What we learned from collaring 1000+ mule deer in the Blue Mountains
This article appeared in the January-February 2018 issue of Oregon Hunter magazine.
About two years ago, ODFW started collaring female mule deer in the southern Blue Mountains as part of a multi-year study.
The idea was to gather GPS data from collars to replace conventional wisdom on mule deer migration patterns and an older population model, to better manage Oregon’s mule deer population and tag allocation.
One concern was determining how mule deer movements actually line up with wildlife management unit boundaries. Oregon’s 67 units were originally established in the 1950s for socio-political reasons and don’t exactly line up with deer behavior, as deer can winter in one unit (when population counts are done) and spend fall hunting season in another.
According to Phil Milburn, the Malheur District Wildlife Biologist coordinating the project, some of that conventional wisdom proved true while other findings have caught wildlife managers by surprise.
“Some deer movements turned out to be much greater than we expected, particularly around Burns,” said Milburn. “Deer were migrating out of the south end of the Blue Mountains all the way to Malheur Refuge, a distance of 60 miles.”
ODFW was also not expecting the level of deer migration into the John Day Valley (including the Phillip W. Schneider Wildlife Area). “We always knew this was a winter range for a lot of deer but were surprised by the distance deer are coming from to use it,” said Milburn. “Seven different wildlife management units are feeding deer into this area. In some cases, deer are migrating over 60 miles upslope away from other winter ranges before dropping into the John Day Valley. ”
Mule deer around Enterprise and Pendleton moved the least. “If you look at the terrain where these deer live, it makes sense,” said Milburn. “In Hells Canyon, deer don’t have to migrate very far to go from winter to summer range.”
The purpose of ODFW’s study was not to change wildlife management units, but to better align tag allocation with mule deer populations in the future. The Northside and Murderers Creek Units are good examples. Deer in these units cross back and forth on either side of the boundary (Hwy 26) and then disperse into seven different wildlife management units for the summer and fall.
“We can’t really treat these populations separately,” explained Milburn. “Under the new system, we would treat the deer that winter in this area as one population and allocate the harvest back out to management units based on the movements we saw in the study. So, we’ll do our population surveys, modelling and tag allocation based on biological herd ranges, not the artificial boundary of a unit.”
Determining mortality rates was another objective of the study, Milburn said adult doe mortality rates were higher than what was expected or commonly cited in literature. Predation, disease and roadkill led the known causes of mortality. Poaching was also documented. However, the high rate of poaching documented in south central Oregon during a 2005–2011 study (where poachers killed more radio-collared deer than legal hunters) has not been seen in the southern Blue Mountains.
Preliminary data derived from this project is also being used to design and evaluate new helicopter surveys, while the mortality rate is being incorporated into improved population models. Hunters have already seen changes to tag allocations in some units, especially in response to the hard winter of 2016–17. But a few more years of data collection is needed before final population units can be determined.
ODFW is now looking to fill in some information gaps, working around the edges of the main study area to determine how many deer actually migrate these long distances. Next, the project will head to the White River Unit, which is one of the larger migratory herds in Oregon remaining to be GPS collared and studied.
The GPS collaring projects are being funded by Pittman-Robertson dollars, a federal grants program funded by excise taxes on hunting equipment, and some hunter license dollars. Like most technology products, the newer GPS collars provide greater capability at lower cost than was possible even a few years ago. “Before GPS collars, we would have had to fly around for weeks to get the information we needed,” said Milburn. “Technology has finally caught up enough for us to do this work.”
