COUGARS AND CALVES
By Dick Mason
Is a rising cougar population responsible for declining elk calf survival rates in Northeast Oregon?
A promising and much anticipated study led by Oregon Department of Fish and Wildlife biologist Bruce Johnson may go a long way toward answering this question.
For the past three years Johnson's study team has been tracking elk calves in Wallowa County's Wenaha and Sled Springs units and determining their cause of death. Johnson's study may not be completed for another two years, but his preliminary findings are noteworthy.
In 2003 his study team found that cougars were responsible for 60 percent of the deaths of elk calves monitored in the Wenaha Unit. In the Sled Springs Unit, cougars were responsible for 30 percent of the deaths of the elk calves monitored.
Johnson's preliminary findings are of great interest because many speculate that rising cougar population levels are the reason elk calf survival rates have been falling in Northeast Oregon. The survival rates have been falling for about 20 years. 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.
Johnson said that the cougar populations in Northeast Oregon have been increasing for the past 30 to 35 years.
Johnson's preliminary findings are a credit to a technological innovation that helps researchers begin tracking elk calves within hours of their birth. The innovation, developed about 10 years ago, is a transmitter that can be implanted in the vagina of a cow elk. The transmitter is temperature-sensitive. When in a cow elk's vagina it transmits a slow signal because of the elk's warmth. However, when the cow gives birth the transmitter pops out and cools. This transmitter then begins emitting a faster radio signal.
Johnson's research team picks up signals from vaginal transmitters during daily plane flights over the Wenaha and Sled Springs units. When it is determined an elk has been born, members of the research team are called and sent to the location of the newborn elk.
Once located, a radio collar is put on the newborn elk. The radio collar tells researchers when an elk calf has died because its emits a faster beep when it has been immobile for four hours.
When a radio collar begins emitting its death signal, members of the research team are sent to find the dead calf and determine how it died. They can determine if a cougar killed it by things such as the bite mark pattern on the calf, Johnson said.
Johnson's team has found that bears and coyotes are killing some calves but that the number is very small.
In some cases it initially appears that a bear killed a calf when a cougar really did. A bear will chase away a cougar that has killed an elk calf, then it will eat the calf, Johnson said.
Cougars are clearly killing a high percentage of elk calves in the Wenaha and Sled Springs units, according to the preliminary results of Johnson's study. However, this does not mean that cougars are responsible for declining elk calf survival rates.
"Cougars may be taking calves which would have died anyway'' because of poor physical condition, Johnson said.
This could be determined by reducing the cougar population in the area and then determining if elk calf survival rates change. Johnson had planned to have a number of cougars in the study area killed to see if this would impact calf survival rates.
However, a lawsuit filed by an environmental group in southwest Oregon is preventing Johnson from doing this. His research team is now determining what can done to manipulate cougar numbers and see how this impacts elk calf survival.
The cougars could be killed for the project if no federal dollars are used in the last two years of the study, Johnson said. Another option is to have the ODFW encourage more hunters to go into the area so that more cougars could be killed.
Johnson's team has attached radio collars to 35 cougars in the Wenaha and Sled Springs units as part of the study. The cougars were collared after being tracked by dogs and then tranquilized.
The radio collars allow the research team to develop a better estimate of cougars.
In addition to predators, Johnson's team is also looking closely at the impact nutrition has on elk calf survival. To date it appears that almost all calves are getting the nourishment they need to at least 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.
The calf died because it was abandoned by its mother. Johnson said that this is extremely unusual.
The La Grande husband and wife team of John and Rachel Cook are helping Johnson with the nutritional part of the study. The Cooks are with the National Council for Air and Stream Improvement.
The study is also being conducted with the help of Boise Cascade Corp., which is allowing its land to be used.
The Cooks are among many people who are assisting Johnson with the study.
"It is labor-intensive. There is a lot of field work,'' Johnson said.
The study is affiliated with the Starkey Elk Research Project that started in the late 1980s. Johnson has been with the Starkey Project for 14 years.
Johnson said the current cougar-elk study is possible because of what has been learned earlier about elk productivity through the Starkey Project.