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
  • NOVA SCOTIA OCEAN FRONT
    Camp or Build on 2+ acres in Guysborough. FSBO. $36,000 US firm. Laurie's phone: 585-226-2993 EST.
  • COMMUNITY FORESTER
    The Clearwater Resource Council located in Seeley Lake, Montana is seeking a full-time community forester with experience in both fuels mitigation and landscape restoration. Resumes...
  • GUNNISON BASIN ROUNDTABLE
    The Gunnison Basin Roundtable is currently accepting letters of interest for ten elected seats. Five of the elected members must have relevant experience in the...
  • PCTA TRAIL CREW TECHNICAL ADVISORS IN WASHINGTON'S NORTH CASCADES
    Seasonal Positions: June 17th to September 16th (14 weeks) - 3 positions to be filled The mission of the Pacific Crest Trail Association is to...
  • WE'RE LOOKING FOR LEADERS!
    As we celebrate 50 years of great Western journalism, High Country News is looking for a few new board members to help set a course...
  • MEMBERSHIP DIRECTOR
    Job Announcement Job Title: Membership Director Supervisor: Executive Director Salary: Up to $65,000/year DOE Benefits: Generous benefits package — health insurance, Simple IRA and unlimited...
  • UTAH PUBLIC LANDS MANAGER
    Who we are: Since 1985, the Grand Canyon Trust has been a leading voice in regional conservation on the Colorado Plateau. From protecting the Grand...
  • EXECUTIVE DIRECTOR
    Executive Director Walker Basin Conservancy Reno & Yerington, NV Background The Walker Basin Conservancy (Conservancy) leads the effort to restore and maintain Walker Lake while...
  • WIND RIVER WRITERS AND PHOTOGRAPHERS RETREAT BY THE NATIONAL BIGHORN SHEEP CENTER
    Enhance your writing or photography skills with world-class instructors in the beautiful Wind River Mountains. All skill levels welcome. Continuing education credits available.
  • EARTH CRUISER FX FOR SALE
    Overland Vehicle for travel on or off road. Fully self contained. Less than 41,000 miles. Recently fully serviced Located in Redmond, OR $215'000.
  • ENVIRONMENTAL GEOPHYSICS
    identifies suspect buried trash, tanks, drums &/or utilities and conducts custom-designed subsurface investigations that support post-damage litigation.
  • EXECUTIVE DIRECTOR
    They [Northern Plains] confound the common view that ordinary people are powerless in the face of industry. - Billings Gazette editorial The venerable Northern Plains...
  • SMALL FARM AT BASE OF MOUNT SHASTA, CALIF.
    Certified organic fruit/berry/veggie/flower farm. Small home, 2 barns (one has an apartment), and more. Approx. two acres just in the City limits. Famously pure air...
  • FRESHWATER SCIENTIST
    The Freshwater Scientist provides technical and scientific support and leadership as a subject matter resource (SMR) for conservation initiatives in surface and groundwater hydrology including...
  • TAOS HORNO ADVENTURES
    A Multicultural Culinary Memoir Informed by History and Horticulture. Richard and Annette Rubin. At nighthawkpress.com/titles and Amazon.
  • LAND & CABIN ON CO/ UT LINE
    18 ac w/small solar ready cabin. Off grid, no well. Great RV location. Surrounded by state wildlife area and nat'l parks.
  • CANYONLANDS FIELD INSTITUTE
    Field seminars for adults in natural and human history of the Colorado Plateau with lodge, river trip and base camp options. Small groups, guest experts.
  • WESTERN NATIVE SEED
    Native plant seeds for the Western US. Trees, shrubs, grasses, wildflowers and regional mixes. Call or email for free price list. 719-942-3935. [email protected] or visit...
  • THE LAND DESK: A PUBLIC LANDS NEWSLETTER
    Western lands and communities--in context--delivered to your inbox 3x/week. From award-winning journalist and HCN contributor Jonathan P. Thompson. $6/month; $60/year.
  • CONSERVATIONIST? IRRIGABLE LAND?
    Stellar seed-saving NGO is available to serious partner. Package must include financial support. Details: http://seeds.ojaidigital.net.