30 November 2008

Beaver dam at Hoyles Mill

Towards the end of our field trip at Hoyles Mill Conservation Park on Friday, Tim Pearce and I were following a creek that, according to the map, intersected with the road that was to take us back to the car. Along the way we started seeing trees that had been felled by beavers. Soon, we were amidst an arboreal carnage.

BeaverDamHM1

Naturally, the scenery around us lead to freewheeling questions. What would happen if there were as many beavers on earth as there are people? Well, there couldn't possibly be 6 billion beavers, because there wouldn't be enough trees for all of them. Do beavers have predators? They must, because they've evolved a warning behavior—tail slapping on the water. Is the lack of beaver predators in suburban parks leading to unchecked population growth and consequently, excessive tree destruction? We couldn't answer that one.

BeaverDamHM2
Better not stand too close to this one.

Then we noticed that the flow rate of the creek had slowed down considerably: we were probably approaching a dam. Sure enough, first we came to a flooded area and had to take a detour to avoid getting wet. And finally, the beaver dam came into view.

BeaverDamHM3

We estimated the length of the dam to be about 20 m and the height about 1.5 m.

BeaverDamHM4

The beavers themselves and their lodge were nowhere to be seen. I will be visiting that area throughout the winter. I will try to post updates here.

1 comment:

George said...

I couldn't resist a quick web search to look up predation on beavers. Gray wolves are reported to be the most important predator on beavers, but black bears sometimes attack them, and may learn to dig them out of their lodges. Otters, lynx, coyotes, minks and bobcat probably at least attack juvenile beavers when they can. Beavers changed foraging behavior in response to the scent of canids, lynx, otter, bear, and African lion (?), so I bet cougars are a threat as well.
http://www.springerlink.com/content/x4n12757x7786736/

http://www.jstor.org/stable/2426580