Tuesday, April 24, 2012

Beavers in Centennial Woods

beaver swimmingbeaver slapping its tail

What: Our first rains in ages!! And that new rain seemed to be a bit too much for the beavers of Centennial Woods. The rain started on Saturday night and continued well into today (Monday). I was out yesterday and the lower dam (which burst in January and was repaired in February) blew out by about 1pm. Sometime later on Sunday the upper dam blew out. Luckily over the last week they had built a new dam in between that kept up a channel about 3' deep. 

Ecological notes: The water was awfully murky from the heavy siltation due to all the rains. Not only was this the first rain in a while, but the temperature has dropped considerable. I watched the beavers from about 4:30 to 8:30 and by the end I could see my breath pretty clearly. Since the beavers are right next to the trail, it was neat to watch how they respond to dogs and hikers. They definitely perceived the hikers with dogs well before those without. It also took the beavers less time to return to baseline following a hiker without a dog. Hikers with dogs were less likely to notice the beavers. Everyone was definitely enthused about the beavers though and it was great to get to share their excitement.

And I'm still trying to wrap my head around why the beavers will slap their tail. It's not as easy as they do it when they feel threatened and to ward of would-be-predators. I think they will do it to communicate to others over longer distances. This one slapped its tail while it was on one side of the bridge and the other two beavers were upstream. It was as though it were saying, "Hey don't forget about me, I'm down here where all the people are (there were 8 of us at one point)." It seems to also serve as an indication of investigation, as with the chickadees, "Chicka-dee-dee" call they make when they get close to people. It seems like they're saying, "I"m going to go investigate something, would you check in with me in a little bit to make sure I'm still alright." I've seen beavers make this sound to nothing in particular before they headed upstream out of eyesight of other beavers.

Where: Middle terrace of the beaver dam under the Velco powerlines.

Other notes: Twas also a great afternoon for birds. Saw a pair of geese land in the retention pond, a Cooper's Hawk, flicker, and phoebe skirting the edge of the pond, winter wrens singing, and lots of cardinals, robins, song sparrows, grackles, and red-winged blackbirds. Surprised I haven't seen more nests yet - I'll have to spend some more time tracking individual birds. And no sign of Ryan's ruby-crowned kinglets today.


  1. How close were you to the beaver in the footage? He's not nervous - doesn't even seem to be aware of human presence

    1. I was across the bank for the video, about 15' away. I was closer for the photos. What's interesting is actually how aware they are of the human presence; I think it's more that he just wasn't threatened by us. The beavers always noticed people before people notice the beavers (same is true for domestic dogs). The beavers' response was variable from person to person, the most dramatic response is a tail slap when the person is still about 100yds away, for others they'll simply slip into the water and swim up or downstream.