Relationship Between Fecal Pellet Counts and Snowshoe Hare Density in Western Wyoming

1. What they did

Snowshoe hares are the main prey of Canada lynx, a threatened species in the contiguous United States, and lynx in the Greater Yellowstone Ecosystem (GYE) are likely the southernmost natural population in North America. Land managers need to know where hares are and how many there are. A common way to estimate this is to count hare droppings (fecal pellets) in small plots, then use a regression equation to convert the counts into hares per hectare. Because the rate at which hares drop pellets and the rate at which pellets decay change with diet, habitat and climate, researchers recommend building a local equation for each region. No equation existed for the GYE, so the authors built one for the Bridger-Teton National Forest in western Wyoming.

• Trapping grids. They set up 18 trapping grids of 9 ha each, chosen to cover a wide range of hare densities, in several forest types.
• Pellet plots. On each grid they marked 50 circular plots of 1 m², 50 m apart. In summer they counted the pellets already there (uncleared plots, built up over an unknown time), cleared the plots, and counted again about a year later (annually cleared plots).
• Counting the hares. In autumn and winter they live-trapped hares on each grid for 6 to 9 nights, ear-tagged them, and estimated the number of hares with a mark-recapture estimator. They turned this into density by dividing by the area the trap grid effectively sampled.
• Hard edges. Seven grids bordered non-forested habitat. In the snow, they saw no hare tracks going out into this habitat, so they also tried a smaller sampling area that left out the strip beyond these hard edges.
• Comparing. They related pellet counts to hare density with linear regression, and compared their equations with ones from Idaho, Montana and Minnesota.

2. What they found

Pellets and hares

• Uncleared plots averaged 46.2 pellets per plot (range 6.2 to 109.9), almost three times more than cleared plots (15.8 per plot, range 2.1 to 47.7).
• Between 1 and 64 hares were caught per grid (average 19.1). By the sixth day of trapping, more than 75% of hares caught each day had already been marked.
• Estimated density averaged 1.51 hares/ha (range 0.07 to 4.82) with the full sampling area, and 1.61 hares/ha when hard edges were left out. Some of these are among the highest hare densities reported in recent years in the contiguous United States and parts of Canada.

The equations

• Pellet counts on both kinds of plot were significantly related to hare density.
• Counts from annually cleared plots fitted much better (r = 0.94 to 0.95) than counts from uncleared plots (r = 0.66 to 0.71).
• Leaving out hard edges improved the fit for both kinds of plot (r = 0.943 to 0.954 for cleared plots and 0.656 to 0.707 for uncleared plots, from the figures). The authors describe the gain in precision as minimal.

Other regions’ equations give very different answers

For 30 pellets per plot, the Wyoming equations gave 2.96 and 2.77 hares/ha. The Minnesota equation gave 2.20, a back-transformed Idaho equation 5.63, and a back-transformed Montana equation 0.14 hares/ha. The Wyoming and Minnesota equations had similar slopes; Idaho and Montana were markedly different.

Seasonal habitat use

Where forest patches were surrounded by sagebrush or willow-meadow, the authors saw signs of hares (live animals and pellets) beyond the forest edge in snow-free periods, but these signs were noticeably absent from the same areas in winter. This suggests hares shift their habitat use with the seasons.

3. What they concluded

• Equations from other regions are not interchangeable with local ones. The authors agree with those who call for regionally specific equations, especially when accurate density estimates are needed to identify important foraging habitat for lynx.
• Annually cleared plots are recommended when a precise estimate is needed. Uncleared plots may give a coarse picture of relative abundance and distribution, but their usefulness may be limited because they were imprecise at low hare densities.
• In fragmented landscapes like this one, equations should be built both with and without adjusting for hard forest edges.
• Their equations give an important reference point for future pellet surveys in the southern GYE.
• Possible reasons for the strong fit compared with other northern Rocky Mountain studies include long trapping sessions with high recapture rates, careful trap placement, trapping mostly on snow, and a drier climate that may affect how fast pellets decay.

4. How tracking was or was not used

The whole method rests on one kind of sign: counting snowshoe hare pellets (scat) in marked plots. Observers counted and removed all pellets inside each plot, counted only half of the pellets lying on the plot boundary, and did not count pellets already incorporated into the forest floor. Hare tracks in the snow were also used to make a decision about the analysis: because no tracks were seen heading out of the forest into the open habitat beyond hard edges, the authors tested a smaller sampling area that left out those edges. They also report signs of hares (live animals and pellets) beyond the forest edge in summer but not in winter. No trailing was reported.

5. Tracker or observer certification

Not reported. The paper does not say who counted the pellets or looked for tracks, or how they were trained. Technicians, volunteers and two named field assistants are thanked. The decision about hard edges rests on not seeing hare tracks in the snow, and how this was checked is not described.

6. Other technologies, skills or innovations

• Permanent pellet plots marked with a rebar stake; counts made by rotating a marked string around the stake.
• Single-door live traps baited with alfalfa cubes and apple slices, screened at the back and sides with sticks, pine boughs or logs.
• Hares double ear-tagged and handled in zipper-topped pillowcases.

7. Implications for conservation (from the paper)

• High hare densities in parts of the southern GYE matter for whether lynx could live there and for habitat quality, yet lynx numbers in western Wyoming were low. Other factors may also limit lynx: competition with coyotes, the amount and layout of suitable habitat, climate change, past and incidental trapping, habitat connectivity, and too few lynx arriving from source populations in Montana and Canada.
• Because lynx are often too rare to study directly, hares are used as a stand-in for finding lynx habitat. Managers should be cautious about using pellet equations to identify lynx habitat until lynx prey needs are better understood.
• At low hare densities, both pellet counts and mark-recapture estimates may be unreliable. Even so, pellet counts are valuable for sorting areas into low, medium and high hare density for lynx management.
• Land managers may use the equations to monitor changes in hare numbers among habitats and during prescribed management actions.