Beavers, like many mammals, communicate with chemical signals. In scent marking, beavers actually build a mound of mud on which to place their scent. First they dive down to the bottom of their pond, dig up an armful of mud with their front feet and swim to shore with the mud held against their chest. Walking on to the shore on its two front legs, the beaver deposits this mud next to the water. Beaver scent mounds can be quite small, or as high as three feet or more, depending on how many loads of mud they contain. The beaver straddles this pile of mud and applies castoreum from its castor glands, or anal gland secretions, or both. The purpose of building a mound is to elevate the odor (helps with scent dispersal), to intensify the odor by putting it on a moist substrate, and to protect it from flooding when the pond level fluctuates. Beavers build most of their scent mounds in the spring, when young beavers are dispersing and claiming new ponds, but I have found several fresh ones this fall, including the one in the photograph. (Click on photo to enlarge.)
Like the majority of songbirds, American goldfinches use their nest only once — to raise one brood — and do not return to it after their young have fledged. This time of year, when leaves have fallen off of shrubs and trees, is a great time to try and locate where birds you saw all summer nested. Just as each species of bird has its own song, each species of bird builds a nest unlike those of other species. By noting the habitat in which it’s built, the material with which it was built, and the dimensions of a nest, it is often possible to determine the species of bird that constructed it. Female American goldfinches build a very neat nest composed of plant fibers, and line it with the down of cattails or thistles. The walls are quite thick, making it quite durable – the nest in the photograph even withstood the wind and rain that Irene delivered this fall. While it’s fun to hunt for nests, bear in mind that you need a federal permit to collect them.
Dog-tooth lichen (Peltigera canina) is often found growing on lawns and rocks. Like all lichens, it consists of an alga or cyanobacterium and a fungus living together in a symbiotic relationship. The fungus provides a structure for taking up moisture and nutrients; the alga or cyanobacterium is capable of photosynthesizing and producing food for both itself and the fungus. The brown structures in the photograph are the fruiting (spore-producing) bodies of this lichen, and their resemblance to dog teeth gives this lichen its common name. In the Middle Ages, dog-tooth lichen was used to treat rabies — it was felt at the time that this lichen’s resemblance to dog teeth indicated that it could cure dog-related ailments.
Depending on the woods you walk in these days, you may be greeted by a flurry of inch-long, tan wings belonging to male Bruce Spanworm moths (Operophtera bruceata). From October to December these moths emerge , mate and lay eggs. Females cannot fly; they crawl up the trunk or branch of a tree and send out pheromones to attract winged males. After mating, the female lays eggs which initially are pale green, but become bright orange with age. The eggs hatch in the spring, and the larvae feed on a wide variety of deciduous leaves, favoring trembling aspen, willows, sugar maple and American beech. Periodic outbreaks of these caterpillars can result in heavy defoliation. In 1958 in Alberta, Canada, at the peak of a 10-year infestation, over 50,000 acres were moderately or heavily affected by Bruce Spanworm larvae.
If you wake up and your lawn is full of small (1”-2” diameter) conical holes you can be sure of two things. One is that you have an infestation of grubs in your lawn. Secondly, a striped skunk has done you the favor of decreasing your grub population. Skunks are omnivorous, eating everything from snails and birds’ eggs to nuts and berries. In the summer, roughly half of their diet consists of insects. One of their favorites is beetle larvae (grubs), particularly the immature June bug larvae, which reside an inch or so beneath the surface of the soil. When skunks have been feeding under a pine tree, the circular motion with which they presumably dig the hole is obvious in the circular arrangement of the needles surrounding the hole.
It’s hard to believe, but even after Irene, several inches of snow and an occasional night that’s below freezing, there are still butterflies and moths to be seen. Yesterday this sulphur butterfly (probably clouded, Colias philodice) was flying from dandelion to dandelion, sucking up nectar with its long, black proboscis. Clouded sulphur and orange sulphur butterflies, two different species, are similar looking, and on top of that, they even hybridize, so distinguishing between the two is often difficult, at best. Both species have several broods in a summer; you can see them flying in fields and along roadsides from spring to fall.
There’s a period of time in the fall, and again in the spring, when pond ice is thin enough to break under the pressure of a beaver’s head punching it from underneath, but is not quite hard enough to support the beaver’s weight. After an audible crack, a beaver’s head emerges from the recently-made hole in the ice, and immediately the beaver lifts its front feet up onto the edge of the ice in front of it and then lunges forward, breaking a path with its body through the ice to where the beaver wishes to go. Over and over the beaver lunges, pausing periodically to catch its breath. Why the beaver doesn’t swim under water from point A to point B (beavers can swim up to half a mile underwater, and remain submerged for up to 15 minutes), which would mean having to break through the ice only once, when it gets to where it’s headed, instead of laboriously breaking trail through the ice is unknown to me, but the process is great fun to observe.
Every fall ruffed grouse grow skin-like fringes called pectinations on either side of each toe. They serve as snowshoes, helping grouse stay on top of the snow when walking, and also help them cling to icy branches while eating the buds of poplars and other trees in the winter. In the spring grouse shed these adaptive fringes. The bird whose foot is in this photograph met its untimely death about a week ago (they frequently fly into windows, as this one did), and I was curious to see the stage of development of the pectinations at this time of year. They appear to be about half to two-thirds the size they will attain when fully developed.
One nice thing about having the ground covered with snow in October and November is that there is an additional tool available for tree identification. Like all flowering plants, trees have fruits which contain seeds. The fruits of many trees fall to the ground this time of year. They are very helpful identification tools, especially when they are so obvious against the white snow. In the photograph, there are fruits from five different trees: starting at the top and going clockwise is the fruit of the sugar maple (Acer saccharum), referred to as paired samaras by botanists. Each of the two seeds contains a papery wing that aids in dispersal. Next is the fruit of the white ash (Fraxinus americana), which has winged seeds borne in clusters. Eastern hophornbeam’s (Ostrya virginiana) fruit is a cluster of papery bladders, which usually separate upon dispersal. Each bladder contains a seed. Along the bottom is the fruit of American basswood or linden (Tilia americana) ; several round seeds are borne on a stalk which is attached to a single modified leaf. The last two clusters are the fruit of yellow birch (Betula alleghaniensis). They consist of structures that look like little bird feet (of which there are several in the photograph) that contain individual, tiny winged seeds (scattered throughout the photograph).