THE MERLIN FALCON

 

The merlin (Falco columbarius) is a small species of falcon from the Northern Hemisphere,^[2] with numerous subspecies throughout North America and Eurasia. A bird of prey, the merlin breeds in the northern Holarctic; some migrate to subtropical and northern tropical regions in winter. Males typically have wingspans of 53–58 centimetres (21–23 in), with females being slightly larger. They are swift fliers and skilled hunters which specialize in preying on small birds in the size range of sparrows to doves and medium-sized shorebirds. In recent decades merlin populations in North America have been significantly increasing, with some merlins becoming so well adapted to city life that they forgo migration; in Europe, populations increased up to about 2000 but have been steady subsequently.^[3] The merlin has for centuries been well regarded as a falconry bird.

Merlin, nominate subspecies F. c. columbarius, in Prospect Park, New York

 The merlin was described and illustrated by the English naturalist Mark Catesby (as the "pigeon hawk") in his Natural history of Carolina, Florida and the Bahama Islands published in 1729–1732.^[4][5] Based on this description, in 1758 Carl Linnaeus included the species in the tenth edition of his Systema Naturae and introduced the present binomial name Falco columbarius with the type locality as "America".^[6] The genus name is Late Latin; falco derives from falx, falcis, a sickle, referring to the claws of the bird.^[7] The species name columbarius is Latin for "of doves" from "columba", "dove".^[8] Thirteen years after Linnaeus's description Marmaduke Tunstall recognized the Eurasian birds as a distinct taxon Falco aesalon in his Ornithologica Britannica. If two species of merlins are recognized, the Old World birds would thus bear the scientific name F. aesalon.^[9][10]

 

 The name "merlin" is derived from Old French esmerillon via Anglo-Norman merilun or meriliun. There are related Germanic words derived through older forms such as Middle Dutch smeerle, Old High German smerle and Old Icelandic smyrill.^[11] Wycliffe's Bible, around 1382, mentions An Egle, & agriffyn, & a merlyon.^[11] The species was once known as "pigeon hawk" in North America.^[12]

 

Although the merlin's name looks and sounds like the name of the wizard Merlin prominent in Arthurian legend, the bird is not named after the wizard.^[13] The wizard's name is an English cognate of the Welsh name "Myrddin" and is unrelated to the name of the bird.

 

European subspecies F. c. aesalon, Dumfries & Galloway, Scotland

The relationships of the merlin are not resolved to satisfaction. In size, shape and coloration, it is fairly distinct among living falcons. The red-necked falcon is sometimes considered more closely related to the merlin than other falcons, but this seems to be a coincidence due to similar hunting habits; it could not be confirmed in more recent studies. Indeed, the merlin seems to represent a lineage distinct from other living falcons since at least the Early Pliocene, some 5 Ma (million years ago). As suggested by biogeography and DNA sequence data, it might be part of an ancient non-monophyletic radiation of Falco species from Europe to North America, alongside the ancestors of forms such as the American kestrel (F. sparvierus), and the aplomado falcon (F. femoralis) and its relatives. A relationship with the red-necked falcon (F. chicquera) was once proposed based on their phenetic similarity, but this is not considered likely today.^{[9][10][14][15][16]} More recently, a genetic link to two tropical African species, grey kestrel Falco ardosiaceus and dickinson's kestrel F. dickinsoni has been found.^[17]

 

In that regard, a fossil falcon from the Early Blancan (4.3–4.8 Ma)^[18] Rexroad Formation of Kansas. Known from an almost complete right coracoid (specimen UMMP V29107) and some tarsometatarsus, tibiotarsus and humerus pieces (V27159, V57508-V57510, V57513-V57514), this prehistoric falcon was slightly smaller than a merlin and apparently a bit more stout-footed, but otherwise quite similar. It was part of the Fox Canyon and Rexroad Local Faunas, and may have been the ancestor of the living merlins or its close relative. With its age quite certainly pre-dating the split between the Eurasian and North American merlins, the fossil falcon supports the idea of the merlin lineage originating in North America, or rather the colonization thereof. After adapting to its ecological niche, ancient merlins would have spread to Eurasia again, with gene flow being interrupted as the Beringia and Greenland regions became icebound in the Quaternary glaciation.^[10][14][19]

That the merlin has a long-standing presence on both sides of the Atlantic is evidenced by the degree of genetic distinctness between Eurasian and North American populations. They are probably best considered distinct species, with gene flow having ceased at least a million years ago, but probably more;^[10][17] but more study is required, particularly in the less-sampled subspecies, before a formal split can be made.^[20]

By and large, color variation in either group independently follows Gloger's Rule. The Pacific temperate rain forest subspecies F. c. suckleyi males are almost uniformly black on the upperside and have heavy black blotches on the belly, whereas those of the lightest subspecies, F. c. pallidus, have little non-dilute melanin altogether, with gray upperside and reddish underside pattern.^[9] Nine subspecies are currently accepted:^[20]

Coastal forest merlin (F. c. suckelyi), Lake Los Carneros Park, Goleta, California, United States

Northern Eurasia from British Isles through Scandinavia to central Siberia. Population of northern Britain shows evidence of gene flow from F. c. subaesalon. British Isles population resident or short-distance movement from moors to coasts, rest migratory; winters in Europe and the Mediterranean region to about Iran.

 

 

Male (presumably F. c./a. pallidus) wintering in Little Rann of Kutch (Gujarat, India)

 

Juvenile, F. c. columbarius

The merlin is 24–33 cm (9.4–13.0 in) long with a 50–73 cm (20–29 in) wingspan.^[22] Compared with most other small falcons, it is more robust and heavily built. Males average at about 165 g (5.8 oz) and females are typically about 230 g (8.1 oz). There is considerable variation, however, throughout the birds' range and—in particular in migratory populations—over the course of a year. Thus, adult males may weigh 125–210 g (4.4–7.4 oz), and females 190–300 g (6.7–10.6 oz). Each wing measures 18.2–23.8 cm (7.2–9.4 in), the tail measures 12.7–18.5 cm (5.0–7.3 in) and the tarsus measures 3.7 cm (1.5 in).^[22][23] Such sexual dimorphism is common among raptors; it allows males and females to hunt different prey animals and decreases the territory size needed to feed a mated pair.^[9][24]

 

The male merlin has a blue-gray back, ranging from almost black to silver-gray in different subspecies. Its underparts are buff- to orange-tinted and more or less heavily streaked with black to reddish brown. The female and immature are brownish-gray to dark brown above, and whitish buff spotted with brown below. Besides a weak whitish supercilium and the faint dark malar stripe—which are barely recognizable in both the palest and the darkest birds—the face of the merlin is less strongly patterned than in most other falcons. Nestlings are covered in pale buff down feathers, shading to whitish on the belly.^[24]

Upperside pattern of male (presumably F. c./a. pallidus) wintering in Little Rann of Kutch, Gujarat, India

The remiges are blackish, and the tail usually has some three to four wide, blackish bands, too. Very light males only have faint and narrow medium-gray bands, while in the darkest birds the bands are very wide, so that the tail appears to have narrow lighter bands instead. In all of them, however, the tail tip is black with a narrow white band at the very end, a pattern possibly plesiomorphic for all falcons. Altogether, the tail pattern is quite distinct though, resembling only that of the aplomado falcon (F. berigora) and (in light merlins) some typical kestrels. The eye and beak are dark, the latter with a yellow cere. The feet are also yellow, with black claws.^[24]

Light American males may resemble the American kestrel (F. sparverius, not a typical kestrel), but merlin males have a gray back and tail rather than the reddish-brown of the kestrels. Light European males can be distinguished from kestrels by their mainly brown wings. In the north of South Asia, wintering males may be confused with the red-necked falcon (F. chicquera) if they fly away from the observer and the head (red on top in F. chicquera) and underside (finely barred with black in F. chicquera) are not visible.^[24]

Merlins inhabit fairly open country, such as willow or birch scrub, shrubland, but also taiga forest, parks, grassland such as steppe and prairies, or moorland. They are not very habitat-specific and can be found from sea level to the treeline. In general, they prefer a mix of low and medium-height vegetation with some trees, and avoid dense forests as well as treeless arid regions. During migration however, they will utilize almost any habitat.^[9]

 

Most of its populations are migratory, wintering in warmer regions. Northern European birds move to southern Europe and North Africa, and North American populations to the southern United States to northern South America. In the milder maritime parts of its breeding range, such as Great Britain, the Pacific Northwest and western Iceland, as well as in Central Asia, it will merely desert higher ground and move to coasts and lowland during winter. The migration to the breeding grounds starts in late February, with most birds passing through the US, Central Europe and southern Russia in March and April, and the last stragglers arriving in the breeding range towards the end of May. Migration to winter quarters at least in Eurasia peaks in August/September, while e.g. in Ohio, just south of the breeding range, F. c. columbarius is typically recorded as a southbound migrant as late as September/October.^[9][21] In Europe, merlins will roost communally in winter, often with hen harriers (Circus cyaneus). In North America, communal roosting is rare.

F. c. columbarius hunting a northern blue jay (Cyanocitta cristata bromia), Mount Auburn Cemetery, Massachusetts, United States

Merlins rely on speed and agility to hunt their prey. They often hunt by flying fast and low, typically less than 1 m (3.3 ft) above the ground, using trees and large shrubs to take prey by surprise. But they actually capture most prey in the air, and will "tail-chase" startled birds. Throughout its native range, the merlin is one of the most able aerial predators of small to mid-sized birds, more versatile if anything than the larger hobbies (which prefer to attack in mid-air) and the more nimble sparrowhawks (which usually go for birds resting or sleeping in dense growth). Breeding pairs will frequently hunt cooperatively, with one bird flushing the prey toward its mate.^[9][25]

 

The merlin will readily take prey that is flushed by other causes, and can for example be seen tagging along sharp-shinned hawks (Accipiter striatus) to catch birds that escape from this ambush predator into the open air. It is quite unafraid, and will readily attack anything that moves conspicuously. Merlins have even been observed trying to "catch" automobiles and trains, and to feed on captive birds such as those snared in the mist nets used by ornithologists. Even under adverse conditions, one in 20 targets is usually caught, and under good conditions almost every other attack will be successful. Sometimes, merlins cache food to eat it later.^[9][26]

 

In particular during the breeding season, most of the prey are smallish birds weighing 10–40 g (0.35–1.41 oz). Almost any such species will be taken, with local preferences for whatever is most abundant—be it larks (Alaudidae), pipits (Anthus), finches (Fringillidae),^[27] house sparrows (Passer domesticus), other Old World sparrows (Passeridae), northern wheatears (Oenanthe oenanthe), thrushes (Turdus), kinglets (Regulidae)^[28] or buntings (Emberiza)^[27]—and inexperienced yearlings always a favorite. Smaller birds will generally avoid a hunting merlin if possible. In the Cayman Islands (where it only occurs in winter), bananaquits were noted to die of an apparent heart attack or stroke, without being physically harmed, when a merlin went at them and they could not escape.^[26]

 

 Larger birds (e.g. sandpipers, flickers,^[29] other woodpeckers,^[30] ptarmigan, other grouse,^[27] ducks^[31] and even rock doves^[32] as heavy as the merlin itself) and other animals—insects (especially dragonflies, moths, grasshoppers, butterflies and beetles^[33][34]), small mammals, (especially bats,^[35] shrews,^[36] rabbits,^[33] voles, lemmings^[37] and other small rodents^[38]) reptiles (such as lizards and snakes)^[27] and amphibians^[39]—complement its diet. These are more important outside the breeding season, when they can make up a considerable part of the merlin's diet. But for example in Norway, while small birds are certainly the breeding merlin's staple food, exceptional breeding success seems to require an abundance of Microtus voles.^[9]

 

 

Corvids are the primary threat to eggs and nestlings. Adult merlins may be preyed on by larger raptors, especially peregrine falcons (F. peregrinus), eagle-owls (e.g., great horned owl, Bubo virginianus), and larger Accipiter hawks (e.g., northern goshawk, A. gentilis). In general however, carnivorous birds avoid merlins due to their aggressiveness and agility. Their desire to drive larger raptors away from their territory is so pronounced that it is an identifying characteristic. Quoting from one popular raptor watching reference,^[40] "An observer may use this aggressive tendency for identification purposes and as a means of detection. High-flying merlins often betray themselves and distinguish themselves because they are vigorously harassing another raptor (even ones as large as the Golden Eagle)."

Nestlings

Breeding occurs typically in May/June. Though the pairs are monogamous at least for a breeding season, extra-pair copulations have been recorded. Most nest sites have dense vegetative or rocky cover; the merlin does not build a proper nest of its own. Most will use abandoned corvid (particularly Corvus crow and Pica magpie) or hawk nests which are in conifer or mixed tree stands. In moorland—particularly in the UK—the female will usually make a shallow scrape in dense heather to use as a nest. Others nest in crevices on cliff-faces and on the ground, and some may even use buildings.^[9]

 

 

Three to six (usually 4 or 5) eggs are laid. The rusty brown eggs average at about 40 mm × 31.5 mm (1.57 in × 1.24 in).^{[citation needed]} The incubation period is 28 to 32 days. Incubation is performed by the female to about 90%; the male instead hunts to feed the family. Hatchlings weigh about 13 g (0.46 oz). The young fledge after another 30 days or so, and are dependent on their parents for up to 4 more weeks. Sometimes first-year merlins (especially males) will serve as a "nest helper" for an adult pair. More than half—often all or almost all—eggs of a clutch survive to hatching, and at least two-thirds of the hatched young fledge. However, as noted above, in years with little supplementary food only 1 young in 3 may survive to fledging. The merlin becomes sexually mature at one year of age and usually attempts to breed right away. The oldest wild bird known as of 2009 was recorded in its 13th winter.^[9][41]

 

 

John James Audubon illustrated the merlin in the second edition of Birds of America (published in London, 1827–38) as Plate 75, under the title, "Le Petit Caporal – Falco temerarius". The image was engraved and colored by Robert Havell's London workshops. The original watercolor by Audubon was purchased by the New York History Society,^[42] where it remains as of January 2009.

William Lewin illustrates the merlin as Plate 22 in volume 1 of his Birds of Great Britain and their Eggs, published 1789 in London.

In medieval Europe, merlins were popular in falconry: the Book of St. Albans listed it as "the falcon for a lady", where it was noted for classic "ringing" (circling rapidly upward) pursuits of the English skylark.^[43] Though the merlin is only slightly larger than the American kestrel in dimensions, it averages about one third to one half larger by weight, with this weight mostly being extra muscle that gives it greater speed and endurance than the kestrel.^[43] Like the American kestrel, the merlin offers the modern falconer the ability to hunt year round against sparrows and starlings, in urban settings not requiring large tracts of land or hunting dogs, with the additional advantage of being able to reliably take small game birds such as dove and quail during hunting season. A large and exceptionally aggressive female merlin may take prey 

 

 as large as pigeons and occasionally even small ducks.^[44] They also offer an exciting style of flight, generally at closer range than large falcons where it may be more clearly witnessed and enjoyed by the falconer. In addition to horizontal tail-chases in the manner of American kestrels, they will also "ring up" in pursuit of prey that seeks to escape by out-climbing them, and perform high speed diving stoops on prey beneath them in the manner of larger falcons. Quoting from one popular falconry book on the eagerness of merlins to chase a swung lure, "Every stoop, outrun, dodge, and aerial maneuver of a hard flight to real quarry can be duplicated with no risk of loss of the falcon. Merlins regularly flown to the lure take most field quarries with such ease and such assurance as to make the field flight the less interesting and exciting of the two."^[43]

 

 Quoting expert falconer Matthew Mullenix, author of the book "American Kestrels in Modern Falconry", in an article comparing the American kestrel to the merlin he states "What a merlin gives you is raw power: lots of it. It brings an ability to negate wind as a factor, to stay airborne at a tremendous clip then gear down further at any time for more performance. One merlin can dominate an entire flock of frightened birds, directing its fate as a whole. The flock responds like bait fish to a barracuda and for precisely the same reason. Merlins demonstrate total mastery of their element."^[45] Concerning suitable game for these two species, he states "To snipe, dove, quail and open-country sparrows, merlins are best suited. For most blackbirds (Icteridea), either falcon can prove effective. Starlings in close are extremely vulnerable to kestrels; but in the open are best prey for merlins."

Altogether, the merlin is not particularly rare, and due to this and its wide range it is considered a species of least concern by the IUCN.^[1] Its numbers are—except in the Asian part of its range, where the situation is less well determined—regularly censused. In about every major country it inhabits, many hundreds to many thousands are found, ranging from a "mere" 250–300 pairs in Belarus to perhaps as many as 30,000 pairs of aesalon in European Russia as determined in 1993. It is listed on CITES Appendix II and on a local level protected as other birds of prey; while some countries allow to capture merlins, e.g. for falconry, international trade requires an export permit.^[1][9]

 

 

By far the most serious long-term threat to these birds is habitat destruction, especially in their breeding areas. Ground-nesting populations in moorland have a preference for tall heather, and are thus susceptible to overmanagement by burning vast tracts instead of creating a habitat mosaic containing old and new growth. Still, the merlin is rather euryoecious (adaptable to various conditions) and will even live in settled areas, provided they have the proper mix of low and high vegetation, as well as sufficient prey (which is usually the case) and nesting sites (which is a common limiting factor).^[9]

 

 In North America, the species seems to have been more widespread in the past, or perhaps its range has shifted northwards: F. c. columbarius was an uncommon breeding bird in Ohio before the 20th century, but in Seneca County, as early as the 1900s even single adults were rarely seen in the breeding season. It is encountered in Ohio as a passage migrant and rarely as a winter guest, though two recent nestings have been confirmed. Changing land-use in Ohio mainly turned forest into agricultural land and thus is not very likely to have rendered the region inhospitable to the merlin; global warming on the other hand cannot be dismissed as a reason, given that the merlin is essentially a subarctic species that barely ranges even into temperate climes. Also, it may be that the number of merlins wintering in the northern USA has increased during the 20th century.^[12][9][21]

 

Perhaps the most frequent cause of accidental death for individuals is collision with man-made objects, particularly during attacks. This may account for almost half of all premature deaths of merlins. In the 1960s and 1970s, organochlorine pesticides were responsible for declines—particularly in Canada—due to eggshell thinning and subsequent brood failure, and compromising the immune system of adults. This has since been remedied with restrictions on the use of DDT and similar chemicals, and numbers have rebounded. Overall, merlin stocks appear globally stable; while they may decline temporarily in places, they will usually increase again eventually, suggesting that this phenomenon is due to the fluctuations of supplementary food stocks discussed above.^[9]

 

 

 

 

 

 

 

 Range of F. columbarius

 

 

  Summer only range

  Year-round range

  Winter only range

 

 

 

THE SUGAR GLIDER

 

The sugar glider (Petaurus breviceps) is a small, omnivorous, arboreal, and nocturnal gliding possum. The common name refers to its predilection for sugary foods such as sap and nectar and its ability to glide through the air, much like a flying squirrel.^[8] They have very similar habits and appearance to the flying squirrel, despite not being closely related—an example of convergent evolution.^[9] The scientific name, Petaurus breviceps, translates from Latin as "short-headed rope-dancer", a reference to their canopy acrobatics.^[10]

 

The sugar glider is characterised by its pair of gliding membranes, known as patagia, which extend from its forelegs to its hindlegs.^[11] Gliding serves as an efficient means of reaching food and evading predators.^[8] The animal is covered in soft, pale grey to light brown fur which is countershaded, being lighter in colour on its underside.

 

 

The sugar glider, as strictly defined in a recent analysis, is only native to a small portion of southeastern Australia, corresponding to southern Queensland and most of New South Wales east of the Great Dividing Range; the extended species group, including populations which may or may not belong to P. breviceps, occupies a larger range covering much of coastal eastern and northern Australia, New Guinea, and nearby islands.^[4][5] Members of Petaurus are popular exotic pets; these pet animals are also frequently referred to as "sugar gliders", but recent research indicates, at least for American pets, that they are not P. breviceps but a closely related species, ultimately originating from a single source near Sorong in West Papua.^[12] This would possibly make them members of the Krefft's glider (P. notatus), but the taxonomy of Papuan Petaurus populations is still poorly resolved.^[13]

The genus Petaurus is believed to have originated in New Guinea during the mid Miocene epoch, approximately 18 to 24 million years ago. The modern Australian Petaurus, along with New Guinean members of what were formerly considered P. breviceps, diverged from their closest living New Guinean relatives ~9-12 mya. They probably dispersed from New Guinea to Australia between 4.8 and ~8.4 mya, with the oldest Petaurus fossils in Australia being dated to 4.46 million years.^[14] This may have been possible due to sea level lowering from about 7 to 10 mya, resulting in land bridges between New Guinea and Australia.

 

The taxonomy of the species is complex, and is still not fully resolved. It was formerly understood to have a wide range across Australia and New Guinea, being the only glider to have this distribution, and to be divided into seven subspecies, with three occurring in Australia and four in New Guinea.^[15] This traditional subspecific division was based on small morphological differences, such as colour and body size.^[14] However, a 2010 genetic analysis using mitochondrial DNA indicates that these morphologically-defined subspecies may not represent genetically unique populations.^[15]

 

 Further studies have found significant genetic variation within populations traditionally classified in P. breviceps, sufficient to warrant splitting the species into multiple. The subspecies P. b. biacensis, from Biak Island off of New Guinea, was reclassified as a separate species, the Biak glider (Petaurus biacensis).^{[note 5]} In 2020, a landmark study suggested that P. breviceps actually comprised three cryptic species: the Krefft's glider (Petaurus notatus), found throughout most of eastern Australia and introduced to Tasmania, the savanna glider (Petaurus ariel), native to northern Australia, and a more narrowly defined P. breviceps, restricted to a small section of coastal forest in southern Queensland and most of New South Wales. In addition, other sugar glider populations throughout this range (such as those on New Guinea and the Cape York Peninsula) may represent undescribed species or be conspecific with previously described species. This indicates that contrary to previous findings of a large range (which in fact applied to P. notatus and, to a lesser extent, to P. ariel), P. breviceps is a range-restricted species that is sensitive to ecological disasters, such as the 2019-20 Australian bushfires, which significantly affected large portions of its habitat.^[4][5][16]

 

P. breviceps and P. notatus are estimated to have diverged ~1 million years ago, and may have originated from long term geographic isolation. The early-mid Pleistocene saw an uplifting of the Great Dividing Range, contributing to and coinciding with aridification of the interior of Australia, including on the western side of the range.^[15] This, as well as other climactic and geographic factors, may have isolated the ancestors of P. breviceps to refugia on the eastern, coastal side of the Great Dividing Range.^[4] This would be an example of allopatric speciation.

Sugar gliders are distributed in the coastal forests of southeastern Queensland and most of New South Wales. Their distribution extends to altitudes of 2000m in the eastern ranges. In parts of its range, it may overlap with Krefft's glider (P. notatus).^[5][17]

The sugar glider occurs in sympatry with the squirrel glider and yellow-bellied glider; and their coexistence is permitted through niche partitioning where each species has different patterns of resource use.^[18]

 

 

Like all arboreal, nocturnal marsupials, sugar gliders are active at night, and they shelter during the day in tree hollows lined with leafy twigs.^[19]

The average home range of sugar gliders is 0.5 hectares (1.2 acres), and is largely related to the abundance of food sources;^[20] density ranges from two to six individuals per hectare (0.8–2.4 per acre).

Native owls (Ninox sp.)^[17] are their primary predators; others in their range include kookaburras, goannas, snakes, and quolls.^[21] Feral cats (Felis catus) also represent a significant threat.^[17][21]

 

 The sugar glider has a squirrel-like body with a long, partially (weakly)^[22] prehensile tail. The length from the nose to the tip of the tail is about 24–30 cm (9–12 in), and males and females weigh 140 and 115 grams (5 and 4 oz) respectively.^[23] Heart rate range is 200–300 beats per minute, and respiratory rate is 16–40 breaths per minute.^[24] The sugar glider is a sexually dimorphic species, with males typically larger than females. Sexual dimorphism has likely evolved due to increased mate competition arising through social group structure; and is more pronounced in regions of higher latitude, where mate competition is greater due to increased food availability.^[25]

 

The fur coat on the sugar glider is thick, soft, and is usually blue-grey; although some have been known to be yellow, tan or (rarely) albino.^[a] A black stripe is seen from its nose to midway on its back. Its belly, throat, and chest are cream in colour. Males have four scent glands, located on the forehead, chest, and two paracloacal (associated with, but not part of the cloaca, which is the common opening for the intestinal, urinal and genital tracts) that are used for marking of group members and territory.^[17] Scent glands on the head and chest of males appear as bald spots. Females also have a paracloacal scent gland and a scent gland in the pouch, but do not have scent glands on the chest or forehead.^[17]

The sugar glider is nocturnal; its large eyes help it to see at night and its ears swivel to help locate prey in the dark. The eyes are set far apart, allowing more precise triangulation from launching to landing locations while gliding.^[26]

Each foot on the sugar glider has five digits, with an opposable toe on each hind foot. These opposable toes are clawless, and bend such that they can touch all the other digits, like a human thumb, allowing it to firmly grasp branches. The second and third digits of the hind foot are partially syndactylous (fused together), forming a grooming comb.^[22] The fourth digit of the forefoot is sharp and elongated, aiding in extraction of insects under the bark of trees.^[17]

 

 

The gliding membrane extends from the outside of the fifth digit of each forefoot to the first digit of each hind foot. When the legs are stretched out, this membrane allows the sugar glider to glide a considerable distance. The membrane is supported by well developed tibiocarpalis, humerodorsalis and tibioabdominalis muscles, and its movement is controlled by these supporting muscles in conjunction with trunk, limb and tail movement.^[11]

Lifespan in the wild is up to 9 years; is typically up to 12 years in captivity,^[10] and the maximum reported lifespan is 17.8 years.^[27]

The sugar glider is one of a number of volplane (gliding) possums in Australia. It glides with the fore- and hind-limbs extended at right angles to the body, with feet flexed upwards.^[26] The animal launches itself from a tree, spreading its limbs to expose the gliding membranes. This creates an aerofoil enabling it to glide 50 metres (55 yards) or more.^[28] For every 1.82 m (6 ft 0 in) travelled horizontally when gliding, it falls 1 m (3 ft 3 in).^[26] Steering is controlled by moving limbs and adjusting the tension of the gliding membrane; for example, to turn left, the left forearm is lowered below the right.^[26]

This form of arboreal locomotion is typically used to travel from tree to tree; the species rarely descends to the ground. Gliding provides three dimensional avoidance of arboreal predators, and minimal contact with ground dwelling predators; as well as possible benefits in decreasing time and energy consumption^[29] spent foraging for nutrient poor foods that are irregularly distributed.^[30] Young carried in the pouch of females are protected from landing forces by the septum that separates them within the 

 

Sugar gliders can tolerate ambient air temperatures of up to 40 °C (104 °F) through behavioural strategies such as licking their coat and exposing the wet area, as well as drinking small quantities of water.^[17] In cold weather, sugar gliders will huddle together to avoid heat loss, and will enter torpor to conserve energy.^[31] Huddling as an energy conserving mechanism is not as efficient as torpor.^[31] Before entering torpor, a sugar glider will reduce activity and body temperature normally in order to lower energy expenditure and avoid torpor.^[32][33] With energetic constraints, the sugar glider will enter into daily torpor for 2–23 hours while in rest phase.^[31] Torpor differs from hibernation in that torpor is usually a short-term daily cycle. Entering torpor saves energy for the animal by allowing its body temperature to fall to a minimum of 10.4 °C (50.7 °F)^[31] to 19.6 °C (67.3 °F).^[34] When food is scarce, as in winter, heat production is lowered in order to reduce energy expenditure.^[35] With low energy and heat production, it is important for the sugar glider to peak its body mass by fat content in the autumn (May/June) in order to survive the following cold season. In the wild, sugar gliders enter into daily torpor more often than sugar gliders in captivity.^[33][34] The use of torpor is most frequent during winter, likely in response to low ambient temperature, rainfall, and seasonal fluctuation in food sources.^[31]

Sugar gliders are seasonally adaptive omnivores with a wide variety of foods in their diet, and mainly forage in the lower layers of the forest canopy.^[18][36] Sugar gliders may obtain up to half their daily water intake through drinking rainwater, with the remainder obtained through water held in its food.^[29] In summer they are primarily insectivorous, and in the winter when insects (and other arthropods) are scarce, they are mostly exudativorous (feeding on acacia gum, eucalyptus sap, manna,^[b] honeydew or lerp).^[40] Sugar gliders have an enlarged caecum to assist in digestion of complex carbohydrates obtained from gum and sap.^[41]

To obtain sap or gum from plants, sugar gliders will strip the bark off trees or open bore holes with their teeth to access stored liquid.^[36] Little time is spent foraging for insects, as it is an energetically expensive process, and sugar gliders will wait until insects fly into their habitat, or stop to feed on flowers.^[36] Gliders consume approximately 11 g of dry food matter per day.^[29] This equates to roughly 8% and 9.5% of body weight for males and females, respectively.

They are opportunistic feeders and can be carnivorous, preying mostly on lizards and small birds. They eat many other foods when available, such as nectar, acacia seeds, bird eggs, pollen, fungi and native fruits.^[42][43] Pollen can make up a large portion of their diet, therefore sugar gliders are likely to be important pollinators of Banksia species.^[44]

Like most marsupials, female sugar gliders have two ovaries and two uteri; they are polyestrous, meaning they can go into heat several times a year.^[20] The female has a marsupium (pouch) in the middle of her abdomen to carry offspring.^[22] The pouch opens anteriorly, and two lateral pockets extend posteriorly when young are present. Four nipples are usually present in the pouch, although reports of individuals with two nipples have been recorded.^[17] Male sugar gliders have two pairs of bulbourethral glands^[45] and a bifurcated penis to correspond with the two uteri of females.^[46]

The age of sexual maturity in sugar gliders varies slightly between the males and females. Males reach maturity at 4 to 12 months of age, while females require from 8 to 12 months. In the wild, sugar gliders breed once or twice a year depending on the climate and habitat conditions, while they can breed multiple times a year in captivity as a result of consistent living conditions and proper diet.^[22]

 

 

A sugar glider female gives birth to one (19%) or two (81%) babies (joeys) per litter.^[20] The gestation period is 15 to 17 days, after which the tiny joey 0.2 g (0.0071 oz) will crawl into a mother's pouch for further development. They are born largely undeveloped and furless, with only the sense of smell being developed. The mother has a scent gland in the external marsupium to attract the sightless joeys from the uterus.^[47] Joeys have a continuous arch of cartilage in their shoulder girdle which disappears soon after birth; this supports the forelimbs, assisting the climb into the pouch.^[48] Young are completely contained in the pouch for 60 days after birth, wherein mammae provide nourishment during the remainder of development.^[47] Eyes first open around 80 days after birth, and young will leave the nest around 110 days after birth.^[17] By the time young are weaned, the thermoregulatory system is developed, and in conjunction with a large body size and thicker fur, they are able to regulate their own body temperature.^[49]

Breeding is seasonal in southeast Australia, with young only born in winter and spring (June to November).^[20] Unlike animals that move along the ground, the sugar glider and other gliding species produce fewer, but heavier, offspring per litter. This allows female sugar gliders to retain the ability to glide when pregnant.^[50]

Sugar gliders are highly social animals. They live in family groups or colonies consisting of up to seven adults, plus the current season's young. Up to four age classes may exist within each group, although some sugar gliders are solitary, not belonging to a group.^[20] They engage in social grooming, which in addition to improving hygiene and health, helps bond the colony and establish group identity.

Within social communities, there are two codominant males who suppress subordinate males, but show no aggression towards each other. These co-dominant pairs are more related to each other than to subordinates within the group; and share food, nests, mates, and responsibility for scent marking of community members and territories.^[51]

 

 

Territory and members of the group are marked with saliva and a scent produced by separate glands on the forehead and chest of male gliders. Intruders who lack the appropriate scent marking are expelled violently.^[8] Rank is established through scent marking; and fighting does not occur within groups, but does occur when communities come into contact with each other.^[17] Within the colony, no fighting typically takes place beyond threatening behaviour.^[52] Each colony defends a territory of about 1 hectare (2.5 acres) where eucalyptus trees provide a staple food source.^{[citation needed]}

Sugar gliders are one of the few species of mammals that exhibit male parental care.^[53] The oldest codominant male in a social community shows a high level of parental care, as he is the probable father of any offspring due to his social status. This paternal care evolved in sugar gliders as young are more likely to survive when parental investment is provided by both parents.^[53] In the sugar glider, biparental care allows one adult to huddle with the young and prevent hypothermia while the other parent is out foraging, as young sugar gliders aren't able to thermoregulate until they are 100 days old (3.5 months).^[53]

Communication in sugar gliders is achieved through vocalisations, visual signals and complex chemical odours.^[17] Chemical odours account for a large part of communication in sugar gliders, similar to many other nocturnal animals. Odours may be used to mark territory, convey health status of an individual, and mark rank of community members. Gliders produce a number of vocalisations including barking and hissing.^[54]

 Under the prior taxonomy, the sugar glider was not considered endangered, and its conservation rank was "Least Concern (LC)" on the IUCN Red List.^[2] However, with newer taxonomic studies indicating that it has a small and restricted range, it is now thought to be far more sensitive to potential threats. For example, the species' native range was hit hard by the 2019-20 Australian bushfires, which occurred just a few months prior to the publishing of the study indicating the true extent of its range. Sugar gliders use tree hollows, making them especially sensitive to intense fires.^[55] However, despite the loss of natural habitat in Australia over the last 200 years, it is adaptable and capable of living in small patches of remnant bush, particularly if it does not have to cross large expanses of cleared land to reach them. Sugar gliders may persist in areas that have undergone mild-moderate selective logging, as long as three to five hollow bearing trees are retained per hectare.^[56] Although not currently threatened by habitat loss, the ability of sugar gliders to forage and avoid predators successfully may be decreased in areas of high light pollution.^[57]

 

 

 

Conservation in Australia is enacted at the federal, state and local levels, where sugar gliders are protected as a native species. The central conservation law in Australia is the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).^[58] The National Parks and Wildlife Act 1974 is an example of conservation law in the state of South Australia, where it is legal to keep (only) one sugar glider without a permit, provided it was acquired legally from a source with a permit. A permit is required to obtain or possess more than one glider, or if one wants to sell or give away any glider in their possession. It is illegal to capture or sell wild sugar gliders without a permit.^[59]

In captivity, the sugar glider can suffer from calcium deficiencies if not fed an adequate diet. A lack of calcium in the diet causes the body to leach calcium from the bones, with the hind legs first to show noticeable dysfunction.^[60] Calcium to phosphorus ratios should be 2:1 to prevent hypocalcemia, sometimes known as hind leg paralysis (HLP).^[61] Their diet should be 50% insects (gut-loaded) or other sources of protein, 25% fruit and 25% vegetables.^[62] Some of the more recognised diets are Bourbon's Modified Leadbeaters (BML),^[63] High Protein Wombaroo (HPW)^[64] and various calcium rich diets with Leadbeaters Mixture (LBM).^[65] Iron storage disease (hemochromatosis) is another dietary problem that has been reported in captive gliders and can lead to fatal complications if not diagnosed and treated early.^[66]

A large amount of attention and environmental enrichment may be required for the highly social species, especially for those kept as individuals. Inadequate social interaction can lead to depression and behavioural disorders such as loss of appetite, irritability and self-mutilation.^[67]

In several countries, the sugar glider (or what was formerly considered to be the sugar glider) is popular as an exotic pet, and is sometimes referred to as a pocket pet. In Australia, there is opposition to keeping native animals as pets from Australia's largest wildlife rehabilitation organisation (WIRES),^[68] and concerns from Australian wildlife conservation organisations regarding animal welfare risks including neglect, cruelty and abandonment.^[69]

In Australia, sugar gliders can be kept in Victoria, South Australia, and the Northern Territory. However, they are not allowed to be kept as pets in Western Australia, New South Wales, the Australian Capital Territory, Queensland or Tasmania.^[70][71]

DNA analysis indicates that "the USA (sugar) glider population originates from West Papua, Indonesia with no illegal harvesting from other native areas such as Papua New Guinea or Australia".^[12] Given that the West Papuan gliders have been tentatively classified as Krefft's gliders (albeit to be changed in the future),^[13] this indicates that at least the captive gliders kept in the United States are Krefft's gliders, not sugar gliders. 

 

 

 

 

 Range map of the formerly recognized

    P. b. breviceps (introduced in Tasmania)
   P. b. longicaudatus
   P. b. ariel
   P. b. flavidus
   P. b. tafa
   P. b. papuanus
   P. b. biacensis