Recent survey shows a largely healthy Cody elk herd, high cow/calf ratiosWritten by Saige
Cody – Most elk in the Cody area are doing well, a fact that’s been confirmed by a recent survey by the Wyoming Game and Fish Department (WGFD).
“We found the elk residing around Carter Mountain, the south side of the South Fork and Boulder Basin were characterized by high calf ratios and large sample sizes,” explains WGFD wildlife biologist Doug McWhirter. “Those herds are thriving and that is reflected in our winter herd numbers.”
Elk in the extreme north end of the herd unit, however, are characterized by lower densities and very low calf ratios. These areas, primarily in the Upper North Fork of the Shoshone River and associated areas of Yellowstone National Park, are struggling.
This year the WGFD surveyed the Cody elk herd in late summer in an attempt to determine how different segments of the herd are doing. This is the first time this survey has been done for the herd.
“We have migratory elk and non-migratory elk,” says McWhirter. “We usually do our surveys in the winter, when all the migratory elk are wintering with the non-migratory elk, so it is hard to figure out how specific populations are doing.”
WGFD flew the survey this year on Aug. 13 and 14, before elk migrations occurred and hunting seasons began.
“As opposed to our traditional winter surveys, we looked at animals where they are hunted, so we had access to the specific population segment that we are concerned with,” says McWhirter.
The WGFD looked primarily at calf-cow ratios, yearling bull ratios and mature bull ratios. Calf-cow ratios are determined by looking at the number of calves per each 100 cows.
“The numbers are somewhat meaningful, but not having done this specific survey in the past, we aren’t trying to do a count. Rather, we are looking for that ratio data,” explains McWhirter.
“We didn’t know if non-migratory elk are doing well, or how the migrants affect those numbers,” says McWhirter, noting the population around Carter Mountain saw calf ratios in the 50s, which is very high.
They also studied the herd in a remote area known as the Thorofare.
“The Thorofare is a remote backcountry area, and it is one of the specific areas we were really interested in learning about, because there are no elk that winter there,” explains McWhirter. “That area also produces the majority of the mature bull harvest, and is a very popular place for hunters.”
The results of the survey in the area showed calf ratios were better than expected.
“It was really important for us to get a handle on what happens there,” adds McWhirter. “What we found was better than expected calf ratios and yearling bull ratios. The numbers aren’t great, but it was definitely better than we were expecting to find.”
Calf ratios came in at between 25 and 30 calves to 100 cow elk.
“We were expecting to see numbers similar to the migratory elk of the Clarks Fork herd, and what we found was much better,” comments McWhirter, noting that calf ratios in the Lamar Valley where migratory elk from the Clarks Fork herd summer, hit in the mid-teens.
McWhirter says this information is useful for assessing elk populations for management, and the WGFD will continue to replicate the survey to gather some trend data, although the surveys are dependent on funding.
“When we have the information that paints a trend, it is a lot more meaningful than data for one particular year,” McWhirter notes. “We plan to gather some additional information, but what we learned from this one survey was extremely revealing.”
A similar survey was done in the Clarks Fork elk herd for four years, and McWhirter anticipates doing a “spot check” in the future to see if trends have changed. The impetus for conducting a preseason survey in the Clarks Fork herd was to look for the presence of significant predation on elk calves, largely by grizzly bears, but also by wolves.
“Those calf ratios are very low. When we see low calf ratios by August and September, that is almost undoubtedly a signal of bear predation,” explains McWhirter. “The bears hit the calves at a very young age. We’ve noticed that in the Lamar Valley, and we were interested in seeing how predation may be affecting the Cody herd unit.”
McWhirter notes that surveys of the Clarks Fork herd were part of a larger study called the Absaroka Elk Ecology Project, a collaborative effort by the Wyoming Cooperative Fish and Wildlife Research Unit, WGFD and the U.S. Fish and Wildlife Service.
The project, which began in January 2007, aims to study the behavior, physiology and demography of the Clarks Fork elk herd in the Absaroka Range. The data has found that decreased pregnancy rates of cow elk as well as calf predation has lead to lower herd productivity.
The project has focused on identifying the factors limiting pregnancy rates, and, more broadly, at improving understanding of predator influence on prey and influence on elk migration in the Greater Yellowstone Area. The Absaroka Elk Ecology project anticipates a completion date in 2012 and 2013.
“The surveys in the Lamar Valley were part of that project, and we took some of what we learned from those surveys and are applying it to the Cody elk herd,” says McWhirter.
“Determining adult female survival rates was one of the biggest findings as far as elk management we learned from that project. If we remove hunting from the equation and just look at natural mortality, the survival of adult female elk remains quite high, even in areas of significant wolf and grizzly densities,” explains McWhirter.
“It is less than what we see in an area with no predation, but remains high enough to maintain and build hunting opportunity and population sizes.
However, significant calf mortality rates due to predation don’t produce a surplus for hunting, so hunting opportunities are diminished,” continues McWhirter.
The Cody elk herd occupies the north and south forks of the Shoshone River, the headwaters of the Yellowstone and areas north of the Greybull River and has an estimated population of between 6,000 and 7,000 elk.