CASTOR FACT The scientific name for the beaver family is Castoridae Members of this family are called castorids The North American beaver’s historical range Before 1500 Castor canadensis inhabited almost every part of the continent where there was wood and water THE BEAVER DISTRIBUTION MAP HINTERLAND WHO’S WHO CANADIAN WILDLIFE SERVICE ENVIRONMENT CANADA REPRODUCED WITH PERMISSION OF THE MINISTER OF PUBLIC WORKS AND GOVERNMENT SERVICES 2005 Humans have significantly changed the beaver’s world over the past 500 years PHILIPPE HENRY DESIGN PICS GETTY IMAGES different genetic blueprints Nevertheless they do all the same beaverish things like felling trees and building dams This book is mostly about Castor canadensis but a mighty beaver is a mighty beaver no matter where it lives Beaver Geography In ancient times Eurasian beavers were common through out Europe northern Asia and Great Britain Unfortunately humans nearly drove them to extinction By the 1600s there were no more beavers in Britain In Europe and Asia their numbers hit bottom around 1900 At that point only about 1,200 Eurasian beavers remained mostly living in remote parts of Scandinavia Russia and Mongolia Today the Eurasian beaver is making a comeback across much of its range The North American beaver’s homeland is you guessed it North America Long ago beavers populated populated almost every corner of what we now call Canada and the United States plus a sliver of northern Mexico Their domain stretched from the Atlantic coast to the Pacific coast and from just south of the Rio Grande all the way to the northern tree line In a few places it even reached the Arctic Ocean Pretty much the only parts of North America without beavers were those with no trees
or shrubs hot dry deserts alpine areas high in the mountains mountains and the Arctic tundra Most of the Florida peninsula was also off-limits Too many hungry alligators lurk in the swamps there Back then this continent was home to tens of millions of beavers Or maybe hundreds of millions no one knows for sure We do know that Indigenous Peoples had been sharing this continent with beavers for a very long time before Europeans showed up in the late 1400s and that the newcomers rapidly reduced the number of beavers Four-Legged Lumberjacks Beavers are famous for doing two things that no other animals except humans ever do They cut down trees and they build dams These two activities are closely connected because before beavers can start building a dam they have to gather their construction materials Although beavers are sometimes active during the day they usually work the night shift starting near dusk and quitting as the sun rises Their nocturnal habits make it hard to see them in action But if you go for a walk in any beaver neighborhood you’ll find signs of their work Felled trees are hard to miss and their stumps have an unmistakable unmistakable shape they look like the pointy end of a pencil Building isn’t the only thing beavers have in mind when they cut down trees Their first priority is dinner or lunch or breakfast Beavers eat many things but their most important food is cambium the soft nutritious layer of bark that lies between the hard inner wood and the tough outer bark After they’ve eaten the edible parts of a tree including the twigs and leaves they use the trunk and branches to build their dams and lodges Parallel tooth-sized grooves in the wood of these aspen stumps are a sure sign that a beaver cut them down FRANCES BACKHOUSE For beavers the inner bark of a freshly cut tree is delicious and nutritious food FRANCES BACKHOUSE 7
BEAVER TALES ANCIENT ANCESTORS Paleontologist Frederick C Kenyon stands beside the fossilized spiral-shaped burrow of an extinct beaver called Paleocastor in 1892 The site of this excavation is now part of Agate Fossil Beds National Monument in Nebraska ERWIN H BARBOUR MUSEUM DIRECTOR PAPERS ARCHIVES SPECIAL COLLECTIONS UNIVERSITY OF NEBRASKA-LINCOLN LIBRARIES THE BEAVER FAMILY got its start in North America about 37 million years ago Although there are only two beaver species alive today dozens of others have come and gone Some of these now-extinct beavers inhabited dry treeless grasslands Others were semi-aquatic like modern beavers Very few of them cut wood with their teeth or built dams Several years ago I visited the Canadian Museum of Nature to learn more about ancient beavers from Natalia Rybczynski She’s a paleobiologist a scientist who studies fossil plants and animals Natalia got her start in paleobiology when she was 16 in this same museum as part of a high school mentorship program One of the beavers Natalia studies is called Dipoides It lived in the Arctic millions of years ago when the climate was warmer and forests grew in the Far North Down in the museum’s storage rooms Natalia opened a cabinet and pulled out a drawer filled with fossilized Dipoides bones and teeth She and other researchers dug them up on Ellesmere Island which is only about 500 miles 804 kilometers from the North Pole They’ve also unearthed lots of sticks with Dipoides tooth marks on them During my visit she showed me some four-million-year-old sticks with gnawed ends the oldest beaver-cut wood ever found The largest beaver that roamed the earth was at least as big as a Saint Bernard dog Its scientific name is Castoroides but most people call it the giant beaver When Natalia handed me one of this beaver’s incisors I was surprised by its size and weight It was nearly 6 inches 15 centimeters long and as heavy as a brick That’s partly because tooth enamel is the hardest material in the body Natalia explained My favorite extinct castorid is Paleocastor These prairie-dog-sized beavers used their teeth and long claws to dig vertical shafts that spiraled 6 to 10 feet 2 to 3 meters down to their underground burrows Some of the diggings eventually filled with sand and solidified into trace fossils It’s hard to believe these rock-hard corkscrews were made by relatives of modern beavers but fossilized Paleocastor bones found inside them confirm their origins 8
Summer on Ellesmere Island in Nunavut can be cold and wet That didn’t keep Natalia Rybczynski on the left and her research assistant from their work at this prehistoric beaver pond MARTIN LIPMAN The giant beaver’s big blunt teeth were no good for cutting down trees or gnawing bark This ancient animal mostly ate soft succulent pond weeds FRANCES BACKHOUSE
