Hi Tweeters,

Dave Hutchinson asked me to post the following message about Mountain Beavers for him. ?Please direct comments and questions about this interesting information to him (contact info at bottom of his post):

In a previous discussion I commented on the apparent disappearance of Flying Squirrels from Seattle's Parks in the last thirty years. As part of these thoughts I have turned to examine the role of ?the Mountain Beaver. Quite often, when one mentions "Mountain Beaver" in polite conversation, the response is: "What's that?" Or else: " Oh I've heard of them, but never seen one." Around ?Seattle's larger parks and forested places, ?two groups know the critter well: the larger owls and Green Seattle Partnership forest restoration volunteers.

Aplodontia rufa rufa ?is a rodent endemic to Western North America and is quite common in the Seattle area. It is one of Washington State's endemic species. It is not related to the freshwater animal we also call Beaver. Apparently it can be 15 to 25 inches long, though it always seems much smaller to my eye. It's weight in the wild can be up to ?1.4 kg. and ?is ?a usual prey item for skunks, fox, badger, species of cat, weasel and coyote. Of course, some of these are uncommon within the city's limits.?

In evolutionary terms, it is an ancient animal, going back to the Miocene, perhaps radiating from other, earlier continental formations. It' s mating system has never been described. Because its inefficient kidneys cannot concentrate urine, it requires a constant source of surface water and succulent vegetation to process its vegetarian diet. Mountain Beaver start breeding in late January to early February. The gestation period is 28-30 days (March/April), while weaning begins in June. Smaller home ranges tend to have greater concentrations of native saplings and ground covers. ?Mountain Beaver density is lower in older forest stands with a more closed canopy than in recently logged stands. Open canopy habitats, created ?after commercial harvesting are preferred. This fits well with the largely open canopied, second and third growth mixed forests typical of Seattle's green belt and some of its larger parks.

In our region its most common foods includes: Vine Maple, Sword Fern, Bracken Fern, Salal, Red Elderberry, Salmonberry and Oregon Grape. All ?these ?native plant species are often heavily "clipped" by Aplodontia, which makes the logging companies mad and ?GSP forest restoration volunteers frustrated, to say the least.?

The problem on commercial forest-lands, is the "clipping" of seedling coniferous trees, such as Douglas Fir and deciduous trees, often right after planting. The leaders are chiseled off, fresh side shoots consumed. The same damage ?takes place in our parks, with the aforementioned native plants, particularly Sword Fern and Western Red Cedar. After initially planting a restoration site, one returns to find the tender leaves of saplings chewed off, while the animal uses the stubby side branches as a ladder to climb the little tree,chopping off the top. One well-known park volunteer has been heard to state: "I am NOT running a delicatessen for Mountain Beaver! Another volunteer claims to keep a particular restoration site open by removing tall grasses and exotic shrubs, while leaving branches as perches, to encourage the predation of Mountain Beaver by raptorial species.

Adult Mountain Beaver are solitary, so that the mass of tunnelings you might have come across, is the work of merely one rodent. Each individual has an extensive burrow system with high soil humidity ?and good soil ?drainage. Each burrow is often five to six feet deep and contains extensive woody debris and stripped herbaceous vegetation. Consequently soil is churned, organic matter is incorporated and infiltration routes ?for water and air are created, with soil profiles generally improved by this bio-turbation. Because of the associated soils disturbance and vegetation "management" by Aplodontia, their workings are often important sources of habitat and biotic diversity in otherwise uniform or depauperate forests, both commercial and park-land. However the extensive presence of Mountain Beaver workings can lead to increased soil erosion and damaged tree roots. Thus trees in and around them can be weak and unstable.

Managers of commercial forest lands control them by lethal trapping. Forest restoration volunteers try to practice self-control, but know that owls are part of their team. In Discovery Park, for example, many volunteers have seen a live Mountain Beaver, had one slowly walk over their foot as a Great Horned Owl looks on, or had a swooping Barred Owl snatch and carry one off. The Barred Owl ?diet (Birds of N.America Acct. 508) is described as: small mammals and rabbits, birds up to the size of grouse, amphibians, reptiles and rodents. From my own observations ?in Discovery Park, I can specifically add: American Crow, Bonaparte's Gull, squirrels, mice, freshwater snails and Mountain Beaver .Again from personal observations, ?I have seen Barred or Great Horned Owls in the following Seattle open spaces: Discovery and Seward Parks, the Interlaken area and the Washington Arboretum. All these sightings have occurred next to ?or in the middle of Mountain
Beaver workings. Correspondents also mention Bainbridge Island, Lake Forest Park and Carkeek as having healthy populations of either or both Barred and Great Horned Owls as breeding species. Again in Discovery Park, Long-eared Owls occupied a Mountain Beaver zone over several years and I have seen what looked suspiciously like an Aplodontia being carried by a Barn Owl back to its nest.

Clearly Mountain Beaver and Barred Owls ?like to occupy the same habitats for breeding or wintering in our area. To this list can certainly be added Red-tailed Hawk and Cooper's Hawk, both of which breed in Seattle and which use forest perches for hunting. ?I am unsure that the Aplodontia - owl ?relationship has previously been studied. Therefore it is only a surmise that Mountain Beaver is a major prey species for owls in our urban park settings. If so, owls may be playing a silent but critical role in controlling Many of the latter are under active restoration by the Green Seattle Partnership.

Thanks to: Clay Antieau & Miller Myers for critical comments; Miller for the great photos; several correspondents from Tweeters for important information.Special thanks go to Wendy Arjo for allowing me to use her Aplodontia research. Please note my (Dave Hutchinson) current email:
florafaunabooks at hotmail.com


Evan Houston
Seattle, WA