Differences in Body Condition of Elk, Cervus elaphus, by Location in Yellowstone’s Northern Range
By Auri Pfeifer
University of Washington School of Environmental & Forest Sciences
Results
Introduction
•
My initial inquiry, that elk in certain locations
in northern YNP have a significantly lower BCS
than others, proved true. In BDCP, the elk have
a significantly lower overall BCS than the rest of
the study area.
• This was not in line with my prediction since
BDCP is close to Mammoth and should not
have had a lower BCS than the Lamar Valley.
• The elk surveyed in BDCP were not significantly
more vigilant than other locations.
• The amount of time elk spent vigilant had no
significant effect on BCS for any location.
In winter, Rocky Mountain Elk (Cervus elaphus) are
the main source of prey for the Grey Wolf (Canis
lupus) in the northern range of Yellowstone
National Park (YNP). Indeed, elk make up
approximately 90% of wolf kills (Smith et al. 2004).
Since the reintroduction of wolves in 1995, there
has been concern that the elk in Yellowstone are at
risk of decline both in numbers and birth rate
(Barber-Meyer et al. 2008). One way that wolves
might affect elk populations is by inducing
vigilance, which can limit foraging and lead to
declining condition. If so, then elk in areas of the
northern range where wolf risk is high may be in
relatively poor condition.
Differences in BCS by location
Male elk interacting with a wolf yearling
Hypothesis
•
Lone female elk
I first wanted to see if certain locations
within the northern range of YNP would
yield a statistically significant lower Body
Condition Score (BCS). Upon finding
differences between the locations, I formed
the following hypothesis:
• Elk in risky locations would have a lower
BCS due to spending more time vigilant.
• I predicted that you would see elk spending
more time vigilant and have a lower BCS in
locations furthest from Mammoth (where
there is the most human development and
low wolf predation risk). Specifically, I
predicted that the Lamar Valley would have
the lowest BCS.
Discussion
Fortin said that the time elk in YNP spent vigilant reduced their
ability to forage, (2004). A lower ability to forage should in theory
yield a lower BCS. One reason this was not the case could be that we
are missing several ratings of BCS for elk that were surveyed. It is
possible that individuals that were recorded as being vigilant often
were not close enough for a BCS, but would have been given a low
score. Also, many of the sample sizes were small. In later years, the
larger sample sizes for each location may yield more significant
results. For future research I suggest raising the occurrence of
surveys in locations away from Mammoth (this is where the majority
of the follows were done) and selecting elk that you can adequately
measure their BCS.
Acknowledgments
Materials and Methods
Vigilance and condition data were collected in March from 2012 to 2015 in the Northern Range of
Yellowstone National Park as part of ESRM 459 (Wildlife Conservation in Northwest Ecosystems). Each
year, students in this class conduct elk focal follows at locations off of highway 89 and highway 212. The
follows involve observing between 1 and 4 individuals at a location for 15 minutes each. During these 15
minute intervals, we record what action the elk was doing (vigilant, foraging, resting, traveling) every 30
seconds. To determine the condition of the individual elk that was being surveyed, we used binoculars to
examine their ribs, spine, hip bone / rump, tail head, and belly. Each category was given a Body
Condition Score (BCS) of 1-5, 5 being the highest. While evaluating the environment and surroundings,
we recorded what location we were at, the gender of the individual, the size of the herd, the gender
composition of the herd, and the date. We divide the Northern Range into several sections – Mammoth,
Blacktail Deer Creek Plateau (BDCP), Hellroaring, Tower Junction, Slough Creek, and Lamar Valley.
All of this data was entered into excel. From there I conducted several two-tailed t-tests to determine if
there was a significant difference between the locations we surveyed. I regarded a P-Value of 0.05 or
below as significant.
Aaron Wirsing and John Marzluff in
YNP
BDCP is closer to Mammoth than I predicted the location with the
lowest BCS would be.
I thank Aaron Wirsing for
going on the trips to
Yellowstone and assisting me
with my capstone. I also thank
the instructors John Marzluff,
Monika Moskal, and David
Manuwal for driving and
assisting the groups with the
surveys. Lastly, I thank all the
students who contributed to
this project by doing the elk
follows.