Sunday, June 24, 2012

Disaster at the Beaver Pond

The 20 foot gap in the dam that drained Sarah's Pond
Somewhere between last Wednesday night and Thursday morning, disaster struck our main beaver pond when a 20 foot section of its dam collapsed. The Pond drained very rapidly and the resulting torrent of water destroyed other canals, ponds and dams located downstream. Such a rapid draining of a pond containing hundreds of thousands of gallons of water has the potential of killing beavers, but so far I have found no evidence that any of the colony were killed. I still have yet to account for all of the members of the colony –but that’s not too unusual even in normal circumstances.

The 6 foot tall dam was built up by our beaver colony over the course 12 years

The Pond (named Sarah’s Pond after one of the original beavers that created it) had been steadily increasing in size during the last several months as the beavers worked to heighten its dam and at the same time dredge its bottom. The increasing amount of water in the pond exerted a greater and greater amount of pressure on the earthen dam and caused it to finally give way. More typically, these dam failures happen during significant rain storms.

Visible for the 1st time since they were originally laid down - a line of the dam's foundation stones
The pond is now largely empty of water, with the exception of the wide stream channel and a relatively small pool in front of the remaining dam. Now in only about one foot of water, stranded fish are easy prey for Great Blue Heron and Belted Kingfisher, which have increased their presence following the disaster. Newly exposed mud flats now bring in Killdeer and even some songbirds like Robins and Grackles that are looking to pick off the invertebrates that are lurking in the mud. Butterflies also gravitate to the mud, but their interest is to imbibe water and minerals.
A Belted Kingfisher finds easy hunting at the small pond that remains

The lodge at Sarah’s Pond is completely intact, but all of its normally underwater entrances are now exposed to the air. This means that the lodge is no longer safe from predators and the beavers will be forced to quickly build a new lodge or to refurbish an old one. This lodge had just been expanded to accommodate a larger family and a deeper pond. New beaver kits had been recently heard inside the lodge, but no new kit had been seen outside of it. That is until Thursday, when one of them was finally seen at one of the lodge's exposed entrance tunnels.
The beaver lodge with its entrance tunnels exposed

The beavers wasted no time in getting one of their ponds back into shape. On Thursday afternoon, shortly after I discovered that there had been a disaster, I found 2 of the one year-old beavers down at the 4th pond (called Secret Pond) working on the dam. The water level of that pond had already risen fairly high, and though this pond is much smaller than the one that they lost, it would adequately serve the beavers’ immediate needs.

May Apple works to restore the dam at the 3rd Pond
There is no lodge at Secret Pond, but there is an old dilapidated lodge in the 3rd pond –one that was originally build around the stump of a large Black Willow tree. In order to use this lodge, work began immediately to repair the 3rd Pond’s pulverized dam. The beavers' objective is to raise the pond level and resubmerge that lodge’s entrance tunnels.

Beavers take these kinds of disasters in stride. Certainly none of them were moping around or even caught without some ready plan to implement. Julia, the adult female appeared as calm as ever as she rhythmically munched on a care package of poplar branches that I had brought to her new home pond. This disaster served to bring out this year’s new beaver kit(s) a little prematurely. Normally, the kits would not be seen outside of the lodge for at least another week. There may in fact be only one new beaver kit this year, but I have yet to determine the litter size for certain.
A single new beaver kit is seen climbing over the dam to join his mother

Other animals were quick to make the move to Secret Pond. On my visit there, I saw that a Mallard family, and several of the resident muskrats where already there. Frogs and dragonflies were also there –as was one of our mink.

Secret Pond is a relatively small pond - and quite a shady place

Back in 2006, during a July rain event, Sarah's Pond's dam gave way in a similar manner . In that instance the beavers did begin repairs on the broken dam nearly immediately following the breach. But their main response was to shore up the dam at Secret Pond and at the 3rd pond and to move into to the lodge at 3rd  Pond -which is essentially the same thing that they are doing this time.
Julia enjoys her care package of Quaking Aspen boughs

It may or may not be be a long time before the beavers resurrect
Sarah's Pond. For sure, beavers are difficult to predict. Whatever they do, the pond bed's appearance is sure to change. If the beavers leave it alone, it will quickly begin to sprout grasses and within a month it will look more like a grassy meadow and less like a brown impact crater. Often beavers wait until the grass grows in thick and lush before they flood the pond again. In this way they can feed on the submerged grasses. This is one way that beavers farm their land.
The stream now flows relatively unencumbered through the remains of several dams

A Mink bounds over a half-downed willow trunk at Secret Pond


  1. Nice writing and kindly attention to beaver detail. What lousy timing for a washout with a new kit and maybe more! We have certainly watched our share. I'm glad you brought poplar, one thing we have noticed over the 5 years watching our colony is that regardless of the crisis (or maybe because of it) beavers are happy to sit aside and chew something delicious while they settle their nerves and decide what's to be done! The worst washout we ever observed was man-made (when Skip Lisle installed our flow device) and the entire family worked ALL night to restore the dam. Kits were even taking sticks OFF the lodge to fix the dam!

    Heidi Perryman, Ph.D.
    President & Founder
    Worth A Dam

    1. Hi Heidi,

      Thanks for the interesting comment. Yes, beavers are very good recyclers. Of course, the washout has left a lot of building materials scattered around for them to work with. Yesterday, I spent some time watching them as they pried branches out of the stream banks where the torrent had deposited them. They were cutting them to size and adding them to the dam at Secret Pond.
      Beavers in a crisis work double shifts and so they already have Secret Pond’s water level up to respectable levels. Simultaneously, they have repaired the dam enough at the 3rd pond to submerge some of that pond’s lodge’s entrance tunnels. I still haven’t accounted for about half of the colony, but I’m still hopeful that I will be able to in the coming weeks.

      - Matt Perry