The Order Chiroptera includes 202 genera and over 1116 species (Wilson & Reeder 2005). Seventy-nine species are recognised in Australia. The Family Pteropodidae (fruit-bats or pteropodids) includes 13 of these species, which also occur in New Guinea or surrounding islands. This Family is distinguished from others by external appearance and dietary preferences and includes the blossom bats, tube-nosed bats, fruit-bats and flying-foxes. In this chapter, unless otherwise specified, we use the term ‘pteropodids’ to refer to these species. The insectivorous and carnivorous bats (Families Megadermatidae—ghost bats, Rhinolophidae—horseshoe-bats, Hipposideridae—leaf-nosed bats, Emballonuridae—sheath-tailed bats, Molossidae—free-tailed bats and Vespertilionidae—ordinary bats) include 66 species of which 27 also occur in New Guinea or surrounding islands. Identification is made through their significant morphological (Table 14.1) and dietary diversity (Jackson 2003; Strahan 1995; Wilson & Reeder 2005).
The majority of Australian bat species probably entered from New Guinea. The high species diversity on Cape York is a reflection of this migration, its close geographical proximity and diversity of habitats. Bat diversity diminishes with increasing latitude with only six species found in Tasmania (Strahan 1995; Hall & Richards 2000).
Both the spectacled (Pteropus conspicillatus) and grey-headed (P. poliocephalus) flying-foxes are listed as vulnerable, as are several species of insectivorous and carnivorous bats. Six other insectivorous and carnivorous bat species are thought to be extinct, critically endangered or endangered (Environment Australia 1999).
Over much of their range, pteropodids are now affected by increasing urbanisation and exotic fruit cultivation which can lead to fragmentation of traditional roosting sites. Pteropodids normally move from one part of their roost site to another over the seasons, preventing significant damage to the roost trees, but the restricted size of the urban camps means there is now a greater impact on the trees and many are significantly damaged or killed before the colony moves on. However, in spite of these limitations, pteropodids often choose urban campsites where they are sheltered by surrounding buildings, protected from shooting and have ready access to flowering garden trees and cultivated fruit trees. Together with the increased media focus on the potential zoonotic disease risks of pteropodids, increased pressure is being placed on government agencies to relocate or destroy populations in urban areas.
2 ANATOMY AND PHYSIOLOGY
The anatomy and physiology of bats is similar to most other eutherian mammals. However, there are a few notable exceptions, primarily in relation to their capacity for fight.
Chiropterans are distinguished from other mammalian Orders by the characteristic wing membrane (patagium) of the fore limbs and their ability to achieve sustained fight. Most insectivorous and carnivorous bats, but no pteropodids, have a uropatagium or membrane that extends between the hind legs and partially or totally covers the tail (Jackson 2003).
The wing is essentially the mammalian forearm highly modified for fight. Major skeletal adaptations for fight include a keeled sternum and lightweight but solid bones. The radius is the main forearm bone to which the ulna is fused over most of its length. A thumb (digit one) is present in all species but is larger in pteropodids. This digit controls the shape of the propatagium (the part of the wing membrane attached anterio-laterally to the arm bones between the shoulder and the carpus) during fight. For pteropodids, digit one is also an essential tool for manipulating branches and food items, hanging for defecation and urination, and for fighting. The remaining digits (two to five) are elongated rigid spokes supporting the wing membranes. Each digit is made up of a metacarpal and phalanges one and two (Hill & Smith 1986; Hall 7 Richards 2000; Heard 2003). With the exception of the bare-backed fruit-bat (Dobsonia magna), a distinguishing feature of pteropodids is the presence of a nail at the end of digit two (Fig. 14.1).
All bats have three fight membranes that form the main body of the wing. The membranes are essentially modified skin stretched around the framework of bones. They are the propatagium, the plagiopatagium and the dactylopatagium (Fig. 14.1). In most insectivorous and carnivorous bats the tail is connected to the legs by a fourth broad membrane (uropatagium), which is used during abrupt changes in fight direction (Hall & Richards 2000). The uropatagium is represented in pteropodids by a small fap of skin down the inside of the legs. The membranes are very elastic and have numerous parallel bands of elastin running through the plagiopatagium perpendicular to the humerus and radius (Fig. 14.1), making the wing pliable and resilient.
Although the primary function of wing membranes is fight, they also serve a number of other purposes. The membranes are well-supplied with blood vessels that dilate to promote heat loss in hot and humid environments. In pteropodids, heat loss is further assisted by wing fanning or allowing the wings to hang in a breeze. Additionally, they urinate on the wing membranes to promote evaporative cooling. In cold, windy or wet weather pteropodids wrap their wings tightly around their bodies to reduce heat loss and keep warm and dry. Tube-nose bats (Nyctimene spp.) have tan wings dappled with unpigmented patches that provide camoufage when wrapped around their bodies at rest.
Figure 14.1 Ventral view of a grey-headed flying-fox showing key anatomical features. a) Propatagium. b) Dactylopatagium. c) Bands of elastin. d) Plagiopatagium. e) Uropatagium. f) Digit one. g) Digit two. h) Digit three. i) Digit four. j) Digit five. k) Median vein. l) Wing or cephalic vein. m) Uropatagial vein.
Bats use their wing membranes during birth to assist the pup from the vulva to the nipple. Wing membranes also serve as a cradle when the pup is suckling or sleeping and insectivorous bats use their wings to help capture prey before transferring it to their mouth (Hill & Smith 1985).
Transillumination of the wing is used to age insectivorous and carnivorous bats by visual identification of the translucent epiphyseal cartilages of juveniles (Parnaby 1992). Fusion takes place over several months. Pre-fight bats have three bands of cartilage visible; bats flying for 1 mo have two visible bands; those flying 2–3 mo have one band; those flying for more than 3 mo have no visible bands and epiphyses are fused (approximately 5 mo of age). In insectivorous and carnivorous bats changes in appearance and pelage colour or texture are unreliable guides to distinguishing juveniles from adults.
2.2 Pelvic girdle and hind limbs
In insectivorous and carnivorous bats the sacrum and ilium are fused to the level of the acetabulum, whereas in pteropodids they are entirely fused (Heard 2003). In all species the hind limbs are rotated at the hip so the legs can bend anteriorly towards the ventrum. The patella is absent in all species.
2.3 Locking mechanism
Since bats perch inverted with their entire body weight suspended from the toes, their legs are adapted for pulling rather than pushing. Most bats have a locking mechanism, consisting of a small tendon in each toe that keeps the claws in a flexed position without muscular contraction. This allows them to sleep while hanging. To take off they must flap to attain a horizontal position to reduce pressure on the hind limbs and allow the hind limb claws to unlock.
The claws are compressed into blade-like hooks to assist with hanging as well as grooming (Hall & Richards 2000).
2.4 Gastrointestinal tract
Pteropodid dentition reflects a diet of fruit, nectar and leaves, with large canine teeth and flattened molars that have a smooth hollow trough and high cusps. The cheek pouches can expand to hold pieces of fruit temporarily during feeding. Food is repeatedly chewed then pressed between the tongue and well-defined palatine ridges to extract the juice. Most fibre is eventually spat out after the juice is extracted (leading to the common misconceptions that bats vomit fibre or defecate from their mouths). The gastrointestinal tract has evolved into a shortened simplified structure, designed predominantly for digesting fruit juice, nectar and pollen (Nelson 1989). Blossom bats have a brush-tipped tongue for collecting nectar and pollen from flowers. Insectivorous bats possess molars with sharply pointed cusps and clearly defined ridges. They also have a muscular callus-like papilla on the gingiva at the level of the lower premolars for breaking off and ejecting chitin pieces. In most species the upper third of the oesophagus is lined with keratinised epithelium for protection from the sharp chitin pieces (Heard 2003).
The gastrointestinal transit time is very short relative to other mammals. Insectivorous bats generally have longer transit times (35 min in fully active animals to 170 min in animals at rest) than Pteropus spp. (>12–34 min for cultivated fruits) (Jackson 2003). These anatomical and physiological modifications reduce the weight of gut contents while flying.
Neonates have fine recurved milk teeth (teeth that point backwards) that assist in holding onto the nipple, especially during fight. These are replaced by permanent dentition about the time pups begin to fly.
2.5 Sensory system
Pteropodids have large forward-facing eyes well-adapted for nocturnal vision, while still retaining a high degree of visual acuity in broad daylight. The retina is avascular; the central artery is absent and nourishment presumably occurs by diffusion from choroidal capillaries. As would be expected of nocturnal mammals the retina consists almost entirely of rod cells. In many pteropodids colour vision and a tapetum lucidum that causes the eyes to shine bright red in a spotlight are present (Hall & Richards 2000). In contrast, insectivorous and carnivorous bats have small eyes and may have poor vision, but compensate for this by their ability to image their environment acoustically via echolocation (Hall & Richards 2000). The imaging system is made up of a transmitter (larynx) and a receiver (ears and associated neural systems) (Heard 2003).
Insectivorous and carnivorous bats have very acute hearing and most species have a well-developed tragus (a prominent flap of skin at the entrance to the ear) to help catch sound outside the normal mammalian acoustic range (Fig. 14.2). The nose may be relatively unmodified to complex with dermal appendages (e.g. nose-leaf). These structures are thought to be involved in catching and redirecting sound for navigation and hunting by echolocation.
All pteropodids have simple and relatively small external ears with no tragus. The inner ear of pteropodids shows no special modifications. Internally, the cochlea is relatively small (Hall & Richards 2000).
The majority of neonatal insectivorous and carnivorous bats are born without visible fur on their bodies. This gradually appears everywhere except the wings and the ventrum, which remains bare until 2–3 wk of age (Bogan 1972).
Most adult bats have furred bodies and unfurred wings. A healthy coat in an adult bat is thick and glossy. Most male pteropodids have modified sebaceous glands around the neck ruff. These exude sebum with a distinctive straw colour (pink in the spectacled flying-fox) and fruity odour. This is very pronounced during the breeding season and in the presence of other adult males. In females a white discharge may be noted from perivulvar glands during the periparturient period (D Heard pers. comm.).
Wing membranes are normally dry, supple and smooth, with numerous parallel bands of elastin visible in the patagium. The wing pits (axillae) of pteropodids may feel greasy and smell strongly of bat musk.
2.7 Cardiovascular system
The cardiovascular system is typically mammalian but because bats fly the heart is larger, primarily in the right atrial and ventricular muscle mass (Heard 2003).
Body weight varies from 3–10 g for small insectivorous bats (e.g. free-tailed bats, Mormopterus spp.) to >1 kg (e.g. grey-headed, spectacled and black flying-foxes (P. alecto)). Monitoring body weight in hospital patients is critical in assessing adequate food intake and hydration status.
Some bats use daily torpor and hibernation to minimise their metabolic rate. Bats enter torpor by allowing their body temperature to drop almost as low as the air temperature. This lowers their respiratory and heart rate and conserves energy. Hibernation is similar to torpor but is generally much more prolonged (up to several months); torpor is usually limited to several hours or days. Hibernation allows many species of bats to survive winters on small flat stores. Disturbing bats during hibernation wastes these limited resources and may mean that they do not survive (Churchill 1998).
Pteropodid and some insectivorous and carnivorous bats’ core body temperatures are 37–39°C. However, smaller pteropodids and insectivorous and carnivorous bats that undergo torpor may exhibit extreme body temperature variability. Generally, rectal temperature is unreliable as a measurement of core body temperature, especially in smaller species.
Heart rates vary between species, time of day and level of activity. Larger species have rates of 100–400 bpm while smaller species can have rates of 250–450 bpm, and up to 1000 bpm.
Although there are many features common to all mammalian species the chiropterans have the greatest diversity of reproductive strategies of any mammalian Order (Crichton & Krutzsch 2000; Hall & Richards 2000).
Although most bats are polygynous, some will pair during the mating season (Nelson 1965). Breeding cycles usually commence in response to changes in natural photoperiod. There is considerable variation in the number and timing of oestrous cycles. All temperate species are monoestrus and all tropical species are polyoestrus. Some species exhibit sperm storage in females over winter. Others use delayed blastocyst implantation or embryonic diapause as a reproductive strategy for controlling the timing of births (Heard 2003). Gestation periods are long relative to those of other mammals (Table 14.2): 40–60 d in small vespertilionid or ‘evening’ bats (Family Vespertilionidae) up to 90–180 d in pteropodids (Heard 2003; Jackson 2003). Australian pteropodids are born in October-December, except for little red flying-foxes (P. scapulatus) which are born around April. Pteropodid offspring are generally weaned by about 5–6 mo (at approximately 60–70% of adult weight), whereas insectivorous bat species are generally weaned within 2 mo (usually around 80% of adult body weight).
Pteropodids are preferably housed outdoors in snake-proof enclosures with access to direct sunlight, natural air flow and rain. Galvanised wire may cause rubbing injuries to the flexor surfaces of joints and can be a source of zinc if animals lick either the wire or rainwater off it, which may result in toxicity. Vinyl-coated wire is preferable; polyethylene trawler netting hung from the ceiling and sides of the enclosure is a suitable alternative. Bats occasionally become tangled in mesh regardless of mesh size but heavier-gauge mesh carries a lower risk of cutting injuries if entanglement occurs. Ropes, vines and netting are appropriate perches. At least some netting or rope should extend to the ground to give grounded pteropodids a means to climb back up into the canopy. It is recommended that enclosures be double-meshed to reduce contact with free-ranging bats to minimise the risk of transmission of diseases such as Australian bat lyssavirus (ABLV).
Fight enclosures for pteropodids should be at least eight times the animal’s wing span long (Fascione 1995) and 1.8 m high. Landing and hanging material such as branches, ropes or towels should be placed at either end away from the walls to reduce injury from attempts to land on wire. Towels hung vertically from the roof also provide privacy and hanging and landing opportunities. Provided the towels are not flat against a solid wall, impact injuries rarely occur.
Insectivorous and carnivorous bats are housed indoors or outdoors but, like pteropodids, have better breeding success with natural light and temperature cycles. However, microclimate control is easier with indoor enclosures. This is particularly important for tropical species housed in temperate climates. All enclosures must be snake-proof. Housing requirements differ between species but all need a hide or shelter and a white or blue light source for attracting live insects. The required area of a fight aviary depends on the species to be housed. It should be greater than 3 × 4 m for highly manoeuvrable bats such as horseshoe, (Rhinolophus spp.), leaf-nosed (Hipposideros spp.) and forest bats (Vespadelus spp.) and greater than 7.5 × 7.5 m for fast flying, less manoeuverable species such as free-tailed and sheath-tailed bats (Saccolaimus spp. and Taphozous spp.) (Lollar & Schmidt-French 1998; Jackson 2003). The social behaviour of any species should be taken into account before setting up an exhibit or rehabilitation enclosure to avoid overcrowding and interspecies competition (Barnard 1995; Jackson 2003; SM Barnard unpub).
A standard dog or cat hospital cage is suitable for initial assessment and treatment of pteropodids and large carnivorous bats (e.g. ghost bats, Macroderma gigas). The cage must have a secure perch placed near the top and a cover to limit visual stimuli. A wire-top cat cage is adequate for temporary holding of smaller pteropodid species (e.g. little red and spectacled flying-foxes) and tube-nosed bats. A towel hung vertically in the cage provides shelter and, in smaller species, perching. The cage must be tall enough (greater than 2 × body length) for an adult bat to hang without its ears touching the floor and wide enough for the bat to extend and flap both wings. Avoid cages with vertical bars that may entangle a wing.
Insectivorous and carnivorous bats and small pteropodids (e.g. eastern blossom bats, Syconycteris australis) can be hung on a towel in a securely closed cardboard or wooden box or a plastic tank with a mesh lid.
The ideal substrate for hospital cages is newspaper, changed regularly. Boxes in which animals can hide (hide boxes) can be made from a variety of cardboard boxes. Hotboxes or incubators maintained at 22–25°C are ideal for most hospitalised species.
4.3 Feeding and water
Diets and detailed information on feeding hospitalised and debilitated bats is given in section 5. Food is presented in shallow trays to self-feeding insectivorous and carnivorous bats. Pteropodids eat from small hanging buckets or spill-proof dishes on the cage floor (if the cage is small). Nectivorous bats are fed from a shallow dish or (preferably) a feeder bottle. To avoid bacterial and fungal colonisation, feeder bottles should be thoroughly cleaned and sterilised daily.
Water should be provided for all species. Pteropodids drink from a hanging dish or bowl. Small insectivorous bats are offered water from a shallow dish or bowl with marbles or pebbles in it to avoid bats drowning. Spectacled and black flying-foxes are known to drink sea water (A Olsson unpub; D Heard pers. comm.) and should be provided with a salt lick ad lib.
Pteropodids and ghost bats can be transported in a small pet carrier made from plastic and/or wire. It is advisable to line the carrier with fine mesh or shade-cloth to prevent accidental injury to animal and people. These species require a roosting perch or trawler netting secured near the ceiling of the box from which to hang. Insectivorous and carnivorous bats <100 g body weight are safely transported on a cloth in a small plastic container, or secured inside a cloth bag.
Bats which may be injured or ill are best wrapped securely in a towel or cloth which is then placed in the transport cage. This minimises the risk of further injury to the animal, and protects the rescuer from bites and scratches. Care must be taken in hot or humid conditions that animals do not overheat.
4.5 Individual marking and identification
When a number of bats are kept together it is important to have a reliable means of identifying individuals. Hand-reared bats can be identified temporarily by painting different combinations of claws with brightly coloured nail varnish. The bat should be restrained while the varnish dries. Varnish is rarely groomed off and lasts several weeks to months. More permanent methods include passive integrated transponder (PIT) tags (or microchips), tattoos of the patagium or ears, ear notching, forearm and thumb bands, and necklaces (Jackson 2003). All banding in Australia is regulated by the Australian Bird and Bat Banding Scheme (ABBBS) and all banders are licensed under the ABBBS. PIT tags are inserted SC on the dorsal midline between the scapulae. The needle should be directed toward the head so that gravity pulls the chip into the channel created by the needle. The needle hole should be sealed with tissue glue to prevent the PIT tag falling out soon after implantation (L Vogelnest pers. comm.).
Chiroptera have the greatest diversity of diet and feeding habits of any mammalian order (Heard 2003). Bats consume large quantities of food relative to their body size but process it rapidly through their modified gastrointestinal tract. They are usually fed at dusk as they are most active at night.
5.1 Wild diets
Pteropodids consume a very wide variety of native plant species including fruits, blossoms and leaves. Preference is generally given to highly aromatic and light-coloured fruits and blossoms highly visible in moonlight (e.g. Melaleuca blossoms) and fruits or blossoms on the periphery of the forest canopy (Hall & Richards 2000). The grey-headed flying-fox is considered a generalist feeder, while the spectacled flying-fox is a specialist frugivore. The tube-nosed bats are fig specialists. The volume of fruit ingested in all species is determined by its protein content (Hall & Richards 2000).
Nectar is the principal food source for the blossom bats (Synconycteris and Macroglossus spp.). While collecting nectar they ingest significant amounts of pollen, which is also an important source of protein.
Folivory is widespread in pteropodids (Hall & Richards 2000; A Olsson pers. obs.; P Tully pers. comm.; J Maclean pers. comm.). It is thought this provides protein and trace minerals. Fig and lilly pilly leaves (any species) are readily accepted and usually readily available in urban areas.
The insectivorous and carnivorous bats are primarily insectivorous. Their diet is high in chitinous roughage from wing cases of mature insects. The exceptions are the ghost bat, which feeds predominantly on rodents, birds, frogs and other bats, and the southern myotis (Myotis macropus) which feeds on fish (Jackson 2003).
5.2 Captive diets
5.2.1 Frugivorous and nectivorous bats
Flying-foxes (Pteropus spp.) and the bare-backed fruit-bat usually readily accept commercial fruits. While larger species can hold and chew large pieces, dicing the fruit reduces wastage and is easier for smaller bats and recovering patients to manage. Most fruits are low in calcium, except figs, which are calcium-rich. Canned fruits are suitable and are convenient to store for long periods. Fruit purees can be offered as emergency nutrition but the high fibre load impairs absorption of nutrients if fed regularly (George 1990) and gastrointestinal tract problems such as rectal prolapse can result (see 9.2.3c). Fruit and nectar eaters are fed commercial lorikeet nectar mixes or Wombaroo high-protein supplement (Wombaroo Food Products) blended with fruit juice or blossom bat mix (Table 14.3). This diet can be fed alone or with Wombaroo Lorikeet and Honeyeater mix, or Wombaroo high-protein mix.
5.2.2 Insectivorous bats
Insectivores are initially fed whole mealworms or their viscera (squeezed directly into the mouth of a bat restrained between thumb and forefinger). These are usually readily accepted and high in calories. They eat 25–50% of their body weight each night (Hopkins 1990). This is equal to 6–10 mealworms for a small bat and up to 30 for a larger bat. However, for long-term maintenance mealworms alone are not adequate as they are high in fat and low in calcium, phosphorus and vitamins A, E, D3 and B complex. Mealworms should be fed Wombaroo Insectivore, Wombaroo Small Carnivore powder or similar for 48 hr prior to feeding out so their gut is filled with nutrients (Hopkins 1990; Jackson 2003). Adult insects (moths, cockroaches, grasshoppers, crickets) should be offered ad lib (Table 14.3).
5.2.3 Carnivorous bats
Carnivorous bats are fed a diet that approximates the wild diet (e.g. mice, baby rats, day-old chickens, larger insects, fish). The items can be fed whole or chopped to allow easy consumption and digestion. Carnivorous bats eat 10–20% of their body weight in food per night (Hopkins 1990) which equates to one day-old chick, one mouse and 5–10 mealworms per animal per day.
Quantity per bat per day
Chopped fruit, e.g. banana, apple, pear, pawpaw, mango, figs, any soft fruit in season, tinned fruit
Fresh native flowers, e.g. bottlebrush, eucalypts
Fresh mulberry leaves
Blossom bat mix:
10 mL mixed with 10 mL of water
500 mL apple juice
150 g raw sugar
150 g Glucodin (generic)
120 g S26 Soy3
Blend bananas and apple juice to total 500 mL.
Blend in sugar and Glucodin.
Add S26 Soy and blend for 1.5 min.
Pour into smaller containers and freeze (icecube trays for small numbers of bats).
Thaw for use as required.
Fresh native blossoms, e.g. banksias, bottlebrush, Melaleuca spp.
Ad lib twice daily
Crickets, grasshoppers, cockroaches, moths, other large insects
Flies, crickets, cockroaches, other flying insects
Wombaroo1 Insectivore or Small Carnivore mixed with very lean mince
3:1 (finely minced heart)
Manufacturers: 1 Wombaroo Food Products. 2 Complan Foods. 3 Wyeth Nutritionals.
Source: Adapted from Jackson (2003).
5.3 Feeding sick animals
Sick or injured animals that are not eating require assisted feeding or gavage. Assisted feeding is maintained until voluntary food intake is adequate for maintenance and healing. Patients should be weighed daily to monitor progress.
In an inappetant bat, injectable fluids containing 5% dextrose and vitamin supplements are sufficient to maintain energy levels for short periods. However, prolonged use of simple carbohydrate therapy will induce osmotic diarrhoea and does not correct protein or fat depletion. If treatment is to be prolonged, early enteral nutritional support decreases recovery time, weight loss and morbidity.
High-energy supplements such as Poly-Aid Plus (Vetafarm) (1 g/10 g body weight q 12 hr) or any pureed or liquid diet appropriate to the species, made up to a runny paste, may be used to provide readily absorbable energy, protein and fats to the debilitated patient and are easily administered via gavage if required. Probiotics at domestic animal dose rates appear to be a useful adjunct in debilitated animals, particularly following antimicrobial therapy, to assist restoration of normal gut flora.
Debilitated or inappetant bats may be assist fed using a syringe held to the mouth of the hanging or recumbent bat, allowing the animal to lick the liquid food off the tip. If the animal does not take the food it may need to be fed by gavage. A 14–18 G stainless steel bird crop feeding needle, fine nasogastric human infant feeding tube (size 3–4) or IV cannula (14–18 G) can be used. If mouth or head injuries are present, a pharyngostomy or nasogastric tube may need to be placed. Gavage is performed with the bat in the head up position (gravity assists food retention in the stomach) in the same manner as for any small mammal. A very rough guide for gavage volumes in debilitated patients is 2–3 mL/100 g body weight, given every 3–4 hr.
The following liquid diets are ideal for initially feeding debilitated patients.
- Pteropodids—apple or pear juice blended with a high-protein supplement or Poly-Aid Plus.
- Insectivorous and carnivorous bats—a blend of mealworm viscera and Poly-Aid Plus initially, gradually replaced by Wombaroo Insectivore or Small Carnivore mix.
The liquid diet is gradually replaced by a maintenance diet appropriate to the species as the patient recovers. Maintenance diets may be pureed (with added liquid if required) for ease of swallowing if patients are reluctant or unable to chew solid food.
All bats are capable of inflicting bites and scratches and may harbour zoonotic pathogens. While physical restraint may be adequate for simple procedures, chemical restraint allows a safer and more thorough assessment with less stress to the animal.
Veterinarians should ensure that only people vaccinated against rabies handle bats, that the vaccinations are up-to-date with appropriate levels of seroconversion and that carers have been properly trained in handling bats (see 9.8.1a). A major contact with an ABLV bat includes not only a bite but also saliva contamination of broken skin and mucus membranes. The use of personal protective clothing is recommended during handling. This may include long pants, a long-sleeved shirt (preferably of medium-weight cloth), covered footwear, gloves, a surgical or other industrial safety mask and safety glasses (Fig. 14.3). Safe physical restraint also depends on common sense and experience—larger bats are capable of inflicting a bite even through protective clothing if given the opportunity.
6.1 Physical restraint
Most insectivorous and carnivorous bats are small and adequately restrained by grasping over the dorso-ventral thorax between finger and thumb. Ghost bats and diadem leaf-nosed bats (Hipposideros diadema) are an exception due to their larger size and long sharp canines. They are handled as for a pteropodid.
Pteropodids are restrained by wrapping them with a thick towel while they hang. Once the towel is wrapped around the body to contain the wings and envelop the head, one hand is used to grasp the feet. The other hand grips the head through the towel under the mandible or with the middle finger and thumb on either temporomandibular joint. The index finger is placed over the top of the cranium. Pteropodids accustomed to handling can be minimally restrained by the hind feet, and loosely wrapped in a towel (Fig. 14.4). To release, place the wrapped bat in a cage then gently withdraw the towel as the animal orients itself.
Some species (e.g. tube-nosed bats) are solitary and easily stressed (A Olsson pers. obs.; J Maclean pers. comm.; P Tully pers. comm.). Handling time should be minimised to prevent stress. Stressed bats can be placed in a dark quiet box to recover. Administration of glucose syrup (5 mL to 200 mL water) PO given at 1–2 mL/100 g body weight or 5% dextrose saline given at 5–10 mL/100 g SC at the time of handling appears to aid recovery.
6.2 Chemical restraint
Fasting is unnecessary prior to chemical restraint except immediately after feeding or drinking. This is because rapid gastric emptying and short gastrointestinal transit times, as well as a tight oesophageal sphincter (Heard 2003), make it very unlikely a bat will regurgitate while under anaesthesia. Fasting is also contraindicated in debilitated bats because of their high metabolic rates and greater likelihood of developing hypoglycaemia.
Once chemical restraint is achieved bats should be placed in ventral or lateral recumbency with the head slightly lower than the feet to avoid postural hypotension and accumulation of pulmonary secretions.
The most common IM sites for drug administration are the dorsal neck muscles (Booth 1994) and the body of the scapular and triceps muscles. Avoid the pectoral muscles in insectivorous and carnivorous bats as they largely control wing movement and fight. Poor injection technique causes muscle trauma and scar tissue formation which reduces manoeuvrability in fight. Additionally, bats do not possess a broad sternum and the needle may penetrate between the ribs and enter the thorax if the animal struggles during injection (D Heard pers. comm.).
Heart and respiratory rates vary with changes in anaesthetic depth. Additional responses to monitor include the palpebral reflex (disappears at light to medium depth), pupillary light response, foot grip (the locking mechanism that allows the bat to hang by a foot is lost under deep anaesthesia) and corneal reflex. Loss of the last two responses is indicative of deep anaesthesia.
Due to a high surface area to body weight ratio, hypothermia is common in anaesthetised bats and can occur rapidly. All anaesthetised bats should therefore be provided with supplementary heat. However, the patagium is very sensitive to thermal injury. Electric heating pads, heat lamps and heated water bottles and rice bags must never be used. Appropriate heat sources include circulating water blankets and forced air warmers as used in human operating and recovery rooms. The water pad should be set at 32–38°C. Recovering bats should be maintained in a temperature-controlled cage at 25–28°C. During recovery they should be wrapped to avoid wing flapping, placed in lateral recumbency with their head lower than their feet, and have the feet hooked onto the cage wire or a towel.
6.2.1 Injectable agents
Diazepam (0.5–2.0 mg/kg IM or IV) produces sedation for between 30 min and 4 hr. Highly agitated or aggressive bats require a higher dose than calm bats and duration of effect is generally shorter. Sedation is useful in larger bats to facilitate examination and prior to general anaesthesia.
In pteropodids, medetomidine (0.3–0.8 mg/kg IM) is a useful sedative. However, as with other alpha-2-adrenergic agonists it induces profound bradycardia, poor peripheral circulation and altered thermoregulation. It is antagonised with atipamezole at 5 times the medetomidine dose IM.
Propofol is used for induction or maintenance of anaesthesia in pteropodids. It can be diluted 1:4 with sterile water for accurate dosing in small animals. At 8–10 mg/kg IV it produces rapid induction and 5–15 min of anesthesia, which can be maintained by continuous infusion or repeated boluses. It appears very safe, providing rapid smooth inductions and recoveries (J Barrett & A Olsson unpub). Its disadvantage is that IV administration is difficult if the bat is excited or aggressive.
Ketamine alone is not recommended because of poor muscle relaxation, and struggling and flapping during recovery (Heard et al. 1996a). The addition of an alpha-2-adrenergic agonist (xylazine, medetomidine) improves muscle relaxation, reduces the ketamine dosage and improves analgesia. Several combinations of ketamine and xylazine have been used in pteropodids: 10–20 mg/kg ketamine with 2–4 mg/kg xylazine (Heard et al. 1996a; A Olsson pers. obs.) or 20–40 mg/kg ketamine with 2–4 mg/kg xylazine (J Barrett & A Olsson unpub). The preferred dose rate is 10–20 mg/kg ketamine with 2–4 mg/kg xylazine IM. Induction occurs within 2–5 min, immobilisation lasts 10–40 min and recovery is usually quiet without wing flapping. The combination can be partially antagonised with atipamezole (0.02–0.06 mg/kg IM) but this is not recommended because it may unmask the adverse effects of ketamine (Heard et al. 1996a).
Ketamine (6 mg/kg) and medetomidine (60 μg/kg) combination administered IM has been used to anaesthetise pteropodids. The eyes frequently remain open with this combination and the corneas should be protected with a lubricating ophthalmic preparation. The medetomidine is antagonised with atipamezole at 5 times the medetomidine dose (J Barrett & A Olsson unpub). Note that when dealing with very small volumes of drugs, making a 1:10 or 1:100 dilution with sterile water facilitates accurate dosing of small patients.
Tiletamine/zolazepam (10–40 mg/kg IM) (J Barrett & A Olsson unpub) produces rapid induction and has a wide safety margin. The higher dose rate is used to sedate aggressive animals whose injury or illness necessitates euthanasia. In pteropodids, tiletamine/zolazepam (20 mg/kg) sprayed into the mouth produces rapid and effective immobilisation of unrestrained aggressive animals. This is particularly useful if ABLV infection is suspected (L Vogelnest pers. comm.) and when rescuing pteropodids trapped in netting or barbed-wire fencing. Recovery from tiletamine/zolazepam may be prolonged and violent with wing thrashing and extreme agitation (D Heard pers. comm.; A Olsson pers. obs.).
Following IM anaesthesia, patients should be allowed to recover in dim lighting until the pupillary light reflex returns. Bats placed in a semi-vertical recovery position usually climb to a hanging position within 1–2 hr.
6.2.2 Inhalation anaesthesia
Inhalation anaesthesia is the method of choice for bats. Induction is via induction chamber for very small animals or, for larger animals, a mask using a non-rebreathing system (e.g. Ayre’s T-piece) and precision vaporiser. Anaesthesia is maintained via the mask or an uncuffed (to avoid pressure necrosis of the delicate tracheal mucosa) 2–3 mm endotracheal tube (Heard 1994).
If a pteropodid is aggressive and difficult to handle, an injectable agent can be used for sedation or induction prior to inhalation anaesthesia. If a bat is in shock (e.g. hypovolaemia, endotoxaemia), inhalation anaesthesia is safer than an injectable agent. Ideally, these animals should be stabilised prior to induction.
Isoflurane (induction 4–5%, maintenance 2–2.5%) in oxygen (1–2 L/min) is presently the inhalant of choice because of the wide safety margin and rapid smooth induction and recovery. The bat respiratory system is very efficient and induction (2–3 min) and recovery times are rapid. Although it renders the animal unconscious, isoflurane is a poor analgesic. Opioids or non-steroidal anti-inflammatory drugs are used as part of a balanced anaesthetic regimen for surgery and other painful procedures (Table 14.7).
Atropine (0.02 mg/kg SC) administered at or following induction reduces the profuse pharyngeal secretions occasionally encountered under inhalation anaesthesia in bats, but this is usually unnecessary.
7 CLINICALL PATHOLOGY
7.1 Haematology and biochemistry
7.1.1 Sample collection
In insectivorous and carnivorous bats, total circulating blood volumes range from 4.8–13.0 mL/100 g (Kallen 1977). The volume of blood that can be safely collected is 0.5–1% of body weight, which is roughly equivalent to 5–10% of the total blood volume.
Physical restraint for venipuncture is adequate for some species. However, chemical restraint is recommended for safety and greater control during venipuncture. Keegan (1979) devised a plastic cylinder with a slit through which a wing could be extended, and blood drawn from the cephalic (wing) vein.
Venipuncture in bats <100 g can be performed with either a 0.5–1 mL heparinised syringe and a 25 G needle or a heparinised microhaematocrit tube to draw blood from the needle hub by capillary action or with a calibrated modified micropipette under gentle controlled suction (Gustafson & Damassa 1985). Alternatively, a 25 G needle with the hub snapped off is inserted into a vein and the blood allowed to drip into an open-topped tube containing EDTA or heparin (R Speare pers. comm.).
Cardiocentesis is only performed in anaesthetised bats prior to euthanasia. Blood collection from the infra-orbital sinus is traumatic and unnecessary and therefore not recommended (Baer 1966). The external jugular veins are large in insectivorous and carnivorous bats and are used for collection in some larger species (Heard 2003). In pteropodids they are relatively small vessels and are difficult to access for blood collection (Heard 2003; A Olsson pers. obs.).
Peripheral limb vessels are preferred for venipuncture. These include the median, cephalic (wing) vein and uropatagial veins (Fig 14.1). The median vein is located on the medial aspect of the humerus and yields relatively large volumes of blood rapidly in pteropodids (Heard 1998). It is difficult to access in the conscious animal. The wing or cephalic vein (located along the leading edge of the wing membrane) is readily accessible in all bat species but collapses when even light negative pressures are applied (Figs 14.1, 14.5).
In insectivorous and carnivorous bats the uropatagial (interfemoral) vein is accessed in the tail membrane, close to and parallel with the long bones of the hind limb. In pteropodids, the uropatagial vein is visible across the posterior aspect of the hind foot. To access the vessel for blood collection the bat is placed on a towel so that it grips with its feet. The uropatagial vein is useful in conscious pteropodids (Fig 14.1).
7.1.2 Reference ranges and interpretation
Chiropteran haematology and biochemistry values are similar to domestic carnivore species. Hyperkalaemia (in excess of 8 mEq/L) in otherwise healthy animals is due to prolonged collection time and/or poor technique, or due to collection into EDTA (Heard et al. 2006; Olsson 2000). Bats, particularly pteropodids, have low blood cholesterol, urea and creatinine values (Heard 2003). Table 14.4 provides haematology and biochemistry values for some Australian bats.
Bats usually urinate when restrained. A midstream voided sample can be collected by placing the bat head up and collecting urine in a container (with a funnel) placed under the animal. Gentle stimulation of the urogenital region with a stroking motion using a finger or soft cloth stimulates micturition. Alternatively, cystocentesis can be performed as for small domestic species, with the bat restrained in dorsal recumbency. Urinalysis and urine specific gravity can be interpreted as for domestic species.
The urine of fruit-eating bats may be clear, or range in colour from yellow to pink. Urine composition and odour are influenced by diet. The occasional fruity odour is a normal physiological finding associated with ketone production in an otherwise healthy animal.
7.3 Faecal analysis
Faecal smears, wet preparations and flotation are prepared and interpreted as for domestic species. Stained faecal smears of pteropodids contain relatively low numbers of Gram-positive rods and cocci. Budding yeasts are abnormal. Pollens are frequently seen. It has been our experience that insectivorous and carnivorous bats have predominantly Gram-negative bacteria.
Hand-rearing of bats is well-described in numerous publications (Barnard 1995; Barnard & Sachs 1992; SM Barnard unpub; George 1990; Lollar & Schmidt-French 1998). Indications for hand-rearing include abandonment of the pup by its mother due to disturbance of roost sites or creches and illness or injury in mother or pup. Prognosis for successful rearing of both pteropodid and insectivorous and carnivorous bat pups is good even from birth if proven protocols are followed. Pups with significant injuries (including but not limited to open humerus fractures, open phalangeal fractures, compromised blood supply to more than one-third of the patagium, extensive wing tears, loss of thumbs), congenital defects or serious illness should be euthanased. A limiting factor in the decision to hand-rear bats in some areas is availability of rabies-vaccinated carers.
In the first 4 wk of life, pteropodids have a bare ventrum and difficulty thermoregulating. Naked premature pups have been successfully reared when strict hygiene principles are applied. Neonatal pups are kept wrapped snugly in a triangular cloth (Fig. 14.6). They usually suck the edge of the cloth or a dummy teat. A folded tissue used as a nappy keeps the pup clean. Care is taken to ensure urine and faeces are removed from the skin and wing membranes at every feed to prevent fungal and bacterial infections (see 9.1). Alternatively, the ‘Mumma technique’ is used—wrapping pups to give them more freedom and keep them cleaner (Parry-Jones 2000). With this technique the pup is given a roll of towelling to cling to. The whole roll is then wrapped snugly in a cloth, resembling the mother’s wings. The pup can crawl up and down the roll beneath the covering cloth, and can move away from its urine and faeces.
Initially pups are kept wrapped up in a small pet carrier or basket at 28°C. It is important to expose pups to 10–15 min of sunlight every day during feeding or cleaning as exposure to ultraviolet light is important for drying the skin and may be important in vitamin D synthesis and calcium metabolism (see 9.9.3a). After 4 wk they are encouraged to hang from towelling-covered walls or towels hung on a plastic-coated clothes-horse. Towels are hung as hammocks and curtains to provide a secure environment. Most pups flap vigorously by 4–6 wk and are flying at 8–12 wk. They are housed at this time in a small snake-proof aviary. Towels, foliage and perches are placed at either end with ropes or netting extending to the floor so bats have a way of returning to the canopy if they fall. Bats are encouraged to fly by calling from one end of the aviary (George 1990).
Pteropodids are released in groups once all are flying. Ideally the release cages are winched high into the canopy adjacent to an existing colony (J Maclean pers. comm.). The juvenile bats are allowed to come and go for support feeding for several weeks before the cage is removed.
A number of milk formulae have been used to successfully raise pteropodids (George 1990; Wilson 1988). These include Wombaroo Flying-fox Milk, Complan and Nan Number One (Nestle Australia) human infant formulae and Di-Vetelact (Sharpe Laboratories).
Although flying-fox teats (Wombaroo) are best, little red flying-fox and blossom bat pups require a smaller teat (e.g. a possum teat). For pups less than 4 wk of age, a 10 mL syringe fitted with a teat allows better control of milk flow. This reduces milk aspiration and ensures adequate intake, particularly if the pup has a weak sucking reflex. By 2–4 wk of age, when the sucking reflex is strong, the syringe is replaced with a small glass bottle and by 6 wk pups can lick from a guinea pig self-feeder bottle. Milk or feeding formula is changed every 4 hr and the self-feeder thoroughly cleaned and disinfected.
Newborn pups are fed every 2–3 hr. This is reduced to every 4 hr by 1 wk of age, to every 6 hr by 6 wk of age.
Once pteropodids are hanging and flapping, fruit juice and small pieces of soft fruit are offered and the amount of fruit increased weekly until release. Pteropodids in the wild suckle for at least 6 mo, so milk formula or a high-protein source (e.g. Wombaroo high-protein powder supplement) is added to the fruit, and bottle feeds are withdrawn over this time.
8.1.4 Care of pteropodid pups
The infant must be warm and active (George 1990) before feeding, and the formula should be warmed to body temperature. Care is taken to ensure the milk is evenly warmed to prevent oral and oesophageal burns. It is much easier to feed a bat that is securely wrapped to contain the wings and feet. The head is held slightly lower than the feet and the animal turned to one side. These precautions reduce the risk of milk aspiration.
Before each feed the bat is inverted (head up) and the anogenital area stimulated using a moist finger or soft cloth to induce urination and defecation. This area, as well as the wing pits and membranes, is then thoroughly cleaned with a soft cloth and warm water or baby change lotion. The latter sanitises but does not oil the skin. A full shower under a running tap is usually unnecessary unless major soiling has occurred. After any bathing or sponge-down, the bat is thoroughly patted dry with an absorbent cloth or paper towel. It is then hung in the sunlight for at least a few minutes and encouraged to flap and groom by gently extending each wing in turn. Tickling under the wing will usually produce a wing stretch.
8.2 Insectivorous and carnivorous bats
Most species breed in colonies containing large numbers of bats which keep neonatal pups warm. Consequently, an artificial heat source is required to keep the temperature at 27–38°C (Barnard 1995; Lollar & Schmidt-French 1998). Humidity should be kept at 55–80% (Barnard & Sachs 1992).
Newborn pups are housed in a small bag or box (Hopkins 1990), styrofoam container (Barnard 1995; Barnard & Sachs 1992), or bird brooder (Lollar & Schmidt-French 1998). Whatever the housing, a maximum/minimum thermometer should be used and humidity monitored to prevent hyperthermia and dehydration. As pups become well-furred and more active they are moved to larger cages.
Two formulae are regularly used: Wombaroo Insectivorous Bat Milk and Biolac Puppy Milk (Biolac Milk Products). Insectivorous and carnivorous bats grow and develop very rapidly, and all require high-energy milk with a high fat and protein content in early life.
8.2.4 Care of young insectivo and carnivorous bats
Bats are initially hung upside down to feed to prevent aspiration of milk. Small eyedroppers, IV catheters and other fine tubing apparatus are used to feed pups (Hopkins 1990; Barnard & Sachs 1992; Lollar 7 Schmidt-French 1998). Feeds are small (0.1–0.5 mL depending on species and body weight) and frequent (1–4 hr).