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Beavers

Special thanks to local artist and naturalist Scott Schuldt for this fantastic article! Be sure to click on Scott’s illustrations to view the Beaver Blueprints in their full detail.

Beaver in Union Bay
By Scott Schuldt

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Aside from man, beaver are perhaps the most dominant mammal in Union Bay. If you walk to the end of the west trail in Yesler Swamp, you’ll find an active beaver lodge just 50 yards south. This is one of five lodges in the bay. Many of the wilder parts of Union Bay look the way they do because of the beaver.

North Beaver Lodge.
Beaver are the largest rodents in North America with a mature beaver weighing 35 to 60 lbs. The largest recorded beaver was 105 lbs. They build two types of homes, the conical lodge and the bank burrow. The beaver that live in these structures are related and are referred to as a colony. A colony of beaver is headed by a monogamous life-long mated pair. There will usually be two sets of offspring – newborns and a few adolescents. The adolescents are kicked out of the lodge when they are 2 to 3 years old, but until then they help care for the youngest. So, there can be anywhere from two to twelve beaver in a lodge, with 6 or 7 being more common. The lodges have two underwater entrances and a vent hole near the peak. The interior has two levels – a bedding level and about 6-8 inches lower, a drying/entrance level. The lodge is built by making a pile of sticks and mud and then hollowing it out from underneath. It takes about a week to build a “starter” lodge. Canada geese often build nests on the lodges. There are no beaver dams in Union Bay since the purpose of a dam is to create a pond to build a lodge in (Although it wouldn’t entirely surprise me if a beaver did at some time try to dam Ravenna Creek.)
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Beaver have a fairly massive skull with four large and very sharp orange-colored incisors and 16 molars that are especially well adapted to grinding woody material. They are strictly vegetarians. They have very keen senses of smell and hearing and reasonably good eyesight. The front paws are raccoon-like so that the beaver is capable of some fairly nimble “handwork”. The hind feet are very large and webbed (a hind track that I cast in Yesler swamp is over 6 inches long and spans 6 inches from toenail to toenail) and when combined with the broad flat tail provide a good amount of horsepower for towing branches through the water. They can stay underwater for about 5 minutes. They do slap their tails and it will get your attention if you are near. In fact, that is the main purpose of the tail slap – to startle whatever is out there so that the beaver can figure out if you are a threat or not.

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Beaver are most active between dusk and dawn (the best times to spot them), but they are not strictly nocturnal and may be seen at anytime of the day. But, they do learn to avoid people. They are highly territorial and they mark and defend their area to keep out unrelated beaver. Because of this, the adolescents are particularly vulnerable when they are forced out of the lodge. An intruding beaver may be severely injured or killed in a territorial spat (as will a dog if it should corner one). Otherwise, they are not dangerous.

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Signs to look for:

Where to find the lodges- (I have given the lodges names to help me keep track of my observations)
The North Lodge – Yesler Swamp
The Big Lodge – east of the marsh just off of the south shore park land at 37th Ave E.
The Hidden Lodge – south shore of Foster Island in the arboretum lagoon (yes, it’s hard to find)
Workbench lodge – an island lodge by the eastbound arboretum entrance to SR520
The West Lodge – near the Conibear Shell House at the UW
Collapsed Lodge – east of Foster Island, just north of SR520 (abandoned and collapsed, of course)
Portage Bay Main Lodge – just off the canoe launch at Montlake Park
Portage Bay Bank Burrow – west shore of Portage Bay

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I would guess that there are a few more bank burrows that I haven’t found. Watch for fresh peeled limbs showing up on the lodges. This mostly occurs in October and November and at that time you might also find 3 or 4 muddy paths leading from the bottom to the top of the lodge as the beaver do seasonal home repairs. When you see that you know that you have an active lodge. Several of the lodges have been in use for a long time and are considered to be quite large. If you look at the Union Bay lodges on a map, you’ll see that each colony has a fairly large territory.

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Scent mounds

The territorial marker for beaver is a scent mound. They pile up mud and squirt it with a musk oil, castoreum, from glands in their hind end. The scent is rather pleasant and is used in the perfume industry. The mounds may be anywhere from a splash of mud on a grass hummock to an 18-inch high cone. One of the best places to see these is along the channel that separates Foster Island from the Broadmoor Driving Range. There are at least a dozen large scent mounds in this short stretch and one can often smell the castoreum from several yards away. At times they will leave a little woody material on top to hold the scent. Several times, I have found golf balls perched on the top of the Foster Island mounds!

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Felled trees, leftovers and drags

During winter, the beaver diet is mostly the inner bark of trees, while in summer they convert to mostly marsh greenery. They go a bit inland to cut down saplings or a tree and then lop the branches. They then drag those back to the safety of the water’s edge where they will eat. Watch for peeled limbs near the shoreline. On a cattail island, this spot will be tramped down. Also, look for the trail known as a beaver drag. The process of dragging branches to the shore will create a pretty clear path. You probably won’t find beaver tracks because the tail and the branches wipe them out in most cases. Just south of the West Lodge are several felled alder trees that can be reached from shore if you would like to see a great example of the beaver’s lumberjack skills.

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Canals

Dragging brush through wetlands not only creates a path, but in time it excavates a canal. There aren’t any canals in Yesler Swamp, but there are a few in the islands over by the UW and there are several in the south end of the bay. There are also several paths that are gradually becoming canals, so the whole evolutionary process can be seen. The home repair process of dragging branches to the lodge also has a tendency to excavate the ground surrounding the lodge. This is most evident with both the North Lodge in Yesler Swamp and the Hidden Lodge, which were both built on “firm” ground. Both of these lodges seem to be developing moats around them.

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Destructive?

There’s no doubt that beaver can cause damage, but most of what they do is beneficial. They are classified as “keystone” animals in that they create habitat for other wildlife. Most successful beaver management programs seem to use the strategy of fooling the beaver into doing something rather than attempting to stop them or remove them from the area (they just come back anyway). The trees that they prefer are fast growing and fast sprouting – willow, alder, sometimes birch, cypress and cottonwood. The roots of the cut trees survive and sprout more trees and this ends up knitting the loose marsh together which in time will become firm ground as more and more biomass accumulates. Likewise, trees that fall towards and into the water act to stabilize the shoreline. So, it’s tree cutting in the short term, but land creation with a long-term view. Sometimes they don’t finish the job and leave a dead tree standing. Even this becomes bird and insect habitat. When I show people the trees that they cut about half of the people comment on the destruction. I like to point out that “destruction” is only valid if one assigns different monetary values to different parts of nature. West of Yesler Swamp, and in large areas of the south part of the bay, are areas I call “beaver forests”. These areas are dense tangles of misshapen trees mixed in with swamp plants. One thing visitors will notice in these spots is that there are hardly any trees without the beaver gnawing. I can get my canoe into some of the beaver forests during high water, but it is difficult (which also makes it a fairly safe place for wildlife). The water is filled with extensive root systems, down wood and low hanging branches. It really is a free form knitting of plant life with small pockets of new dry land hidden inside.
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Recently, I came across a WSU paper on ecorestoration where the author pointed out that in the case of restoring streams, letting beaver do the work when possible was the most efficient method because they do not require federal, state and county permits nor extensive environmental impact statements.

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