Understanding how animals adapt to their environment has kept biologists busy for centuries. The forelegs of moles, for example, function as living shovels, and penguins "fly" through water.

Similarly, beavers are ideally suited to a semi-aquatic lifestyle.

Trapped by the ice that covers the pond, beavers spend most of the winter confined to their lodge. Underwater exits from the lodge permit access to the pond, where they eat the green branches and small logs they stored underwater the previous fall.

Though adult beavers weigh 25 to 60 pounds, making them the largest rodent in North America, they swim effortlessly thanks to powerful webbed hind feet. They groom and waterproof their lush fur by applying oil from two abdominal glands. The oil is applied with a unique double claw found on an inner toe of each hind foot.

Navigating underwater is facilitated by a transparent inner eyelid -- a nictitating membrane -- that permits clear vision while submerged. Muscular valves close the ears, nose and mouth while underwater, and beavers' lips close behind their huge chisel-like teeth so they can gnaw while submerged. Large lungs permit beavers to remain submerged up to 15 minutes. Finally, the beaver's flat tail serves as a rudder while swimming, stores fat, and functions as a communication device.

A quiet summer evening float on a beaver pond is likely to be interrupted by the harsh slap of a beaver tail on the surface whenever a canoe gets too close for comfort. The slap signals any other beavers within earshot that an intruder is present.

Two weeks ago I reported that Arizona wildlife officials trapped and released a rare, wild jaguar southwest of Tucson on February 18. It was fitted with a GPS collar so its activities could be monitored.

After two weeks, the jaguar began moving erratically, so biologists relocated and recaptured it. Veterinarians at the Phoenix Zoo determined it to be in "severe and unrecoverable kidney failure," according to Bill Van Pelt, nongame birds and mammals manager for the Arizona Game and Fish Department.

Kidney failure is a common illness among older big cats, so it was euthanized on March 2. The jaguar, nicknamed Macho B after being photographed a number of times by motion-activated cameras over a 13-year period, was the first ever captured in Arizona and was approximately 15 years old.