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A Dugong and Diver (photograph by Duane Yates)

There are about 120 living species of marine mammals (although that total may tragically become much smaller in the very near future).  Of this number, only one species is herbivorous.  The mighty dugong (Dugong dugon) is the last animal of its kind, a gentle lumbering remnant of the giant herds of sirenian grazers which once graced the world’s oceans. Dugongs are distinct from the three extant species of manatees (the world’s other remaining sirenians) in that they never require fresh water at any point of their lives.  Additionally dugongs possess fluked tails in the manner of dolphins and whales.

Dugong Range

Dugongs live in shallow tropical waters of the Indian Ocean and the Pacific Ocean.  They range from Madagascar to the Philippines, but are only common along the north coast of Australia (where conservation efforts and a limited human population have allowed them to live in peace).  Dugongs can swim in deep oceans for a limited time, but prefer to stay on continental shelves where they can feed on seagrass and marine algae.  Their all-salad diet does not prevent them from growing to substantial size: some individuals have been known to reach more than 3.5 meters in length (11 feet) and weigh over 950 kilograms (nearly a ton).  Although Dugongs can live more than seventy years, they reproduce extremely slowly.  Females gestate for over a year and then suckle their calf for around 18 months. Calves may stay with their mothers for many years after being weaned and need almost contact with their mothers for security and affection until they are almost grown. Young dugongs swim with their short paddle-like flippers, but adults use their tail for propulsion and only steer with their flippers.

Dugong and Calf

Dugongs have a variety of vocalizations with which they communicate.  Usually they live in small family units.  Great herds are not unknown but  seagrasses do not grow in sufficient quantity to support such numbers together for long.

Like the other sirenians, Dugongs have dense bones with almost no marrow (a feature known as pachyostosis).  It has been speculated that such heavy skeletons help them stay suspended just beneath the water in the manner of ballast.  The lungs of dugongs are extremely elongated, as are their large elaborate kidneys (which must cope with only saltwater).  Additionally, the blood of dugongs clots extremely rapidly.

Dugongs face a number of natural threats, particularly storms, parasites, and illnesses.  Because of their large size they are only preyed upon by alpha predators such as large sharks, killer whales, and salt-water crocodiles.  As with other marine animals, the greatest dangers facing dugongs come from humankind.  For millennia Dugongs have been hunted for meat, oil, and ivory. Traditional medicine from various portions of their range (wrongly) imputes magical properties to parts of their bodies. Worst of all, dugongs are frequent victims of boat collisions or are killed as by-catch by fishermen trying to catch something else.

Close-up of a Dugong (Julien Willem)

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.

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