Mesocarnivores of Northern California: Biology, Management, and Survey Techniques

1. What they did

This is the manual for a four-day workshop on mesocarnivores (medium-sized mammalian carnivores) held in August 1997 at Humboldt State University, Arcata, California, by the California North Coast Chapter of The Wildlife Society. It brings together 17 short, non-refereed background papers by the speakers, edited by John E. Harris and Chester V. Ogan.

The manual has six parts:

• Introduction. A short history of mesocarnivore (“furbearer”) management in California, by Reginald H. Barrett.
• Species accounts. Forest mustelids (fisher, American marten, wolverine), aquatic mustelids (mink and river otter), canids (coyote, gray fox, Sierra Nevada red fox), “miscellaneous” mesocarnivores (weasels, skunks, ringtail, raccoon, badger and bobcat) and non-native species (red fox, ferret and feral cats). Most accounts cover description, distribution, reproduction, diet, habitat, survey techniques, conservation status and management.
• Snow tracking, by James C. Halfpenny and four co-authors.
• Aluminum track plates, by Richard R. Klug.
• Videography (remote video cameras), by Keith B. Aubry and two co-authors.
• Monitoring mesocarnivore populations, by William J. Zielinski.

2. What they found

History

• Fur hunting set sea otters in California on a “dive towards near extinction” from the late 1700s, and by 1845 beaver were “economically extinct”. Later, poisoning campaigns of the 1950s and 1960s killed many mesocarnivores, with no monitoring in place to know the effect.
• Today habitat loss is described as the main concern, and mesocarnivores have long been a low funding priority in California.

Species accounts (examples)

• Wolverines live at low densities and need very large home ranges. Resident males in Idaho averaged 1,522 km².
• Marten are easy to attract to bait and are readily detected at track plates and cameras. Their tracks in snow can be confused with fisher, and near water with mink. Tracks and a photograph of a marten found in 1996 renewed interest in the Humboldt subspecies, thought possibly extirpated.
• Mink and otter presence can easily be found by searching for tracks, scats and other signs, for example at road bridges, but the amount of sign does not appear to match density.
• Gray fox can be detected by tracks, scat or sightings, and smoked track plates work well for them. Track plates generally do not work for coyotes; siren surveys and scat counts along fixed routes have been used instead.
• Sierra Nevada red fox tracks are easily told apart from other species in their range, so snow tracking would seem to be an effective way to survey for them.
• Badger tracks can look like coyote tracks but are “pigeon-toed” with long toenail marks; digging near prey remains is the best evidence of badgers. Raccoons leave a five-toed track like a small human hand, usually in pairs.

Snow tracking

• Designed to detect marten, fisher, lynx and wolverine, in 4-square-mile (about 10 km²) sample units. Search on skis or snowshoes for at least 10 km, or until the target species is found, ideally on the second morning after snowfall.
• Survey each unit at least three times a winter. For lynx, whose numbers cycle, survey three times a winter for three winters.
• At bait stations (at least 5 kg of road-killed deer or fish), check for tracks for at least 30 days: wolverine tracks were first found after a mean of 26.7 days.
• Footprints are the basis of identification, but clear prints are often missing in snow. The authors advise examining the whole scene, following trails forward and backward, studying gaits, and casting or photographing the best prints. Snow metamorphism can make bobcat or coyote tracks look like lynx, and mistaking a gallop for a walk can make a lynx look like a mountain lion.
• The Minimum Outline (MO) measurement, which leaves out the sides of the track, is more consistent across surfaces and observers than the Variable Outline (VO). Trails are measured for stride, straddle, center straddle and trough, preferably in the walking gait on level, straight sections.
• A review of more than 40 papers found little consistency in snow tracking techniques, and the methods have never been tested for their power to detect change. Estimated cost for a 20-square-mile survey: $4,250.

Track plates

• Carbon-sooted aluminum plates record tracks either on sticky white Con-Tact® paper inside a plywood box (good for marten and fisher, and detailed enough to separate male marten from female fisher) or on a larger open plate (the only well field-tested track-plate method for lynx and wolverine).
• Run at least 12 nights, checking every other day. One cited study found a 22-day survey was needed to be 95% confident of detecting radio-collared marten whose home range held track plates.
• Track plates confirm presence only: no detection does not mean the species is absent.
• A two-survey, 30-station project costs about $5,936 with two-person crews; Klug found no advantage to two people and estimated $4,961 with one.

Video cameras

• Modified commercial video systems cost about eight times more than 35-mm Trailmaster cameras ($5,000 versus $600) but had far fewer technical problems, need no film developing, and record behaviour that single-frame cameras cannot.

Monitoring

• Mesocarnivores are hard to monitor because of their low densities. Detecting a 20% decline in a fisher index across California would need about 1,150 sample units spaced about 10 km apart.
• Detection-based methods cannot tell the sex or age of individuals.
• Zielinski suggests an “atlas” approach (presence or absence in each block of a grid over time) as a practical way to track distribution, and recommends recording habitat at every survey site.

3. What they concluded

• Mesocarnivores need attention as a whole community, not only the politically “hot” species of the moment, and progress depends on funding and on dedicated individuals.
• Survey methods (snow tracking, track plates, cameras and video) should be rigorous and standardized, because survey results may be challenged, even in court, when they affect timber harvests or developments.
• Most survey methods show presence only. Monitoring true population trends is often too costly for rare carnivores; detecting presence, then protecting the species and its habitat and prey, may be the only practical option.
• Every survey is a chance to map distribution, build a time series and learn about habitat, and none of these opportunities should be wasted.

4. How tracking was or was not used

Tracking is a main subject of the manual. The snow tracking chapter is a guide to finding and identifying marten, fisher, lynx and wolverine from tracks and trails in snow: searching routes for tracks, checking bait stations, following suspect trails forward and backward, reading gaits, measuring prints (MO and VO) and trails (stride, straddle, center straddle, trough), and preserving tracks by drawing, casting and photographing. It recommends collecting suspect scat and hair for laboratory or DNA identification. The track plate chapter covers identifying tracks recorded on sooted plates and paper, building a reference library of real track copies, and faxing unidentified tracks to a qualified biologist. Several species accounts give tracks and signs for detection (scat, digging near prey remains, distinctive tracks of badger, raccoon and red fox, and kill patterns of weasels and skunks).

5. Tracker or observer certification

Not reported. The manual is a guide, not a field study, so no observers are evaluated. The snow tracking chapter notes that becoming a good tracker takes time, and recommends field experience, learning from others (including local trappers), tracking seminars and workshops, and training from biologists experienced in tracking lynx, wolverine, fisher and marten. It warns that metamorphosed tracks can easily mislead “the inexperienced or unprepared tracker”. The track plate chapter says crews should be familiar with the tracks of potential species.

6. Other technologies, skills or innovations

• Carbon-sooted aluminum track plates with Con-Tact® paper for positive track prints, sooted with an acetylene torch.
• Remote video cameras (modified Compu-Tech RM-680) with dual infrared sensors, external flood lamps and marine batteries.
• 35-mm remote cameras (Trailmaster), scent stations, siren surveys and radio telemetry (in the species accounts).
• DNA identification from hair, scat and tissue, and bile acids to identify carnivore scat.
• Aerial snow tracking (mentioned, not covered).
• Standard data forms (Snow Tracking, Track Observation, Survey Record, Track-Plate Results, Species Detection), mapping in a Geographic Information System (GIS) and Global Positioning System (GPS) locations.
• Field safety: winter hazards and avalanches, disease risk from scats and raw chicken bait, and sooting safety.

7. Implications for conservation (from the paper)

• Habitat loss, rather than trapping, is now the main threat to California’s mesocarnivores. Snags, cavities, logs, stumps, brush piles and rock outcrops are valuable habitat features that land management has often removed.
• The Sierra Nevada red fox, Humboldt marten and other species are of special concern and need surveys to establish where they still occur.
• For rare species, surveys may only be able to detect presence; managers may then need to protect the species from harvest while maintaining habitat and prey.
• Survey and monitoring data can also support habitat models, which may help shift monitoring from costly animal surveys toward monitoring habitat features linked to viable populations.