The furry ecosystem engineers of the Copper River Delta

Swimming beaver towing an alder branch in a pond on the Copper River Delta. Photo courtesy of Mike Truex

In a breath, the height of the Alaskan summer has passed. The green, tender buds of willows and marsh flowers on the Delta have withered, replaced by frozen stalks and stiff branches poking out of the snow. Birdsongs have stilled, migrating to warmer and sunnier places in the south. Wandering brown and black bears have eaten their last salmon and berries, curling up to sleep until spring. Moose remain on the windswept meadows of the delta, standing belly-deep in the snow, motionless like statues. Land-locked freshwater ponds and sloughs have frozen solid. The delta’s web of meandering rivers, once bursting with life, have slowed to a slushy crawl. The once-busy beavers have now retreated to their well-insulated huts. Indifferent, the snow falls silently outside. Grey clouds coat the tips of the otherwise glowing Heney Range. Winter on the delta is in full rhythm.

The Copper River Delta is dominated by a coastal marine climate, making both the summer and winter seasons mild and wet. The climate is maintained by the Alaska Current, which delivers warm ocean air and low-pressure systems to Alaska’s Gulf. Wet, coastal air masses from the Alaska Current must either precipitate as they climb over the Chugach Mountain Range or remain trapped on the coast, increasing ambient humidity. The climate of the delta is also influenced by Alaska’s interior which has much colder winters and much hotter summers. One of the main routes for this interior-air to reach the delta is through the Copper River corridor. This corridor provides a funnel for the interior air to rush to the coast, causing strong sustained winds. The delta thus acts as a mixing zone of steady winds, cold to moderate ambient temperatures, and lots of snow or rain. All of this means, humidity is very high, ground water is flowing like veins through the soft earth, soils remain saturated year-round, and we are left with a landscape sprinkled in jewels, known as wetlands.

The climate, mixed with the natural history of the Copper River Delta, provides an ecosystem that is dynamic and thriving. Whether it is summer, or winter, you will be sure to find a furry animal, scurrying off on a mission. One of these furry animals, has picked a luxurious career as a landscape architect. Due to their ability to cut large trees and turn streams into ponds, they have rightfully received the title of ecosystem engineers. On the Copper River Delta alone, they have left a noticeable signature that can be seen when driving the Copper River Highway. Since the 1964 earthquake and geologic uplift, they have expanded their range southward, to new areas of uplifted marsh on the delta. After many years, the dams created by these furry engineers have created new habitats for other plants and animals. This animal has a variety of adaptations to prepare and survive the winter season on the delta.

Late winter on the Copper River Delta, taken from Alaganik Boat Launch. Photo courtesy of James Ianni/U.S. Forest Service

This furry, winter resident is the North American Beaver (Castor canadensis). The North American Beaver is the largest rodent in North America. Most adult beavers weigh around 35-70 pounds and can reach a length of almost 4 feet With heavily muscled bodies supported by large bones, beavers are short and thick. Their most noticeable feature is their flattened, paddle-like tail, which is covered in black, leathery scales. Adult beavers can walk upright on their hind legs, partially supported by their tail, while carrying mud or sticks with their front legs. In the water, beavers will alternate kicking with their hind legs. Their back feet have webbed toes that allow for graceful and efficient swimming. Interestingly, beavers have closeable nostrils, ear valves, a second pair of transparent eyelids (i.e., goggles), and lips that close behind their large incisors—allowing them to feed underwater. These intriguing animals spend the winter living in a snow-covered house, or hut. Unlike most small mammals, the North American Beaver does not hibernate. Beavers will stay awake all winter long – a feat that takes ingenuity. Beavers start planning for winter as soon as spring arrives. When the spring ice melts, the search for the perfect “home” is on. Beavers will examine the landscape, honing in on steady sources of water and mapping out potential areas to construct a dam. The dams they build are strong enough to hold back the force of a stream that will flood to become a pond. Once the area is flooded, they begin floating larger branches to the construction site. Once the dam is satisfactory, the beavers switch their attention to building their huts.

A hut is an essential part of a beaver’s life, like a house for us humans. Their huts provide shelter from predators and severe weather (e.g., the wintry delta). When building a hut, beavers must gather tons of branches, debris, and aquatic vegetation. Once the materials are gathered, they form them into a cone-shape. Most of the structure is then coated with mud, leaving the “peak” open for ventilation. This peak is the equivalent of a chimney. Within the hut is a chamber that has been dug out. This chamber typically has two underwater tunnels with openings above the water level. These openings are the entrance and exit to the hut. The main chamber is divided into two levels. The first level is a platform just above water level that is used for feeding and drying off. The second is a higher, drier platform cushioned with shredded wood fibers and grasses, used for sleeping. The chamber walls are thick (2-3 feet at the bottom) keeping the beavers warm. The snow that covers the hut in the winter also acts as insulation, keeping the temperature, inside the hut, relatively stable. This makes for a rather warm and cozy living area, compared to the cold, stark, windy conditions of Mother Nature, just outside the hut.

Late spring on the Copper River Delta of a beaver and dusky Canada goose, captured on a game camera. Photo courtesy of U.S. Forest Service, Cordova District Office Wildlife Program

In the fall, beavers also pack on their own form of insulation — fat! Beavers have a ravenous appetite in the months approaching winter. The fat layers they pack on act like a down jacket that we might put on before heading outside in the cold. To make sure they have enough food to last through the winter beavers will store branches, twigs, and any other vegetation that they can find. These winter snacks are staked in the mud, underwater near their huts. Acting as a refrigerator, the cold water keeps their food cold, crisp and fresh. All winter under the frozen surface, beavers swim back and forth, from their food cache to their hut! In addition to insulation, their fat is also very high in energy. This means they have a portable energy source ready to be burned at a moment’s notice. Did you know that one of the best fat reserves on a beaver is in its paddle-shaped tail? This means that their tails are continuously changing size! In the spring and summer, the fat stores grow increasing the size of their tail. In the winter, their tails shrink as the fat stores are used. Another cool fact about a beaver’s tail is that it is lined with a web of blood vessels, called rete mirabile (Latin for “wonderful net”). These blood vessels exchange heat and help regulate the beaver’s body temperature.

To make the icy water more comfortable, beavers have thick fur. Beaver fur is so thick that a stamp-sized patch of skin is carpeted with over 125,000 individual hairs — this is more than the average human has on their entire head! This thick, fuzzy coat helps insulate them from the cold. To give their coat extra waterproofing, beavers will groom themselves with natural oil. The oil is produced from glands beneath their tails. When grooming, a beaver will use a modified toenail on each hind foot, to coat themselves in the waterproof oil. Once coated, they can comfortably swim beneath the frozen surface. Grooming also creates a thin layer of air near the skin. This air pocket acts as another insulating layer while underwater. Historically, however, having this beautiful, thick fur coat was not always very advantageous. When Europeans arrived in North America, as many as 400 million beavers swam the continent’s rivers and ponds. Between the 1700s and 1800s, most beaver populations were decimated by fur trappers, primarily to support the European fashion for felt hats. Because of this, beaver populations in the eastern United States were largely removed and the continent’s population was estimated at only about 100,000. Fortunately, these declines caught public attention. Concern for the beaver eventually led to regulations that controlled harvest and methods of take, generating a continent-wide recovery of beaver populations. Although pristine beaver habitat has been heavily reduced in the lower 48 states via human land-use practices, beaver have proven to be a highly adaptable animal, able to occupy a variety of human-made habitats.

Aerial photograph of remnant beaver dams on the west Copper River Delta. Photograph courtesy of Wildlife Biologist Melissa Gabrielson/U.S. Forest Service

Beavers now occupy much of their former range in North America, although habitat loss has severely restricted population growth. Since the 1830s, about 195,000-260,000 square kilometers of wetlands have been converted to agricultural or other use areas in the United States. Many of these wetlands were most likely beaver habitat. Beaver are adaptable, being marginally able to subsist above timberlines in mountainous areas and occupy very cold regions. Beaver have yet to colonize Alaskan or Canadian arctic tundra, possibly due to the lack of essential woody plants for winter food and lodge construction, or because thick ice limits surface access in the winter. However, in milder areas of Alaska, beavers thrive. The Copper River Delta supports a healthy population of beavers due to their low natural mortality and an abundance of suitable habitat. Because of their large size and limited amount of time away from the protection of water, adult beavers have relatively few natural predators! Young beavers, also known as kits or yearlings, on the other hand may be eaten by black bears, coyotes, bobcats, and even great horned owls.

Next time you are out on the Delta, look for signs of beaver including newly cut alders or a hut on the edge of a pond or slough. Take note of the area, see if you can find aquatic plants and insects in the water, look for waterfowl and fish. Take a minute to count how many different species you find and think about the natural relationships that might be happening. You might not have to ask scientific questions or consider the ecological richness that beavers create in order to enjoy them! Maybe sitting and soaking in the serene area, while beavers motor across the pond is enough. But while enjoying the vast, lush landscape, be sure to thank the furry ecological engineer that is the North American Beaver.

If you would like to know more about the world of beavers out on the Copper River Delta or their natural history, please feel free to contact Erin Cooper, Terrestrial Program Manager (Wildlife/Ecology/Vegetation) at the U.S. Forest Service, Cordova District Office at 907-424-4757 or

James Ianni is a Biological Science Technician on the Chugach National Forest, working for US Forest Service in the Cordova District Office. James has spent about a year working on the Chugach National Forest, studying a variety of wildlife, ecology, and vegetation resources in both Glacier and Cordova Ranger Districts respectively. In addition to assisting in research efforts on the Chugach, James has also been consistently involved in a variety of public outreach events including guided hikes, school programs, local festivals, and writing educational articles for the public.

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James Ianni is a Biological Science Technician on the Chugach National Forest, working for US Forest Service in the Cordova District Office. James has spent about a year working on the Chugach National Forest, studying a variety of wildlife, ecology, and vegetation resources in both Glacier and Cordova Ranger Districts respectively. In addition to assisting in research efforts on the Chugach, James has also been consistently involved in a variety of public outreach events including guided hikes, school programs, local festivals, and writing educational articles for the public.