THE DOUGLAS SQUIRREL

 

The Douglas squirrel (Tamiasciurus douglasii) is a pine squirrel found in the Pacific Northwest of North America, including the northwestern coastal states of the United States as well as the southwestern coast of British Columbia in Canada. It is sometimes known as the chickaree or pine squirrel, although these names are also used for the American red squirrel. Variant spellings of the common name are Douglas' squirrel and Douglas's squirrel. The Native Americans of Kings River called it the "Pillillooeet", in imitation of its characteristic alarm call.

 

Description

 

John Muir described the Douglas squirrel, Tamiasciurus douglasii, as "by far the most interesting and influential of the California Sciuridæ". Adults are about 33 cm in length (including its tail, which is about 13 cm long), and weigh between 150 and 300 grams. Their appearance varies according to the season. In the summer, they are greyish or almost greenish-brown on their backs, and pale orange on the chest and belly, while legs and feet appear brown. In the winter, the coat is browner and the underside is grayer; also, the ears appear even tuftier than they do in summer. Like many squirrels, Douglas squirrels have a white eye-ring.

Anacortes Community Forest Lands (Washington)

 

Breeding

Mating can occur as early as February. Gestation is about four weeks, and the young (which are altricial) are weaned at about eight weeks of age. There may be up to six kits in a litter, though four is more usual. In the southern and lower parts of their range, they produce two litters each year.

 

Habitat

 

Douglas squirrels live in coniferous forest habitats along the Pacific Coast, from the Sierra Nevada (mountains) of California, northwards to the southwestern coast of British Columbia. Tamiasciurus douglasii prefer old-growth forests or mature second-growth forests, and some authors regard them as dependent on its presence. They essentially replace the American Red Squirrel, which inhabits the coniferous forests of the rest of North America, in these areas. The two species have very minimal overlap in the territory.

They are territorial; in winter, each squirrel occupies a territory of about 10 000 square metres, but during the breeding season a mated pair will defend a single territory together. Douglas squirrels are active by day, throughout the year, often chattering noisily at intruders. On summer nights, they sleep in ball-shaped nests that they make in the trees, but in the winter they use holes in trees as nests. Groups of squirrels seen together during the summer are likely to be juveniles from a single litter.

 

Diet

 

Douglas squirrels mostly eat seeds of coniferous trees such as Douglas fir (Pseudotsuga menziesii), Sitka spruce (Picea sitchensis) and shore pine (Pinus contorta). They also eat acorns, berries, mushrooms, the eggs of birds such as yellow warblers, and some fruit including strawberries and plums. Douglas squirrels are larder hoarders,^[4] storing their food in a single location or 'larder' called a midden. As the squirrel peels the scales of cones to get at the seeds, the discarded scales accumulate into piles that can grow to several meters across as the same site is used by generations of squirrels.

Their predators include American martens, Bobcats, domestic cats, northern goshawks, and owls; although they quickly acclimatize to human presence, humans can be a threat to them, through robbing of their cone caches to find seeds for tree cultivation and through the destruction of old-growth forest. However, the squirrels' numbers appear to be unaffected by commercial thinning of forests.^[5]

Pacific silver fir cone debris from feeding Douglas squirrels, North Cascades National Park

 

 

 Binomial name

 

 Tamiasciurus douglasii

(Bachman, 1839)^[2]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE BROWN- EARED WOLLY OPOSSUM

 

The brown-eared woolly opossum (Caluromys lanatus), also known as the western woolly opossum, is an opossum from South America. It was first described by German naturalist Ignaz von Olfers in 1818. The opossum is characterized by a brown to reddish brown coat and similarly colored limbs, yellow to orange underbelly, hairless, brown ears with a hint of pink, and a tail furred on the back for up to half of its length. The brown-eared woolly opossum is nocturnal (active mainly at night), solitary and omnivorous. The IUCN lists it as least concern.

 

Taxonomy

 

The brown-eared woolly opossum is one of the three members of Caluromys, and is placed in the family Didelphidae. It was first described by German naturalist Ignaz von Olfers as Didelphys lanata in 1818.^[3] It was given its present binomial name, Caluromys lanatus, by American zoologist Joel Asaph Allen in 1900.^[4]

A 1955 revision of marsupial phylogeny grouped Caluromys, Caluromysiops, Dromiciops (monito del monte) and Glironia (bushy-tailed opossum) under a single subfamily, Microbiotheriinae, noting the dental similarities among these. A 1977 study argued that these similarities are the result of convergent evolution, and placed Caluromys, Caluromysiops and Glironia in a new subfamily, Caluromyinae.^[5] In another similar revision, the bushy-tailed opossum was placed in its own subfamily, Glironiinae.^[6]

The following four subspecies are recognized:^[2][4]

• C. l. cicur (Bangs, 1898): Occurs in northeastern Colombia and northwestern Venezuela.
• C. l. lanatus (Olfers, 1818): Occurs in Bolivia and Mato Grosso (southwestern Brazil).
• C. l. ochropus (Wagner, 1842): Occurs in western Brazil, extreme southeastern Colombia, eastern Ecuador, Peru and southern Venezuela.
• C. l. ornatus (Tschudi, 1845): Occurs in southern Colombia, the lowlands of Bolivia, Ecuador and Peru, and the valleys of eastern Andes.

Two additional subspecies, C. l. nattereri and C. l. vitalinus, are sometimes recognised, but have been considered to be junior synonyms of C. l. lanatus and C. l. ochropus, respectively.^[2]

The cladogram below, based on a 2016 study, shows the phylogenetic relationships of the brown-eared woolly opossum.^[7]

	Bushy-tailed opossum (Glironia venusta)   Caluromyinae   Black-shouldered opossum (Caluromyopsis irrupta)       Derby's woolly opossum (Caluromys derbianus)       Bare-tailed woolly opossum (Caluromys philander)     Brown-eared woolly opossum (Caluromys lanatus)               Kalinowski's mouse opossum (Hyladelphys kalinowskii)       Marmosini       Didelphini     Thylamyini

 

Description

A captive animal, photographed in Peru

The brown-eared woolly opossum is characterized by a brown to reddish brown coat and similarly colored limbs, yellow to orange underbelly, hairless, brown ears with a hint of pink, and a tail furred up to half of its length dorsally (on the back) and up to 20% of its length at the base. The coat may be tinged with gray, and develops a shade of orange on the shoulders, limbs and the crown; young are typically grayer. The fur is fairly long, soft and thick. The tail becomes less bushy towards the tip, leaving the last 30% of the length bare. This naked part is typically white with a yellowish tinge, and spotted with brown. Faint orange rings circle the eyes on the grayish white face. A dark stripe runs up the nose and between the eyes up to the back of the ears. The subspecies may vary in coloration; C. l. circur is largely grayish brown, while C. l. lanatus is a pale brown and does not show spots on the tail.^[2][8]

The head-and-body length is between 20 and 32 centimetres (7.9 and 12.6 in), and the tail is 33 to 45 centimetres (13 to 18 in) long. The opossum weighs 31–52 grams (1.1–1.8 oz). Hindfeet measure 3–5 centimetres (1.2–2.0 in), and the ears measure 3–4 centimetres (1.2–1.6 in). The dental formula is 5.1.3.44.1.3.4 – typical of didelphids. The brown-eared opossum differs from the bare-tailed woolly opossum in having a bushier tail (in the bare-tailed opossum, the tail turns bare abruptly after the first one-third of the length) and a pouch that opens to the front rather than along the midline. Derby's woolly opossum differs from the brown-eared opossum in having white limbs and gray fur between the shoulders. The brown-eared opossum differs from other opossums in having a comparatively large braincase.^[2]

 

Distribution and status

 

The brown-eared woolly opossum inhabits humid tropical forests (such as primary, secondary and gallery forests), plantations, in mangrove and xerophytic forests, and even in the more densely wooded parts of the cerrado and pantanal. It typically occurs up to 500 metres (1,600 ft) above the sea level, though individuals have been recorded up to 2,600 metres (8,500 ft). The range lies to the east of the Andes – from Bolivia, central Colombia, eastern Ecuador, Peru and western and southern Venezuela to northeastern Argentina, western, central and southern Brazil, eastern and southern Paraguay.^[1][2] The IUCN lists this opossum as least concern given its wide distribution and presumably large numbers, though it is threatened by deforestation in some parts of the range.^[1]

 

Ecology and behavior

 

The brown-eared woolly opossum is nocturnal (active mainly at night) and solitary, though individuals have been observed foraging in pairs. These opossums are omnivorous and feed on fruits (of plants such as Cecropia, Piper and Solanaceae species), nectar, small invertebrates and vertebrates.^[2] A study presented it as a typical frugivore, with a well-developed cecum.^[9] By feeding on nectar, the opossum could probably help in the pollination of Pseudobombax tomentosum and Quararibea cordata flowers.^[10][11] They are nocturnal, and generally silent and solitary, although they have occasionally been seen foraging in pairs.^[2]

The estrus cycle is 27–29 days long; females will develop a pouch prior to carrying young.^[2] The litter size ranges from one to four,^[12] while the bare-tailed woolly opossum can have up to seven young.^[13]

 

 

 Binomial name

 

 Caluromys lanatus

(Olfers, 1818)

 

 

 

 

 

 Brown-eared woolly opossum range

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE WATER OPOSSUM

 

The water opossum (Chironectes minimus), also locally known as the yapok (/ˈjæpɒk/), is a marsupial of the family Didelphidae.^[2] It is the only living member of its genus, Chironectes.^[3] This semiaquatic creature is found in and near freshwater streams and lakes from Mexico through Central and South America to Argentina and is the most aquatic living marsupial (the lutrine opossum also has semiaquatic habits). It is also the only living marsupial in which both sexes have a pouch. The thylacine, commonly referred to as the Tasmanian tiger, also exhibited this trait, but it is now believed to be extinct.

The water opossum lives in bankside burrows, emerging after dusk to swim and search for fish, crustaceans and other aquatic animals, which it eats on the bank.

 

 

Origin of the name

 

The local name for the water opossum, "yapok", probably comes from the name of the Oyapok River in French Guiana.

 

Physical appearance

The water opossum is a small opossum, 27-32.5 cm long, with a 36–40 cm long tail. The fur is in a marbled grey and black pattern, while the muzzle, eyestripe, and crown are all black. A light band runs across the forehead anterior to the ears, which are rounded and naked. There are sensory facial bristles in tufts above each eye, as well as whiskers. The water opossum's tail, furred and black at the base, is yellow or white at its end. The hindfeet of the water opossum are webbed, while the forefeet ("hands") are not. The forefeet can be used to feel for and grab prey as the animal swims, propelled by its tail and webbed back feet.^[4] Unlike other didelphids, the water opossum does not have a cloaca.^[5]

Aquatic adaptations

The water opossum has several adaptations for its watery lifestyle. It has short, dense fur, which is water-repellent. The broad hindfeet are webbed and are used for propulsion through water, moving with alternate strokes. They are symmetrical as well, which distributes force equally along both borders of the webbing; this increases the efficiency of the water opossum's movement through the water. The water opossum's long tail also aids in swimming.

Being a marsupial and at the same time an aquatic animal, the water opossum has evolved a way to protect its young while swimming. A strong ring of muscle makes the pouch (which opens to the rear) watertight, so the young remain dry, even when the mother is totally immersed in water.^[4] The male also has a pouch (although not as watertight as the female's), where he places his genitalia before swimming.^[5] This is thought to prevent them from becoming entangled in aquatic vegetation and is probably helpful in streamlining the animal as well.

 

Reproduction

 

Water opossums mate in December and a litter of 1-5 young is born 12 to 14 days later in the nest. By 22 days the offspring are beginning to show some fur, and by 40 days or so their eyes are open, their bodies protruding from the mother's pouch. At 48 days of age, the young opossums detach from the nipples, but they still nurse and sleep with the mother.

 

Fossil record

 

The water opossum seems to have a history dating as far back as to the Pliocene Epoch.

Holocene subfossil fragments of Chironectes have been discovered in São Paulo, Brazil. Also, there are fossil specimens from the late Pleistocene-Recent cave deposits in Minas Gerais, Brazil, as well as from the late Pliocene in Entre Ríos Province, Argentina.

 

Binomial name

Chironectes minimus

(Zimmermann, 1780)

Water opossum range