Northeast
Washington Cougar and Deer Study
By Hugh Robinson, Ph.D. Candidate, Washington
State University
Across much of the west mule deer populations
have declined Conversely, white-tailed deer populations have
expanded in range and increased in population in many regions,
possibly in response to habitat modifications brought about
through timber harvest and irrigated agriculture.
When deer
numbers decline, deer managers adjust harvest rates or evoke
habitat management measures. When deer populations are at
their lowest, sportsmen have traditionally switched their
attention to the impacts of predators. Cougar control has
been proposed in some areas as a means to increase deer and
elk populations, and decrease risk to the public and their
property.
Predator
control has been used to reduce deer mortality, however no
study has shown a long-term relaxation of predation rates.
Once predator control is halted, predator densities frequently
recover and predation rates return to pre-control levels.
One study found that grey wolves increased by 800% over six
years following the cessation of a wolf control program in
Alaska. My own research found that in the presence of an overlapping
population of whitetails, mule deer experienced a significantly
higher predation rate by cougars and therefore population
decline, in spite of liberal hunter-harvest of the cougars.
The “apparent
competition hypothesis” predicts that as alternate prey
(white-tailed deer) numbers increase, so do numbers of predators,
resulting in increased incidental predation on native prey
(mule deer) sharing the same range. Apparent competition can
result in population declines and even localized extinction
of more limited prey in some cases. Such a phenomenon may
largely account for declines of mule deer where the two species
overlap. I believe that much of the increase in white-tailed
deer range and population is due to human induced habitat
modifications, and that this increase in whitetails is the
foundation for an increase in the cougar population. Further,
I believe that through apparent competition this increased
white-tailed deer density is resulting in unsustainable cougar
predation of mule deer.
I wish to test the hypothesis by conducting a controlled experiment
in northeast Washington. I propose to reduce densities of
white-tailed deer on treatment areas in consecutive years,
and observe changes in cougar predation on mule deer. Mule
deer will be divided into treatment and control groups based
on their choice of winter range. The numbers of white-tailed
deer in treatment areas will be reduced in late fall and early
winter, once the animals have returned to their winter ranges.
The number of animals removed will be based on the relative
abundance of each species as determined by aerial surveys
from the previous spring. White-tailed deer reductions will
be accomplished through increased public sport harvest and
special permit late season, antlerless hunts in treatment
areas, and will be overseen by the WDFW. For the 2004 hunting
season, 400 special second white-tailed deer antlerless tags
have been allocated within two small zones of Game Management
Unit 105. This is called “The Wedge Special Hunt”,
and includes Deer Areas #1030 (Flat Creek) and #1040 (Summit
Lake).
Preliminary
Results
Captures
and Monitoring: To date 26 cougars have been captured
and fitted with radio-collars including 16 adult females,
6 adult males, and 4 juvenile males within Game Management
Units 101 and 105. An additional 5 cougars (4 adult females
and 1 adult male) from a previous study have been monitored
for supplemental population data.
Mortalities:
Thirteen of the 31 radio-collared cougars have died over the
course of the study. Four animals were taken as part of the
public safety hunt to reduce the cougar population. Five animals
were taken in legal hunts (3 in British Columbia, and 2 in
Washington). One female died of natural causes and one male
was shot on a depredation tag after he killed several of a
local landowner’s sheep. One female died while recovering
from the drugs used to tranquilize her and has thus been censored
from the data. One collared female is missing and has not
been heard since December. As of May 5, 2004, seventeen cougars
remain on the air.
Emigration:
Three sub-adult male cougars have emigrated south across the
Columbia River. One returned to the Wedge and was harvested
by an elk hunter. One cougar established a home range in the
Onion Creek area and was killed in December as part of the
public safety hunt. One cougar continued southeast and is
currently 20 miles south of Priest River, ID (74 miles from
his maternal home range). Two sub-adult males have traveled
north into Canada. One established a home range near Fouqier
B.C. (85 miles north of his maternal home range), and the
other sub-adult male is now near Cristina Lake, B.C.
Predation:
To date we have found 63 deer killed by radio-collared
cougars (31 whitetails, 22 mule deer, and 10 unidentified
deer species). The average period between kills is 6.9 days
(6.3 summer, and 8.1 winter). Although fewer mule deer are
being killed, because of their lower abundance, they suffer
a higher predation rate. Based on initial indications of prey
availability, cougars on a landscape level are strongly selecting
for mule deer (statistically highly significant). This selection
is less strong when broken down into individual cougar home
ranges (i.e. what is available vs. what is selected within
an individuals cat's home range). More data are needed to
show us if cougars are actually selecting mule deer over whitetails,
or if cougars simply range more often within habitat in which
mule deer also concentrate.
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