How do you sex a beaver? Squeeze and sniff

Unlocking the secrets of rodent scent glands could help restore Western watersheds.

 

Pop quiz for all you amateur wildlife biologists: How do you determine the sex of a beaver?

That question might sound like the set-up to a raunchy punchline, but for the Methow Valley Beaver Project, it’s a pressing concern. The Methow Project, as I reported this month for High Country News, captures tree-felling, ditch-clogging nuisance beavers in eastern Washington and relocates them to public lands in the Cascades. There, the buck-toothed engineers construct salmon-sheltering wetlands, recharge groundwater and create habitat for wildlife from salamanders to moose.

In between live-trapping and release, the Project houses its wards at the Winthrop National Fish Hatchery, where males and females form pair-bonds that help them better survive in the wild. Of course, to set up Harry with Sally, you have to know who’s Harry and who’s Sally. That’s where the critters make matters difficult.

Beavers, you see, lack familiar mammalian plug-and-socket genitalia. Instead, the creatures possess cloacas — fleshy vents, analogous to the anatomy of birds and reptiles, that do triple duty in the departments of waste disposal, scent secretion, and, yes, reproduction. A male beaver’s cloaca looks almost exactly like a female’s. Not even the sharpest-eyed matchmaker can reliably tell the sexes apart — at least not visually.

screen-shot-2015-11-09-at-2-06-24-pm-png
Hendrix, a 44-pound male, surveys his human captors from his enclosure at the Winthrop National Fish Hatchery
Ben Goldfarb

This, in a roundabout way, is how I ended up kneeling on the concrete floor of the Winthrop hatchery — one hand pressed against the damp fur of a beaver’s belly, another swabbing its hindquarters with a tissue, nostrils puckered by the potent odors rising from below its leathery tail. Harry or Sally? My nose, in theory, would know. 

Katie Weber, Methow Project biologist and beaver-sexing coach, peered over my shoulder at the rodent writhing in my uncertain grasp. “Once you get the anal gland expressed, put some pressure on it, and you’ll see oil,” she offered, like a cornerman urging a boxer to lead with a left jab. Biologist Catherine Means had wrestled the beaver, a weathered male named Half-Tail Dale, into a blue cloth sack, leaving only his nether regions exposed. The bag’s darkness had calmed Dale, though he still occasionally kicked out with his clawed feet. I didn’t blame him — the experience must have been like visiting a very clumsy proctologist. 

High Country News: showing you things you can't unsee since 1970.
Methow Valley Beaver Project

Beneath my fumbling, Latex-wrapped fingers, the scent glands — angry twin volcanos of pinkish flesh — popped from the cloaca. A drop of amber liquid glistened on one tip, and I dabbed at it gingerly. Weber encouraged me to squeeze a bit harder. “Be careful where you position yourself,” called Torre Stockard, another scientist, from behind the safety of a fence. “You’re in the splash zone!” 

The scientists seemed to think they were offering me a once-in-a-lifetime opportunity. To me the experience seemed more akin to a hazing ritual. With a whispered apology to Dale, I applied additional pressure on his glands, which poured forth a viscous stream of caramel beaver juice. (From the Beaver Restoration Guidebook: “Obviously this procedure should be done with your face a reasonable distance from the cloaca, with your mouth shut.”) Weber swooped in to wipe up the mess. Dale’s ordeal at the inexpert hands of a journalist had, mercifully, concluded.

Weber held up the tissue, blotched with hard-won scent secretion. Males, she explained, excreted darker, thicker fluid than females. The odor provided another diagnostic key. A hint of motor oil indicated a Harry. If you smelled old cheese, you had a Sally on your hands. “Once you’ve done five, you can pretty well tell,” Weber assured me. According to a recent genetic analysis, the Methow Project has misidentified the gender of just one beaver since it began using the glandular technique.

I took the tissue and, against my better judgment, inhaled deeply. Motor oil? Maybe. But the bouquet also contained notes of overripe fruit, pet store interior, dead muskrat, paint, and countless other olfactory sensations. Indeed, a single anal secretion may contain upwards of 100 different chemical compounds. It wasn’t unpleasant, but it was powerful. I felt a touch lightheaded, and wondered if the Food and Drug Administration had ever seen reason to ban the use of beaver glands as a narcotic.

Methow Project biologist Katie Weber ponders a tissue full of diagnostic beaver secretions.
Ben Goldfarb

While glandular discharges aid the efforts of beaver relocators like Weber, they’re also fundamental to the lives of the rodents themselves. Beavers have poor eyesight, which means they experience the world primarily through their noses (their hearing is excellent, too). Each beaver has a distinct, fingerprint-like scent, which the animals use to identify relatives — three generations typically share a single lodge — and mark “scent mounds,” piles of leaves, mud and sticks that delineate the domain of individual colonies. (Incidentally, don’t confuse beavers’ anal glands with their castor sacs, oil-producing organs that beavers use to map their territory and waterproof their fur. Castoreum has some applications in the world of humans, though contrary to the claims of the Food Babe, there is virtually no chance that “beaver butt” flavors your vanilla ice cream. Your perfume? That’s another story.) 

Understanding the creatures’ sensory abilities isn’t just an academic question: In one 1990 study, scientists in upstate New York used manmade scent mounds to manipulate the establishment of wild beaver families. For their part, the Methow Project’s scientists use scent lures — gloppy brown paste concocted from beaver secretions and other substances — to lure the creatures into live traps. Further unraveling the animals’ aromatic mysteries, therefore, could help advance C. canadensis’ restoration. And that, Weber told me once we were safely removed from the line of fire, would be a very good thing. 

“It’s amazing how many people start out saying, ‘Hmm, beavers, I don’t like those guys,’” Weber said as we watched Dale, now free and reconfirmed as male, cruise the waters of his concrete-walled enclosure. “And then you show them the benefits, and they say, ‘Oh — I didn’t think of it that way.’” The best smell of all, perhaps, is that of success.  

Ben Goldfarb is a correspondent for High Country News. 

High Country News Classifieds
  • ENVIRONMENTAL JUSTICE ASSOCIATE
    Job Announcement: Environmental Justice Associate Announcement date: June 18, 2021 Applications will be reviewed on an ongoing basis and first review will begin: July 13,...
  • COMMUNICATIONS ASSOCIATE
    Job Announcement: Communications Associate Announcement date: June 18, 2021 Applications will be reviewed on an ongoing basis and first review will begin: July 13, 2021...
  • COMMUNITY ENGAGEMENT DIRECTOR
    Colorado Wild Public Lands (COWPL), based in Basalt, is an exciting nonprofit working to keep public lands open and accessible. Our growing organization is seeking...
  • BUSINESS SUPPORT ASSISTANT (PART-TIME)
    High Country News, an award-winning media organization covering the communities and environment of the Western United States, seeks a part-time business support assistant to provide...
  • SOCIAL MEDIA AND DIGITAL ADVERTISING SPECIALIST
    The Southern Utah Wilderness Alliance (SUWA), Utah's largest conservation organization, has an immediate opening for a full-time Social Media and Digital Advertising Specialist. This position...
  • SPRING-FED PARCELS ON THE UPPER SAC RIVER
    Adjacent parcels above the Upper Sacramento river, near Dunsmuir. The smaller is just under 3 acres, with the larger at just under 15 acres. Multiple...
  • DEVELOPMENT COORDINATOR
    Greater Yellowstone Coalition seeks a development professional to coordinate the organization's individual giving program. The position description is available at http://greateryellowstone.org/careers Please email a letter...
  • IDAHO STATE DIRECTOR
    The Wilderness Society is seeking a full time Idaho State Director who will preferably be based in Boise, Idaho. At least 8-10 years of experience...
  • COMMUNICATIONS MANAGER AND BEARS EARS EDUCATION CENTER MANAGER
    Conservation nonprofit Friends of Cedar Mesa in Bluff, Utah is hiring for two positions. We seek a Communications Manager to execute inspiring and impactful communications...
  • EXECUTIVE DIRECTOR
    Wilderness Volunteers Wilderness Volunteers (WV), a 24-year leader in preserving our nation's wildlands, is seeking a motivated person with deep outdoor interests to guide our...
  • HECHO POLICY AND ADVOCACY MANAGER
    Hispanics Enjoying Camping, Hunting, and the Outdoors (HECHO) was created in 2013 to help fulfill our duty to conserve and protect our public lands for...
  • FISHERIES BIOLOGIST
    Under the direct supervision of the Director of Shoshone-Paiute Tribe's Fish, Wildlife & Parks, in coordination with the Tribal Programs Administrator and the Tribal Chairman,...
  • REGIONAL EXECUTIVE DIRECTOR NORTHERN ROCKIES, PRAIRIES & PACIFIC REGION
    Founded in 1936, the National Wildlife Federation has grown into America's largest and most trusted grassroots conservation organization with 53 state/territorial affiliates and more than...
  • STEWARDSHIP MANAGER
    STEWARDSHIP MANAGER Job Vacancy and Description Posted June 2, 2021: Open until filled The New Mexico Land Conservancy (NMLC) is a non-profit, regional land trust...
  • KSJD - MORNING EDITION HOST/REPORTER
    KSJD is seeking a host/reporter. Please see for www.ksjd.org for more information. EEO compliant.
  • ON THE EDGE OF CEDAR MESA/BEARS EARS
    Quiet, comfy house for rent in Bluff, Utah. Walk to San Juan River. Bike or hike to many nearby ruins and rock art sites. Beautiful...
  • CARPENTER AND LABORER WANTED.
    Come to Ketchikan and check out the Rain forest on the coast, Hike the shorelines, hug the big trees, watch deer in the muskeg meadows,...
  • PROJECT MANAGER
    Title: Project Manager Reports To: Program Director Salary Range: Negotiable; starting at $60,000 Location: Bend, OR The Deschutes River Conservancy seeks a Project Manager to...
  • PROGRAM DIRECTOR
    The Deschutes River Conservancy seeks a Program Director to join our dynamic team in restoring streamflow and improving water quality in the Deschutes Basin. WHO...
  • POEM+ NEWSLETTER
    Start each month with a poem in your inbox by signing up for Taylor S. Winchell's monthly Poem+ Newsletter. No frills. No news. No politics....