Tallest Beaver Dam?

Beaver dams are amazing constructions of wood, rocks, and mud that dwarf their makers. Apart from termite mounds they may be the tallest structures made by animals other than humans. Unfortunately there aren't many measured records of dam-building champs to rely on. I've heard reports of and found dams that were about 12 feet (about 3.7 meters) tall but I've never seen a study describing dam dimensions and the folks at the Guiness Book of World Records don't seem to be too interested in beaver dams.

The photo with this post shows a tall beaver dam from Algonquin Park in Ontario. Using Norma as a guide (she's 64" tall) and considering she's not standing at the lowest base of the dam I estimate this dam is pretty close to 10 feet tall.

Feeding the Beavers 2010

This fall marked the 4th year of my annual fall beaver feeding program. I do this to reduce damage that the beavers do to trees that people don't necessarily want to lose, and to ensure that the beaver colony doesn't eat all their food supply. And the feeding program creates a great opportunity to see the beavers at their food gathering best. Despite the free food, the beavers cut quite a few trees of their own this fall. I'm going to count them and make that into the subject of a future post.

This year I gave the beavers 32 pickup loads of aspen and balsam poplar branches. The photos show one load. It might not seem like much, but the aspen saplings shown in the lake are about 5 m long. That's a lot of branches for me to haul. What's truly amazing though is the removal rate by the beavers. This particular load was dropped off in the late afternoon and it was entirely gone the next morning. Working through the night, the beavers cut up and hauled off the entire load, floating the loot about 300 m from the depot to the food cache they built beside the lodge. Of course all that work takes lots of energy, so the beavers are eating a lot of food as well. What amazes me though is how they take 32 loads like this and make them into one pile at the lodge. The underwater architecture of that pile must be amazing to cram so much into such a small space.

Plastering the Lodge

Beaver winter preparations include additions to the lodge. There are usually some more logs and branches, but the main ingredient is a fresh coating of mud. When frozen the mixture of mud and wood becomes pretty much impenetrable armour for any predator that might try to break into the winter safehold. It's a little comical to watch the plastering process. The beaver dives to the bottom and scoops up a huge wad of wet mud. When swimming with this load the beaver is front-heavy and tends to sink, so more often the beaver surfaces right where it intends to exit the water. Standing upright on it's hind legs and using the tail for support, the beaver more or less waddles up the lodge to just the right spot.

I've yet to get really good photos of the lodge plastering. These two show a beaver just out of the water with the mud just visible, and a beaver high on the lodge about to dump it's load.

Thistle Clipping 2010

Last year volunteers clipped 2 heaping pickup loads of Canada thistle along the beaver dam while the plants were flowering. The idea was to remove the plant while all of it's energy was devoted to flowering but not to stimulate the roots to end up new shoots. Pulling the plants would have that effect - clipping is more time consuming but doesn't stimulate the roots. Over time, other plants should be able to out-compete the weakened thistles, and they should either die out or become much reduced.

The plan seems to be working. I finished clipping just one pickup load of thistles last week. So in a single year thistles have been reduced by half. And also where the thistles were still growing they didn't dominate the plant community like they did last year. Other plants are getting a foothold. I hope this positive trend continues next year!

Fall Migration is Underway

Migrating birds wind up in unusual places. Every fall a few birds not usually found in this area stop at the Beaver Boardwalk for a brief rest or visit before moving on to their winter range. In the past several weeks I've seen long-billed dowitcher, pied-billed grebe, horned grebe, and sharp-shinned hawk. Yesterday evening an immature common grackle flew in to roost in the tall shrubs near the beaver feeding area. That was a surprise and I think the first record of common grackle at the Beaver Boardwalk. The horned grebe was a new record also. The list of birds observed at the Beaver Boardwalk continues to grow and now includes more than 150 species. The Whisky-jack Club maintains the official list and publishes a brochure updating the records as they come in.

Red-necked Grebe Rescue

September 14 was a pretty miserable day - cold and raining hard. Numerous puddles and the wet ground fooled a red-necked grebe into thinking the log yard at Hinton Wood Products sawmill was a water body. Not so, and once on the ground the grebe wasn't able to get airborne again. Grebes and loons must have water deep enough to get a run at if for liftoff. They patter across the water surface building speed using both their wings and their feet. For this purpose, the shallow puddles in the log yard wouldn't do.

Fortunately for the grebe, Dave Wallace, Neil Holder, and Morris Archibald came to the rescue. They caught the bird in a fishing net and deposited it in a cardboard box. Of course the bird didn't know they had good intentions and was quite indignant about the whole affair. A bit of a rodeo, according to the guys. After a short drive Morris opened the box at the Beaver Boardwalk and the grebe got a new start on Maxwell Lake. It was gone a few days later, probably carrying on with fall migration.

Dave Wallace took the photos with this post. The first shows the bird on the ground, and the second shows Morris releasing the grebe at Maxwell Lake.

Beavers Grooming

Beavers spend a lot of time grooming their luxuriant fur to keep it clean and waterproof. The waterproofing comes from an oil they secrete from their anal glands and comb through their fur using a split claw on their hind leg. Recently it's been easy to see beavers grooming over at the feeding station by the Maxwell Lake picnic tables. After the free feast they gather as singles or small groups and set about the serious business of grooming. Sometimes they groom each other. Sometimes a youngster wants to play, and the older beaver decides to move and groom somewhere else. In this photo 3 yearlings have finished eating and have started to groom, while the animal on the left is still having dinner.