Blue carpenter’s chalk in ethanol (237 ml to 3.785 litres) as the track medium, which can be refreshed in the field. Primed plates failed because the ethanol dissolved the primer; unprimed aluminium worked.
• Sticky contact paper to lift prints, then clear contact paper to preserve them as a reference collection.
• Scent baits from captive animals in nylon stockings.

7. Implications for conservation (from the paper)

• The national recovery goal is 10 or more separate, self-sustaining ferret populations, and very little was known about the reintroduced and wild-born ferrets in Aubrey Valley. Detection surveys could help direct spotlighting and other surveys to where ferrets are, and reveal dispersal and movements.
• Track stations are cheaper, less labour intensive and lower risk to animals than mark and recapture methods, so they could suit sensitive species, but this design did not detect wild ferrets.