Acrobates pygmaeus ( Shaw, 1794 )

Harris Abstract, Jamie M., 2015, Acrobates pygmaeus (Diprotodontia: Acrobatidae), Mammalian Species 47 (920), pp. 32-44 : 32-38

Acrobates pygmaeus ( Shaw, 1794)

Feather-tailed Glider

Didelphis pygmaea Shaw, 1794:5 . Type locality “New Holland” (= Australia).

Voluccella pygmaea: Bechstein, 1800:352 , 686. Name combination.

Phalangista pygmaea: Geoffroy Saint-Hilaire, 1803:151 . Name combination.

Acrobates pygmaeus: Desmarest, 1817:405 . First use of current name combination.

Petaurista pygmea: Desmarest, 1821:270 . Name combination.

Petaurus pygmaeus: Desmarest, 1821:270 . Name combination.

Acrobata pygmaea: Desmarest, 1821:270 . Name combination.

Cercoptenus pygmaeus: Gloger, 1841:85 . Name combination.

Acrobates pulchellus Rothschild, 1892:546 . Type locality “one of the small islands in Northern Dutch New Guinea;” (see “ Nomenclatural Notes ”).

Dromicia frontalis De Vis 1887:1134 . Previous synonym, now a recognized species.

CONTEXT AND CONTENT. Context as for genus. Acrobates pygmaeus is monotypic.

NOMENCLATURAL NOTES. A junior synonym for Acrobates pygmaeus is A. pulchellus ( Rothschild, 1892; holotype in Natural History Museum, London—NHM 1939.2988), but the place of origin for pulchellus has long been the subject of suspicion. It was reportedly collected by A. Bruijn from “one of the small islands in northern Dutch New Guinea ” ( Rothschild 1892:546). However, the lack of detail on the collection place and the absence of any supporting evidence led Tate (1938) to suggest the record to be in error; that is, the specimen may have been carried as a pet from Australia and its type locality was simply wrong. This was later accepted by several authorities ( Van Deusen 1960; McKay 1988; Groves 2005; Jackson and Thorington 2012). However, a 2nd Acrobates from “New Guinea ” found in the Swedish Museum of Natural History, Stockholm (NRM A58- 3160) has now been reported ( Helgen 2003). This was collected in 1899–1900 and received from the dealer J. Riedel. Hence, it may have been premature to discard the locality for A. pulchellus altogether because the composition of the New Guinea mammal fauna is probably not completely finalized ( Flannery 1995; Helgen 2003).

Acrobates was once placed in the Phalangeridae ( Simpson 1945) , but serological data ( Kirsch 1977) led to its inclusion in the Burramyidae ( Ride 1970) . Numerous other authorities also affiliated A. pygmaeus with the burramyids ( Tyndale-Biscoe 1973; Kirsch 1977; Szalay 1994). More recently, however, significant differences were found in basicranial and dental morphology (Aplin and Archer 1987) and microfixation of albumin data ( Baverstock et al. 1990), which led to Acrobates being assigned to the new family Acrobatidae (Aplin and Archer 1987) .

Its scientific name is quite befitting of its size and energetic movements and translates as the “pygmy acrobat.” The genus name is from the Greek akrobates; the specific name is Latin for pygmy ( Strahan 1981). Vernacular names have included pygmy opossum ( Shaw 1794), opossum flying mouse ( Perry 1811), pigmy squirrel ( Bennett 1837), dwarf petaurus ( Partington 1837), pigmy flying-opossum ( Waterhouse 1838, 1846), opossum mouse ( Gray 1843; Gerrard 1862; Gould 1863), flying mouse ( Waterhouse 1841; Krefft 1864), pigmy flying-phalanger ( Thomas 1885, 1888), and pygmy glider (Iredale and Troughton 1934; Troughton 1943; Simpson 1945). A standard name finally arose when a committee of the Australian Mammal Society, formalized it as “feathertail glider” ( Strahan 1980). However, due to the revival of A. frontalis ( Aplin 2013) , the common name “narrow-toed feathertail glider” has been offered for A. pygmaeus and “broad-toed feathertail glider” for the resurrected taxon. Traditional Aboriginal names recorded include “cubbie-cubbie,” “toan,” “tu-an-tu-an,” “wrangun,” “tirhatuan,” “turnung,” “tarrn-nin,” “teed’thung,” “gniin guutch,” “gnuundiit” and “gnuundeetch,” “wonggo,” “wangku” and “wanga” ( Troughton 1943; Tunbridge 1991; Harris and Maloney 2006).

DIAGNOSIS

Acrobates pygmaeus is highly distinctive and tiny. Adult A. pygmaeus are generally <15 cm in total length and <15 g in body mass (Fanning and Watkins 1980). It is the smallest of the gliding possums ( Acrobates , Petauroides , and Petaurus ) and is immediately distinguished by its gliding membranes and a flattened tail on each side of which is a distichous fringe of long stiff hairs, giving the tail a feather-like appearance and the animal its popular name ( Fig. 1 ).

GENERAL CHARACTERS

Acrobates pygmaeus is about the size of a very small mouse (ca. 12 g), but its form is more elegant. It has soft and silky fur that is grayish brown dorsally and white ventrally. Coloring is sharply divided at the edge of the gliding membrane. The tail is oval in cross-section, with very short ashy-brown fur on the upper and lower surfaces, and this fur is paler below than above. The stiff long hair on either side of the tail (about 8 mm in length— Nowak 2005) resembles the barbs of a feather. The eyes are large, forward-directed, dark brown, and encircled with black fur. The rhinarium is naked, flesh colored, finely granulated, and deeply cleft; the nostrils are lateral ( Wood Jones 1924; see also Hill 1951). The ears are fairly large, flattened, oval, and moderately well furred externally. Ears laid forward reach the center of the eyes. Long vibrissae are present, unusually numerous and extend from the snout, cheeks, and base of each ear (see Thomas 1888; Aplin and Archer 1987; Flannery 1994).

On the pes, digit I (the hallux) projects from the foot at an angle, is opposable, flattened, clawless, twice as broad as the other digits, and has an enlarged apical pad with well-developed epidermal ridges (see scanning electron micrographs in Rosenberg and Rose 1999). Digits II and III are short, clawed, and joined at their bases only, in an incomplete form of syndactyly. Digits IV and V are clawed and are similar in form. On the manus, all 5 digits have similar claws and prominent apical pads (each about 1 mm wide and 1 mm thick). The longest digit is IV, the next longest digits are III and V, and the shortest digits are the equally sized I and II. Palmar and plantar pads, that flatten considerably when loaded, are also present (Rosenberg and Rose 1999).

Mean body mass for males is 12.3± 2.2 g SD (n = 4—Tyndale- Biscoe and Renfree 1987). Males are about 7.5% heavier than females ( Ward 2007). One study reported males are up to 3% larger than females in some linear measurements (Fleming and Frey 1984); another study found that adult males are 1.1 times heavier than adult females ( Ward 1990a). Greatest length of skull (mm ± SD) is 20.2 ± 0.5 (19.0–21.3; n = 22); greatest width of skull is 13.2 ±0.3 (12.4–14.0; n = 25— Helgen 2003; see also Fig. 2 ).

DISTRIBUTION

Acrobates pygmaeus is restricted to mainland Australia (not in Tasmania) and has a wide distribution through most of the open and closed forests of the eastern and southeastern parts of the continent ( Fig. 3 ), from the extreme northern tip of Cape York Peninsula ( Van Deusen 1960), to the southeastern corner of South Australia ( Watts 1990; Richardson and Carthew 2004). The elevational range is from sea level to above 1,200 m ( Henry 1995). Although this species is widely distributed, few specimens are collected in surveys or seen by the public, owing to its small size, nocturnal habits, and difficulties associated with regularly trapping or observing it.

FOSSIL RECORD

Acrobates pygmaeus has been recorded from at least 20 late Pleistocene or Holocene fossil sites in southeastern Australia. In southeast Queensland, it is recorded as a fossil from the Texas Caves ( Archer 1978). Oldest dated site with A. pygmaeus is Cathedral Cave in South Australia (292 ± 19 thousand years ago— Prideaux et al. 2007). Sites in Victoria include Murrindal Cliffs and Mabel Cave ( Wakefield 1960a), Pyramids Cave ( Wakefield 1960a, 1972), Cloggs Cave ( Hope 1973), Mitchell River National Park ( Bilney et al. 2006), New Guinea II Cave ( Ossa et al. 1995), Steiglitz Cave ( Peake et al. 1993), Fern Cave near Portland ( Wakefield 1963a, 1964a), McEachern’s Cave ( Wakefield 1967), McEachern’s Deathtrap Cave (listed as Acrobates — Kos 2003), Natural Bridge near Mount Eccles ( Wakefield 1964a, 1964b), Victoria Range ( Wakefield 1963b), and Grampians Owl Cave ( Marshall 1985). Sites in New South Wales include Yarrangobilly Caves in Kosciusko National Park ( Drummond 1963; Aplin et al. 2010), Capertee Valley ( Johnson 1979), Nettle Cave ( Morris et al. 1997), Upper Mangrove Creek ( Attenbrow 2004), Wellington Caves (Dawson and Augee 1997), and possibly Douglas Cave, near Stuart Town (see Gorter 1977). The oldest extinct fossil acrobatids ( Acrobates ) currently documented come from the Mount Etna deposits in Queensland (ca. 0.50–0.28 million years ago— Hocknull 2005; Hocknull et al. 2007). Riversleigh (23.03–15.97 million years ago) and the Kutjamarpu Local Fauna (middle Miocene) have also produced supposed acrobatid material ( Archer 1984; Archer et al. 1999; Archer and Hand 2006), but these have not yet been formally described.

FORM AND FUNCTION

Dentition of Acrobates pygmaeus is diprotodont with a formula of i 3/2, c 1/ 0, p 3/3, m 4/4, total = 40 ( Fig. 2 ; Nowak 2005). Further dental descriptions are published elsewhere ( Owen 1845; Waterhouse 1846; Thomas 1885, 1888; Tate 1945; Archer 1984; Long et al. 2002; Archer and Hand 2006). The tongue is elongated (ca. 9–11 mm long, 2.3–2.4 mm wide) with a short-pointed apex (Jackowiak and Godynicki 2007). When viewed under a scanning electron microscope, the tongue resembles a brush and has a unique pattern of lingual papillae well adapted to the efficient ingestion of semiliquid food and the collection of pollen (Jackowiak and Godynicki 2007). Brain mass is recorded as 0.36 g ( Byers 1999; photomicrographs are in Aitken and Nelson 1989).

The patagium is well developed in A. pygmaeus and consists of a thick fold of skin that has connective tissue and muscle fibers extending from the shoulder girdle ( Johnson-Murray 1987). Stretching between the elbows and knees, the patagium is a specialized aerodynamic structure ( Smith 1982; Strahan 1992). Although relatively narrow compared to the petaurids, a fringe of long hairs extend the patagium’s effective size ( Wood Jones 1924; Turner and McKay 1989), such that it can glide for up to 300 times its head and body length ( Strahan 1992). The tail is used for balance and directional control when the animal is gliding and is only slightly prehensile ( Wood Jones 1924; Fanning and Watkins 1980).

Muscles within the lower legs and feet ( Dodson 1883) and within the gliding membranes ( Johnson-Murray 1987) have been anatomically described. As is typical for marsupials, A. pygmaeus lacks a bony patella (located in the quadriceps femoris muscle— Reese et al. 2001). The external ear is uniquely complex, with a prominent anterior helical process, paired antitragal processes, and a well-defined bursa (further detail provided in Aplin and Archer 1987). The ear canal has a small bony disk in front of the tympanic membrane leaving only a narrow crescentic space for sound pressure waves to pass onto the eardrum ( Segall 1971; Archer 1984; Aplin 1987; Aitken and Nelson 1989). This resembles a Helmholtz resonator and may contribute to selective sensitivity to very high or very low frequencies. Calculations indicate a resonant frequency of 57 kHz and peak attenuation at 78 kHz (Aitken and Nelson 1989). However, the significance of this unique specialization remains to be determined (Aitken and Nelson 1989; Ward and Woodside 2008; Ashwell 2010).

Blood parameters measured to date are for cholesterol (3.39–3.42 mmol/l; standard error of the mean, SEM = 0.12), triglycerides (1.55–1.74 mmol/l; SEM = 0.05), and glucose (6.69–7.70 mmol/l; SEM = 0.49— Herrmann et al. 2013). Blood erythrocytes have slight to moderate central paleness, and neutrophils have 3–7 nuclear lobes of reticula ( Clark 2004). The chemical composition of secretions from the sternal glands of A. pygmaeus has been investigated ( Zabaras et al. 2005; see also Biggins 1984) as has the bacteria (aerobes, anaerobes, yeasts, and streptococci) occurring in feces ( Salminen et al. 1992). Hair tracts are very simple, no special features anywhere apart from median convergence in the throat area ( Boardman 1943; Hill 1951). The primary guard hairs have a diameter up to 17 µm (Brunner and Coman 1974). Microscopically, hairs clearly have a scale pattern alternating several times along the length of hair (Brunner and Coman 1974). The simple gastrointestinal tract of A. pygmaeus is neatly figured in Hume (1999), and some information on the gastrointestinal flora is in Salminen et al. (1992). At room temperature (ca. 20°C), body temperature (T b) was recorded at its highest level at 2200 h (T b = 38.2 ± 0.5, n = 7) and lowest at 1200 h (T

b

= 34.7 ± 0.8, n = 7; Fleming 1985).

Acrobates pygmaeus can cling to and run on smooth vertical planes of glass ( Russell 1980; Rosenberg and Rose 1999). Capillary adhesion is achieved using the specialized epidermal ridges on the manus and pes (see Rosenberg and Rose 1999). Moisture from sweat glands creates surface tension and helps the footpads act like mini suction cups ( Lindenmayer 2002). In the wild, capillary adhesion assists in movement on large smooth leaves or on the relatively smooth trunks of Eucalyptus trees (Rosenberg and Rose 1999; Lindenmayer 2002).

Torpor in this species is not seasonally restricted and can be induced throughout the year (Frey and Fleming 1984; Fleming 1985; Geiser 1994; Geiser and Ferguson 2001). Torpor bouts at ambient temperature (T a) of 12°C typically lasted 2.5 days and at T a 8°C up to 5.5 days (Jones and Geiser 1992). During torpor, the mean minimum body temperature was 2.0 ± 0.5°C (n = 5) and the lowest recorded in one individual was 1.3°C (Jones and Geiser 1992). The mean oxygen consumption at T a 5°C during rest was 5.86 ± 1.48 ml O 2 /g h (n = 5), and during activity was 9.94 ± 0.70 ml O 2 /g h (n = 5—Jones and Geiser 1992). During torpor, mean oxygen consumption was 0.069 ± 0.013 (SD) ml O 2 /g h (n = 5), which is about 1% of that used by resting, normothermic animals (Jones and Geiser 1992). This great reduction in oxygen consumption during torpor, together with multiday torpor bouts, provides A. pygmaeus with the potential to save large amounts of energy when access to food is limited and when foraging is energetically costly because of low ambient temperatures (Jones and Geiser 1992). During torpor, the breathing pattern is generally pulsed, with apnea lasting up to 20 min (at T a of 7.0°C— Fleming 1985). The fastest rewarming rate of 1.03°C/ min over 10 min, exhibited by an individual A. pygmaeus , is similar to some of the fastest rewarming rates reported in placentals and is about 28% above the predicted for a 12-g marsupial (0.74°C/min—Jones and Geiser 1992). Torpor on a diet rich in polyunsaturated fatty acids was deeper and longer than for animals on a saturated diet ( Geiser et al. 1992), suggesting diet selection forms part of the preparation for the cold season (Geiser and Stapp 2000).

During torpor, its typical posture is curled into a ball, with the ears folded down and the tail wrapped over the body ( Fleming 1985; Geiser and Ferguson 2001). Huddling reduces the exposed surface of each participating animal, thereby providing metabolic savings. The usual shape for 4 huddling animals is a tetrahedron with 3 animals hunched close to each other and the 4th lying flat over them ( Fleming 1985). At T a of 10°C, a group of 4 gliders reduced their oxygen use per gram by 14%, whereas the reduction is 40% for a group of 8 ( Fleming 1985). Groups ceased to huddle at T

a

of 32°C ( Fleming 1985).

ONTOGENY AND REPRODUCTION

Data on growth rates and development for 1 male and 1 female Acrobates pygmaeus from about 6 weeks of age to adulthood are available (Fanning and Watkins 1980). Eyes open at about 6 weeks of age (Fanning and Watkins 1980). At about 8 weeks of age, the lateral tail hairs are obvious but <1 mm in length, growing to 4 mm on each side of the tail by about 14 weeks (Fanning and Watkins 1980). At about 5 months old, the gliders are close to their full adult size and coloration (Fanning and Watkins 1980).

Females have a well-developed pouch that opens anteriorly (type 5— Russell 1982), typical of diprotodont marsupials ( Ward 1998). In comparison with pygmy possums, Cercartetus ( Harris 2008, 2009a, 2009b), A. pygmaeus has a lower ovulation rate, grows more slowly, and is less fecund, both annually and over a female’s lifetime ( Ward 1990a). Females also have smaller vaginal culs-de-sac compared with pygmy possums; corpora lutea and ovaries are smaller (mean weight [± SD] is 2.04 ± 0.85 mg; n = 23—Ward and Renfree 1988a), and the median septum is more prominent ( Ward 1990b). Two median vaginae are present; they converge into a single urogenital sinus and open with the rectum to form a distinct cloaca (Ward and Renfree 1988a; Hill 1900). A female can remate at a postpartum estrus, shortly after the 1st litter in a season is born, and the resultant embryos go through a special form of embryonic diapause in which there is only very slow growth of the blastocysts (Ward and Renfree 1988a). These embryos are reactivated as the 1st litter approaches weaning and form the 2nd cohort of births in the population that season. Pouch life lasts 65 days, weaning occurs at about 105 days of age ( Ward 1990a). When they are well furred, the young ride on the mother’s back ( Nowak 2005), although it is not clear whether this occurs any distance away from the den tree. Multiple paternity has been identified in 60% of A. pygmaeus litters sampled (6 of 10— Parrott et al. 2005). Female A. pygmaeus was also found nesting with, and presumably suckling, young that were not their own ( Parrott et al. 2005; Ward 2007).

Males show a significant increase in testis and epididymal weight during the breeding season, with the testes comprising 1.5–1.8% of the total body weight at the height of the breeding season (Fleming and Frey 1984; Ward and Renfree 1988b). Mean testes weight is 0.178 ± 0.08 mg (n = 4—Tyndale-Biscoe and Renfree 1987). Measurements of scrotal width are available from 1 museum specimen (13.0 mm—Woolley and Vanderveen 2002). The scrotum is well furred and nonpendulous; the prostate is heart-shaped; tunica vaginalis are unpigmented; and there are 2 Cowper’s glands (Ward and Renfree 1988b). Spermatozoa are 100.6 ± 4.5 µm, n = 70 ( Parrott et al. 2005). Sperm competition is suggested due to large relative testes size, male-biased sexual dimorphism, and behavioral aspects, including communal nesting, promiscuity, and multiple paternity within litters ( Rose et al. 1997; Parrott et al. 2005).

The breeding season is relatively long in Victoria (July– January—Fleming and Frey 1984; Ward 1990a, 2007) and may start earlier at lower latitudes (e.g., Goldingay and Sharpe 2004). Adult females usually produce 2 litters within a season (Fleming and Frey 1984; Ward 1990a, 2007). Maximum litter size is 4 imposed by the number of teats (4— Ward 1998). There is a slight trend toward male-biased litters, but the pattern is inconsistent with the 1st-cohort advantage hypothesis (see Ward 2007). Some 10–15% of A. pygmaeus survive to their 1st breeding season ( Ward 1990a), and 3 females have been found breeding in their 5th annual breeding season (males to 4 seasons— Ward 2007). Maximum longevity is at least 5 years in the field ( Ward 2000a) and 4 years in captivity ( Collins 1973).

ECOLOGY

Population characteristics. — Acrobates pygmaeus may occur at densities exceeding 50/100 ha ( Russell 1980; Braithwaite et al. 1983; Ward 2000b). However, published statements that as many as 40 can be observed in profusely flowering trees (Turner and McKay 1989; Henry 1995) are based on secondhand reports that have not been able to be replicated by others (e.g., Goldingay and Sharpe 2004). One report of “hundreds” seen on or about one tree ( Fleay 1947:97) seems in all likelihood to be a significant exaggeration. At Wombat State Forest, Victoria, a density estimate of only 1.7–4.4 gliders/ha was measured over a 24-month period ( Ward 2004).

Space use. —The nests are usually constructed in tree hollows from Eucalyptus or Casuarina leaves or shredded bark and have a characteristic ball-shape (Le Souef and Burrell 1918; Fleay 1932; Troughton 1943; Fanning 1980). Nine observations of nest-site use by Acrobates pygmaeus in the Central Highlands of Victoria showed that tree holes with a small entrance cavity were preferred, and these holes were at 27 ± 7 m (SD) above ground ( Lindenmayer et al. 1991). Also in Victoria (Wombat State Forest), space use over a 1-week period were measured as 0.15–1.24 ha for females and 0.26– 0.39 ha for males (χ = 0.48 ± 0.39 ha [SD]— Ward 2004). In a Queensland study, short-term home range estimates were 0.4– 2.1 ha ( Kirk et al. 2000). The greatest distance between nest boxes, known to have been used by a single individual, was 225 m at Daylesford and 224 m at Nar Nar Goon North ( Ward 1990a). In Queensland ( Kirk et al. 2000), a maximum distance moved during hourly radio-tracking was 219 m, with an average range span between fixes of 167 m (SD = 47.5, n = 4 animals). However, patterns of space use and nest use have been found to vary considerably between individuals.

Habitats used by A. pygmaeus in New South Wales are variously described as open dry sclerophyll forests and woodland ( Marlow 1958), tall open forest ( Barnett et al. 1976), wet sclerophyll forest ( Robinson 1985), dry peppermint forest (Kavanagh and Stanton 1998), and mature woodlands (Paull and Date 1999). In Victoria, it has been found in wet, moist, and dry forests ( Land Conservation Council 1973; Thomas and Gilmore 1976; Horrocks et al. 1984; Pyrke et al. 1988; Lumsden et al. 1991), subalpine woodlands ( Land Conservation Council 1977), tall open forest and woodland ( Gilmore et al. 1979), riparian forest ( Cherry et al. 1987), coastal woodland ( Norris et al. 1983), peppermint forests ( Andrew et al. 1984), montane forest ( Lobert et al. 1991), swamp gum open forest (Conole and Baverstock 1992), tall open forest (Westbrooke and Prevett 2002). It has also been reported from remnant vegetation in farmland and along roadsides ( Norris et al. 1983). The species does not occur in exotic pine plantations ( Pinus radiata — Suckling et al. 1976; Friend 1982) but will use regrowth forest when provided with nest boxes (see Goldingay and Sharpe 2004; Goldingay et al. 2007). A number of studies have shown that A. pygmaeus prefers sites containing older forest (trees> 40 cm girth), which may also relate to food abundance (Goldingay and Kavanagh 1995; Goldingay and Eyre 2004).

Diet. —The natural diet of Acrobates pygmaeus is omnivorous, consisting of nonfoliage plant materials and invertebrates. This includes nectar and pollen from a variety of native plant species, particularly Angophora , Banksia , Corymbia , and Eucalyptus ; also other plant exudates such as manna (a clear carbohydrate-rich substance found on the leaves of Eucalyptus ), honeydew (a sugar-rich secretion produced by insects), and phloem sap (a watery mixture with sugars, hormones, and mineral elements dissolved). Seeds and insects including arthropods such as lerps, soft-bodied termites, or white ants are also consumed ( Turner 1984; Huang et al. 1987; Turner and McKay 1989; Goldingay and Kavanagh 1995). Loose shedding bark, blossoms, branches, and foliage provide important foraging substrates (Goldingay and Kavanagh 1995). Observed seasonal shifts in habitat use are most likely related to food availability ( Davey 1984; Kavanagh 1984) and switching between food types to meet its protein requirements ( Hume 1999). In captivity, artificial feed for A. pygmaeus includes fruits, honey, baby cereal, evaporated milk, moths, and fresh high nectar flowers ( Fleming 1985; Slater 1985; Geiser et al. 1992; Jones and Geiser 1992; Salminen et al. 1992; Geiser and Ferguson 2001; Jackowiak and Godynicki 2007).

Diseases and parasites. —At least 6 parasites are recorded for Acrobates pygmaeus : the fleas Acanthopsylla pavida , Choristopsylla thomasi , C. tristis , and C. ochi ( Jordan and Rothschild 1922; Thompson and Plomley 1938; Holland 1971; Dunnet and Mardon 1974) and the mites Gymnolaelaps annectans and Ornithonyssus acrobates ( Domrow 1987) . Tumor formation (sarcomata) with local metastases has been reported subsequent to the implantation of passive integrated transponders (Vogelnest and Woods 2008).

Interspecific interactions. — Acrobates pygmaeus has been recorded as prey of carpet python Morelia spilota ( Van Deusen 1960) , Stephen’s banded snake Hoplocephalus stephensii ( Fitzgerald et al. 2004) , forest raven Corvus tasmanicus (McCulloch and Thompson 1987) , gray shrike-thrush Colluricincla harmonica (Hindwood and Salmon 1955; Rowley 1989), southern boobook Ninox novaehollandiae ( Rose 1996) , barn owl Tyto alba ( James 1980) , sooty owl Tyto tenebricosa ( Loyn et al. 1986; Bilney et al. 2007), barking owl Ninox connivens ( Schulz 1998) , possibly masked owl Tyto novaehollandiae ( Wakefield 1963b) , cat Felis catus ( Orchard 1926; Loyn et al. 1980; Jones and Coman 1981; Brown et al. 1986; Lunney and Leary 1988; Dowling et al. 1994), canids (i.e., domestic dogs Canis lupus familiaris and dingo C. l. dingo and the red fox Vulpes vulpes — Brunner et al. 1975, 1976; Triggs et al. 1984; Brown et al. 1989; Brown and Triggs 1990; Lunney et al. 1990; Barker et al. 1994), spotted-tailed quoll Dasyurus maculatus ( Belcher 1995; Dawson et al. 2007; Jarman et al. 2007), sugar glider Petaurus breviceps (Winter in Ward 2000a), possibly agile antechinus A. agilis ( Ward 2000a) , possibly ghost bat Macroderma gigas (Ward and Woodside 2008) , and possibly lace monitor Varanus varius ( Henry 1995) .

Acrobates pygmaeus has been found occupying abandoned nests of common ringtail possums Pseudocheirus peregrinus ( Dorward 1976; Fanning 1980). In areas where A. pygmaeus is sympatric with eastern pygmy possums Cercartetus nanus ( Harris 2008) , the 2 species may have very similar diets ( Huang et al. 1987). Their coexistence without partitioning of food resources is suggested to be a consequence of the low densities of both species and the wide breadth of their food niches ( Huang et al. 1987). Like eastern pygmy possums, A. pygmaeus may serve as an important pollinator of many plant species in forest habitats ( Turner 1984; Turner and McKay 1989; Goldingay and Scheibe 2000; Herrmann et al. 2013).

Miscellaneous. —Spotlighting is most often reported as a successful method for detecting Acrobates pygmaeus ( Conole 1980; Norris et al. 1983; Goldingay and Kavanagh 1988; Kirk et al. 2000; Goldingay and Sharpe 2004), despite it having only weak eyeshine ( Ward 2000b). A. pygmaeus is detected during spotlighting due to its bright white ventral surface that contrasts markedly with dark-colored substrates and because it moves rapidly along branches and in tree canopies (Goldingay and Eyre 2004). Nest boxes are also a useful survey method, but there is debate about whether nest boxes are more reliable than spotlighting ( Ward 2000b; Goldingay and Sharpe 2004; Richardson and Carthew 2004) and any preferences for different nest box designs is not yet fully clarified ( Goldingay et al. 2007). For a review of nest box studies, see Beyer and Goldingay (2006). Other methods used include Elliott trapping in trees (Smith and Phillips 1984; Craig 1985), small hair tubes in trees ( Lindenmayer et al. 1994a, 1994b; Alexander 1997), stagwatching ( Brown et al. 1989; Lindenmayer et al. 1990), and pitfall trapping ( Bennett et al. 1988; Lumsden et al. 1991; Loyn et al. 1992). Inadvertent captures have resulted from monitoring of pipeline trenches ( Doody et al. 2003) and use of harp (bat) traps ( Schulz 1997).

There are suggestions that A. pygmaeus would make a delightful domestic pet ( Gould 1863; Fleay 1947). Early natural history illustrations are depicted in Shaw (1794), Perry (1811), Waterhouse (1841), Gould (1863), and Lydekker (1896). A. pygmaeus was featured on the obverse side of the Australian 1-cent coin (circulated from 1966 to February 1992). These coins were later melted down to make bronze medals for the 2000 Sydney Olympics (M. Balaz, in litt.).

BEHAVIOR

There is only limited knowledge of the breeding behavior of Acrobates pygmaeus in the wild due to its small size, nocturnal nature, cryptic and arboreal lifestyle, and because it uses tree hollows to nest and raise young ( Ward 1990a; Parrott et al. 2005). It is a social animal that shares nests, with a group size typically of 2–5 individuals (Fleming and Frey 1984). Females have been found sharing nest boxes with several males during the breeding season and when young are in the nest (Fleming and Frey 1984; Ward 1990a), although there is little evidence of prolonged associations ( Ward 1990a).

It spends most of its time high in trees, 87% of the time above 15 m and 72% above 20 m, much of this spent in the canopy of eucalypts (Ward and Woodside 2008; see also Davey 1984; Goldingay and Kavanagh 1995 for additional height preference data). However, it is not confined to the canopy and may forage through the shrub layer to ground level ( Smith 1982; Goldingay and Kavanagh 1995). In the wild, A. pygmaeus reportedly becomes active within about 55 min after dusk ( Kirk et al. 2000), although in the laboratory, the period of activity has been observed to begin 42.5 ± 21.9 min (n = 5 observations) after the onset of darkness (Jones and Geiser 1992). Stagwatching observations (n = 9) in the Central Highlands of Victoria recorded the emergence time as 6 ± 4 min after dusk ( Lindenmayer et al. 1991).

Acrobates pygmaeus makes short fast agile movements punctuated by glides between branches and between trees ( Troughton 1943; McQueen 1965; Russell 1980; Ward 2004). Results of studies in Victoria found gliding frequency averaged 3–5/h, with gliding distances of up to 28 m recorded (X = 14 m from n = 64 glides—Ward and Woodside 2008).

In captivity, 2 juvenile gliders were heard to make 3 different sounds (Fanning and Watkins 1980). A faint, wispy, aspirant sound (psss-psss-psss-) was often made during handling. On occasions, they interspersed these with a faint ticking sound. The 3rd sound was a small popping noise, often made when the animals were licking their handlers’ fingers or licking fruit (Fanning and Watkins 1980). Other descriptions of the vocalization are of a hiss ( Biggins 1984) or a low twittering bird-like noise (Dixon and Huxley 1989).

Acrobates pygmaeus is generally regarded as difficult to establish in captivity ( Slater 1985; George 1990), but there have been some recent breeding successes at Taronga Zoo, Sydney (Geiser and Ferguson 2001). However, captive-bred A. pygmaeus at Taronga (4th or 5th generation animals) has been found to have poor expression of torpor and thermal performance compared with wild-caught animals (Geiser and Ferguson 2001) and to have suffered from eye cholesterol plaques ( Herrmann et al. 2013). The problems appear to be related to ad libitum supply of artificial nectar feed and consequently a reduced need to forage. Recently, some efforts have been made to improve these animals long-term health by supplementing to provide a more natural diet using native browse ( Herrmann et al. 2013).

GENETICS

Acrobates pygmaeus has a XY/XX sex determination and the diploid number (2n) is 14 (Hayman and Martin 1969). The phylogenetic study of Aplin and Archer (1987) placed acrobatids and tarsipedids alongside Pseudocheirdae and Petauridae in the superfamily Petauroidea , whereas burramyids were placed in their own superfamily Burramyoidea . Studies of mitochondrial ND2 have since found high levels of sequence divergence between Acrobates and Tarsipes (about 33%) suggesting that although they constitute sister taxa, they are not particularly closely related and family level separation (as Acrobatidae and Tarsipedidae ) is appropriate ( Archer 1987; Osborne et al. 2002).

CONSERVATION

Acrobates pygmaeus is rated as “Least Concern, Lower Risk” on the 2008 International Union for Conservation of Nature and Natural Resources Red List of Threatened Animals (International Union for Conservation of Nature and Natural Resources 2008). Although its range has undoubtedly been reduced due to land use changes, current data suggest it persists in> 50% of its former range within 13 bioregions; has declined 50–90% of its former range within 9 bioregions; and has declined severely (> 90% of its former range) or become extinct in 2 bioregions ( Burbidge et al. 2008). In New South Wales, more localized assessments suggest it is common at Eden ( Recher et al. 1980; Braithwaite et al. 1983), moderately common on the southwestern slopes (Kavanagh and Stanton 1998), scarce in the Clouds Creek area ( Barnett et al. 1976), and rare in the coastal forests near Bega (Lunney and Barker 1986, 1987) and on the northwest slopes (Paull and Date 1999).

In Victoria, available (but now outdated) information suggests it is “Common” in Gippsland ( Norris et al. 1979; Norris et al. 1983; Brown et al. 1986), Westernport ( Andrew et al. 1984), Dartmouth Dam (Thomas and Gilmore 1976), Otway’s ( Bennett 1982), and Bairnsdale ( Westaway et al. 1990). Historically, it was also considered “Common” in the Greater Melbourne area ( Land Conservation Council 1973), but a recent assessment found its distribution has reduced from 13 local government areas to 11 ( van der Ree 2004). Also in Victoria, it is apparently “Uncommon” at Toongabbie ( Friend 1982), in the southwestern region ( Emison et al. 1978; Menkhorst and Beardsell 1982), Bendigo ( Land Conservation Council 1978), Wallaby Creek Catchment ( Ambrose 1979), north-central region (Menkhorst and Gilmore 1979), Portland ( Ruppin 1981), Whitfield ( Menkhorst et al. 1984), Central Highlands ( Lumsden et al. 1991), Dandenong Ranges ( Mansergh et al. 1989), and on Wilsons Promontory (Menkhorst and Seebeck 1999). In South Australia, A. pygmaeus is considered “Endangered” ( Watts 1990; Kemper et al. 2000; Richardson and Carthew 2004). Although there appear to be no major threats to this species, it may be locally threatened by logging of stands of mature forests (and by reduction in the availability of trees with suitable nesting hollows) and predation by feral cats and red foxes ( Henry 1995; International Union for Conservation of Nature and Natural Resources 2008).

Figures

Fig. 1.—An adult male Acrobates pygmaeus on a flowering Banksia ericifolia from southern Sydney, New South Wales. Used with permission of the photographer S. Mahony.

Fig. 2.—Dorsal, ventral, and lateral views of skull and lateral view of mandible of an adult Acrobates pygmaeus (sex unknown), from Cox River, Lithgow, New South Wales, registered on 23 April 1923 and donated to the Australian Museum by Henry S. Grant (museum registration number M3294). Greatest length of skull is 19.8mm. Photographs by J. M. Harris.

Fig. 3.—Geographic distribution of Acrobates pygmaeus. Adapted from Jackson and Schouten (2012).