Wednesday, March 28, 2012

Boomer aka Mountain Beaver

It seems odd that an animal the size of a rabbit and indigenous to the Pacific Northwest, could be completely unknown to so many people who live here. But then the mountain beaver is an odd sort of animal.

For one thing, it hosts the world's largest flea (3/8th of an inch long--yeeks!). And despite the name, they're not beavers, and they are more commonly found at lower altitudes than in the mountains. Another common name for this rodent is boomer, because they can emit a low moaning sort of sound.

Though boomers are primarily nocturnal, burrowing creatures, occasionally day hikers have peered at one in the rustling underbrush and wondered, "What the heck is that?" (Well, okay, at least I have...)

But tree farmers and foresters know all about mountain beavers. Although they favor sword fern, at certain times of the year they'll also eat seedlings and can girdle--and thereby kill--young trees.

Boomers have extensive burrows that include food chambers, a sleeping chamber, another chamber for fecal pellets, and tunnels that link all. You may not see a boomer on your next hike in the PNW, but chances are there's one somewhere along the trail, right under your nose/boots.


  1. How big is this rabbit size you speak of?  I've seen rabbits at the county fair that were smaller than a chihuahua and others that were big as a baby.  So I see the boomer as somewhere between 2 and 14 pounds.  I may have seen one in the twilight and thought it was a young nutria.  Same rodent teeth, right?  

    World's largest flea?  Well, I'm just as glad that I HAVEN'T encountered a boomer.          

  2. DaveOnFidalgo ...March 28, 2012 at 7:47 AM

    Amazing.  I guess we can add it to the list of NW things that are not something.  Like the Douglas Fir which is not a fir.  Instead it's a not-a-hemlock.  They eat Sword Ferns? 

  3. Boomers go up to 14 inches long. Same rodent teeth as a nutria, yes, but they don't stick out of their mouths as nutria's tend to. And mountain beavers are not as likely to be found by water or out in the open. They're usually more secretive than nutrias--though there's at least one story of a guy seeing one walking up his driveway.

  4. And western red cedar is not a cedar (it's in the cypress family--but not related to the bony-kneed bald cypresses of the South, because they are not really cypresses...)

    Boomers eat sword ferns, fireweed, oxalis, etc. They gather these in piles in front of their burrows and let them wilt out there--when ready, the animal carries these down to one of the food chambers, where the food stay moist.

    They also often have another chamber for "mountain beaver baseballs," which are rocks or clay balls about 3 inches in diameter, apparently unearthed during excavation or maybe gathered. It's thought that they chew on these to file their ever-growing front teeth.

  5. How positively fascinating. Didn't know of boomers OR nutrias.  You simply must write a book about a family of boomers!  Like Robert Larson's Rabbit Hill :-)

  6. DaveOnFidalgo ...March 29, 2012 at 3:29 PM

    I think it's even worse than that.  The Alaska Yellow Cedar is the Cypress.  The Western Redcedar is an Arborvitae.  Both cedars are not-cedars.  Who can keep it straight?  :- |

  7. Or Hope Ryden's "Lily Pond" (about real beavers).

  8. I saw a boomer when we were visiting the people we bought our property from 27 years ago. :}  Haven't seen them since, but were  worried when we reforested 0ver 800 Douglas Fir trees, but they haven't seemed to hurt our "babies"  of which I am glad.  Trees are almost at the "free to grow" stage (4.5feet).  Can my dogs "catch" their fleas?

  9. Or, solitarily, Box Turtle at Long Pond.

  10. And the common [fill in animal name], too often no longer common. Perhaps, though, it's good to keep those names to twang the realization that it doesn't take long to make a common animal not a common animal.

  11. My husband and I are both native Oregonians. He grew up in Toledo, I in Portland. I had never heard of a Boomer until I met my husband and went to Toledo to visit his family. I did see one, they are real.

    1. We live in Mapleton. I moved here 30 plus years ago, had a bunch on our mountain out back, don't remember what I did to get rid of them...Now we have at least one little cutie living right out front, perfect habitat for them. So freakin cute...and mellow, like a sloth..Today it kept running back and forth and peeking out at us from different tunnel entrances, We're going to leave it be for now, pretty sacred little animal