Deer-Coyote Study

by: Brent Patterson, Biologist

When coyotes made their first appearance in Nova Scotia in 1977, many people were concerned about the potential impact this predator would have on the province's ecological balance and, more specifically, its white-tailed deer population. Passions about coyotes have since cooler somewhat, though not the need to find out more about them and their effects on Nova Scotia wildlife. The spring of 1997 marked the end of five years of field work for the Department of Lands and Forestry' deer-coyote-habitat ecological study. This study was designed to examine the relationship between deer, coyotes, and their habitat especially under different winter weather conditions such as deep snow or cold.

The study was conducted in two areas. The first contained the Eden Deer Wintering Area (DWA) near River Denys on Cape Breton Island. Winters there are relatively severe and the Eden DWA has historically contained a large number of deer during periods of heavy snow cover. The second study area was located in Queens County, partly within Kejimkujik National Park and extending to the east of the Park. Winters are typically less severe in the area and deer do not normally congregate in the DWA.

The study showed that the winder density of coyotes was approximately 6/100². Many people probably think coyotes are more numerous than this. However, it is important to remember that two sets of tracks observed six to seven kilometers apart on the same day could easily have been left by the same animal(s). We believe that our estimates accurately reflect coyote densities in forested areas, however we suspect that densities may be considerably higher in agricultural areas.

Two methods were used to gauge minimum annual deer losses to coyotes. The first involved estimating how many deer each pack killed per year using intensive snow-tracking in winter and scat analysis during the rest of the year. The second method was to monitor collared deer. During the course of the study, 124 deer and 50 coyotes were captured and radio-collared. On average, about 10 per cent of the collared deer were predated each year. Interestingly, one deer was killed by either bobcat or lynx for every two killed by coyotes. In the Cape Breton study area, human harvest (registered, illegal, and native harvest combined) took about the same proportion of deer as predation, though many of the deer in that area were protected within the National Park. Winter kill was only a minor factor, however the last few winters have been fairly mild.

To properly assess the significance of coyote predation on a deer population, consideration must be given to the sex, age, and physical condition of deer killed by coyotes. During this study coyotes did not show a preference based on these factors, but rather appeared to kill deer in proportion to their occurrence in the local populations. This is often the case when prey populations exist at relatively low densities. Given the mild winters and low deer numbers in Nova Scotia recently, most deer killed by coyotes during the study likely would have survived and reproduced in the absence of coyotes.

Overall, it was estimated that coyotes were removing 4 to 18 per cent (depending on the year/area) of the postnatal deer population (the total population immediately following the birth of the current years fawns). We believe that during recent years in the Eden area, deer and hare numbers have been high enough (and the winters mild enough) to make the effects of coyote predation on deer population dynamics relatively minor. Deer numbers in this area should continue to increase during the next few years barring one or more severe winters. In the Queens County study area, predation on deer has decreased in recent years as coyotes have switched to the slowly increasing hare population. However, deer population growth is still quite low. Extensive predation on fawns in summer may be a major factor in this lack of growth. Eventually, hare numbers should become high enough to cause coyotes (and bobcats) to switch most of their feeding activities from deer, to hare.

From a scientific point of view, this study has given a variety of information that helps better understand deer-coyote-habitat relations in Nova Scotia. This improved knowledge will allow the Department of Lands and Forestry to continue to improve its management of Nova Scotia's wildlife resources.

Some of the factors which strongly influence coyote predation rates on deer are as follows:
  1. Snowshoe hare density - More hare generally means less deer killed by each pack.
  2. Winter severity - In a more severe winter, coyotes will switch from hare to deer if they are vulnerable.
  3. Deer Density - Deer density is very important in determining the outcome of coyote-deer relations. Although coyote numbers will generally increase when there is more food available, the changes do not come close to matching potential changes in both deer and hare numbers over the span of several years.
  4. Farm Carrion - In the Queens County area, the study showed that coyotes living in areas with relatively few deer and hare can still thrive if they have access to domestic carrion. In areas such as the Annapolis Valley, where carrion is readily available, coyotes exists at high densities and yet prey on relatively fewer deer than coyote populations living in "wilderness" areas.