Selection of Winter Habitat by Bobcats (Lynx rufus) on the Quabbin Reservation, Massachusetts

1. What they did

Bobcats were known to favour broken country with dense cover, conifers and rocky ledges, but their habitat choices had never been studied closely. Over two winters, the author followed bobcat trails in the snow on the Prescott Peninsula of the Quabbin Reservation in Massachusetts, an area closed to the public with many deer and no deer management.

• Following trails. He followed 48 bobcat trails (22 in 1969-1970 and 26 in 1970-1971), covering 167 km, from December to March. To avoid disturbing the cats he back-tracked fresh trails, and he abandoned a trail if he disturbed a cat or if a radio-collared cat was nearby. About half the data came from cats of known sex and age that he had radio-collared (10) or toe-clipped (8).
• Measuring habitat use. He plotted each trail on aerial photographs, measured the distance in each of 13 cover types, and compared it with how common each cover type was to give a selection index.
• Reading what happened on the trail. He recorded prey tracks crossing the bobcat trail (only tracks as fresh or fresher than the bobcat’s) as an index of prey abundance; collected scats; recorded beds, sittings, standing stops, attempts at prey, kills, caches and carrion visits; and noted logs, animal trails and roads used to avoid deep snow.
• Measuring weather. He compared wind in hardwoods and a spruce plantation with two anemometers.

2. What they found

Cover types

• Roads (index 10.0), spruce plantations (8.0), cliffs (8.0) and hemlock-hardwoods (2.17) were preferred.
• Hardwood, exposed shore, abandoned field, pine, pine-hardwood and reservoir ice were selected against. Hemlock, pine plantations and wet areas were used about as often as they occurred.
• Road use rose from 4% of travel in the first winter to 15% in the second; otherwise behaviour was the same both winters.

Prey and food

• Prey tracks were most abundant in hemlock-hardwoods and spruce plantations (about 62 intercepts per km of bobcat trail in each). Deer made up 53% of prey tracks in 1970-1971. Snowshoe hare tracks fell by about 60% and gray squirrel tracks by 30% between winters.
• Of 43 scats, 79% held deer, 23% gray squirrel and 5% small birds and mice; raccoon, chipmunk and snowshoe hare were traces. 35% held vegetation.
• The deer in the diet came from bobcat kills, not carrion. Cats visited carrion deer 17 times and their own cached deer 16 times, but fed on 79% of cache visits against 18% of carrion visits.
• 96% of cached deer were in conifer cover types, most (six, 38%) in hemlock-hardwoods.

Hunting

• He found 20 attempts at prey (0.12 per km): nine at deer, three at snowshoe hare, three at gray squirrel, two at mice and one each at a cottontail, a raccoon and a bird (Bonasa umbellus). The most attempts (six) were in spruce plantations, half of them at hares.
• Two-thirds of the deer attempted were bedded, and two-thirds of visits to cached deer were in bedding areas. One old female (8.6 kg) circled round to stalk a bedded deer to within 2.6 m and leapt onto it; the struggle marks and deer hair showed the deer escaped.
• Beds, sittings and standing stops per km were nearly three times higher in spruce plantations than anywhere else, matching the slow hunting style used for hares. Of 34 beds in 1969-1970, 12 were hunting beds, 58% of them in spruces.
• Marked cats stayed near a deer kill for 3 to 4 days. On five occasions cats hunted in the spruces while they had fresh deer cached; one killed a mouse, appeared from the marks in the snow to have played with it, and left it uneaten.
• Half of the six successful attempts at prey other than deer were left uneaten or partly eaten and cached.

Snow and weather

• Wind in hardwoods averaged 163 km per week against 16 km per week in the spruce plantation.
• Cats walked normally in snow under 15 cm, but retreated, circled or bounded when they met deeper drifts.
• In deep snow, 40% of distance was on logs, in other animals’ trails (mainly deer, porcupine and other bobcats) or on plowed roads and snowmobile paths, against 4% in shallow snow. They walked on logs 72 times in deep snow and 33 times in shallow snow.
• After a late-autumn thinning drew deer to feed in one pine plantation, cats changed their route between two cliffs to cross there (all six cats followed in the first winter crossed north of it; all three in the second winter crossed at it).

3. What they concluded

• Food was readily available, so prey and weather alone do not explain where bobcats go; behaviour matters too.
• Hemlock-hardwood: chosen for prey, especially bedded deer, the main winter food.
• Spruce plantations: used for resting and hunting, especially for hares. As no hare kill was found, hare use did not drop when hares declined, and cats hunted there before and after feeding on cached deer, the author suggests much of this hunting was a behavioural need rather than a physical one.
• Cliffs: give shelter and seem important for breeding and other social behaviour.
• Roads: used purely to save energy in deep snow, when travelling between resting, feeding and hunting areas.
• Hardwoods, exposed shore and ice: avoided, probably because of deeper snow, more wind and colder nights, and because open cover suits stalking less.
• Pine and pine-hardwood: avoided because prey was more abundant elsewhere.

4. How tracking was or was not used

The whole study rests on trailing bobcats in snow. The author back-tracked fresh trails, mapped them, and read the tracks and signs along them: prey tracks crossing the trail and their freshness, beds and hunting beds, sittings and standing stops, attempts at prey, struggle marks and deer hair, kills, caches, scats, carrion visits, and where cats walked on logs, in other animals’ trails or on roads. Deer killed by bobcats were told apart from dog kills by the method of attack and the signs at the kill site; kills that could not be definitely attributed to bobcats were counted as carrion.

5. Tracker or observer certification

Not reported. The author did the trailing himself; nothing is said about his tracking experience or how the accuracy of his sign interpretation was checked.

6. Other technologies, skills or innovations

• Radio collars and toe-clipping identified individual cats of known sex and age.
• Trails were plotted on 1966 aerial photographs and measured with a map measure.
• Cup anemometers 0.5 m above the snow compared wind between cover types.