News
Study Shows Effect of Predators
on Idaho Elk
n the past few years, some Idaho big game hunters have http://fishandgame.idaho.gov/ s within objective Leading known causes of death of female elk in the study launched its elk survival study, the 3 Female elk survival by zone. 4 of population removed by cause 3 1 Other 2 Cause of death determined to be from predation, but specific predator unknown. Includes death caused by accidents, disease, malnutrition, other predator, and unknown causes. Calves monitored from December to June. Percentages may not add up to 100 because of rounding. Survival of elk calves more than six months old and leading known cause of death, 2005-2009. on adult female
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complained that they no longer see elk in places they
have hunted for years. Idaho Fish and Game spends
more than $2 million annually tracking the state's big game
populations, and recent aerial surveys do show some elk
population declines.
But elk numbers have not declined everywhere – 10 of
Idaho's 29 elk zones
are above management
objectives for female
elk, 13 zones are
within objectives
and six are below
objectives. (See
Figure 1, next page)
Elk populations are
affected by a number
of factors, including
predators.
Since the return
of wolves to Idaho
15 years ago, Idaho's
overall elk population
has dropped by 20
percent from 125,000
to about 100,000.
To find out why,
Idaho Fish and Game
biologists have been looking closely at the effects of
predation in general on elk herds, and wolf predation in
particular. They are learning how delisted wolves will fit into
state management of big game and other wildlife species.
An ongoing study in 11 elk management zones shows that
predators today are the primary cause of death among female
elk in five zones. The zones represent the range of habitat,
hunting opportunity and predator densities found in Idaho.
In at least three of those zones, wolves are the primary cause
of death of female elk and calves over six months old. (See
Table 1, next page.)
Elk population trends depend on the survival rates of
female elk and calves.
To maintain the population, typically about 88 percent
of the breeding female elk must survive, and enough calves
must survive to
replace the adult
animals that die each
year.
Elk survival
depends primarily on
four factors: habitat
conditions, weather,
predation and hunter
harvest.
The influence
of habitat on elk
tends to be subtle.
Pregnancy rates and
calf survival may
be 10 to 20 percent
lower in poor habitat
– small changes that
can have important
consequences over
decades.
In the winter of 1996-97, unusually heavy snows arrived
early in much of central and northern Idaho. Elk mortality
during that winter was extensive, as high as 40 percent in
some herds.
In 1995 and 1996, the U.S. Fish and Wildlife Service
released 35 wolves into central Idaho – reintroducing a top
predator to the landscape. Today, wolves in Idaho number
more than 800. (See Figure 2 next page).
Biologists captured, radio-collared and monitored more than
500 adult female elk since the study began. They found the
number of adult female elk surviving from one year to the next –
survival rate – ranged from a low of 75 percent in the Lolo Zone
to 89 percent in the Tex Creek and Weiser zones (See Table 2).
Predators were the primary cause of death in five zones, and
of those, wolves were the primary cause of death in three zones
– the Lolo, Smoky Mountains and Sawtooth zones. In the other
two zones – the Elk City, and Salmon zones – mountain lions
either equaled or exceeded wolves as the primary cause of elk
deaths.
Since 1995, elk populations have declined in these five zones.
Elk numbers are below management objectives in the Smoky
Mountains, Lolo and Sawtooth zones, and within objectives in
the Elk City and Salmon zones.
Harvest was the primary known cause of death in six zones
– the Pioneer, Weiser, Tex Creek, Island Park, McCall and Boise
River zones. Elk populations declined in the Pioneer and Island
Park zones since 1995, while increasing in the Tex Creek and
Weiser zones. Elk populations in the McCall and Boise River
zones have been relatively stable since 1995.
Causes of elk calf mortality
Though most of the research focused
elk, it also evaluated calf survival and mortality in the Lolo
and Sawtooth zones.
Between 2005 and 2009, biologists captured and
radio-collared 272 six-month-old elk calves. In both
zones, calf elk survival from December through June was
considerably less than normal, which is about 82 percent.
(See Table 3)
In the Lolo Zone, deteriorating habitat and other factors
contributed to a long population decline, dropping from
about 16,000 in 1988 to fewer than 8,000 elk by 1998.
Since 1998, the numbers have dropped to about 2,000 – a
decline of more than 70 percent. (See Figure 4 on back
page)
Survival of the radio-collared six-month-old calves was
52 percent; wolf predation took nearly one-third of the calf
population
In the Sawtooth Zone, elk
numbers also have declined (See
Figure 5). Here survival of sixmonth-
old calves was about 30
percent during the study. Overall,
predation by wolves was the leading
cause of death, but malnutrition was
also an important factor during the
difficult winter of 2007-08. (In both these zones, wolfpredation was the leading cause
of death of six-month-old calves.
Earlier research shows that in some
areas predation by black bears was
the primary cause of death of calves
less than six months old.
As the elk numbers in the Lolo and Sawtooth zones have
declined (See Figures 4 and 5), Fish and Game has raised limits
on predators, reduced hunting opportunities and stopped female
elk harvest in the Lolo Zone since 1998.
Meanwhile, in some other areas elk are so numerous they are
causing trouble for landowners.
The information from this study may not apply in other parts
of the state, but it may help Fish and Game biologists evaluate
declines in other areas.
Wildlife managers have no
control over the weather and only
little control over habitat. In 2009,
however, Idaho Fish and Game
conducted the state's first regulatedwolf hunt. Hunters harvested
188 wolves in an orderly hunt
and followed the strict reporting
requirements.
Recognizing that effects of
predators on elk would increase
as the numbers of predators
increase, the Idaho Fish and
Game Commission has set a wolf
population goal at about 500 – the
population in Idaho in 2005, the year
when wolf depredations on elk herds
and domestic livestock began to rise
sharply.
Fish and Game has shown that professional wildlife
managers can manipulate wildlife populations to limit their
effects on each other and on people, as they have done with elk
that cause damage to crops or take over habitat occupied by
mule deer. They will to do the same with wolves in places, such
as the Lolo – not to wipe them out, but to reduce their effects
where elk herds are in trouble.
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