Sunday, October 20, 2013

The Spring Farm Beavers Prepare for Another Winter

Julia swims in to grab a poplar branch
She swims back toward the lodge with her prize in tow
Over the last month Spring Farm's beaver family has been collecting and storing branches in their underwater food cache. This year work on the cache was started a little later in the season than normal, but not nearly as late as in some years. Its tempting to make a correlation between how early beavers start assembling a cache, how large that cache is, and how severe the coming winter will be. Do the beavers have some foreknowledge that we lack? Are they able to tailor their provisioning based upon intuition? My guess would be - probably not. According to my observations, sometimes a large cache would be assembled in fall, and then the winter that followed turned out mild. Other years the cache was smaller and then harsher winter conditions led to the beavers to exhaust their supplies before the ice fully retreated from their ponds.
The upstream area where beavers are currently logging
The view looking back at the back at the beaver pond from the logging zone
The beavers do their tree cutting in late evening or early morning hours
Interestingly, food cache size isn't always indicative of the size of the colony that will be drawing from it. Food cache size seems to have more to do with how ambitious the individual food collector are - and of course, how many edible trees are available for cutting. Also the number of beavers actively collecting food makes a difference in the size of the cache. Not all beavers in a colony will be food collectors. In our colony, it’s usually the adult male that has taken on the primary role of procuring food, with 2-year old offspring also playing a not insignificant part. The adult female will also contribute, especially if there are no adult males or near-adult offspring. This year our colony is very much reduced from what it was last year. We now only have the adult female (named Julia) and 3 of her offspring from 2012. So far as I can determine, it seems to be primarily the yearlings that are collecting food for the cache, but Julia is also doing some of the heavy work.

The food cache is placed in front of the lodge - it looks like a partially submerged brush pile
It often takes many successive nights of work to cut a single large tree
The tree was cut through but then got hung up in the branches of other trees
An overnight wind storm brought the tree now - and now it's time to move it
Over the last few weeks I've had the trail camera set on an area just upstream from the beaver ponds. Here the beavers have been actively cutting down trees. Their main targets are medium sized Yellow Birch trees that grow right along the stream-side  but they are also taking Sugar Maple and White Ash saplings. The work they do takes place after sunset, with the most activity taking place between 11:00 PM and 3:00 AM. Smaller trees may be taken down in a matter of minutes, but when dealing with larger diameter trees, it often takes the beavers multiple nights and even weeks. With their amazingly sharp chisel-like teeth, they pry out chip after chip of wood until they create a large gash at the base of the tree. Sometimes, a trunk will be chewed completely through, only to become lodged in the branches of neighboring trees. In a case like this, the beaver may need to cut through the trunk all over again, in an attempt to make the tree fall free.
Tree trunks are cut into sections to make them more manageable 
It's always easier when trees fall into the pond, but  some cutting is still necessary
One of the yearlings uses his weight to pull free a branch
Sometimes, the beavers are lucky, and the tree falls into the pond or across the creek. Wood that is already in the water is easier for them to deal with, but they are fully capable of wrangling branches and even tree trunks that fall very far from the water. They are adept at chewing off large branches and then using brute strength and ingenuity to pull them free from all obstructions. They will twist, turn and tug at a branch until it starts to slide and then they will do their best to keep up their forward momentum. Beavers are as tenacious as  any terrier, and they have a lot of weight, which they use to clever advantage. They will grab wood in their teeth, pull it upward and then use their weight to trust is forward. This might just get them a few inches, and they may need to alter their hold many times - anything it takes to move the piece further along. Trunk pieces that are too large to drag will be chewed into segments. Occasionally beavers will work cooperatively to move a large tree. I was hoping that my camera might pick up this behavior, but so far, no luck.
Is that a camera in that tree?
A Raccoon checks out the beaver's work
A Turkey Vulture visited the logging site one day
Beavers can be very quick in their reactions, and when it sounds like a whole tree might be coming down, all beavers make a fast dash to the water and to safety. They react in a similar manner when they sense a predator or hear any suspicious sound.
Beaver tooth etchings on a tree trunk
Beaver sculpture

No comments:

Post a Comment