Estimating Oregon’s Black Bear Population

June 30, 2009

Each spring Oregon Department of Fish & Wildlife employees set out across the state to mark black bears and the information is then used to estimate the population in the state. What is a mark and how do we go about marking bears? A mark could be an ear tag, tatoo, or some other means of identifying an animal that has been captured and released back into the population. In the case of Oregon’s black bears, they get their teeth marked with the aid of tetracycline. Here’s how it works…

In the Southwest Region, we kick things-off in May with an early morning get together and invite volunteers to a hearty breakfast meal. Once the tables are cleared, volunteers roll their sleeves up and slip on a pair of gloves. They dive into the mountain of sliced bacon and pile of tetracycline laid before them and begin rolling individual capsules in a slice of bacon. Several people walk around and collect the rolls and stuff nine of them into a plastic mesh bag (approximately one pound). The bag gets knotted and twist-tied with a piece of rebar tie wire and placed in a cooler. The bacon bait rolling usually takes a few hours to complete and each wildlife district takes their coolers and enough bacon baits for their respective area.

ODFW employees, Dave & Dave serving up breakfast to volunteers before rolling baits.

Rolling tetracycline capsules into bacon slices, stuffing them into mesh bags and tying them with rebar tie wire

Hanging bacon baits begins as early as June 1. Baits are placed no closer than five miles apart from each other. This is to avoid potentially marking an individual bear more than once. The baits are placed high off the ground in trees with smooth bark. This means the bear must climb the tree to get the bait and it leaves telltale claw marks in the bark when taking the bait. Each bait is drenched with a special mixture to lure bears to the bait. The baits are left out for three weeks before checking for results.

Putting out baits in the spring is a great time to be out in the woods, it’s gorgeous country and there’s no phones.

Gourmet bait hung in a tree and drenched with scent to lure bear to the tasty treat!

An alder tree is raked by bear claws as it climbed this tree to take the bait. Result is a marked bear.

(ODFW)

Bears recovered from damage complaints, roadkills, or hunter harvest have a small pre-molar tooth extracted to look for a mark.

(ODFW)

With the aid of a special light and microscope, a cross-sectioned tooth will fluoresce if the bear consumed a tetracycline bait. The rings indicate years of age and when the bear was exposed to tetracycline (could be multiple years).

The actual numbers of marked and unmarked bears that are recovered each year are used to calculate the bear population estimate. If you’re interested in reading the details on how this estimate is calculated, visit the ODFW website and read the report on The Effectiveness of Tetracycline as a Marker to Estimate Black Bear Numbers in Oregon.

However, from my perspective, I can tell you that there are a lot of bears in southwest Oregon. There are plenty of damage complaints from people who live in bear country and from those on the edge of town. Just driving around the back roads will find you seeing lots of sign. More often than not the bears don’t get marked by us, they leave their own marks…

Bears have an entirely different idea of how a treated 4×4 sign post is to be treated