Monday, November 17, 2014

The Beavers' Prediction for the Upcoming Winter?

One of this years beaver kits swimming with purpose
Predicting the severity of an upcoming winter based upon animal behavior is a hazardous enterprise. I wouldn't indulge in it myself if it weren't for the fact that it provides some fun. Every year when the beavers at the nature preserve assemble their winter food cache, they provide us with a great opportunity to prognosticate. The purpose of the food cache is to provision the beaver colony through the winter months when ice cover prevents them from foraging away from the home pond. Is the size of the cache indicative of what the beavers believe they need to survive the winter? Can we then accurately predict the length and/or severity of the winter based on the mass of the food cache? I think not, and past years show no identifiable correlation between cache size and winter length or severity. But if we suspend fact-based disbelief for just a minute, we can "confidently" predict a humdinger of a winter - because this food cache is a big one. The beavers started working on it in August and as of yesterday they were still adding to it.   
The food cache is brimming over with edible branches and it's still growing
10 kinds of trees make up the cache but willow, poplar and birch are the most common
It's somewhat difficult to gauge just how much beaver food is contained in the food cache since the vast bulk of it is underwater. The top of the cache looks like a fairly well contained brush-pile. Most of the branches coming in are added at the bottom of the pile. Heavier pieces and less palatable branches are heaped on top in order to keep as much of the mass submerged as possible. When the pond is iced-over, the beavers need as much as possible of the cache to be in deep water and not locked in by ice. This way they can more easily draw on the reserve from the bottom for as long as they need to.

Two of this year's beaver kits have excelled at storing food - unusual for youngsters
The kit's relative light weight makes the chore of submerging branches difficult
Sheer determination and paddle-power finally drive the branch down
Usually the season's new kits are not big on storing food. They are much more likely to latch onto and nibble on food that adults are trying to convey to the cache. However this year 2 of the season's 6 new kits have taken on provisioning roles. Most of the real heavy work is being done by GenLo, a 2-year old male, but the 2 kits are showing great determination in getting the job done. I've watched them struggle to submerge large logs - pieces so big that an adult would have difficulty managing them. The kits don't always succeed, but they take failures in stride and quickly set off to find another more manageable branch to deal with. 
A kit takes a break from storing food
At night GenLo cuts down some stream-side Yellow Birch Trees
The tops of birches became entangled in the branches of other trees, which stopped them from falling
Poor GenLo had to keep cutting down the same 2 trees over and over
The same scene by day
Beaver sculpture

Quaking Aspen - the beaver's favorite dish - is one of the last deciduous trees to change color and loose its leaves

Another branch meant for the cache
The kit rolls into the water and tries to drag the branch in behind
The beaver's tail disappears last
A cutting job that would've taken an adult beaver about 20 seconds takes the kit a few minutes
Nearly cut through it
A kit tries to wrangle a large aspen log
Unable to sink it, he decides to nibble on it instead
Julia (the colony's matriarch) swims in front of a kit
Tippy (2 year-old female) feeds at the dam with a kit alongside her
A beaver canal extends from the 2nd pond and out toward a field of willow saplings the beavers have been harvesting
Looking downstream at the main beaver pond from a smaller headwaters pond
An active beaver dam is characterized by the fresh mud plastered against it and by freshly peeled branches

Many years worth of branches piled up on the downstream side of the dam