STUDY: COUGARS RESPONSIBLE FOR 75% OF ELK CALF DEATHS

Published: September 1, 2006


Cougars like this one have been radio collared during a study on elk predators being conducted via the Starkey Project.
Photo/TED CRADDOCK


- Dick Mason

- The Observer

The numbers are stunning.

Over the past 12 years the percentage of elk calves in Union and Wallowa counties that have survived to their first birthday has declined dramatically.

Once it was common to see survival rates of 30 to 35 percent. Survival rates the past five years have often been under 25 percent and sometimes dip below 20 percent.

Why?

Blame cougars not Old Man Winter.

A study of the Wenaha and Sled Springs units in Wallowa County led by Oregon Department of Fish and Wildlife biologist Bruce Johnson indicates that almost no elk calves are dying in the winter from starvation. However, the study does indicate that cougars are responsible for 75 percent of all elk calf deaths.

This may explain why elk survival rates have been falling for about 20 years in Union and Wallowa counties. The rate of decrease has picked up since 1994 when Measure 18 was passed by Oregon voters. The measure prohibits the use of dogs for cougar hunting and has led to an increase in the cougar population.

Johnson's preliminary findings are a credit to a technological innovation that helps researchers begin tracking elk calves hours after birth. The innovation, developed about 15 years ago, is a transmitter that is implanted in the vagina of cow elk. The transmitter is temperature sensitive. It transmits a slow signal until the cow gives birth. When the transmitter pops out and cools it begins emitting a faster signal.

Johnson's research team picks up signals from these transmitters during plane flights over the Wenaha and Sled Springs units. When it is determined that a calf has been born, members of the research team are sent to that location.

Once located, the newborn elk gets a radio collar. The collar tells researchers when the calf dies because it emits a faster beep when it has been immobile for four hours.

When a radio collar emits its death signal, research teams are sent to find the dead calf and determine how it died. They can determine if a cougar killed it based on things such as a bite mark pattern, Johnson said.

Johnson's team has found that bears and coyotes are killing some calves but that number is small.

In some cases it initially appears that a bear killed the calf when it was really a cougar, because bears sometimes chase away a cougar that has killed an elk calf, said ODFW biologist Scott Findholt, who is helping conduct the study.

Biologists have found bears eating radio-collared elk calves, Findholt said. The bears always ran off when they saw the biologists.

"They have never caused problems,'' Findholt said.

Biologists are learning about more than predators of elk calves through the study. They are also gaining insights into cougar behavior. Radio collars have also been attached to many cougars as part of the project, helping biologists determine the population density of cougars. Biologists believe that the Wenaha Unit has 13 or 14 cougars per 100 square miles, and the Sled Springs Unit has 9 or 10 cougars per 100 square miles.

Biologists have never found a cougar eating a dead elk calf, but sometimes they knew they were nearby because of radio collar transmissions. Once Findholt saw two cougar kittens 40 or 50 yards from a dead elk calf but the mother remained hidden.

Findholt thinks this is significant since the cougar had reason to view him as a threat to its kittens and its food yet it never appeared.

In addition to predators, Johnson's team is looking closely at the effect of nutrition on elk calf survival. To date it appears that almost all calves are getting the nourishment they need to survive.

"Starvation does not seem to be a factor. In three years we have found just one elk that has starved to death,'' Johnson said.

This calf died because it was abandoned by its mother. Johnson said this is extremely unusual.

A hard winter does not mean automatic death for elk calves, but being born after July 1 does. Calves born after July 1 have almost no chance of survival, according to study results. In fact all of the elk calves monitored in the study born after July 1 died before winter.

The few calves born after July 1 are much smaller than those born a month or two earlier, and stand out as easy targets to predators.

Calves born late are doomed but those born early have no guarantees.

"Just because you are born early is not a ticket for survival,'' Johnson said.

The study, which ends in about two years, is being conducted with the help of the Boise Cascade Corporation, whose land is being used.

The study is affiliated with the Starkey Elk Research Project, which started in the late 1980s. Johnson said the current cougar-elk study is possible because of what was learned earlier about elk productivity through the Starkey Project.