The North American river otters (Lontra canadensis), also known as the northern river otter, the river otter, or the common otter, are probably one of the most energetic semi-aquatic mammals on earth. No matter where they are, once they get started, they just keep going and going… like the Energizer bunny. But, endurance is only part of the story. For an animal of their size, their stunning speed of swimming and running is beyond imagination. To support their exceedingly active lifestyle, many special adaptations have evolved. In the nature, they are found in the waterways and along the coast of the North America continent Canada and the United States. They prefer bog lakes with banked shores that have semi-aquatic mammal burrows and lakes with beaver lodges. In general, they adapt to these habitats exceptionally well. Therefore, they have a decent lifespan of 15 years.
“The sky’s the limit!”
These northern river otters are rather versatile compared to their semi-aquatic peers. In the water, they are the aquatic acrobats. They can make challenging turns without losing speed. They can dive or resurface in precise, vertical movements. Their tumbling tricks are show grade. Not only they are performers, but they are also great athletes. On average, they can swim at speeds approaching 11 km/h (6.8 mph), dive to depths as deep as 20 m (22 yd.), and travel up to 400 m (440 yd.) while underwater. On land, when they are in a hurry, they can run as fast as 15 mi per hour, nearly the speed of a car. But, when they have a moment, they stand tall on two hind limbs and take time to explore their surroundings, which is a rare specialty for a four-limb semi-aquatic animal. Whether moving slowly or fast, they have the capacity of traveling up to 42 km (26 mi) in one day. What about ice-covered land, a familiar winter scene in North America? Not a problem. On ice, they run and slide, a much more entertaining sight than the polar bears’ strolling image. Because of these outstanding aquatic and terrestrial talents, transition from land to water or vice versa is a piece of cake to them. Anywhere they wish to go, they surely can get themselves there—The sky’s the limit!
Thanks to unparalleled adaptations
These river otters truly thrive in the water, thanks to their unparalleled adaptations. As agile swimmers, they have wide, webbed feet for pushing them against the water and long, powerful tails for propelling them through the water. This combination of swimming apparatus places some faster river otters at a record of 9 miles per hour. As if those adaptations were insufficient, their slender body and flattened head allow them to create one of a kind streamlined movement in the water. As productive aquatic predators, they possess multiple lengthy whiskers that can detect preys even in the dark or murky water. Their clawed feet can secure the most slippery prey. Their musculature and skeletal structure enable them to make sharp, sudden turns that not only startle their preys but also grant them no chance of escape. Most importantly, they are extremely comfortable in the water. As sustainable divers, they can stay underwater for as much as eight minutes. They have transparent nictitating membranes to protect their eyes while swimming like wearing a pair of natural goggles. Even better, they have valves in their ears and nose that close automatically when they submerge. Most importantly, to keep their body warm under the water, they grow dense underfur over their body that contains about 156,000 hairs per square inch, and lay longer guard hairs on top of the underfur. These guard hairs, as the name suggests, guard the underfur from getting wet. What this unique integration of under fur and guard hair does for an otter is that it traps a layer of dry, insulating air to maintain its body temperature during an extended length of time under water such as 4-6 minutes of diving. In this aspect, it’s reasonable to say that these otters swim/dive in a virtually waterproof down coat. Can any other swimmer or diver be better equipped than these otters?
A nonstop eater
Since these river otters are constantly on the move, they must eat throughout the day to keep up with their extremely high metabolism. They can digest food as quickly as less than 3 hours. Their diet includes both aquatic and semi-aquatic preys. Considering their lightning speed, slow-moving fish, mollusks, aquatic insects, crayfish, turtles, and frogs are their “fast food”. But, birds and small mammals are also appealing to them. To handle such a variety of food items, they have many teeth (36 teeth in an adult otter), and some of them are specialized teeth. The large molars, for example, are used for crushing hard objects, like the shells of mollusks. Their well-evolved teeth and high demand for energy justify their huge appetite. An adult river otters can consume 1 to 1.5 kilograms (2.2 to 3.3 lb.) of fish, the primary component of their diet, per day. If fish alone cannot satisfy them, they go after beavers and birds. But, interestingly, they leave bird eggs intact, sparing the life of the prospective chicks.
A pragmatic inhabitant
Because of their ability of tolerating a broad range of temperature and elevations, the North American river otter are present in many aquatic habitats other than rivers. Those include lakes, inland wetlands, coastal shorelines, marshes, and estuaries. In other words, so long as there are a steady food supply and an easy access to a body of water, these otters will make it their home regardless of a freshwater habitat or a coastal marine habitat. Although these criteria might make them look like a very flexible animal, they are, rather strict about the living quality of their habitat. Being on the top of the food chain, any water pollution or other factors that contaminate their habitat would reduce their food supply. As soon as they discover that they are short of meals, what they do? They pack and go. Never expect loyalty from these animals! As emotionless as these otters might sound, there is a bright side to their pragmatism. Since they are so sensitive to the pollution in their habitat, the departure of these otters has served as a warning signal for an unbalanced or unhealthy ecosystem to the professionals who monitor them— that is to say, these otters are a perfect bio-indicator, if you will.
With a little help from their human friends
The North American river otters have relatively few aquatic predators and don’t usually coexist with their terrestrial predators within the same habitat. However, even with this great blessing that any animal would dream of, their population is still declining. This is mostly due to the negative impact of human activities, for instance, oil spill and the presence of toxic chemicals etc., on their habitats. The corresponding food loss makes withstanding an active lifestyle a grueling task for them. If we hope to continuously have these vibrant creatures enrich the world we are living in, we must commit ourselves to improving water quality at their favorite spots so that their survival can be guaranteed.