All posts by traderscreek

Opossum – Didelphia virginiana

December 7, 2013 traderscreek

General: The opossum (Didelphia virginiana) is one of the oldest known mammals, having been traced back 70 million years through fossilized remains. Over 60 species of this common mammal are now found across North and Central America. The opossum is the only marsupial found in North America1 and is notable for the unique presence of a pouch that is used to protect, nourish and raise young. You may come across one of these nocturnal animals wondering quietly at night or even hanging from their prehensile tails from a tree branch. Unfortunately, many opossums are killed by automobiles because of their tendency to eat carrion. Despite their high mortality rates, opossums are widespread with healthy populations and are listed as least concern on the IUCN Red List.

Description: Opossums are slow, clumsy heavyset mammals that reach a mature weight of 8.8 to 13.2lbs. and nose-to-tail length of up to 30”, with males being slightly larger than females. They have easily identifiable elongated heads with conical snouts and long whiskers. The skull of the opossum contains 50 teeth, more than most other mammals within their habitats (a feature that is indicative of the opossum’s ancient lineage2.) Opossums are possibly best known for their long, tapered prehensile tails that are scaly in appearance. This type of tail is used as a fifth limb and is adapted for gripping and wrapping, aiding in climbing and allowing opossums to hang from their tails for short periods of time. Opossums also have hand-shaped feet with sharp claws that aid in climbing and an opposable hallux located on the interior of each rear foot. A hallux functions similar to a thumb and aids in gripping3. Opossums use these digits to groom their fur, faces, and front feet4. As members of the Didelphidae family (and the only marsupials found in North America,) female opossums have wooly, fur-lined pouches on their abdomens that are used to carry their young.

The coloration of opossums varies by region, but opossums generally appear gray with small black eyes set into a lighter or white face, black feet with white or pink toes, and leathery black ears with white or pink tips. Their coloration is a result of a dense white undercoat that is tipped in gray (or sometimes brown) with dark or black guard hairs. Southern populations tend to have a sparser undercoat. Albino mutations are not uncommon and result in a white coat, ears and feet and pink eyes5.

Opossums are nocturnal and use their senses of smell to locate food. While their level of intelligence is undetermined, opossums are known to have poor and limited social interactions. Males tend to be solitary and aggressive when in close proximity to other males. Females often live in groups. Opossums exhibit a number of behaviors when threatened (both aggressive and passive,) including growling, urinating, defecating and belching. Outside of growling and audible aggressive displays, opossums are relatively quiet. Most notably, opossums may play dead or “play ‘possum” when threatened. This includes rolling over and lying stiff with closed or fixed eyes, drooling, sticking out their tongues, and slowing their breathing until almost undetectable. This behavior may last for hours until the threat has passed. Opossums may run from threats and have also been known to swim to escape danger.

Opossums do not hibernate but will retreat into dens during extreme temperatures to avoid the risk of frostbite on their hairless extremeties6.

Habitat: Opossums are skilled climbers and nest and spend much of their time in trees in habitats including deciduous forests, farmlands, and open forests. They may be found in arid environments, but prefer moist habitats, including marshes, streams, and swamps.

Opossums do not establish territories (except for when females tend to remain in a small range when raising young7.) Instead, opossums tend to constantly move in unusual patterns in search of food.

Within their habitats, opossums fall prey to many predators, such as birds of prey, foxes, coyotes, and humans, who often hit opossums with cars. The young are susceptible to predators such as snakes and birds of prey8.

Location: Opossums may be found across North and Central America, including parts of the United States east of the Rockies as well as along the west coast. Opossums were introduced to California in 1890 and proceeded to spread along the west coast9. Their range continues to spread northward and populations can now be found in southwestern Ontario and British Columbia, Canada.

Diet: Opossums are omnivorous scavengers whose diets range from human garbage and carrion, to grass, fruit, nuts, berries, insects, snails, mice, birds, worms, and pet food. Their developed senses of smell allow them to locate sources of food at night, when they are most active.

Reproduction: Female opossums may have up to 3 litters in a year, depending on geographic location, at anytime from early spring through summer. Females nest in trees or dens built by other animals. The young are born approximately two weeks after mating occurs and the last litter of the year may still be traveling with the mother when the first litter of the next year is born10. Males offer no parental care or support beyond fertilization. Females may give birth to up to twenty young, born helpless and the size of jellybeans, but litters typically contain 5 to 8 babies. Immediately after birth, the young crawl into the mother’s pouch in search of one of her thirteen teats. Some young do not survive the trip to the pouch and only those that make it to the pouch and find a teat have a chance at long-term survival. The young develop within the pouch attached to the teats for approximately a month, at which point they begin leaving the pouch for periods of time to travel along with their mother, sometimes atop her back or clinging to her tail. The young may remain with their mother for as long as three months11.

Few opossums live past 18 months old because of high mortality rates (many deaths due to car accidents.) The oldest opossum captured was determined to be 3 years old12.

Notes of Interest: Opossums are one of the oldest mammals on Earth. Fossilized remains have determined that opossums existed during the age of the dinosaurs, approximately 70 million years ago13.

Opossums are hunted as furbearers as well as food.

Opossums earned their westernized name in 1608 when first spotted by Captain John Smith, derived from the Algonquin word for ‘white animal,’ apasum14.

Footnotes
1. http://animals.nationalgeographic.com/animals/mammals/opossum/
2. http://www.in.gov/dnr/fishwild/3367.htm
3. http://www.nhptv.org/natureworks/opossum.htm
4. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
5. http://www.in.gov/dnr/fishwild/3367.htm
6. http://www.nhptv.org/natureworks/opossum.htm
7. http://www.opossum.org/
8. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
9. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
10. http://www.in.gov/dnr/fishwild/3367.htm
11. http://www.in.gov/dnr/fishwild/3367.htm
12. http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/
13. http://www.opossum.org/
14. http://www.nhptv.org/natureworks/opossum.htm

http://animals.nationalgeographic.com/animals/mammals/opossum/
http://www.opossum.org/
http://www.nhptv.org/natureworks/opossum.htm
http://www.in.gov/dnr/fishwild/3367.htm
http://animaldiversity.ummz.umich.edu/accounts/Didelphis_virginiana/

Mammals, Wildlife

Javelina – Pecari tajacu

December 6, 2013 traderscreek

General: Collared Peccaries (Pecari tajacu,) also known as Javelinas because of their javelin-like tusks, are members of the peccary family, and

bear a physical resemblance to (and are commonly mistaken as) wild pigs. These highly adaptable mammals have spread their range northward and now inhabit territories from northern Argentina to the American Southwest. Collared Peccaries are one of the most popular game animals in the southern United States and their populations remain stable and healthy. Listed as Least Concern on the IUCN Red List, these animals are prized by some for their hides, kept by others as domesticated farm pets, and considered nuisances by others who have to tolerate them on their property in search of an easy meal.

Description: Collared Peccaries are sometimes mistaken for wild pigs because of their physical appearances. Their coarse, bristly hair and hog-like snouts lend to this misnomer.

Adult peccaries measure 12”-19” at the shoulder, are 30” to 39” long and weigh an average of 33lbs. to 55lbs1. They have large heads with short, nearly straight tusks (that earned the collared peccary its common name, javelina- after the tip-shaped spear,) crushing molars, small legs and hoofed feet (with four toes on the front feet and three toes on the rear, due to the absence of dewclaws.) The Collared Peccary earned its nickname “musk hog” because of its posterior, dorsal musk gland, used to mark territory and to identify individuals. Females have two sets of inguinal mammary glands2.

Collared Peccaries have grizzled gray-black coats, with yellowish cheeks, dark dorsal manes and white or yellow coloration extending from the mane, across the shoulders and onto the throat.

Sexual dimorphism is not strongly articulated within this species. However, the young are born with a reddish or yellow overall coloration.

Collared Peccaries activity levels adjust according to the climate and time of year. During the summer they are most active at night, sleeping in the shade during the heat of the day. In the winter, peccaries commonly forage during the day in order to take advantage of the sun and at night sleep in groups to share body heat3.

Collared Peccaries are a highly social mammal, living in stable groups with complex communication, social hierarchies, and relationships. These groups, numbering from five to up to thirty individuals, maintain a gender ratio of roughly 1:1 and are comprised of codependent individuals, relying on the each other to eat, sleep, groom, and survive. Each group contains a dominant male who is responsible for the majority of breeding. Typically, the rest of the social hierarchy is determined by size. Within these groups, it is not uncommon for a feeding group to break away from the herd and become the start of a new group4.

Collared Peccary groups have territories that are determined by the number of individuals within the group and food resources and can be 6 to

1260 hectares in size5. These ranges rarely overlap with other peccary groups. These territories are fiercely defended by males and females within the group, who establish and mark their borders with glandular secretions and feces. Collared Peccaries may also aggressively defend their territories, by squaring off, chattering their teeth, charging, biting, or locking jaws. When greeting and identifying other group members, individuals use their dorsal glands for scent recognition and rub together along the lengths of their bodies.

Collared Peccaries have poor eyesight. They do, however, have good hearing. Because of this, vocalizations play an important role in their social interactions. Collared Peccaries are able to make upwards of fifteen vocalizations, used to communicate alarm, submission and aggression6.

Habitat: Collared Peccaries live in a range of habitats from tropical rainforests and forests in South and Central America, to arid, desert or dune habitats of the American Southwest (including Saguaro deserts and mesquite habitats.) Collared Peccaries have also adapted to living in urban and residential environments, attracted to the ample food sources.

Within their habitats, coyotes, bobcats, pumas, jaguars, and humans prey upon Collared Peccaries7.

Location: Collared Peccaries are the only species of Peccaries (there are three total) to live outside of South America8, with populations of fourteen subspecies spanning from northern Argentina, across Central America, and into the American Southwest (Texas, New Mexico, and Arizona9.)

Diet: Collared Peccaries diets are dependent on seasonal changes, including temperatures and the availability of food sources. Temperatures determine foraging practices, with peccaries tending to feed during the day in the winter to take advantage of the heat from the sun and later at night in the summer to avoid extreme heat.
Collared Peccaries are mainly herbivorous, and their diets are primarily composed of agaves and prickly pears (food sources that are well suited for the peccaries dry habitats because of their high water contents, which eliminates the peccaries need to frequent water holes.) Additionally, peccaries eat roots, bulbs, beans, berries, nuts, fungi, and grasses, as well as fish, eggs, some reptiles and amphibians, insects, and carrion. A highly adaptable species, Collared Peccaries have also learned to frequent urban environments, where they become nuisances in search of food. The stomach of the collared peccary is complex and is able to break down coarsely chewed food10.

Reproduction: Collared Peccaries are the only hoofed animals found in the western hemisphere that have breeding seasons not constrained by season, but rather climate. Collared Peccaries can breed year round if conditions allow and tend to have more young during rainy years. Almost all breeding is completed by the dominant male of the herd (subordinate males may not approach a female in estrus11.)

Pregnant females leave the group before having their young to avoid the newborns being eaten by other group members. After a gestation period of 140 to 150 days, females give birth to one to three reddish or yellow young, weighing 1.5lbs, within an earthen den or hollowed log. At a day old, the young are able to travel with their mother and the family may safely return to the herd. Females from previous litters may help the mother care for her young, which are weaned by two to three months of age.

Females reach sexual maturity between eight and fourteen months old, whereas males are fully mature by eleven months old.

Collared Peccaries have been known to live up to 24 years old in captivity12. Some populations, however, are being threatened due to deforestation and destruction of habitat.

Notes of Interest: The Collared Peccary earned its common name, Javelina, because of the resemblance their tusks bear to the tip of a javelin13.

Peccaries were commercially hunted for their hides until 1939, when the species received the status of game animal14. Now, this big game species is prized as one of the most important game species in states such as Arizona ad Texas. In Texas alone over 20,000 peccaries are shot during each hunting season. Each year, approximately 10,000 peccary hides are still exported from Peru15.

It is not uncommon for young peccaries to be captured and kept as domestic farm pets16.

http://animaldiversity.ummz.umich.edu/accounts/Pecari_tajacu/
http://www.mnh.si.edu/mna/image_info.cfm?species_id=246
http://www.nhptv.org/natureworks/peccary.htm
http://www.nsrl.ttu.edu/tmot1/tayataja.htm

Mammals, Wildlife

Deer Mouse – Peromyscus maniculatus

December 5, 2013 traderscreek

General: The deer mouse (Peromyscus maniculatus) is a highly adaptable North American species that is more widespread than any other species of mouse in this geographic range. They are often considered pests, inhabiting human dwellings, invading food and grain stores and carrying potentially fatal viruses.

Description: The deer mouse is a small, slender species, reaching a mature weight of 10g to 24g  and a full-grown length of 4.5” to 8.75” (the tail comprising one-third to around one-half the total length of the body.) Physical characteristics vary geographically. For example, populations living in woodlands tend to be larger overall than prairie populations. In general, deer mice have pointed noses, long vibrissae (like whiskers,) prominent, black eyes, and large ears covered in fine fur. Deer mice have forelimbs that are shorter than their hind limbs and hind feet that are approximately .8” in length.

Deer mice have short, fine, dense fur that is gray to red-brown across their bodies, and white or off-white on their undersides. They often have white hair resembling tufts at the bases of their ears. One of the most distinguishing characteristics of the deer mouse is the two-toned tail, which is covered in fine hair, dark on top and lacking any pigment on the bottom. Compared to the tails of other species of North American Mice, the coloration on that of the deer mouse is much more sharply defined. In general, deer mice are furrier than both the White-Footed Mouse and the House Mouse1.

The deer mouse is a nocturnal species that tends to be most active at twilight. It is a predominantly terrestrial species, that uses walking, running and sometimes leaping as its main modes of transportation, although the deer mouse is also a skilled climber2. Tracks are usually in groups of four with a trail width less than two inches.

Although the deer mouse is generally a solitary animal, basic social units do emerge during breeding seasons or cold months, when ten or more mice may huddle to conserve body heat (during extreme cold, mice may reduce their body temperatures and enter a daily torpor to conserve their energy.) These basic units often consist of mature males and females and some young of varying ages. Deer mice maintain home ranges that vary in size from 2600 square feet to over 32,000 square feet (that of males generally being larger than that of females.) Reproductive females are most territorial of their ranges and rarely overlap ranges with other females, since intruding females are known to commit infanticide. Ranges of males and females may overlap. The majority of activity occurs in close proximity to a mouse’s nest and food caches, constructed below ground, in a tree cavity, in a brush pile, stump or log, or within a human dwelling3. The nests are cup-shaped or spherical and made of vegetable matter, fur, or feathers. During the winter, activity becomes especially restricted and occurs mainly below the snow around the nest or within the nest for up to days at a time4.

Deer mice have highly developed senses of hearing, sight, smell and touch. They communicate with a variety of physical (postures, drumming,) chemical (scent marking,) tactile (grooming,) and vocal cues (with sounds including squeaks, trills, shrieks, and buzzing as well as drumming created by using the front paws possibly as a warning5.)

Deer mice can live up to eight years in captivity, but in the wild, do not often live longer than one year6.

Habitat: A highly adaptable species, the deer mouse can be found in every terrestrial habitat across all elevations, although their preference is for cool, moist, forests habitats. Inhabited zones include boreal and alpine forests, deserts, brush lands, prairies, agricultural areas, grasslands, and arid tropical areas.

Deer mice are a dietary staple of many carnivorous mammal and avian species, including snakes, owls, foxes, bobcats, and coyotes, to name a few7.

Location: Deer mice populations stretch across North America, from Alaska and Canada to Mexico. They are absent only in the southeastern United States and certain coastal sections of Mexico. This species is more widespread than any other species of mouse in North America, both geographically and ecologically8.

Diet: Deer mice are omnivorous and consume a diverse diet of insects, snails, earthworms, seeds, fruit, fungi, nuts, and plant matter. They are also known to eat carrion and at times, their own feces. Their sharp incisors are capable of breaking hard seeds and exoskeletons.

Deer mice cache food, especially in cooler climates or during cold months. Caches hold up to two cups of food each, consisting mostly of seeds, and are located in the ground or within cavities in trees. Despite this hoarding, starvation is a major cause of death for deer mice during winter months9.

Reproduction: Deer mice are polygamous and may breed throughout the year, although the majority of breeding takes place during warm months when there is ample food. During favorable breeding months, deer mice breed, on average, every three to four weeks, based on female estrous cycles of approximately five days.

Breeding pairs may inhabit the same nest, but females often drive males away in order to raise the young along. Typically, males offer no post-natal care. Females have a gestation period of 22 to 25.5 days. Females can experience a post-partum estrus and become pregnant shortly after one gestation period ends. The gestation period for a lactating female tends to be longer, lasting from 24 to 30.5 days. Litter size may range from one to eleven young, but contain, on average, five young. Females’ first five to six litters tend to increase in size consecutively, at which point they begin to decrease in size. The young are born hairless and blind, weighing 1.5g. Juvenile development is rapid. Hair begins to grow by the second day, the ear canals open by the tenth day, and the eyes open by the fifteenth day of life. The young cling to the mother’s nipples as she travels or are held in her mouth (one at a time.) The young are weaned in 25 to 35 days, at which point they may leave the nest and live independently. If the mother becomes pregnant with a second litter, she will eject the first litter from the nest10 (or in some instances, will leave the nest to be used by her mate with the older litter and find a new nest for the second litter11.)
Deer mice reach sexual maturity within 35 to 50 days, and females’ first estrus occurs by 49 days old12.

Notes of Interest: Deer mice are known carriers of a strain of Hantavirus, Sin Nombre virus. Humans who contract this virus develop Hantavirus pulmonary syndrome, a disease that is usually fatal13.

Deer mice that were marked and released by biologists were observed traveling 2 miles over the course of two days to return to their nest14.

http://animaldiversity.ummz.umich.edu/accounts/Peromyscus_maniculatus/
http://www.esf.edu/aec/adks/mammals/deer_mouse.htm
http://calmzoo.org/animals/deer-mouse/

Fish, Wildlife

Pumpkinseed sunfish – Lepomis gibbosus

December 1, 2013 traderscreek

Pumpkinseed

General:

Pumpkinseed sunfish (Lepomis gibbosus) are one of three small to medium sized species of true sunfish, along with bluegills and redbreasts. The species common name was earned because of its distinctive body shape. Pumpkinseeds are often recognized for their eagerness to bite at bait and their catchability, making them popular amongst novice fishermen and children (especially when nothing else is biting.) But anglers beware, pumpkinseeds have sharp spines along their fins that can be painful if handled incorrectly. An abundant species, they fulfill an important intermediate role in their ecosystems and are a common site in shallow waters along the edges of ponds, lakes, and slow running streams or rivers. While easy to catch and quite tasty, their petite size prevents pumpkinseeds from being a sport fish.

Description:

Pumpkinseeds are small to medium, freshwater fish that reach an average mature length of 4” to 8” (but may reach 10” in length) and a mature weight of .35lb. to .65lb. They have laterally compressed, deep-bodies typical of sunfish, which are likened in shape to pumpkinseeds, earning them their common name. They have small mouths and protective spiny, rayed dorsal, pelvic and anal fins.

Pumpkinseeds are colorful fish. Their bodies are olive, brassy yellow or brown in color and densely mottled with copper, gold, orange, blue-green, or red spots. Irregular, crescent-shaped blue or emerald streaks are present on the cheeks and gill covers. The rear portion of the dark gill cover is marked with a crimson spot contained within a pale crescent-shape. Their bellies range from yellow, to bronze to red1.

Juveniles have vertical banding on their sides and pale spots on their gill flaps (called opercle flaps2.)

Pumpkinseeds are most active during the day, feeding and hiding amongst vegetation in schools. At night they rest below cover along the bottom of shallow, fresh waters. Their home ranges average .5 to 2.75 acres.

On average, wild pumpkinseeds live five to six years but may live as long as eight years. In captivity, these fish have lived as long as twelve years3.

Habitat:

Pumpkinseeds live in cool to warm fresh waters, preferring depths of 3’ to 6’ and a temperature of 70° to 75°F. They tend to school in the shallow waters close to the shores of lakes, ponds and slow moving streams or rivers where ample vegetation provides cover.

Within their native habitats, pumpkinseeds are prey to largemouth bass, pike, perch, pickerel, walleye, freshwater eels, other sunfish, cormorants, herons, mergansers, and humans, to name a few. In addition to hiding in aquatic vegetation for cover, pumpkinseeds are equipped with spiny fins that are used for protection from predators. When threatened, pumpkinseeds spread these spines, making them harder to swallow4.

Location:

Pumpkinseeds are found throughout eastern Canada and the United States, with ranges reaching as far north as New Brunswick, as far west as North Dakota and southeast Manitoba and south to South Carolina and Kentucky. Their native range includes the Great Lakes, the Hudson Bay, and upper portions of the Mississippi River. Pumpkinseeds have been introduced in other areas of the United States as well as in South America, Africa and Europe, where they are considered invasive pests5.

Diet

: Like other sunfish, pumpkinseeds have a diverse diet including insects, insect larvae, snails, leeches, crustaceans, mollusks, small fish and aquatic vegetation. The majority of their feeding happens in the afternoon, although sunfish are known to feed in varying water levels throughout the day6.

Reproduction:

Pumpkinseeds spawn from May through August. During this period, females (of two to five years old) deposit from 4000 to 7000 eggs and males may breed up to once every eleven days. Unlike many species, pumpkinseeds are unique in that males provide parental care to the nests and young during early development while females play no role after spawning.

Male pumpkinseeds build colonies of up to fifteen nesting sites amongst vegetation in shallow, coastal waters. These colonies may contain a variety of species of sunfish, resulting in interbreeding. Males may construct several nest sites that are roughly 12” wide and 2” to 3” deep7. Males habitually fan these sites with their tails in order to remove fine sediment that could smother eggs8. These sites, once established, are aggressively defended by male pumpkinseeds, who charge, chase, bite, and mouth-fight intruding fish. However, when female pumpkinseeds approach from deeper waters to spawn, males will chase them into their nesting sites. During breeding times, males have been observed to change color, which is believed to play a role in breeding. Within the nest, males and females participate in a mating display in which they swim belly-to-belly in a circular motion, until the milt and eggs are released (the eggs released at intervals9.) Females may deposit their eggs in several nests throughout the breeding season and multiple females sometimes spawn with one male at the same time in the same nesting site.

With an optimal temperature of 55° to 82°F, eggs hatch in three to ten days. The young are transparent and have no ocular pigmentation for 48 hours. For the next five days, the young remain in the bottom of the nest, receiving nourishment form their yolks. The adult males guard all their nests and the young for approximately eleven days after they hatch, until the young have dispersed and are free-swimming and capable of feeding on their own (with fully developed mouths and pelvic fins, which are last to develop.) During this time, males continually fan the nests with their tails to keep them oxygenated and clean and have been known to return young to the nest within their mouths if they stray too far. For the first year of life, the young remain near the nesting sites and reach lengths of around 2”.

Pumpkinseeds reach sexual maturity in two years of age.

Notes of Interest: The DEC establishes closed seasons, quantity and size restrictions to protect fish species, particularly during vulnerable life stages, to ensure species survival as well as high quality fisheries for sport fishermen. Popular sport species receive particularly strict regulations, since they often develop slower, and have longer life expectancies. Examples of carefully protected species include small and largemouth bass. Sunfish, on the other hand, are not protected under strict regulations (even though they are a popular catch) as they reproduce rapidly and maintain healthy population numbers11.
Several countries with invasive populations of pumpkinseeds have reported negative ecological impacts due to these small fish. Since this species commonly hybridizes with other sunfish species, their presence often results in rapidly maturing, sterile males that overcrowd waters and stunt the growth of native species.

Pumpkinseeds are often kept as pets in aquariums and are also commonly used as the subjects for scientific studies12.

Pumpkinseeds readily bite at bait and have excellent flavor, but their potential as a game fish is hindered by their diminutive size.

Pumpkinseeds are also called punky, pond perch, sunnies, and sun perch.

http://www.dec.ny.gov/animals/7022.html
http://animaldiversity.ummz.umich.edu/accounts/Lepomis_gibbosus/
http://www.dgif.virginia.gov/wildlife/fish/details.asp?fish=010182

Mammals, Wildlife

Meadow vole – Microtus pennsylvanicus

December 1, 2013 traderscreek

General: Meadow voles (Microtus pennsylvanicus), sometimes called the field mouse or meadow mouse, are a small, common rodent that inhabits much of North America. They are prolific breeders whose populations tend to irrupt every few years. They are of the order Rodentia and family Cricetidae. Their presence can be determined by their unique tendency to construct nests that are surrounded by systems of runways.

Description: Meadow voles reach a mature length of 3.5” to 5”. Their tails, which are scaly and have little hair, may reach 1.4” to 2.6” in length, nearly 40% of their complete body length. Their mature weight is between 1oz. to 2ozs. Meadow voles can be identified by their compact bodies, large, slightly angular heads and small noses. Their ears, relative to other rodents, are small and lay fairly flat against the sides of the head.

Meadow voles have coarse dark brown or reddish brown hair mottled with black and lighter or white undersides. In the winter, their hair tends to be duller. There are no noticeable physical variations between males and females.

Meadow voles tend to be active throughout the day (usually above ground,) but become more diurnal during the cold months and nocturnal during warmer months. Because meadow voles do not hibernate, they spend the majority of their time throughout the year in search of food. They are skilled diggers and swimmers¹.

Meadow voles generally build 6” to 8” round nests² above ground but sometimes construct them within shallow burrows, using dry vegetation. During cold months, mixed-age and mixed-gender groups of non-reproducing voles may share a nest to conserve body temperature. The nest is the epicenter of a system of runways, used as sheltered passageways and typically littered with vegetation cuttings and droppings³.

Breeding females tend to be territorial of their home ranges (which are distinct from other females’ ranges,) while males are mobile and have ranges that are generally three times the size of females’ ranges. If more than one female occupies a range, the females tend to be a mother-daughter pair (and in this case, the mother typically prevents the daughter from breeding.)

Meadow voles may become aggressive if they are cornered or caught, stomping their feet and attacking to avoid danger. They use their runways (that are often covered in vegetation) for protection from predators, including birds of prey, snakes, bullfrogs, snapping turtles, foxes, weasels, shrews, raccoons, and cats⁴. The meadow vole is a major component of the diets of many of its predators.

Meadow voles have highly developed senses of hearing and smell, and communicate using chemical markers (droppings and urine are used to determine identity, sexual readiness, and proximity,) physical gestures, and vocalizations (including growls, squeals, and chatters.) The young emit ultrasonic signals. The majority of vocalizations are created in response to threats⁵.

Meadow voles are commonly preyed upon and often do not live more than one year in the wild, although they have been known to live as long as 2.7 years⁶.

Habitat: Meadow voles are predominantly found in low-lying fields, meadows, grassy marshes, grasslands, orchards, open woodlands (deciduous and mixed forests,) and occasionally in low wetlands, flooded marshes, and along river or lake shores.

Location: Meadow voles thrive throughout most of North America, from central Alaska, south to New Mexico and Georgia, as far west as the Rockies and east to the Atlantic coast⁷.

Diet: Meadow voles consume nearly 60% of their own body weight daily, feeding on a varied diet that consists mainly of grass, succulent vegetation, herbs and sedges found within their geographic ranges during warm months. During the fall, their diets consist mainly of seeds and grains and in the winter, meadow voles subsist on the roots and inner bark of trees and shrubs, which they harvest through girdling. They may also eat fruit, tubers, bulbs, flowers, leaves, insects, and at times, flesh.

Meadow voles do not generally store food, except for some small caches in preparation for the winter⁸. Because of their lack of food hoarding, meadow voles spend the majority of their time feeding.

Reproduction: Meadow voles are prolific breeders capable of having more than twelve litters in one year, determined by climate, food supplies, population densities of meadow voles and predators, and individual behavior. Breeding may occur during any month but is more frequent during warm months when food is readily available. Unless their populations are controlled or the carrying capacities of their environments are met, their populations may irrupt every three to five years⁹. Typical population densities average forty to eighty voles per acre¹⁰.

Females in estrous fiercely defend their territories and are sought out by males, who may aggressively compete with each other or establish temporary hierarchies to determine mating rights. After mating, females drive males away.

After a twenty-one day gestation period, the female gives birth to a litter of one to eleven pink, blind, hairless young that weigh just over 2 grams each. After eight days, their eyes open, within twelve to fourteen days, the young are weaned and by three weeks old the young are independent. Females reach sexually maturity within one month (at which point they are capable of having a litter nearly every three weeks for the rest of their lives,) and males reach sexual maturity within thirty-five days¹¹.

Notes of Interest: Meadow voles are considered to be pests because of the destruction they cause in orchards and forestry initiatives¹².

Footnotes

1. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

2. http://www.fcps.edu/islandcreekes/ecology/meadow_vole.htm

3. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

4. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

5. http://www.esf.edu/aec/adks/mammals/meadow_vole.htm

6. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

7. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

8. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

9. http://www.nysipm.cornell.edu/factsheets/treefruit/pests/vole/vole.asp

10. http://www.esf.edu/aec/adks/mammals/meadow_vole.htm

11. http://www.esf.edu/aec/adks/mammals/meadow_vole.htm

12. http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

http://animaldiversity.ummz.umich.edu/accounts/Microtus_pennsylvanicus/

http://www.fcps.edu/islandcreekes/ecology/meadow_vole.htm

http://www.nysipm.cornell.edu/factsheets/treefruit/pests/vole/vole.asp

http://www.esf.edu/aec/adks/mammals/meadow_vole.htm

Mammals, Wildlife

American mink – Neovison vison

November 30, 2013 traderscreek

General: The American mink (Neovison vison) is a medium-sized, semi-aquatic mammal that is a member of the mustelid family. The American mink is native to the United States and Canada and has been introduced to several non-native habitats as a fur-bearer and game animal. The American mink is best known for its glossy, thick, dark coat and long, lean body. Humans pose the biggest threat to this species.

Description: American mink are recognizable because of their long, slender bodies that are covered in thick, dark fur. Full-grown, males are 22.5” to 27.5” in length, while females are smaller, reaching a mature length of 18” to 22.5”. Their thick tail may make-up half their body length. Similarly, mature males tend to be about 20% heavier than females, weighing 2 to 3.5lbs. while mature females weigh 1.5 to 2.5lbs. Their length is emphasized by short sturdy legs and a long neck. American mink have flat faces and conical heads with petite eyes and ears. Because mink are semi-aquatic, their toes are webbed¹.

American mink may be best known for their luxurious dark brown to black fur (made-up of a dark brown undercoat and long, oily guard hairs that waterproof the coat².) Their thick, shiny, soft coat is accented by patches of white fur on the chin, neck and chest.

Mink don’t hibernate and are most active at dawn and dusk. A semi-aquatic mammal, mink are skilled swimmers and tend to spend much of their time in and about the water searching for food. They are capable of swimming up to 100’ underwater and diving up to 15’ below the surface. Because of their dependency on the water for hunting, mink locate their subterranean burrows along the banks of bodies of water, or take residence in the abandoned burrows of other animals. These dens are dug out then lined with dried vegetation and fur. American mink tend to use each den for only a limited time before building a new den.

Because of their aggressive and defensive nature, American mink tend to be solitary animals. Males are especially territorial and mark their home ranges with secretions from their anal glands (similar to skunks.) Mink also use chemical secretions to communicate their sexual status. Mink are known to be aggressive when faced with a threat from a predator. However, mink are skilled at avoiding confrontations because of their agility, sly nature and dark coloration that blends well with their surroundings.

In addition to chemical cues, American mink communicate using visual and auditory cues, since they have highly developed senses of hearing, vision and smell³. Mink are capable of making a limited range of sounds, including a pur when content⁴.

Mink may live up to 10 years old.

Habitat: American mink exist in a variety of habitats, including grasslands, forests, and marshes, but tend to prefer forested areas that offer access to water (near ponds, streams, or lakes,) and areas with brush or rock cover for protection⁵.

Location: American mink populations can be found across the United States and Canada (except for the southwestern United States, Hawaii, coastal areas of Canada along the Arctic and some Canadian islands.) Populations have been introduced to Newfoundland and the British Isles (where mink were accidentally released or escaped from fur farms⁶.)

Diet: The American mink is carnivorous and consumes a diverse diet that changes throughout the year. During warm months, their diets include aquatic animals (frogs, crayfish, and fish,) and small mammals (such as rabbits, muskrats, mice, chipmunks, and shrews.) During cold, winter months their diets consist mainly of small mammals.

American mink have been known to store extra food within their dens⁷.

Reproduction: American mink are promiscuous and mate annually during the winter. Fertile females may mate with multiple males. After a gestational period of 40 to 75 days, the female gives birth in the late spring to a litter of one to eight young, within a fur-lined nest. At birth, the young weigh 8 to 10g, are blind and wrinkled, and have a coat of fine white hair all over their bodies. Their eyes open around 25 days old and by six weeks they are fully weaned (although the young may remain with their mother into their first fall.) By 6 to 10 months old, the young become independent and leave their mother to establish their territories. By 10 months old, American mink reach sexual maturity⁸.

Notes of Interest: Humans pose the greatest threat to the American mink (because of the high value of their fur.) Mink are also hunted by coyotes, bobcats, birds of prey and other carnivores. Common to other mustelids, minks are fearless and defend themselves aggressively when faced with a threat, although their coloration and allusive nature help protect them before these threats present themselves.

Limited trapping seasons for the American mink exist in forty-seven states and in all of the Canadian provinces⁹.

Due to the high demand for their fur, mink are bred on fur farms. Through selective breeding, a broad spectrum of hide colors has been established, ranging from black to white. These colors have become established in some wild populations (including some in South America, Europe and Newfoundland,) because of mink that have escaped from farms or been released from farms (by animal activist groups.)

Tens of thousands of mink were intentionally released into the Soviet Union over the coarse of several decades to provide a new game animal for hunters. However, this introduction caused a severe shift in local eco-systems and had negative impacts¹⁰.

Footnotes

1. http://www.nhptv.org/natureworks/mink.htm

2. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

3. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

4. http://www.nhptv.org/natureworks/mink.htm

5. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

6. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

7. http://www.nhptv.org/natureworks/mink.htm

8. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

9. http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/

10. http://www.sciencedaily.com/articles/a/american_mink.htm

http://animaldiversity.ummz.umich.edu/accounts/Neovison_vison/