Numbats

The numbat (Myrmecobius fasciatus) is the only species in the Family Myrmecobiidae, in the Order Dasyuromorphia. Its closest living relatives are the carnivorous dasyurid marsupials (DeJose 1988). They are one of only two exclusively diurnal marsupial species, the other being the musky rat-kangaroo (Hypsiprymnodon moschatus), and are most active from mid-morning to late afternoon. Their diurnal nature reflects the activity patterns of their termite prey, which ascend to upper soil layers during the warmer part of the day (DeJose 1988; Friend 1997a). They spend nights in logs or in burrows, which they dig themselves and also use for shelter during the day. They are excellent climbers and diggers and are highly agile (Friend 1989; Power & Monaghan 2003).


Numbats were originally widespread across southern semi-arid and arid Australia (Maxwell et al. 1996). Today there remain only two remnant populations and four self-sustaining reintroduced populations, all in the south-west of Western Australia. They are threatened by predation, particularly by foxes, and by habitat destruction. Key factors necessary for survival of numbats in the wild include an abundance of their only food source, subterranean termites, and sufficient ground-level cover to afford protection from predators (Friend 1997a, b).


Numbats can live for up to 5 yr in the wild, although most do not achieve this age (Friend 1997a). In captivity they live longer. Males have been known to live up to 11 yr and females up to 7 yr (Power & Monaghan 2003).


2 ANATOMY AND PHYSIOLOGY


Adult numbats weigh about 500–700 g and have a body length of about 30 cm, with a 20 cm tail. Dorsoventral flattening of their hind quarters affords them manoeuvrability when moving in hollow logs or burrows. Both fore and hind limbs have sharp claws for digging. There are five digits on the manus, of which the fourth is the most prominent. The pes has four digits, the first digit being represented only by a skin pad (Friend 1989).


The pelage is short and stiff, which probably reflects their burrowing habits (Friend 1989). The coat is sparse compared with other marsupials, and has a low reflectivity and high absorptivity for solar radiation. This maximises solar heat gain, thereby minimising the energy expenditure required for thermoregulation. This may be an important adaptation for the species, given the poor nutritive quality of its termite diet (Cooper et al. 2003b).


Adult numbats have a sternal sebaceous gland located on the ventral midline at the cranial aspect of the sternum. The gland is hairless, pigmented and approximately 1 cm in diameter. It is more prominent in males than in females, and is used in territorial marking (Friend 1989; Power & Monaghan 2003). Numbats are unusual among termite and ant-eating mammals in that their dentition is relatively well-developed (Cooper & Withers 2004a). They have 50–52 teeth. Their long thin tongue, which can protrude several centimetres beyond the snout, reflects their dependence on termites as a sole food source (Friend 1989, 1997a). Other anatomical adaptations to their termite diet include an elongated snout, greatly enlarged submaxillary salivary glands and an unspecialised gastrointestinal tract similar to that of dasyurids (Friend 1989; Hume 1999). Their slow gut passage time of 20–30 hr optimises digestion of termites, which are of low energy density and digestibility (Cooper & Withers 2004a).


The external sex organs of the male consist of a prepenile pedunculated scrotal sac and a penis with a cleft tip and a keratinised spiny shaft. Accessory sex glands consist of a prostate and three pairs of bulbourethral glands (Fordham 1928 in Friend 1989).


Female numbats have four nipples, arranged on the caudal abdomen so that the posterior pair is closer together than the anterior pair. There is no pouch present, however, in pregnant animals skin folds may be observed on the lateral margins of the mammary area and swelling develops just cranial and caudal to the mammary area prior to birth, so that the teats are enclosed within a depression (Power & Monaghan 2003).


The ovaries are located ventral to the anterior end of the two uteri. The uteri terminate in two median vaginae close to the upper end of the urogenital sinus. Two lateral vaginal canals emanate from the median vaginae and open via separate apertures into the urogenital sinus. The cloaca is a typical distinct structure into which the rectum opens dorsally and the urogenital sinus ventrally (Friend 1989).


Like all marsupials, numbats have a relatively low basal metabolic rate and core body temperature (Friend 1989; Cooper et al. 2003a). Basking in the sun is an important feature of their thermoregulation. The relatively sparse coat has poor insulative and low reflective properties, enabling rapid and efficient solar heat gain (Cooper et al. 2003b). Numbats are able to go into torpor and reduce their core body temperature to as low as 19°C (Cooper & Withers 2004a). While torpor is an induced response to food shortage in other dasyurid species examined to date, thermal telemetry studies of numbats, both in captivity and in the wild, indicate that they are able to go into torpor spontaneously. Numbats may go into torpor on virtually a daily basis through the colder months, entering torpor around 3.30 am and achieving normal body temperature around 8 am (Cooper & Withers 2004a).


3 REPRODUCTION


Numbats are solitary and territorial, with individual animals occupying distinct home ranges. Females reach breeding age in their first year of life and males in their second. Females appear to remain fertile until they die, with the oldest recorded breeding female being 7 yr old (Power & Monaghan 2003).


Numbats have a short breeding season from December to February, with most mating occurring in January and early February (Power & Monaghan 2003). Females are seasonally polyoestrus and must be mated within 48 hr of oestrus for conception to occur (Friend 1997a). In captivity, the timing of pairing is determined by examining vaginal swabs and samples of voided urine from females to determine vaginal epithelial cell morphology. Samples from females are collected weekly from late December. Urine samples from males are collected fortnightly from December onwards to detect sperm, which usually appear in the urine from mid-December to the end of February. Males with viable sperm are introduced to females when the females are in early proestrus. The pair is kept together until PY are found (Power & Monaghan 2003).


Duration of mating may vary from less than a minute up to an hour. The only evidence of a mating may be wet fur on the scruff of the female’s neck, where she has been grasped by the male during copulation (Power & Monaghan 2003). Gestation length is 14 d and four young are usually born in January or early February (Friend 1989).


Numbat young are pink and hairless and have a total body length of approximately 6–7 mm. The young attach directly to one of four nipples on the female’s caudal abdomen and hold on by entwining their fore limbs in the hair around the mammary area. They remain attached to the mother for up to 6 mo. In late July they are deposited in a nest or burrow and continue to suckle at night. The young weigh approximately 70 g when deposited. Their growth rate is extremely slow and they are not weaned until about 9 mo of age when they weigh 200–300 g. This slow rate of development may reflect the poor nutritional quality of their termite diet. Dispersal occurs soon after weaning, in late November or early December (Friend 1997b, 1998).


4 HUSBANDRY AND HOUSING


Numbats have relatively specific husbandry requirements if they are to breed, display well and remain healthy. Enclosures are generally designed to provide an environment most suited to successful breeding. Numbats are usually housed individually in 5 × 3 × 2 m enclosures that are fully meshed to prevent predator attack. A mesh floor buried 1 m deep allows excavation of burrows (Power & Monaghan 2003).


The wild habitat of numbats is an arid or semi-arid environment and they do not tolerate damp or wet conditions. River sand is an ideal enclosure substrate because it drains well. Shrubs, tussocks and hollow logs are provided for natural protection. Ponds and running water are not provided as moist enclosures are believed to predispose to skin disease. Enclosures are best placed facing north to allow basking. There must be shade protection from the strong sun. Numbats can tolerate moderately cold weather but require hollow logs or nest boxes in winter to protect against severe cold. Enclosures should be cleaned every 1–2 d to remove faecal matter, and water and food dishes washed daily. Cage furniture should be replaced annually (Power & Monaghan 2003).


Numbats are very inquisitive and in captivity may be inclined to hang on wire mesh barriers to investigate adjoining enclosures. If they are startled while hanging on the wire they may become injured as they take flight, breaking nails or injuring their tail or a limb. The provision of climbing branches, anchored to the side of the enclosure, allows animals to climb to elevated positions without needing to climb mesh walls. This strategy has significantly decreased the incidence of traumatic injuries in numbats in captivity.


Numbats are solitary animals and are generally housed individually except at breeding time. Wherever possible, animals to be paired are housed in adjacent enclosures so that introductions may be effected simply by opening a door between the two enclosures. Visual barriers between enclosures (e.g. shadecloth) are important during the breeding season to prevent males becoming stressed and aggressive due to the proximity of competing males (Power & Monaghan 2003). Stress can be reduced by not housing males immediately adjacent to one another.


Pairs are introduced when the female is in proestrus, as determined by assessment of vaginal epithelial cytology (see section 3). If the pair is housed next to one another they can be introduced by opening a gateway between the enclosures. If not, the male is transferred to the female enclosure in his own nest box. Generally, little aggression is observed during introductions but occasionally a male will chase a female rather than show reproductive behaviour. If this persists for more than 24 hr the male should be removed and replaced with another male.


Breeding females require protection from heavy rainfall to prevent collapse of underground nests. For this reason, all breeding females are moved indoors prior to the onset of wet weather. Breeding and lactating females become stressed when there is too much noise or human presence, and there is significant risk of losing young if appropriate visual and noise barriers are not used. It is important to minimise movement of personnel as much as possible during the breeding months.


Provision of natural sunlight is of great importance for maintaining normal metabolism and thermoregulation in numbats, particularly breeding females. Even when ambient temperature is adequate (e.g. in numbats housed indoors) numbats actively seek out natural sunlight, and basking is their first activity when they emerge from their nest boxes. Numbats emerge from torpor around 8 am in the colder months and are usually slower and less reactive early in the morning, even during summer. Handling numbats before they leave their nest boxes in the morning does not appear detrimental to their well-being. In fact, it is often ideal to handle numbats at this time because they are less likely to become stressed or flighty and do not resist manual restraint. This facilitates captive management activities such as weighing, vaginal swabs and nail trimming.


A very sick or debilitated numbat might appear similar to a numbat in torpor. For this reason, it is preferable to wait until after numbats emerge from their nest boxes in the morning to assess their level of activity. Sick numbats can be housed in a hotbox set at 26–32°C if confinement or intensive care is required, or in a small heated room set at 16–26°C with leaf litter or woodchip substrate and a heat lamp for basking. Numbats are nervous animals and a nest box or some form of visual protection should be provided. Numbats generally head directly for the nest box if they are disturbed. This is helpful when handling is necessary, as they can be shut into the nest box then removed directly from the box rather than having to net or chase them.


Numbats can be transported for short periods using a cotton bag, pillowcase or secure nest box. For longer periods of transport, numbats should be placed in a pillowcase, which is then put into a 350 × 400 × 200 mm wooden box. The box should be lined with sea grass or similar absorbent cushioning material; only one animal should be placed in each box (Power & Monaghan 2003). Wherever possible, numbats should be transported during the cool hours of the night and early morning, for periods of less than 24 hr.


Passive integrated transponders are used for individual identification. They are inserted with the animal under general anaesthesia and are placed SC in the dorsal interscapular region (Power & Monaghan 2003). The insertion site may be clipped and surgically prepared, but chips have been inserted without clipping or surgical preparation of the site. The very thick skin of the numbat’s dorsal neck region tends to resist closure using tissue glue, so to prevent transponder loss the insertion site should be closed using an absorbable suture. In the past, numbats have been identified by tattooing the inner thigh, but this technique is now obsolete due to the ease and reliability of transponder implants. The experienced observer may identify numbats by the banding pattern of their fur, which is unique to each individual (Power & Monaghan 2003).


5 NUTRITION


Numbats are myrmecophagous (eat termites). In the wild numbats feed exclusively on a range of Isoptera termite species. They eat approximately 15 000–20 000 termites per day and ingest large quantities of associated dirt (at least 0.33 g for every gram of organic matter ingested) (Cooper & Withers 2004a; Power & Monaghan 2003).


A reliable termite supply is essential to captive husbandry of numbats. Perth Zoo numbats are supplied with termites harvested from wild nests of Nasutitermes exitiosus and Coptotermes acinaciformis termites. The trapping, harvesting, removal and storage of termites is a complex process; see Monaghan and Power (2003) for diagrams and a detailed description. Briefly, an open-topped drum packed with slats of karri (Eucalyptus diversicula)

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May 28, 2017 | Posted by in GENERAL | Comments Off on Numbats
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