Wyoming Wildlife magazine - 17

bears using their deer and elk license, " Thompson said.
During that same time livestock producers protecting their herds battled bears, while wildlife managers
worked to keep aggressive bears at bay. Those efforts
ran counter to Yellowstone National Park where public
feeding of park bears still was allowed.
" Feeding and viewing bears was creating a dangerous mix, " Thompson said. " Bears were food-conditioned in the area and there were human injuries.
When the park outlawed feeding bears and closed
garbage dumps, populations dropped as problem
bears were dealt with. "
Unfed bears became increasingly aggressive and
populations dwindled to just over 130 animals in
the 1970s, setting the conditions for the first listing
for the grizzly bear.
THE LISTING AND THE COURTS
The low population and ever-reducing range
prompted the federal government to place grizzly
bears on the Endangered Species List as " threatened "
for the first time in 1975. With that, the USFWS
assumed, and has maintained for the majority of
four decades, management authority over the GYE
grizzlies. Long-term monitoring and research efforts
on grizzly bears in the GYE are coordinated within

By some modern estimates, more than 1,000 grizzlies live in the Greater Yellowstone Ecosystem. (Photo by Dawn Wilson)

the Interagency Grizzly Bear Study Team (IGBST),
formed in 1973. The group is federally directed and
consists of representatives from the U.S. Geological
Survey, National Park Service, USFWS, U.S. Forest
Service, Eastern Shoshone and Northern Arapaho
Tribal Fish and Game Department and the states of

COUNTING GRIZZLIES
Population estimation is an important part
of wildlife conservation and is particularly
important for species on the Threatened and
Endangered Species List. Population abundance is one of many metrics used to determine if a species stays on or comes off the list.
Grizzly bears in the Greater Yellowstone
Ecosystem are one of the most studied populations in the world thanks largely to the formation of the Interagency Grizzly Bear Study
Team, which began its research in 1973, and
continues today with data spanning nearly
50 years.
Due to the secretive nature of grizzly bears,
early efforts were focused on the development
of population monitoring techniques that did
not require visually counting bears. Thus, finding a segment of the population that could be
uniquely identified became the goal. Researchers realized observing and counting females
with cubs of the year was a good indicator

because they could be reliably noticed on the
landscape and represent the reproduction of
the species. The numbers of these females
could then be extrapolated to an overall population estimate.
The method, used as part of the Grizzly Bear
Recovery Plan in 1993, is still used today. To
ensure the same bears are not counted twice,
a rule set is established for how females with
cubs are counted. The rule set is conservative, erring on the side of not overcounting.
If multiple females are sighted, they are only
counted as different females when there is
strong evidence to support it.
As biologists continue to gather information
and monitor the population, the methodology
has been refined. The development of a statistical formula known as the Chao2 estimator
has allowed scientists to estimate the number
of females not observed. This method estimates more than 700 bears are in the GYE.

Aerial grizzly counting north of Dubois. Taking to the air is a
common practice in estimating grizzly bear populations in the
Greater Yellowstone Ecosystem. (Photo by Daniel Thompson/WGFD)

With improvements to statistical methods and
monitoring technology, this estimator will likely
be refined in the future to reflect the current
population of grizzlies in the GYE more accurately. Some estimates place the population
at more than 1,000.
- Rebekah Fitzgerald, WGFD

Wyoming Wildlife | 17

Wyoming Wildlife magazine

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