The Beaver

From time to time, Ferrebeeekeeper indulges in a theme week.  Last Halloween featured Greek Monster Week, which highlighted the mythical spawn of Echidna, the great serpent mother of classical mythology.  Other theme weeks have included Tree Week and Small Furry Animals Week (which described the groundhog, the pika, the hyrax, the rabbit, and the wombat).  In order to combat malaise in the world construction markets, Ferrebeekeeper now presents Builders Week, five posts dedicated to great builders and the edifices they have created.  To start off the week, this post is dedicated to the beaver, the most accomplished and tireless builder of the animal kingdom–save perhaps for corals, termites, and humans.  Not only is the busy building beaver a keystone species to ecosystems around the Northern hemisphere, the furry rodent holds a key place in American history.

Eurasian Beavers (Castor fiber) photo by zooadmin

There are two species of beaver, the North American beaver (Castor Canadensis) and the Eurasian beaver (Castor fiber).  Although similar in appearance and habit, the two species are not genetically compatible and, when mated, do not produce living offspring.  Like the other giant rodents (capybara, nutrias, etc) beavers are semi aquatic and spend nearly as much time in the water as on land. In order to get around on land and water, beavers have webbed clawed feet and a flat, hairless paddle-like tail.  Their ears and nostrils clamp shut under water and a special membrane snaps over their eyes.  In order to keep warm in harsh northern winters, beavers have a layer of subcutaneous fat as well as a dense coat which they waterproof with oily castoreum (produced from a scent gland).  To round out their special features, beavers possess formidable upper and lower incisors with which they gnaw down trees. Adult beavers can weigh up to 30 Kilograms (about 60 pounds) and attain lengths of 1.3 meters (about 4 feet).

North American Beaver (Castor canadensis)

Beavers are intelligent animals which form close family bonds. According to the website Beaver: Wetlands and Wildlife:

Wildlife rehabilitators find beavers to be gentle, reasoning beings who enjoy playing practical jokes…. Beavers mate for life during their third year. Both parents care for the kits (usually one to four) that are born in the spring. The youngsters normally stay with their parents for two years, and the yearlings become babysitters for the new litter. After weaning, their favorite foods include water lily tubers, apples and the leaves and green bark (cambium) from aspen and other fast-growing trees.

Above all, the beaver is a masterful builder capable of cutting down large trees and moving them into place to serve as the foundation of a dam.  Reinforced with mud, and “planted” with living green shoots (which grow into the structures and thus add stability), beaver dams curve backwards against the current and are capable of holding immense volumes of water. Not only do beavers fell trees and create timberworks and earthworks, the creatures also excavate canals to provide a quick escape into the artificial lakes produced by their dam building. Within these lakes the beavers build lodges as escape shelters and winter homes.

Cross-section of a Beaver Lodge (DEA Picture Library/De Agostini Picture Library)

Such lodges can only be entered through hidden underwater entrances.  Crafted in sprawling mounds from logs, branches, and mud, the structures contain rooms for dying off and rooms for habitation.  Before winter the beavers coat their lodges with mud which freezes into a hard coat which makes the structures impervious to bears and wolverines. Beavers harvest tender shoots from their favorite softwoods and embed them deep in the mud of the coldest deepest part of their lakes.  In winter when the top of the lake is frozen, the animals can dive down and retrieve food from their underwater refrigerator.

The Largest Known Beaver Dam Photographed from Space

Beavers are ambitious in their work. To date the largest beaver dam discovered was over 850 meters in length (2,790 feet)–more than twice the width of Hoover Dam. Located in the forests of Alberta in Canada the huge dam was spotted from space via Google Earth.

The flooded lands formed by these dams provide a habitat for waterfowl, turtles, frogs, and other aquatic creatures (as well as protected nurseries for salmon fry). Additionally the dams alleviate flooding, allow the water table to recharge, and act as filters which soak up nitrogen and chemicals.  Some writers have (poetically?) described beaver dams and related lakes as the kidneys of a watershed. Since beaver dams are depositional environments, they silt up into rich bottom land when abandoned by their builders. This process is vital to forests and rivers in North America and Europe, where soft quick growing trees have evolved to deal with beavers’ appetite and industry. However beavers have caused disastrous flooding and environmental mayhem when furriers introduced them to areas (like Tierra del Fuega) where trees do not coppice.

The Fur Trade

Furriers have a long dark history with the beaver. Eurasian beavers were over-harvested to the point of near extinction by medieval trappers for their lustrous coats.  When the New World was being conquered and colonized by European nations, the valuable fur of North American beavers was one of the first economic incentives for exploration.  Trappers, traders, and runners-of-the-woods traveled deep into North America for the pelts of all manner of creatures: but they sought beaver hides foremost.  The dense fur was ideal for making the fashionable flamboyant hats of the seventeenth and eighteenth centuries (additionally beavers were classified as fish by the Catholic church and their flesh had special allure for hungry devout French trappers during Friday fasts). Competition between French and English fur traders for the pelts from the territory between the Alleghany Mountains and the Mississippi combined with long brewing national conflict to start the French and Indian War which in turn determined the course of civilization in North America.

The Echidna

The Short-Beaked Echidna (Source: M McKelvey/P Rismiller/)

Last year featured an in-depth examination of Echidna, the terrifying “mother of monsters” from Greek mythology.  To start this year on a glorious high note, here is an essay concerning the actual echidnas (Tachyglossidae), a family of mammals from Australia and New Guinea.  The echidnas were much wronged when explorers named them after a hellish demigoddess.  Although I have never met—or even seen—a living echidna, they are one of my favorite creatures for many reasons.  Combining a gentle temperament with fascinatingly alien intelligence, the echidna is a delightful animal whose taxonomical oddity reveals the strange paths of fate which life takes over great expanses of time.

Along with the charismatic platypus, the echidna is the last of the egg-laying monotremes.  Monotremes are a very different sort of mammal than the other two major divisions of mammals, the eutheria and the metatheria.  The teeming eutheria (familiar mammals like shrews, manatees, picas, goats, and humans) nourish their fetal young by means of a placenta.  The ancient metatheria (marsupials) sustain their developing young in a special pouch.  The monotremes predate both groups and give evidence of mammals’ origins.  Genetic studies suggest that the monotremes originated from some reptile-like ancestor about 220 million years ago.  The long and tangled family history of the mammals and their antecedents will have to wait for another post–suffice to say that monotremes have been here for an extraordinarily long time.  The surviving monotremes, however, are not primitive atavists, but extraordinarily advanced descendants of those ancient progenitor mammals.  They have evolved and survived in varying fashions over the long eons.  Over those millions and millions of years, the echidna developed a very interesting brain.

Echidnas have the largest neocortex relative to bodymass of any creature.  The neocortex (which Hercule Poirot always creepily referred to as “the little grey cells”) is involved in higher brain functions such as spacial cognition, logic, and problem solving.  This special tool has taken the echidna far: like humans, and unlike almost all other creatures, echidnas live in very diverse habitats.  Actually it is the short-beaked echidna (Tachyglossus aculeatus) which lives in different habitats—the other two extant species live in tropical New Guinea and are little known to science.  Although all three species seem to share most traits, I am really writing solely about Tachyglossus aculeatus which ranges from the hot dry desert scrub, to the tropical rainforest, to the coast, to the cold snows of the Australian Alps (where they can lower their body temperature a few degrees above freezing and hibernate).  Echidnas live on termites and ants, omnipresent social insects which are evolutionary winners in their own right.  Echidnas dig up these insects with powerful razor claws and gobble them down using a long sticky tongue which zips in and out of a toothless tube-like mouth.  Echidnas are not known to fight each other or other animals.  In the great evolutionary battle they are pacifists (provided you are not an ant or termite) and if approached aggressively they will curl into a ball and trust their sharp spine-like hairs to keep them safe.  They are also phenomenal burrowers and can quickly tunnel down through anything other than solid stone.

An orphaned puggle being handraised.

Because of their cleverness, relatively little is known about echidnas.  They are difficult to capture since they disdain baits and can figure out most traps.  Similarly, in zoos, echidnas have proven extremely gifted at escape.  Their mating habits are largely mysterious to us but seem to involve non-confrontational competition.  The female echidna is followed for an extended period of time by a train of interested males.  In response to an unknown signal, the male echidnas begin frantically digging, trying to nudge one another out of the way.  Just how the victor emerges from this competition is unknown, but one the female has chosen, the other males walk away with no obvious rancor.  After laying her egg, the female immediately rolls it into a pouch-like fold on her abdomen.  Once the puggle has hatched, the mother echidna solicitously tends it for seven months, after which it roams off free and solitary.

Echidnas have an extra sense, electoreceptivity, but for them it is much weaker than it is in their close cousins the platypuses.  It has also been noted that echidnas vibrate. Water placed near captive echidnas shows distinct ripples in the surface. Perhaps they vocalize on frequencies beneath the range of human hearing (as do elephants).  Speaking of captivity, Echidnas have survived for up to 30 years in zoos even though it is a difficult environment for the blithesome free-roaming animals.  It is believed they live twice that long in the wild—but, again, nobody really knows.

Agh! Get away from there! I though you had a large neocortex!

Likewise nobody knows the echidnas’ total population numbers or how healthy the species is.  What is known is that, sadly, even the intelligent and peaceful echidnas are running into problems in the modern world.  Like other good-hearted pedestrians, echidnas are often killed by careless drivers.  Echidnas face increasing habitat destruction from human houses, farms, and roads.  Likewise they must deal with new predators, the dingos, which have discovered that urinating on balled-up echidnas will cause the latter to uncurl for a moment in stunned disgust (giving the ruthless dogs a chance to rip into their guts).

I wonder what echidnas think of us.  They know of our traps, our radio-tracking devices, and they know how to avoid aborigine hunters.  They are becoming wise to our deadly cars and to the dirty tricks of dingos.  Still they remain curious about people and will sometimes come out of the wilderness in groups to examine our suburbs and cities before melting back into the wild.  Humankind took a long while to understand that echidnas are not dim-witted reptilian pincushions but rather clever and highly developed generalists.  Do they generously think the same of us, or do they put humankind from their mind as something foul when they head back to the ancient, open outback?