MARYLAND NATURALIST (July/December 1997) - A long-term mammal study of Fort
Belvoir, VA, was conducted from 1987 to 1995.
The following was found:
"Present" indicated a very few observations were made.
FOUND, but expected, was the Little Brown Bat, hoary bat, and the long-tailed
to capture larger mammals were minimal, with tracks and visual sightings used to
document their existence.
HISTORY (5/94) -
Three major groups of mammals have evolved back to a life in the sea.
These are the suborder Pinnipedia (seals, sea lions, and walruses) within
the order Carnivora, and two entire orders; the Sirenia (dugongs and manatees)
and Cetacea (whales and dolphins).
- From 30 million buffalo (Bison
bison), in 1870, only 1,000 existed in 1889.
4,000 now exist (1994) in Yellowstone National Park.
At the Flying D Ranch near Bozeman, MT, Ted Turner has about 5,700, with
another 2,100 at a ranch in New Mexico.
HISTORY (4/94) -
Mammal evolution started with ancestoral shrew-like creatures over 200 million
years ago. Thus, two thirds of the
time line of mammals occurred in the Mesozoic period, the period of the
dinosaurs. While both marsupial and
placental species existed, they were limited in adaptability, being primarily
very small mammals and all noses and ears.
to 63 million years ago, placentals and marsupials arrived in South America; the
placentals being the herbivores, and the marsupial, the carnivores.
With the lowering ocean level creating the Panama land bridge about 3
million years ago, the placental saber-toothed tigers migrated south from North
America and wiped out the marsupial carnivores.
This land bridge was responsible for the northward migration of opossum,
and porcupines and the southward migration of raccoons, weasel, dogs, bear and
cats (including the saber-toothed cat). Mastodons,
tapirs, horses, llamas and deer were the hoofed emigrants southward.
Rabbits and rodents (including the very successful mice) also went south.
Today, fully half of the land mammal genera of South America came by way
of this land bridge, while only three genera (the porcupine, opossum and
armadillo) have found permanent homes in North America from the south.
America is the ancestral home of horses. As
part of the mixing of continental members 3 million years ago, horses traveled
over the Bering Strait to the Old World and over the Panama isthmus to South
America. Dramatic climatic shifts
and the arrival of man contributed to the extinction of Equus in the Americas. Only
one genus world-wide exists in the Old World from their maximum in the Miocene.
This genus, includes all the world's horses; zebras, asses and onagers -
the ancestor of the domesticated horse.
WILDLIFE (12/1 - 93)
- Hair, along with mammary glands, are the hallmark of mammals. It is felt that hair was first evolved in early mammals to
help regulate temperatures. The
earliest mammals, which evolved from reptilian therapsids about 160 million
years ago, grew these sensory cones between the scales of the evolving reptiles,
which, when brushed on objects, gave a stimulus to the brain.
Certain remnant scales still exist on rats' tails, armadillo shells and
the backs of pangolins. Animal whiskers are still sensory receptacles.
Hair is mainly the protein keratin, a form of skin, which is the same
material making up the epidermis, feathers, fingernails, horns, hooves and
claws. Humans have about 100,000
hairs on our head, while sea otters have 170,000 to 1,000,0000 hairs in their
underfur; only one of the otters’ three types of hair.
Polar bear hairs have hollow cores. The cores scatter light, making the
hairs seem white. Actually, they
are colorless. Sunlight passes
through the bear's long guard hairs to its black skin, which absorbs the
radiation as heat. The inner
insulating hair prevents the heat from being radiated back to the air (similar
to glass of a greenhouse). Most
mammals can cause their hair to become erect, thus increasing the air, (i.e.,
heat) retention. Although humans
have lost most of their body hair, goose bumps are the results of our own relic
muscles that still exist which used to control these hairs.
White-tailed deer grow winter coats four times thicker than summer coats.
MAMMALS PROGRAM (Rob Simpson - 3/89)
- Reptile teeth can be either replaceable (rattlesnake fangs) or one set
have growth stage teeth. Hair on
mammals is usually dark on top and light on the belly, so sunlight on top makes
it shiny (light), like the bottom. Caribou
hair is hollow for better insulation and aid in swimming. Forest dwellers are usually dark haired, meadow mammals are
light colored. Porcupines and
fisher have been reintroduced to Dolly Sods and Spruce Knob areas.
Bering hare (snowshoe rabbit) exists both in Dolly Sods/Spruce Knob as
well as parts of NW Virginia (but not the Shenandoah National Park).
New World rats have hairy tails, Old World rats have nearly hairless
tails. Jumping mice hibernate,
meadow mice don't. Eastern woodrat
lives in caves (lots in rocky areas in SNP-especially on Old Rag). Man used to mine excrement (basically KNO4), using it 3 to 1
with wood ashes to make salt peter (gun powder - how the original Dupont fortune
(Winterthur-Longwood fame) was made). Pine
voles are an emerging problem for orchard trees (voles girdle them).
Ungulates are the hoofed animals, although this group has no taxonomic status.
Ungulates include the odd-toed Order Perissodactyla (horses, rhinos, and
tapirs) and the more advanced even-toed Artiodactyla (pigs, camels, deer,
antelope, sheep, goats, and cattle). Exceptional
running abilities dominate the ungulates that evolved among the expanding
grasslands of the increasingly cooler and drier era of the Miocene (25 – 5 mya).
In these cursorial mammals (runners), the limbs have lengthened while the
clavicle has been greatly reduced, allowing a greater stride. Many ungulates have become large to protect them from
predators and to allow temperature regulation.
Being herbivores, vegetation is far less concentrated food than is meat,
and is more difficult to digest. In
addition, plant material is frequently low in protein.
Thus, herbivores have developed specialized adaptations to aid in food
consumption efficiency. In ruminant artiodactyls, a four-chambered stomach allows
undigested foods to be regurgitated, allowing the animal to chew its cud.
(Lagomorphs, which includes rabbits, increase food efficiency by eating
their feces, called coprophagy. God
knows why dogs do it.) This cud
chewing makes for longer time for food to be processed (70 - 100 hours through
the gut) than, say, for a horse (30 -45 hours).
The central difference, then, is that the digestive system of the horse
is less efficient than that of the ruminant, but in compensation the horse eats
greater quantities of food; the emphasis in ruminants is on highly efficient
digestion and on more selective feeding, but not on high rates of food intake.
Given food in short supply, the ruminant will probably survive after the
horse has starved to death.
the Suborder Ruminantia, antlers and horns are found in the most progressive
families. The antlered
include the deer, elk, caribou and moose. Antlers
are usually present and occur in males only, with the exception of caribou,
where both sexes have antlers. Antlers
differ from horns in being annually shed and regrown each year.
In the Giraffadae (giraffe and okapi), both male and female have fur
covered bone protuberances. In the
Antilocapridae (pronghorn sheep), both male and female have a boney spur with an
annually shed sheath. Finally, in
the Bovidae family (antelope, bison, sheep, goats, and cattle), usually both
male and female have horns. The
horns are never shed and in some species grow throughout the life of the animal. Bovid horns are never branched, but can be spectacularly
curved or spiralled. The domestication of bovids about 8,000 years ago was one
of the major factors responsible for the first civilization in the
Tigris/Euphrates River valley in Mesopotamia (annual grain crops, including
wheat and barley were another reason). A
few bovids reached the New World in the Pleistocene via the Bering Strait land
bridge. Because this avenue of
dispersal was under the influence of severe boreal climatic conditions at this
time, it functioned as a filter bridge, and only animals adapted to these
conditions dispersed across the bridge. Migrators
to the New World included bighorn sheep, mountain goat, musk ox, and the bison.
Other Old World bovids that couldn't make the cold crossing included
antelopes and the gazelles. Bovids
inhabit grasslands, making their greatest stand currently in the savannas and
grasslands of Africa.
in many north temperate zone bats. Sperm
is stored overwinter. Seems to
occur with species having continuous or periodic winter dormancy.
Advantageous for species due to males in Fall being in excellent
condition and with plenty of food, rather than in Spring, when the animals are
in their poorest condition and when food (insects) may not yet be abundant.
Early ovulation in spring allows for maximum time for development before
with many carnivores; bear, marten, fisher, badger, otter, mink, long-tailed
weasel. Also several seal, walrus,
Roe deer, armadillos and two species of bat.
Many different Orders, thus probably evolved separately.
WINTER ADAPTATIONS---Insects utilize supercooling-body fluids remain as liquid below freezing (some Alaskan insects do this to 70 Below). The Arctic ground squirrel is the only mammal that can do this. Some reptiles freeze solid---wood frogs, box turtles and garter snakes by flooding the body with glucose.
snakes are the last snake in and first out of winter hibernation (sometimes will
bask on snowbanks). They are also
known to hibernate underwater, with their heart rate dropping from 60 to one
beat per minute (getting air through their skin).
Painted turtles may take one breath every five months, respiration
dropping from a summer 35 to one every 10 minutes. Even hibernators wake up occasionally for a few hours to a
day. Some rodents, shrew and rabbit
family members produce brown fat, full of mitochondria, the engines in cells
that convert food into energy, and its only functions is to generate heat.
and hibernation are costly strategies. In
the case of migration, a large amount of energy must be consumed to make the
trip south and the returning spring trip back north.
And, of course, migration to warmer latitudes is a feasible alternative
only to those species capable of long distance travel.
With the exception of marine mammals, our only migratory mammals are
three species of bats that inhabit our insect-laden deciduous forests.
These bats; the red, hoary, and silver-haired bats, travel to southern
regions of eastern U.S. and Mexico, and then, normally will hibernate.
However, some of these species will stay in their northern (summer)
ranges and will hibernate there in protective locations.
To make the distinction between migrating and hibernating species more
ambiguous, all species of bats have some individuals that will migrate, with
individuals of many species migrating 100 miles (more or less) before entering
in the truest sense, is only practiced by woodchucks, bats, jumping mice and
western ground squirrels. This
strategy is costly in the need to store an adequate amount of energy, in the
form of brown fat that will fuel the body's system over the duration of the
winter season. This strategy is
only suitable in mid-latitudes, since more northern habitats preclude animals
from safely sleeping through the winter without freezing or running out of
are the textbook hibernators, with the oldest (and fattest) entering the burrow
first (late October). In Autumn, after gaining 30% of it's summer weight (mostly
in the form of a half-inch layer of brown fat stored over much of the body,
especially the back and shoulders), the ground hog will line it's hibernaculum
with grass and leaves and then plug the entrances (to maintain constant
temperatures and to keep out curious visitors) before curling into a ball.
During hibernation, heart rate drops from 100 to four beats per minute,
respiration rate drops to one breath per three or four minutes, and the body
temperature drops from 98 to about 40 degrees.
Males usually exit a few days earlier than females in March (similar to
the hibernating jumping mice). They
will awaken occasionally throughout the winter (about every two weeks) to
defecate. This may occur in special
chambers below ground or, less frequently, on the surface.
They will emerge having lost approximately one half their fall weight.
bats of the eastern US are capable of hibernation in winter, and they will also
reduce metabolism and enter torpor during cool days, as an energy-saving
mechanism. Brown bats store energy
as brown fat. About 75% of the
stored fat is used during the wakeup periods, with the other half-gram serving
to maintain the bats life functions through the entire winter of hibernation.
Many studies of big brown bats in hibernation have been conducted.
While normal awake body temperatures are 99 degrees, apparently the body
temperatures match the environment down to a temperature of 30 degrees while
breathing can drop from 200 times a minute to once every four to eight minutes.
As all true hibernators, bats will occasionally awaken during winter to prevent
muscle atrophy and defecate, and may even change caves.
mice are profound hibernators. Meadow
jumping mice put on a substantial layer of fat (about 6 grams - increasing in
total body weight from 15 to 21 grams) and wake every two weeks to stretch and
defecate. Woodland jumping mice put
on 7-8 grams (from 20 to 28 grams total weight).
The woodland jumping mice will spend from October to April or May in deep
torpor in underground moss/grass/leaf nests. They will put on one third their
weight within two weeks in fall. The
biggest cause of death in jumping mice is the inability to put on enough brown
fat in the fall to carry them through to spring.
other animals, like bears and chipmunks, hibernate or not depends on your source
and definition. Animals (as
well as plants and all living material) don't play by any definitive rules, and
thus individual species (in fact, individuals within a species, as our bats have
illustrated) have developed characteristics
that are more of a "smearing" of possible strategies and physical
adaptations, covering an endless number of variations on a common theme. There
is a continuum of sorts between the true hibernation of ground squirrels and
woodchucks, in which all bodily functions are greatly slowed, and the deep sleep
of raccoons, opossums, and gray squirrels.
are said not to truly hibernate, because although their bodily processes are
slowed, they are not suppressed to the extent found in the deep hibernators.
Their metabolism drops by half, and their digestive system tightens into a knot,
with the limited waste products reprocessed into the bloodstream in the form of
proteins. Black bears, however, if
not true hibernators, are certainly close.
Various terms - dormancy, ecological hibernation, and carnivoran
lethargy, for example - have been used to indicate the black bear's various
modifications to hibernation. They
can exhibit continuous dormancy for up to about seven months, without eating,
drinking, defecating, or urinating. (In the Shenandoah National Park, bears
enter their dens around December 1, and emerge in mid-April.)
Their temperature does not fall to the extent it does in true
hibernators, nor is respiration as greatly retarded.
Body temperature decreases from a summertime 99-101 to 88-95, and the
heart rate drops from about 40 to about 8 to10 beats per minute.
Bears feed heavily and become extremely fat, thus well equipped for
winter. They may increase their weight by up to 100% (one bear went
from 110 to 220 lbs). Average loss
of mass in one study was 260 grams per day; over the winter, that amounted to a
drop of 23.1% from peak weight. Most
hibernators wake periodically, but bears do not wake during winter unless
disturbed. If they are disturbed,
they will rouse readily. The
ability of bears to recycle urea and to desist urinating, defecating, eating, or
drinking during the entire denning period is unique.
It has been said that, while bears may not be true hibernators, they are
do not develop a layer of brown fat as does a true hibernator. Unlike true
hibernators, who overwinter on the brown fat alone, chipmunks must wake
occasionally to eat from their caches. They will go through periods of torpor of
variable length and frequency during periods of stressful weather.
During these periods of torpor, their body temperature drops, and their
heart rate and respiration slows for several days. Chipmunks' respiration rate
drops from 60 to less than 20 per minute and a drop in temperature from 100
degrees to 45 degrees. Chipmunks will come out in mild weather any time.
They are also known to overwinter among rattlesnakes, benefiting from
their warmth, while entering and leaving the rattlesnake hibernaculum as the
snakes are dormant.
most mammals "stick it out" in winter by various adaptive methods.
Development of brown fat is not uncommon.
Many mammals produce brown fat, full of mitochondria, the engines in
cells that convert food into energy, whose only function is to generate heat. Winter grouping allows for mutual warmth sharing, allowing a
further northern range. (Raccoon
are known to den together in winter communal “piles” of up to 23 individuals
in a single den. Skunks will also
den together, but only female and young.) Thicker
winter coats, or pelage, provides further cold protection (the winter coat of
the mink is highly prized and is much thicker and heavier than the summer coat),
as does the winter white fur of weasels and snowshoe hare.
White hairs, without the pigment melanin, has more air spaces within the
hairs and thus has greater insulation (Snowshoe hares' white winter pelage has
27% better insulative qualities than the summer brown coat).
A change in diet is also utilized to provide the necessary energy
supplies. (Red fox consume primarily insects and fruits in summer and fall, and
then rodents in the winter. The mink's diet in spring and summer includes
muskrat, crayfish, frogs, fish, snakes, small mammals, and waterfowl. Winter mink diet focuses on muskrat, but small rodents make
up a portion of their diet. Raccoons will feed on anything being omnivorous, but
favor crayfish in the spring, and adding insects in the summer, but switch to
primarily acorns and corn in the winter.) Most
carnivores assume a larger home range to assure an adequate food source (bobcat
and mountain lion). Some animals
will cache food for winter food sources. (Red squirrels cache their food
supplies in "middens" while gray and fox squirrels prefer to store
their acorns individually. Members
of the weasel family also cache their prey.
One winter mink cache was found to contain over a dozen muskrats, two
mallard, and an American coot). Gray
wolves and red foxes become more diurnal in response to weather conditions and
the nature of their winter prey (red foxes feed almost exclusively on voles).
And practically all mammals lay low and minimize energy loss during
extremes of winter cold and food scarcity.
interesting secondary adaptation to winter stress developed by many mammals are
the phenomena of delayed fertilization and delayed implantation.
Delayed fertilization occurs among most of our native bats.
Delayed fertilization is seemingly a highly advantageous adaptation in
mammals with long periods of dormancy. In
the case of bats, copulation, requiring considerable energy, occurs in the late
summer and autumn, when males are in excellent condition and have abundant food,
rather than in spring when the animals are in their poorest condition and when
food (insects) may not yet be abundant. Ovulation
and zygote formation occur almost immediately upon emergence from dormancy,
rather than being delayed until after males attain breeding condition and
copulation occurs. Perhaps the
major advantage is that of hastening the time of parturition and allowing the
longest possible time for development of young before the winter period of
dormancy. Delayed implantation
occurs in bear, marten, fisher, badger, river otter, mink, long-tailed weasel,
certain seal and roe deer. The
advantages are similar in nature to those found for delayed fertilization.
In this case, fertilization occurs normally with early cell cleavage, but
then, the embryonic development is arrested at the blastocyst stage until a more
suitable time of development and ultimate birth can occur.
In the case of the black bear, mating takes place in early summer, when
the males are in prime condition and food supplies are not limited.
Without delayed implantation, mating would have to occur in the fall,
when bear must concentrate its efforts on building up a fat reserve to allow it
to pass through the winter dormancy. The
delayed implantation of five to six months allow for a late fall implantation
and mid-winter birth, allowing the maximum length of summer growth period for
the newborn cubs before the subsequent winter.
The longest period of blastocyst dormancy is attained by the fisher and
river otter, which is ten to eleven months.
(White-tailed deer don't follow this trait since they are active all
winter, commensurate with the availability of their food source.)