Winter Bed-Site Selection by White-Tailed Deer in Central Ontario

1. What they did

In northern parts of their range, white-tailed deer gather in winter concentration areas. Earlier studies showed that deer usually bed at night in closed forest near conifers and bed by day in sunny spots. Both kinds of bed site seem to be needed, so the authors set out to describe what makes a good day bed and a good night bed, to help managers recognize and look after critical winter habitat.

They worked in two winter concentration areas in central Ontario, Canada, in the winters of 1978 and 1979:

• Finding night beds. In the early morning after a cold, windy night (at least -10 °C with some wind), they backtracked fresh deer tracks to the beds and used signs in relation to the snow to judge how fresh they were.
• Finding day beds. They found day beds the same way, on sunny, mild days in mid- to late winter.
• Measuring each site. Conifer share of the nearest 4 trees, tree species and size, distance to the nearest tree and to the nearest live and dead branches, depth of the bed, slope aspect and position on the slope, overhead cover, signs of recent browsing, and the number of beds and fresh beds in each group. In 1979 they also measured snow depth and vegetation volume.
• Comparing them. They used two statistical methods to find which habitat features varied most and which best separated day beds from night beds.

2. What they found

Night beds versus day beds

• They measured 326 night beds and 97 day beds.
• 90% of night beds were near conifers, especially Canada hemlock. 91% of day beds were near deciduous trees, mainly sugar maple, white oak and northern red oak.
• Overhead cover averaged 85% at night beds and 13% at day beds; conifers made up 76% and 11% of the nearest trees.
• Night beds were closer to trees: 66% were within 1 m of the nearest tree, against 31% of day beds. Night beds were also closer to dead branches and next to larger trees.
• Night beds were deeper (22 cm against 19 cm), while snow around day beds was much deeper (76 cm against 36 cm, 1979 only).
• Most day beds were on south-facing (55%) or west-facing (27%) slopes. Night beds were mostly on north-facing (42%) or south-facing (29%) slopes. Most beds of both kinds were high up on slopes.
• Active beds per group averaged 3.1 by day and 2.7 at night.

Telling them apart

• Overhead cover and conifer composition alone sorted 94.3% of the 423 sites correctly into day or night beds.
• The habitat differences fell along three main lines: the amount of overhead cover and conifers, the size of and distance to nearby trees and branches, and compass direction and slope position.

Browsing and reuse

• Signs of browsing were found at 65% of day beds but only 26% of night beds.
• Several night-bed sites were used in both winters (not counted). No day beds were seen reused in a second winter.

3. What they concluded

• Night beds were similar to those in other studies: under dense, deep conifer canopy, near the trunk of a conifer and close to low branches. This combination cuts wind and heat loss and so conserves energy. Less snow under the canopy also makes travel easier.
• Repeated use of night-bed sites, sometimes over successive winters, suggests deer select specific sites.
• Open, south- and west-facing day beds high on slopes let deer warm up in the sun, reducing energy use in late winter, a critical time. Getting both kinds of bed site right should help survival and the number of young raised.
• Deep snow at day-bed sites means day-bedding areas need to be next to travel lanes kept under dense cover. Deer reached some day beds further from cover along crusted snow, snowmobile trails and roads, and in undisturbed places also bedded by day on the sheltered side of islands and the mainland.
• In central Ontario, conifer-covered ridges provided both travel lanes and night beds, and north-facing slopes, where much of the hemlock grew, were used for night beds. Aspect may matter less for night beds here than in Quebec, where deer avoided north-facing slopes.
• These wintering areas need both varied terrain and varied tree cover, and differ from the lowland conifer swamps used elsewhere. Both kinds of bed site should be considered when judging habitat, and management should aim to keep both present and well distributed.

4. How tracking was or was not used

Every bed in the study was found by tracking: the researchers backtracked fresh deer tracks in snow to the bed sites, and used signs in relation to snow accumulation to judge whether beds were fresh. At each site they counted beds and fresh (active) beds in the group, measured bed depth, and recorded signs of recent browsing.

5. Tracker or observer certification

Not reported. No tracker skill or experience is described, although finding and ageing the beds depended on reading tracks and signs in snow. M. Heimberger, D. Freele and M. Wilton are thanked for field assistance.

6. Other technologies, skills or innovations

• The point-quarter technique (nearest 4 trees) to describe tree cover around each bed.
• Principal components analysis (PCA) and discriminant function analysis (DFA), run with the BMDP biomedical computer programs.
• A 1 x 1 m plot for overhead cover, and a 6-point scale for position on the slope (1 for lowland to 6 for a hilltop plateau).

7. Implications for conservation (from the paper)

• Deer in central Ontario winter areas use both day and night beds, and management should try to keep both present, available and well distributed.
• Day-bedding areas need to be next to travel lanes under dense cover, because of deep snow in the open.
• Overhead cover and conifer composition are a simple way to recognize night-bedding habitat when assessing winter range.