|fwg is a long-term project of the ottawa field-naturalists' club|
Beavers (Castor canadensis) at the FWG
by Christine Hanrahan
A surprise visitor
A surprise winter resident in the Amphibian Pond at the Fletcher Wildlife Garden (FWG) has us all aflutter. On 24 October 2009, a young beaver was found sitting on a mat of cattails near the turtle raft, making a meal of cattail stems. When I tried to get a photo, he slid into the water and swam to the other end of the pond near the bridge. I was excited to see this little guy, particularly as he was so active, but not surprised, for we have had this species turn up several times in the past and stay for a day or two, or three.
This visitor was different, however, as I quickly learned the next day when I saw the beginnings of a dam. Walking around to the south shore, I noticed he had been working very diligently on taking down one of the small willow trees. Within a day it was down and he was working on the second one nearby. Meanwhile, the dam was growing quickly and a food raft, or food cache, was already established in the eastern half of the pond.
It was quite a different scenario than any we'd faced before and there was some concern about how many of our trees he'd remove. Even more troubling was the sheer unsuitability of our pond for a beaver's home. We worried that he would not be able to survive. However, as the days went by and the dam progressed, the water deepened, enough so that one evening when I was there he was able to dive down into the depths of the pond.
Eventually, I contacted Donna Dubrueil of the Ottawa-Carleton Wildlife Centre for help and advice. Donna proved to be a great source of information, help and encouragement. She told us that having a beaver in our pond was a wonderful way to educate people about this often misunderstood animal (Canada's national symbol after all). She also said, and this was later corroborated by other knowledgeable folk, that the beaver would most likely leave once spring came. I knew that young beaver left their family in their second year to make their own way in the world, hence the wandering beaver people sometimes find in the most unlikely locations, particularly in the autumn. I never expected one to actually stay and make his home, however temporary, in our pond. But, as Donna said, his time for finding a winter home - where food was available and where he could make a den and lodge or a burrow - was limited. Our pond must have seemed like mecca to this poor guy, and perhaps he thought that while not ideal, he could make the best of a bad situation.
When he started work on the large, self-seeded Manitoba maple on the north side of the pond, a tree of a respectable diameter and height, we realized we had better wrap the other trees in the vicinity of the pond that we wanted to save. This was duly done, but after initially wrapping the partially chewed Manitoba maple, we unwrapped it and let him have his way, which he soon did and the tree now lies over the pond, above his burrow with the tips of its branches in the water. Not quite the successful tree felling he had attempted, but at least some of the branches are reachable!
With all the interest generated amongst both volunteers and visitors to the garden, I decided that it would be useful to provide more information about this intriguing animal.
Introduction to beavers
Beavers are large aquatic, herbivorous rodents. They are non-migratory, they do not hibernate, and they are typically nocturnal, although they can be found during daylight hours at certain times of the year, particularly in fall and spring. When the FWG beaver first turned up in late October, he was very visible during the day, but quickly confined his appearances to late afternoon and evening. Many times after dark, I have seen him swimming around near his food raft, and have sometimes heard him gnawing on a branch or twig. One evening, under a full moon, I watched him swimming leisurely around the pond, holding a twig in his front paws which he was gnawing on, the sound carrying across the pond to where I was standing just above the bridge. It was quite enchanting.
Somewhere along the way, beavers have gone from being admired to being reviled, in the public's mind. It is unfortunate that doing what comes naturally brings these inoffensive animals into conflict with landowners, land managers, residents, and others.
As the FWG dam lengthened and the willows, then sumacs, came down, his presence was noticed by FWG visitors. The misinformation spread about these animals is so prevalent that I found some visitors were horrified at the thought of a beaver living in our pond, even temporarily. Some even demanded to know what we were going to do about the "problem" and some "helpful" souls suggested they could set their dogs on it and drive it away. Others said we should call in a trapper. Naturally all such comments disturbed us.
One woman, dismayed about his presence, told me that we would lose all our trees. I mentioned that it was very interesting how we get upset about the relatively few trees beavers take down (few in the grand scheme of things) yet accept wholesale destruction of acres of woodlands by developers. She conceded she had not thought of that. When told that many places hire trappers to remove beavers she thought I meant live-trapping. I soon set her straight, and the idea that the animals were killed appalled her. I could tell from her subsequent comments that she was thinking rather differently about things.
These and many other comments made us realize we had to let visitors know we were aware of the beaver and happy about his presence. However, by far the majority of comments have been positive. Many people were excited at the thought that they might actually see a beaver, and I was rather surprised by how few were familiar with this delightful species.
We decided to erect a temporary sign by the pond letting people know that we accepted the beaver and at the same time, provide some information.
Our beaver is likely about two years old, for that is the age when the young leave to make their own way in the world. They may leave their natal site in spring, summer or fall but I've most often seen wandering beavers in autumn and often in the most unusual locations. I've seen them trying to cross busy roads in Ottawa and found them in the tiniest of streams trying to establish their home.
Beavers usually mate when two or three years old, the female giving birth to anywhere from one to six kits in the spring (the number usually depends on how much food is available). Eventually these tiny creatures will attain a weight of upward of 25 kilograms. Unusually, they are monogamous and mate for life, which somehow to me, highlights even more, the cruelty of trapping, for one of a pair may be killed, the other left alone.
Family groups typically consist of both adults and the offspring of the previous two years. Once the young reach the age of two, they leave the colony to seek their own territory. As noted above, this is a difficult time for they wander into situations that are not only unsuitable but very dangerous. If they survive attacks by predators and avoid cars on roads, they may end up being trapped (killed) to remove them from areas where they are not wanted, which in the City of Ottawa seems to be most places. Another reason we are letting the beaver remain, is for just that - so many other places are unwelcoming. And we, after all, are a "wildlife garden."
Another hazard young beavers encounter when seeking their own territory is hostility from beavers already established in ponds or wetlands. Normally peaceful animals, resident males will fight off intruders, particularly in situations where the wetland is small and food supply limited. Vanishing wetlands mean that beavers have an ever-harder time finding suitable habitat. Around Ottawa, we can see examples of large wetlands being filled in for development. Beavers dislodged from their natal site often end up in places like the FWG or the Arboretum, where habitat is unsuitable (the latter site) and barely suitable (the former site).
As noted above, beavers do not hibernate. They remain active throughout the winter, warm and cosy in their lodge or bank burrow, dependent on the winter food supply laid up during fall. This is another reason why we decided to let the beaver remain at the pond. If we tried to live trap and move him to another location, chances are it would be too late for him to establish a territory, create a dam, build a lodge or burrow, and lay in food.
Most of us are familiar with the typical beaver lodge, a big cone-shaped pile of logs, branches and mud in the middle of a pond or, sometimes, close to shore (as in the photo at left). However, beavers will also create bank burrows when conditions do not permit construction of a lodge. Sometimes they will construct both lodges and burrows and use the two. "Our" beaver has created a burrow, identified by a pile of sticks forming what looks like a minute lodge against the bank, and smeared with mud. It may be that he began building a lodge but realized it was not feasible given the dearth of trees and/or the lack of time. The entrance is underwater, as is usual for both burrows and lodges.
Lodges are elaborate affairs, allowing a family to live well and dry throughout the winter. During the summer and fall, repairs are made to the lodge, and fresh branches on a beaver lodge are a sure sign that it is inhabited. It is not unheard of for otter or other animals to take over abandoned lodges.
When a beaver finds an area that appears suitable, the first thing it does is start work on a dam. Beavers are not called "nature's engineers" for nothing. They exhibit great skill when dam-building, and are ingenious in situating dams in appropriate locations. Dams are not meant to be impermeable. Water is allowed to trickle, as we saw with the one at the FWG.
Initially, the dam at our pond was small and constructed of mud and bits of vegetation such as cattails, roots of grasses and possibly flowering rush. As the days went by, the dam was lengthened and a few twigs and branches were added. Dams can vary from just mud and vegetation, to elaborate affairs with large branches and even, sometimes, rocks. I've seen all types and sizes over the years. It is an amazing feat when we consider that these animals have no university degree in engineering!
Dams also require constant care and maintenance, sometimes daily. "Busy as a beaver" is not just a trite saying, for these animals seem to work constantly. Remove a dam from a ditch or stream and, by the next day, it will be rebuilt! If a hole forms in a dam, the beavers are there right away, doing repair work. They never stop. This of course is what endears them to many people, but at the same time, makes others dislike them intensely. Dams can create problems - flooding out roads being the one that vexes most people. In extreme situations, some impatient, unpleasant souls dynamite dams as a way of dealing with the issue once and for all. However, there are humane ways to resolve these issues that need not involve killing the animals.
Dams may be small and only a few metres in length, enough to block a ditch or small stream. Or, they can exceed 100 metres and be so solid, deep and wide, that hikers can safely cross them, sometimes two abreast. Indeed, beaver dams are well used by hikers to cross ponds. Some dams, in ponds no longer used by beavers, may be so old that they have trees and shrubs growing on them.
After a particularly heavy rainfall, the water in our pond rose and began to flow over and around one end of the dam. I could only imagine the beaver working frantically to try and control this situation, while trying, at the same time, to accumulate enough food to see him through the winter. Snow and cold weather came not long after the overflow and, for the time being, the area is frozen and water flow has ceased.
Another interesting construction activity is the creation of canals along which beavers can transport food and material for their dams and lodges. I doubt that the beaver at FWG will commence this activity in spring, but I have seen many such canals in areas such as Larose Forest, and they are quite impressive!
When I first saw the FWG beaver, he was perched on a mat of cattails eating cattail roots. This is not as unusual as one may think. While we think of beavers eating only the bark of trees, they will, in fact, eat a variety of vegetation. They are strictly vegetarian, so they don't rely on insects, fish or other animal food.
During summer, beavers are particularly interested in fresh, tasty aquatic vegetation, fruit, grasses, herbaceous plants, and shrubs. They seem to relish water-lilies. I saw one very large beaver in Gatineau Park last summer (2009) plucking the water lily pads and consuming quantities of them. Somewhere I read that they will roll them up like a cigar before eating. I didn't notice that, but it may be that the beaver I was watching was not going to waste time with niceties. Beavers have also been found feeding on purple loosestrife (Darbyshire and Consaul 1999). It would be nice to think that beavers could be added to the list of biocontrol agents for this invasive plant, but there was not a lot of other food around, so the animal was no doubt using whatever was at hand.
When a beaver has finished eating the bark off twigs and branches, he will use them for dam or lodge construction. Waste not, want not!
Another sure sign that a beaver is in residence at a pond or wetland is the presence in fall and winter of a food cache or food raft, an accumulation of branches spread out near the lodge or burrow, sometimes over a considerable area.
Recently, I came across an enormous food cache in Larose Forest, the biggest I've ever seen. It extended far out from the bank (there was no lodge at this site) to at least halfway across the large pond.
Our beaver, in addition to immediately starting dam construction, began accumulating his food cache. Mostly it consisted of Manitoba maple, willow, red osier dogwood and sumac, the trees most readily available nearby. I watched one evening as he dragged some branches under the water and was relieved to see this because it meant he probably had other food beneath the surface cache. The visible part of the cache was fairly meagre in size, so it was good to see him taking food to store underneath it. This is typical behaviour: beavers will build the raft on the surface of the water, then frequently add to it underneath. A large cache such as I saw at Larose would really be twice the size if there was a similar amount underwater. Of course, there is probably a beaver colony present at that site, not a single animal as at FWG. When a beaver family is present, food must be stored in sufficient quantity for the entire crew! Beavers will also resort to eating the roots of aquatic plants, such as cattails, which they will take during the winter under the frozen pond surface.
Beavers have definite food preferences when it comes to trees. Willow, poplar and birch are favourites. However, they will eat other species too, depending on what is available. It may be that the nutritional quality of these three species is higher than that of other trees or it may simply be that they taste the best! Some trees are cut not for food, but for building, and beavers may use the least palatable for this purpose.
I am amazed at times at the sheer size of some of the trees that beavers attempt to take down. Do they think that if they can pull it off, they'll dine well for the rest of the year! Somewhere, I can't recall where now, I came across a gigantic cottonwood that was half gnawed through. I knew that even if it was felled, there was no way that even a team of beavers could drag it back to the pond, which was a short distance away. However, they would probably take as many branches as they could cut.
For obvious reasons, beavers would prefer to not travel far from water when foraging for food. They are more prone to attack, and the work of bringing trees back to the pond from afar takes considerable time and energy. Nonetheless, there are times when these animals have to travel a considerable distance to gather food. It is easy to see how difficult this would be, for not only must they bring down trees, but they must transport them back over often rough terrain to their pond. Around ponds that have been inhabited for some time, well-trod beaver trails are frequently found. I have come across some that are wide, packed down and of quite a considerable length. At the FWG, the beaver has done no more than climb out of the pond and take trees closest to the shore. With the near-constant activity of dogs and people, he is probably afraid to chance even a short trek from the pond.
What happens next?
Once the snow and ice melted off the Amphibian Pond, the beaver made a reappearance. He attempted to repair his dam several times, but what with one thing and another, disruption to his dam by some visitors, lack of adequate food, and increased human and dog activity, the he left one day. We don't know exactly when, but by May it was certain that he'd gone.
But that was not the last of Castor candensis in our pond! One other beaver came by in the spring and again in the fall of 2010, but only for a few days each time. However, by late fall, we all began noticing signs of increased beaver activity. First, a red oak was gnawed at. Then more sumacs by the pond came down, then a dam was built! Cattails were being cut down at a rate greater than the resident muskrats could possibly do, which was another clue.
Eventually, we noticed that some of the bigger self-seeded poplars away from the pond had been cut down by a beaver. Then several volunteers spotted him at different times. So, it seems we once again have a beaver spending the winter in our pond. The habitat is so inadequate that we can't understand why he is staying. Except, lack of good wetland habitat is an increasing problem in our area. Beaver won't last long in ponds and wetlands already occupied by a resident beaver, so they must keep searching and end up in marginal habitat, which is what our pond is (from a beaver's perspective). So, we will see what happens in the spring of 2011. Stay tuned!
In December, David came across the beaver (below) anxiously trying to amass enough food for winter.
He has taken down several trembling aspens and sumacs, both of which grow back quite quickly, but we've carefully wrapped other trees that we'd like to preserve.
Much more information about beavers