Black-tailed deer ecology in Oregon

by Jeff Barnard, AP environmental reporter in SW Oregon for 30+ years (now retired)

I have decided to make my first hunt for black-tailed deer in southwestern Oregon. I can hunt fairly close to home this way. I plan to pick one or two wildlife management units to focus on, and will scout them in September, during the month before general rifle season begins the first weekend in October.

To learn more about these deer, I have been reading Louis G. Terkla’s book, Hunting Black-Tailed Deer, An Oregon Perspective. (I bought it on Amazon.) Though it was published in 1992, I think a lot of the advice is still good. It covers deer behavior and habitat, going about your hunt, field dressing, butchering, and even cooking. I have also been reading the Black-Tailed Deer Management Plan from the Oregon Department of Fish and Wildlife. This is more recent information, since it was adopted in 2008. And it covers habitat, population trends, hunting seasons, foods deer eat, diseases, predators and other mortality factors. You can find it on the ODFW website.

A deer fawn collared in the Umpqua National Forest earlier this year as part of ODFW’s study. Photo by ODFW.

Black-tailed deer are tough to study, and they are not endangered, so not a lot has been done with them. But there is a major study going on now that biologists hope will produce accurate population estimates, as well as a better understanding of how the current habitat affects deer behavior and survival.

The management plan will tell you that blacktails are the predominant deer species in western Oregon, from just east of the Cascade Crest to the coast, and are a subspecies of mule deer, which are bigger and live in the open steppe of Eastern Oregon. Columbian white-tailed also live on the west side, but that is another species and another story.

Blacktails are generally considered well-adapted to living in the forest, but they depend on what is known as the early seral stage of forests for food. That is a scientific term for clearcuts and burned-over areas where brush, which they like to eat, has filled in. It takes several years for trees to dominate again. Old growth is considered late seral. Favorite and most nutritious foods for black tails include buck brush, vine maple, and trailing blackberry. I plan to hunt areas where these species are plentiful.

No one has a really good idea just how many blacktails are out there in Oregon. The latest guess in the management plan is 320,000 in 2004. That is down from an estimate of 452,000 in 1974. These are based on trends in longstanding surveys of hunter success, spotlight surveys, where biologists drive around at night on a standard route, counting how many deer show up in a spotlight beam, and other methods, and other techniques.

ODFW’s Wildlife Research Supervisor for western Oregon, DeWaine Jackson, says confidence in the spotlight surveys has been declining, because there is less open forest than there used to be, so it is harder to see the deer.

An ODFW researcher checks the fit of an expandable GPS collar prototype on a nice black-tailed buck in the Tioga Unit. The opportunity to collect long-term GPS data is a first step towards filling an important information gap on movements and habitat use of male black-tailed deer in western Oregon. Photo by ODFW.

Based on the hunter and spotlights survey data scientists they have, black-tailed numbers appear to have been declining since the 1980s, primarily due to loss of habitat. Jackson says the big reason behind that is changes in logging practices, on both public and private lands, and putting out wildfires.

On national forests, logging has declined by about 80 percent since the mid-1980s, when it started to become more evident that widespread logging was having detrimental effects on habitat for salmon, northern spotted owls and other fish and wildlife. To make up for the decline in timber harvest from federal lands, timber harvesting has increased on private lands, where objectives and regulations are different than on federal lands. Foresters replant after harvest, and herbicides are also applied to help seedlings outcompete weeds and brush. That has meant less food for blacktails, Jackson says. So even though you may see blacktails eating your tulips, peonies, and grass, they really get the most nutrition from brushy species.

Populations have been doing well around farming areas around Corvallis and the southern Willamette Valley, Jackson says. But he and others are working on a better estimate, based on DNA analysis of deer droppings.

The technique was first used in Alaska, but the Oregon study appears to be the biggest to date. People and dogs go out to randomly selected sites in different habitat classifications, and pick up all the deer droppings within a selected area. The areas are 600-meter transects that radiate from a random point selected in advance. Trained dogs and people walk (or climb or even crawl) through whatever habitat they need to in order to collect the droppings.

The samples are sent to a lab at Oregon State University, where analysis shows how many individual deer made those droppings. The numbers get extrapolated around the unit, based on the habitats, which are classified by ownership — national forests, BLM, state forests, large industrial forest lands, and small forest holdings. The idea is that different management practices on the different ownerships translate into different types of habitat. In conjunction with the deer dropping sampling, deer on different ownerships are trapped and fitted with radio collars, which will show survival rates, causes of death, and home range size. The home range size will help verify the density estimates from the DNA samples.

Jackson hopes to have results this fall on four wildlife management units, the Trask and Alsea units in the Coast Range, and the Dixon and Indigo units in the Cascades. Eventually, the results could be duplicated throughout western Oregon.

Radio collar studies have shown that predators, primarily cougar, take out more adult female blacktails each year than hunters, poachers and vehicle collisions combined. Predators account for 46 percent, hunters 36 percent, poachers 6 percent, and collisions 3 percent of known mortalities (when a cause of death could be determined). Disease accounts for 9 percent. There is no way to put a mortality factor on habitat, but biologists believe that is the single greatest limiting factor on population growth.

Studies are going on in Oregon and in western Washington to get a handle on how many fawns survive to adulthood. Both state wildlife agencies are trapping does and inserting radio transmitters in their vaginas, which fall out when the does give birth. That tells scientists where the fawns are, so they can trap them and put radio collars on them and see how they fare in various habitat types and what is most likely to kill them. Both states hope to be able to say what types of forest practices (code for logging) results in the best fawn survival.

According to the Oregon management plan, black-tailed does live up to about 15 years, but bucks only about nine years. Bucks are hunted much more heavily than does, and breeding weakens them. Does generally have two fawns, but can have up to three.

Blacktails will migrate through the seasons up to 60 miles, spending the summers at higher elevation, and fall and winter at lower elevations. That’s why Mark Vargas, district biologist for ODFW in Central Point, suggests general rifle season hunters go to elevations over 4,000 feet to hunt early in the season, and below 3,500 feet at the end of October.

General rifle season happens mostly before the rut and often before good soaking rains make the woods quieter. Success rates reflect this, with generally around 30 percent of hunters getting their buck. During the rut, bucks are so intent on breeding, they are less wary of hunters, and will respond to the sound of antlers clacking together. To hunt during the rut, you can buy an archery tag in time for the late archery season, or apply by May 15 each year for some of the late muzzleloader hunts. I am not sure how I feel about hunting with a bow, but that could be a good reason to try it out.

Jackson hopes the DNA sampling will provide an estimate of how many blacktails are in western Oregon. That way, ODFW can manage them to keep general rifle season the way it is.

“If you want to hunt in Oregon, you are guaranteed a black-tailed deer buck tag. Just go buy it,” he said. “We don’t want to get away from that if we can at all avoid it.

“If we find out some really bad things about population numbers, we may have to make some changes.”