A mouse recycles an abandoned bird nest by adding a roof of milkweed fluff and using it as a winter shelter. (Photo by Mary Holland)

Recycling has become a familiar concept to most people in the past few years. The process of using something over and over again, either for the same purpose or for an entirely new purpose, is something that is currently considered one of the main principles of conservation. Although humans might like to take credit for this practice, we lag way behind other creatures when it comes to not wasting natural resources.

The recycling of bird nests is a primary example of this, in part because of the number of times and ways in which they are recycled. Construction material used to build nests often includes bits and pieces of paper, cellophane, rags, abandoned hornet and wasp nests, snake skins—material that previously served a far different purpose. After young birds have fledged and a nest has been abandoned, a variety of creatures, including both birds and mammals, comes and claims parts of the nest, recycling some of these fragments for a second or third time in further nest-building.

Not only are the individual materials in a nest recycled, but the nest itself can serve more than one purpose, should it remain more or less intact into the fall. In between the use of the nest as a nursery by birds, and its ultimate deconstruction by the elements or animals in search of building material, a nest is often used by mice seeking winter storage space or shelter. Mice are well-known for using abandoned bird nests as larders during the colder months; the cup shape of many nests lends itself to the nest functioning as a storage bin. Even though avian architects do their best to build their nests in relatively inaccessible sites, mice have no trouble climbing as high as 50 feet or more up a tree in order to reach them. They fill the nests with seeds, acorns, rose hips, beechnuts, and other storable food, and, along with other hungry seed-eaters that discover these larders, such as squirrels, return to eat their supply of food repeatedly throughout the winter. In addition, abandoned bird nests also serve as shelters for small rodents. Mice make a practice of renovating old bird nests, creating roofs of different plant material, which offers them some protection from the snow and winter winds as they huddle inside the nests. Most impressive are the roofs made of thistle or milkweed down, which result in fluffy white domes for what must be very well-insulated rodent residences.

Recycling of material is not restricted to birds and their nests. Beavers cut and gather a supply of sticks and branches every fall, which they pile on the floor of their pond, near their lodge. All winter they swim out under the ice to this pile and retrieve branches, which they bring back into their lodge, where they consume the bark and inner cambium layer. They then place the stripped sticks back into the water, where they can be seen floating on the pond's surface after the ice begins to melt in the spring. Taking down a tree, trimming off the branches, and transporting them to a pond requires a great expenditure of energy on the beavers' part, and, efficient creatures that they are, beavers aren't about to waste a natural resource they've worked so hard to acquire. The next time you come upon a beaver dam or lodge, notice that it is constructed primarily of pieces of wood that lack outer bark. These limbs and sticks are the recycled remnants of former meals.

Natural recycling often involves consumption. Consider the hundreds of white-tailed bucks that inhabit eastern Massachusetts, and the fact that each one of them sheds two antlers every winter. One might logically assume that our fields and forests would be littered with antlers come spring, and if it weren't for rodent recycling, this would probably be very true. However, thanks to the strong incisors of porcupines, squirrels, mice and voles, it's quite unusual to find even one antler on the ground once the snow is gone, due to the fact that they are a valuable source of calcium and phosphorus for these rodents.

Many animals recycle by consuming their own, or other creatures', waste material. Snowshoe hares, rabbits and beavers practice autocoprophagy, the act of re-ingesting one's own feces in order to extract as much nutrition as possible from it. We rarely see the original scat, for it is readily consumed; the hare, rabbit, and beaver scat we normally see has been through their systems not once, but twice. A monarch caterpillar recycles within seconds of hatching, for its first meal consists of its own eggshell, a readily accessible source of nutrition. Occasionally you find butterflies congregating on an animal's scat. With their straw-like proboscis, or mouthpart, these insects are obtaining salts and minerals not available in nectar.

The ways in which organisms engage in recycling are as varied as the organisms themselves. Be they vultures, vireos or voles, all animals contribute to the conservation of our natural resources. It is comforting to be counted among them as practitioners.

Visit Mary's natural history blog at www.naturallycuriouswithmaryholland.wordpress.com.