I’ve recenlty been fascinated with a certain mammal. The North American Beaver. My wife and I had an encounter with a few beavers this weekend past and were very curious about their history and motivations.
Things we do know are that they are the largest rodent in north America, they were nearly trapped to extinction in the late 19th century and they are natures construction workers…
It is this latter part I am most interested with. How on earth did beavers as a species learn to dam off a river to create a pond to house it’s lodge and food source? That is an aweful lot of variables to have straight.
Building materials, location, location, location. Position of the dam to allow sufficient water to collect forming a pond, trapping fish and other food sources.* The building of the lodge…from the outside there are no visible entrances, as that is located secretly underwater. How does a species do this? Is there anything else in the mammal world that is this complex?
** The lodge my wife and I stumbled upon in the middle of our hike was huge. Easily 12 feet in diameter and close enough to shore that we could walk right up to it. The inhabitants were elsewhere we think… I plucked one of the larger sticks off the top, it was perfectly straight maybe 7’ tall, and completely stripped of all bark. It looked like it was seasoned very well. The must be eating the bark right? This would allow the wood to season, and not rot, very ingenuitive…
Well, there’s us. We manage to make complex stuff too.
And it’s not a mammal, but there’s a bird that make a very complicated house. I wish I could remember more details, but I can’t recall enough even for a Google search. Hopefully my disjointed ramblings on the subject are enough for someone to know what I’m talking about and provide more details.
Regarding the amount of variables, I suppose there are simply many less complex steps to lead up to the current situation. Perhaps Beaver ancestors only damned off a small eddy first, stuff like that.
It’s also helpful to realize that just because one cannot think of a step thats both useful and less complex, that doesn’t mean nature couldn’t think of one.
He decided that they actually reacted to the sound of running water escaping through their dams and plastered it up where the sound was coming from. So he made recordings of water, and stuck speakers all over a beaver dam. Sure enough, the beaver plastered over the speakers when he played water sounds over them, and otherwise ignored them.
Beavers aren’t actually that efficient in their use of materials - they down a lot of young trees that fall wrong or get hung up on something, and they can’t drag them off, so they leave them lie.
A creek will naturally form snags at good dam building points. I’m going to guess that a beaver operating “from scratch” starts out where it finds a beginning obstruction.
I don’t have a lot of trouble with natural selection evolving dam building behaviour, actually, since it is something that can be gradually improved. An ancestral animal with a proclivity to stack up a few sticks in the creek winds up deepening it a bit, and making it a better habitat for themselves. Over time, the individuals that exhibit more tendency to build dams make bigger ponds, which help them survive, until we get to the modern day animal that spends a great deal of its energies on blocking up creeks.
Muskrats sometimes make similar houses for themselves, although they are smaller animals, and tend to use things like grasses and reeds rather than sticks. They build a mound, then swim underwater and chew out an entrance into it and a chamber. Muskrats may also simply dig out burrows in the bank.
And I recall seeing on several Nature programs that the average termite mound is a miracle of engineering, and that they in fact ‘breathe’ to get air to the lower chambers
Beavers “learned” it partly by instinct, partly from their parents, partly by experience, like most mammals. I’m certain there are some beavers better at it than others.
I suspect it developed out of nest building, & evolved from there.
This thread instantly brought to mind the photograph of a beaver felled by his own tree, which once could be found on www.darwinawards.com. Regrettably, I can no longer find it.