Living Hollow Trees
Occasionally one comes across a living tree with a portion of its trunk, or its entire trunk, hollow. How is it possible for a tree to thrive even when its center, or heart, has completely decayed? It comes down to the different kinds of wood that are produced by a tree: sapwood and heartwood.
Sapwood (often light-colored) is the younger, living, outermost portion of a woody branch or tree trunk (just beneath the bark), while heartwood (often dark-colored) is the dead, inner wood. All wood in a tree is first formed as sapwood. Sapwood’s principal functions are to conduct water from the roots to the leaves (via xylem tissue) and to disperse nutrients made by the leaves to the rest of the tree (via phloem tissue). Heartwood (so called because of its central position, not because it is essential to the health of the tree) is basically non-functioning xylem tissue that has become blocked with resins, tannins, and oils. Although the dead heartwood can lend stability to a tree, it is no longer part of the transport system, and therefore, not vital to the tree.
Cavities and hollows typically result from an injury to a tree (usually caused by fire, storms, lightning, insects or birds) that exposes the heartwood. Bacteria and fungi lose no time moving in and beginning the decaying process, which can result in a hollow tree. Because the sapwood, and therefore the transport system, is still intact, the tree lives, despite the loss of its inner heartwood.
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Huddling to Keep Warm
Animals which remain active year round in northern New England use different strategies to survive the cold winter temperatures. Lowering metabolism through torpidity (on cold nights black-capped chickadees and other species reduce their body temperature as much as 22 degrees Fahrenheit from their daytime level in a process called regulated hypothermia), shivering, caching food in the fall, puffing out feathers to create insulating pockets of air, excavating tunnels under the snow, seeking protection in cavities – these are just a few of the life-saving techniques used by mammals and birds which neither migrate nor hibernate.
Another strategy which some of these animals use is to huddle together to conserve warmth. Huddling reduces the animal’s surface-area-to-volume ratio, since it turns many small animals into a single big animal. The larger the animal, the smaller the surface-area to volume ratio and the less relative area there is to lose heat.
Bluebirds and flying squirrels are two animals which huddle to keep warm. Eastern bluebirds may huddle together in a tree cavity or hollow log in groups of up to ten. Flying squirrels often huddle together in large communal nests, sometimes with populations numbering over two dozen squirrels, in an effort to keep warm. If this is not sufficient, the squirrels will enter a state of torpor until temperatures return to normal. (Thanks to Susan Parmenter for photo op.)
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Coyotes Feeding on Deer Carcasses
Ninety percent of a coyote’s diet is animal matter, including creatures as varied as meadow voles, mice, muskrats, raccoons, beetles and grasshoppers — basically, anything it can outrun. Coyotes have the reputation as major predators of deer. While research confirms that deer (and rabbits) comprise a good portion of a coyote’s diet in the Northeast, the majority of the deer that coyotes consume is scavenged as carrion (see photo). Because they cannot move as fast as adult deer, fawns are more vulnerable to coyote predation.
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How Beavers Digest Cellulose
Some beavers are still managing to find openings in their ponds which give them access to fresh cambium, the soft layer of wood just under the bark of a tree. Cambium contains a lot of cellulose, in addition to starches and sugars. Like all herbivores, beavers do not possess enzymes that are capable of breaking down the large cellulose molecules (cellulases). In their place, beavers employ micro-organisms, such as bacteria, that can break down cellulose.
These bacteria are located in a pouch called a cecum, located at the beginning of the large intestine. (Ruminants such as moose and deer have rumens in place of ceca.) Colonies of these microorganisms in a beaver’s intestines digest up to 30% of the cellulose from the woody material that it eats. Further nutrients are recovered in the form of fecal pellets that the beaver re-ingests.
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Overwintering Red-tailed Hawks
Red-tailed hawks are “partial migrants” — some individuals are migratory, and others are not. Many Red-tails living in the northern portion of the species’ range in southern Canada and northern United States migrate to more southerly locations for the winter. A few northern birds, however, remain on their breeding territories even in the most severe winters.
Overwintering Red-tailed Hawks are generally easy to spot, as they often perch on dead trees overlooking open fields and on telephone poles next to highways, where they watch for prey. Mice, voles, squirrels, snowshoe hares and an occasional bird make up most of their diet. If you notice the coloration of a Red-tailed Hawk’s tail, it will tell you whether the bird is a juvenile or adult. Adults have rufous tails; juveniles have barred, brownish tails. Seconds after this photograph was taken this juvenile Red-tailed Hawk killed and consumed an American Crow while being mobbed by more than 50 other crows.
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Northern Red Oak Buds
There are approximately 600 species of oaks in the genus Quercus, all of which are in the Beech family. This genus has two subgroups, the red oaks and the white oaks. The leaves of trees in the red oak group have sharply pointed lobes with bristles. The white oak group has leaves with rounded lobes lacking bristles. Although usually there are some leaves on an oak tree that persist well into the winter, it is helpful to be able to identify a species by its buds alone. Oaks tend to have multiple terminal buds. Northern Red Oak’s terminal buds are large, pointed, cone-shaped and covered with reddish-brown, mostly hairless scales that overlap like shingles, with one edge covered and the other edge exposed.
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Muskrats Enjoying Last Days Above Ice
Muskrats and beavers are eking out the last few days that they will spend above the ice for perhaps several months. Fortunately for muskrats, they can hold their breath and remain under water for up to 20 minutes, time enough to get from one unfrozen patch of water to another. Once the ice freezes completely, muskrats will use ‘push-ups’ or ‘breathers’ as resting places and breathing holes — masses of vegetation collected from underwater and pushed up through cracks or holes in the ice.
Throughout the year muskrats eat the roots and stems of a number of aquatic plants as well as crayfish, frogs, turtles and other prey, when available. Unlike beavers, muskrats don’t store food for the winter, but forage for vegetation (see green plants on ice). Sometimes muskrats will feed from the winter food supply piles gathered by beavers. They have also been known to use the walls of their own lodge as food.
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Bark Scaling
There are two main ways that woodpeckers and occasionally other birds remove bark in search of insects beneath it. One is bark sloughing, where a bird pries off the entire dead layer of bark on a tree (see NC post on 12/5/14). Another method of locating insect larvae that both woodpeckers and nuthatches employ is the removal of individual scales of bark. This is referred to as bark scaling. The pictured hairy woodpecker has removed much of the bark of a dead eastern hemlock using this method.
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White-tailed Deer Breeding Season Winding Down
The breeding season of White-tailed Deer extends from late October to mid-December. Fresh buck rubs, where bucks literally rub the velvet off of their antlers as well as communicate with other deer via their scent, can be found throughout this period of time.
Mature bucks make two distinct types of visual and olfactory signposts —early-season and breeding rubs. The early-season scraping of antlers builds up neck and shoulder muscles, designates a buck’s territory (both visually and by scent deposited from forehead glands) and releases aggression caused by rising testosterone levels. Later in the season, once the rut begins, bucks move out of their home ranges into doe territory, where they make breeding rubs. These rubs announce the bucks’ presence to does, and are thought to hormonally suppress small bucks to the point where their testosterone levels stay so low that they do not attempt to mate.
When a deer or moose strips bark off a tree to eat it, the de-barked area is torn only at one end — the deer grabs one end of the strip of bark and tears it off of the tree. The rubbing of an antler leaves ragged bits of bark at both the top and bottom of the rub. Staghorn Sumac, as pictured, is a favorite rubbing substrate.
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Snowfleas Appearing
One rarely even thinks about snowfleas (a species of springtail, Hypogastrura nivicola) until snow falls and then starts to melt. This is when these tiny wingless arthropods that catapult themselves through the air with the aid of a fork-like structure, or furcular, seem to magically appear out of nowhere. They actually are present year round, but their dark color makes them visible against the white snow.
The great majority of snowfleas live in soil, feeding on fungi, algae, decaying plant matter and bacteria. They work their way to the surface of the snow, crawling up the trunks of trees, plant stems and side of rocks where an open channel allows their migration. Thousands can be found on melting snow, especially in tracks or other depressions. No-one is absolutely sure of why they exhibit this behavior, though some scientists feel that these migrations are triggered by overcrowding and lack of food. Eventually those that survive on top of the snow make a return trip down into the soil.
Formerly classified as insects, snowfleas are now categorized as hexapods, due to some features they have which insects do not.
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Ruffed Grouse Nostril Feathers
Ruffed Grouse have adapted to cold winter months in a number of ways, from growing “snowshoe” pectinations on their toes to having their legs covered with fine feathers. Equally effective are the feathers covering a grouse’s nostrils, which are thought to heat cold air as the bird breathes in. (Thanks to Sara and Warren Demont for photo op.)
Black Bears Still Active
While some, perhaps most, black bears have entered hibernation in northern New England by now, there are still some active individuals, probably males, who are finding enough food to delay denning. Typically a scarcity of food and cold weather trigger the reduction in the metabolism of a black bear, which signals the onset of hibernation. If the weather remains relatively warm and/or there is a large supply of beechnuts and/or acorns, signs of bears can occasionally be found even this late in the year. While there have been a few years when black bears have been sighted throughout the winter, most wildlife biologists say that it is safe to put up bird feeders in December, as sunflower seed-loving bears have usually retreated to their den sites by now. The pictured tracks and scat discovered in the past few days in central Vermont challenges that assumption (as does the stolen bird feeder). (Thanks to Erin Donahue and Charlie Berger for photo op – sensitive fern fertile frond for size comparison)
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Teasel
Teasel is an introduced biennial, considered an invasive plant in the U. S. due to its ability to crowd out native species. Nonetheless, the seed head that remains after the three- to eight-foot plant has flowered is strikingly beautiful. It consists of a cone of spine-tipped, hard bracts, or modified leaves. Since the Middle Ages, Europeans have used dried seed heads of the teasel plant to raise the nap on woolen cloth. Teasing wool creates a soft, almost furry texture on one side of the cloth. (Baize, the cloth traditionally used to cover pool and card tables, is a classic example of wool that has been teased.)
Because of the demand for these seed heads, farmers in 19th century New England grew fields of teasel, with each acre yielding up to 150,000 heads. In the autumn, they would be harvested and dried. Teasel heads wore out quite quickly with use, so wool manufacturers needed a constant supply of them. Eventually a machine, the “teasel gig,” replaced the seed heads. Today fine combs with steel wires raise the fibers on teased fabrics, although the consensus is that there is still no substitute for teasel heads in producing the finest cloth.
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Wild Turkeys’ Struggle for Food Begins
Wild Turkeys do not migrate. During the winter they often separate into three distinct groups — adult males (toms), young males (jakes) and females (hens) of all ages — and spend their days seeking out plant (90 percent of diet) and animal (10 percent of diet) matter. In the summer, greens and insects make up much of their diet; in the winter, Wild Turkeys rely heavily on acorns, beechnuts, crabapples and hawthorn fruit, as well as agricultural grains such as corn, buckwheat, soybeans and oats.
The winter survival of Wild Turkeys depends much more on snow conditions that impact the procuring of food than on the temperature. While research has shown that turkeys can tolerate very cold temperatures, they need adequate food to keep from losing significant body weight and eventually starving to death. In parts of northern New England, the current Nor’easter has dumped a large amount of deep, loose fluffy snow, which turkeys can’t walk on or dig through in order to reach nutritious nuts. For this reason, turkeys frequently seek out agricultural fields that are windblown and provide relatively easy access to grains.
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Hoar Frost
Frost is to dew as snowflakes are to raindrops. When water vapor condenses into liquid water, you get dew and raindrops. When water vapor condenses directly into ice, then you get frost and snowflakes. Frost is not frozen dew and likewise, snowflakes are not frozen raindrops.
When frost forms as minute ice crystals covering the ground, we just call it frost. But sometimes the frost grains grow larger and are called hoar frost crystals. Under clear frosty nights in winter, especially when there is a source of water vapor nearby, such as an unfrozen lake or stream, soft ice crystals might form on vegetation or any object that has been chilled below the freezing point by radiation cooling. These deposits of ice crystals are hoar frost. The interlocking ice crystals become attached to branches of trees and shrubs, as well as vegetation on the ground and any other object below freezing temperature that is exposed to supersaturated air (the relative humidity is greater than 100%). Hoar frost often vanishes once the sun has risen and warmed the surface of branches, grasses, etc., so it’s most easily observed in the early morning. (Photo: hoar frost on black-eyed Susan seedhead.)
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Why Cardinals Are Red
The diet of a Northern Cardinal consists mainly of seeds, fruits and insects (average annual consumption is 29% animal and 71% vegetable matter). As fall progresses, the proportion of vegetable matter in its diet increases until it reaches a high of 88% during winter. The red plumage color of both males and females (females have some red feathers in wings and tail) results from the ingestion of carotenoid pigments obtained from their diet during the fall molt (September/October). Fruits and insects are high in carotenoids, while most seeds are poor sources. According to Cornell Lab of Ornithology, new research has shown that brighter males have higher reproductive success and territories with greater vegetation density, and that plumage brightness in both the male (breast color) and female (color of underwing-coverts) is positively correlated with parental care (feeding nestlings).
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Woodpeckers Bark Sloughing
Several species of woodpeckers search for wood-boring beetle larvae by removing the bark from a tree (in addition to drilling holes). This is referred to as bark sloughing. Some birds, such as nuthatches, remove only scales of bark, not the whole layer like woodpeckers, and this is referred to as scaling. After finding or creating an opening, a woodpecker repeatedly slips its pointed beak under loose bark, prying it off of the tree. It then uses its long, barb-tipped tongue to capture the exposed insects. Different woodpecker species tend to feed on either trunks or branches, and at different heights. Initially sloughing can resemble the work of porcupines, but close examination can reveal the marks of a beak, which are perpendicular to the trunk or limb, rather than the grooves left by a beaver’s incisors.
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Canada Geese Switch Diet to Berries & Grains
During migration and throughout the winter, Canada Geese are highly gregarious, often gathering and feeding in flocks that consist of over a thousand geese. Almost exclusively herbivorous, they are efficient grazers, having serrations on their stout, flat bills. During summer they feed primarily on grasses and sedges. Considered a nuisance by many people with large lawns Canada Geese are attracted to these lawns not only because they can digest grass, but also because they have an unobstructed view that allows them to detect approaching predators. During and following migration, berries (especially blueberries) and agricultural grains including sorghum, corn and winter wheat make up most of their diet. When you see them in cornfields, they are feeding on fallen kernels as well as corn still on dry cobs — they are very good at removing the kernels.
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Woolly Oak Leaf Gall
Of the 2,000 kinds of galls found on North American plants, 800 different kinds form on oaks. One of these is the woolly oak leaf gall, produced by a tiny Cynipid wasp, Callirhytis lanata. This gall is usually attached to the mid-vein on the underside of an oak leaf, and looks like a ball of wool. It may be as large as three-fourths of an inch and is often bright pink or yellow in color, fading to light brown in the fall. Oak trees have lots of tannic acid in them (a defense which makes the tree unpalatable to herbivores), with the highest concentration found in oak galls. (The bitter taste is where the name “gall” originated.) It’s possible, since tannins are somewhat anti-microbial, high-tannin galls such as the woolly oak leaf gall may protect the larva against fungi and bacteria.
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Nictitating Membrane Provides Moisture & Protection to Eyes
You and I have two opaque eyelids, one above the eye and one beneath. When we blink, they meet in the middle of our eyes. Some birds, amphibians, reptiles, fish and mammals have three eyelids – two similar to ours, and a third translucent or transparent eyelid, called a nictitating membrane. This membrane moves horizontally across the eye from the inside corner to the outer edge of the eye, much like a windshield wiper, when needed for protection, to clear debris or to moisten the eye. Although this American Crow’s nictitating membrane looks as if it was blinding the crow, it isn’t. Because of the membrane’s translucency, the bird can still see when the membrane is covering its eye.
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Slug Scat
Slugs produce lots of mucus – some covers their whole body and makes it difficult for them to be picked up by a predator, some forms a “slime trail” that aids them when they are moving, and some envelopes their waste. After a slug has eaten and digested food (a wide variety of plants, fungi, earthworms and carrion), a mucus string of scat leaves through its anus, which is hidden under the leathery patch called a mantle, located just behind its head. The odd position of this opening is a result of the slugs’ evolutionary descent from snails. In a snail this opening must be outside the shell, and thus is far forward on its body. (Congratulations to Jean and Michele for their spot-on guesses.)
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