The Super-family Macropodoidea includes 19 species in New Guinea and 49 species in Australia, with three species common to both. Another six species have become extinct in Australia since European settlement, and the ranges and distribution of many others have reduced significantly. There are three extant Families: the musky rat-kangaroo (Hypsiprymnodon moschatus) is the only living member of the Family Hypsiprymnodontidae. All other species are placed in the Families Potoroidae and Macropodidae. In this chapter and others in this volume members of the Super-family Macropodoidea are referred to as ‘macropods’, a term meaning ‘big foot’. Although not strictly correct it is in common usage and generally recognised as the term that encompasses kangaroos, wallabies, potoroos, bettongs and the musky rat-kangaroo. Strictly speaking the derivative ‘macropodoids’ should be used for the Super-family and ‘potoroids’ for the Family Potoroidae and ‘macropodids’ for the Family Macropodidae.
The Macropodoidea are a diverse group ranging in size from 0.5–90 kg body weight and are found throughout Australia. They occupy almost all terrestrial habitats including tropical rainforests, woodlands, open grasslands, deserts, mountains, islands and rocky cliffs (Strahan 1995; Menkhorst 2001). Some species are arboreal, some live in caves and two species are fossorial (Tyndale-Biscoe 2005). Most are nocturnal, while the medium and larger species tend to be crepuscular. They are essentially sedentary, occupy a persistent home range and include solitary non-social species through to gregarious species that live in well-organised societies. The degree of gregariousness generally increases with body size, openness of habitat and proportion of grasses in the diet.
The teeth (diprotodont) and feet (syndactylus) of macropods place them in the Order Diprotodontia. With the exception of the tiny musky rat-kangaroo (Hypsiprymnodon moschatus), they are distinguished from other marsupials by foregut fermentation, hopping and embryonic diapause.
There are two extant Families—the musky rat-kangaroo is the only living member of the Hypsiprym-nodontidae. All other species are placed in a second large Family, the Macropodidae, which comprises three living Subfamilies—Potoroinae, Macropodinae and Sthenurinae.
The musky rat-kangaroo is considered the closest to the ancestral stock from which all kangaroos evolved. Although it superficially resembles the other rat-kangaroos, it is only distantly related. Furthermore, it bounds using all its legs rather than hopping. It is the only macropod with five toes on the hind foot, with digit one being opposable. It is omnivorous and its teeth and stomach, which is simple, resemble those of possums more than other macropods. It does not exhibit embryonic diapause (Strahan 1995; Tyndale-Biscoe 2005).
The Subfamily Potoroinae includes nine species of rat-kangaroo (including bettongs and potoroos), which range in size from 1 kg to 3 kg. Rat-kangaroos hop, but in contrast to kangaroos and wallabies can use their tails to pick up objects such as grass. An upper canine tooth is present, the premolars are very large with prominent flutings on the sides, and the four molars behind them decrease in size from front to back. The molars remain in the same position in the jaw throughout life—unlike wallabies and kangaroos, which exhibit molar progression. The rat-kangaroos have a sacculated forestomach, and all species display post partum oestrus and embryonic diapause (Tyndale-Biscoe 2005).
The banded hare-wallaby (Lagostrophus fasciatus) is the only species in the Subfamily Sthenurinae. It has some of the features of the potoroines and macropodines (Tyndale-Biscoe 2005). One diagnostic feature is the lower incisors that bite against the upper incisors, not behind as in other macropodids. The banded hare-wallaby is now extinct on mainland Australia and survives only on Bernier and Dorre Islands in Western Australia.
The largest Subfamily is the Macropodinae, which consists of 45 species and includes the wallabies and kangaroos. Wallabies and kangaroos are distinguished by size. The six largest species are called kangaroos and the smaller species wallabies (Dawson 1995). The kangaroos are not only united as a group by their size, they are also all grazers and, unlike many of the smaller macropod species, none are endangered (Tyndale-Biscoe 2005).
Three species, the spectacled hare-wallaby (Lagorchestes conspicillatus), red-legged pademelon (Thylogale stigmatica) and agile wallaby (Macropus agilis) are found in both Australia and New Guinea. Only three species are found in Tasmania: the Tasmanian pademelon (Thylogale billardierii), Bennett’s or red-necked wallaby (M. rufogriseus) and the eastern grey kangaroo (M. giganteus) (Tyndale-Biscoe 2005).
The musky rat-kangaroo, four species of bettong, the pademelons, most of the rock-wallabies and the quokka (Setonix brachyurus) have 22 chromosomes. The swamp wallaby (Wallabia bicolor) has the smallest number of chromosomes (10). Another unique feature of the swamp wallaby is that the male has two Y chromosomes, giving a total chromosome number of 11 in the male. The male long-nosed potoroo (Potorous tridactylus) also has an extra Y chromosome, giving a total chromosome number of 13 (Tyndale-Biscoe 2005).
2 ANATOMY AND PHYSIOLOGY
2.1 Musculoskeletal system
Macropods have a distinctive body form which primarily relates to their locomotion. Powerful hind limbs with a long narrow hind foot and powerful fourth toe are characteristic of most species. Rock-wallabies and tree-kangaroos are an exception, having hind feet that are shorter and broader. The hind limbs and pelvic girdle are much longer, larger and more heavily muscled than the fore limbs and pectoral girdle. The animal’s centre of mass is in the pelvis. The major role in propulsion and mass-suspension is performed by the hindquarters (Hume et al. 1989). The femur, tibia, fibula and pes are elongated. The tibia and fibula are closely in contact and the fibula is reduced distally to a thin splint. There is no patella. There is a strongly developed, elongate and load-bearing calcaneum. Movement of the tarsus is restricted to a back and forth motion; it cannot twist sideways. This is partly due to an expansion of the lateral process of the calcaneum. Other than in the musky rat-kangaroo, the first digit of the hind foot is absent and the second and third digits are syndactylous. They are very small and take no part in support or propulsion, but are used for grooming. The fourth digit is the largest. The fore limb is relatively small and poorly developed and has a simple manus with five digits of equal length. No digits are opposable.
The tail is long and may be slender and of uniform thickness along its length or proximally robust depending on its function. It is non-prehensile and cannot be flicked. The tail serves as a balancer when hopping or climbing trees and in the larger species it supports the hindquarters in slow ‘pentapedal’ locomotion. Together with the extended hind limbs, it forms a tripod to help the animal stand and move in a vertical posture. The tail of the quokka is short and does not contribute to locomotion. In nail-tailed wallabies the tail has a horny tip (Strahan 1995). Rat-kangaroos can use their tails to pick up grass and other material.
The atlanto-occipital articulation is very flexible. allowing the muzzle to remain horizontal whether the neck is horizontal or vertical. This flexibility may be associated with some weakness at this articulation, which may account for the high incidence of traumatic fractures at this site (Fig. 7.17).
Dimorphism in macropods is related to size. The smallest species are homomorphic and the largest heteromorphic. In the latter the males and sometimes the females grow throughout life, although at a decelerating rate. The males are significantly more muscular, broad-chested and wide-shouldered. In the large kangaroos the females may be a quarter to one-third the size of the male, making these one of the most heteromorphic mammals. Other than in wallaroos (M. robustus) antilopine (M. antilopinus) and red kangaroos (M. rufus), there are only slight differences in colouration between the sexes. Sex-specific colouration is present throughout life and is not assumed by males only upon social maturation (Hume et al. 1989).
The epipubic bones that extend from the cranial aspect of the pubis are proportionately small in macropods but are fully ossified. Since growth is persistent in macropods, the epiphyses of the limb bones remain unfused during life (Hume et al. 1989).
Some distinct features of the skull include palatal vacuities in some species and a deep mandibular masseteric fossa or canal which allows the deep masseter muscle to gain deep insertion in the mandible below the lower molar teeth (Hume et al. 1989). This is a particular feature of the potoroines and to a lesser extent the macropodines, and is not seen in other herbivorous marsupials (Sanson 1989). Posteromedially, the mandible may be concave for the internal pterygoid muscle attachment. At the inferior edge is a characteristic medially-directed infected angle forming a shelf which is characteristic of most marsupials (Dawson et al. 1989).
In most macropods the mandibular symphysis is not fused and is flexible. This allows the lower incisors to spread apart and shear against the upper incisors. In the banded hare-wallaby and the potoroines the symphysis is more rigid and may be fused.
Macropods have a wide range of dental adaptations reflecting their differing diets (Fig. 7.1). Most macropods have 32 or 34 teeth with the following dental formula: I 3/1 C (1)/0 P (2)1/(2)1 M 4/4 (Hume et al. 1989). In the macropodines P1 is missing. In young kangaroos P2 (a large cutting or sectorial premolar) and a large molar-like tooth, called deciduous premolar 3 (dP3), are present. These provide a shearing and grinding tooth in each jaw. Later, when M1 and M2 erupt, P2 and dP3 are shed and replaced by a single cutting tooth rostral to the molars (P3). As the animal ages the remaining molars, M3 and M4, erupt sequentially behind M2. Occasionally, old eastern grey kangaroos, red kangaroos and wallaroos may have a fifth set of molars (Jackson 2003; Tyndale-Biscoe 2005).
Dentition of macropods is typically diprotodont with a large single pair of forward-projecting lower incisors and a large diastema between these and the premolars. The second and third upper incisors, which tend to lie behind the central incisor in other diprotodonts, lie alongside these in macropodines, forming an arc with a continuous cutting edge, within which the large lower incisors fit. The lower incisors press against a tough pad on the roof of the mouth, just behind the upper incisors. This results in a shearing action when biting. The unfused mandibular symphysis also allows the lower incisors to spread apart and increases the shearing action with the upper incisors. As the mandibular symphysis in the banded hare-wallaby and potoroines is fused, the lower incisors meet the upper incisors directly. Canine teeth, while fairly well-developed in the potoroines, are absent or vestigial in the macropodines, other than tree-kangaroos which have a small canine tooth in the maxilla. As in the mandible, there is a diastema between the upper incisors and first premolar (Sanson 1989; Strahan 1995; Tyndale-Biscoe 2005) (Fig. 7.1).
The main difference between potoroine teeth and macropodine teeth is the size and structure of the molars. In all macropodines the four cusps are joined in pairs to form high transverse ridges or lophs, unlike the rounded teeth of potoroines. In the macropodines, additional ridges called links also develop at right angles to the lophs (lophodont molars). In the potoroines, lateral chewing is possible while in the macropodines lateral movement of the mandible is restricted by the position of the lower incisors inside the upper incisor arc. In macropodines, the chewing is more a forward and backward motion with a small degree of sideward motion (Tyndale-Biscoe 2005).
The dentition of macropods has been graded on the basis of degree of adaptation to processing their diets. This is based on the size of P3 and the height of the molar lophs and links, and whether the molar rows are flat or arched (Sanson 1989; Hume 1999).
2.2.1 Potoroids and basal macropodoids
These include the musky rat-kangaroo and the Potoroidea. They primarily eat invertebrates, fruits and seeds. Thus they are ingesting and masticating a variety of materials with quite different physical properties. The premolars are well-developed longitudinal shearing blades and are used to cut or open food items to liberate the contents. The molars are therefore used primarily for crushing and grinding. The premolars are retained throughout life. The molar row is flat with all teeth in occlusion. The gape in these species is larger than other macropods, allowing the ingestion of larger food items.
These include the pademelons, quokkas and swamp wallabies that browse on shrubs and soft plants, and the tree-kangaroos which feed on tree foliage. All have moderately large premolars which are used for cutting (Fig. 7.1a). They are retained throughout life. The retained P3 blocks molar progression. This may result in M1 and occasionally M2 being squeezed out from behind P3 due to molar drift. The four molars in each jaw erupt early in life and are flat with all opposing molars in occlusion. The links between lophs are small. The molars can both shear and crush. Rock-wallabies, whose diet includes more grasses, still retain P3 and some have arched molar rows. The short-eared rock-wallaby (Petrogale brachyotis) does not eat much or any grass and has a large P3. The nabarlek (P. concinna), however, sheds P3 so the molars move forward in the jaw, and because the rows are arched the molars do not all occlude at the same time. The enamel on the molars is thin and the teeth wear down quickly and are replaced by others behind them. The nabarlek is unique in that it has unlimited molar replacement. This is possibly an independently acquired adaptation to feeding on grass.
2.2.3 Intermediate browser-grazers
This includes the hare-wallabies, nail-tailed wallabies and the eight species of wallaby in the Notamacropus Subgenus (M. agilis, M. dorsalis, M. eugenii, M. greyi, M. irma, M. parma, M. parryi, M. rufogriseus). These species are predominantly grazers but will also browse. Their premolars are small and are occasionally shed, allowing some forward movement of the molars (Fig. 7.1b). The molars have higher lophs and well-developed links between them. The opposing molar rows are arched so that occlusion and wear occurs successively throughout life from M1 to M4.
These are the true grazers and feed predominantly on grass which is relatively uniform in physical properties; the food items are smaller than the teeth. The gape of these animals is small. These are the six species of large kangaroos. The premolars are vestigial and are usually shed before all the molars have erupted. The molars have very pronounced lophs and well-developed links between them. Each molar row is strongly curved, with the upper and lower row curving in opposite directions so that only two pairs of molars occlude on each side at any one time (Fig. 7.1c). The molars are adapted for shearing. A feature of this group is molar progression, a phenomenon shared only with elephants, dugongs and manatees. Molar progression is the sequential eruption of the molars. Each whole row of molars moves forward in the jaw throughout life, with the most worn-down molars being shed from the front. In old animals, only the worn-down M3 and M4 may remain.
Figure 7.1 Lateral view of the skulls of macropod species showing dentition. a) A browser. b) An intermediate browser-grazer. c) A grazer.
The rate at which molar progression takes place is related to the quality of grasses eaten. Although there is variation in the rate of molar progression with the type of diet, the rate is reasonably constant within species and can be used for ageing some macropods.
Molar progression can only be used to estimate age in living macropods with the use of radiography. In the dead animal it is relatively simple. A molar index can be calculated and has been used to determine the approximate age of several macropod species (Kirkpatrick 1964; Kirkpatrick 1965; Kirkpatrick & Johnson 1969; McCauley 2003; Jackson 2003).
Molar eruption can also be used to determine the age of macropods and has been determined for several species (Jackson 2003). This is done by observing the proportion of the molar teeth that have erupted from the gum line. This system can be used in the live animal without radiography, and can potentially be used in species that do not exhibit molar progression. The limitations of this method are that it cannot be used to age animals once all molars have erupted and the gape of most macropods is small, making it difficult to examine the inside of the mouth. Most macropods would not tolerate it without chemical restraint. The mean age at which M4 is fully erupted varies between and within species and the literature is somewhat confusing in the ages quoted (Jackson 2003 and references therein). In red kangaroos, complete eruption of M4 is at the age of at least 6 yr (Sharman et al. 1964).
Both molar eruption and molar progression are highly correlated with age; however, the use of molar progression is less accurate. Sexual dimorphism occurs in both molar eruption and progression, with males acquiring their teeth earlier than females, and probably correlates with sexual heteromorphism of a particular species (Jackson 2003).
2.3 Gastrointestinal system
Wallabies of the Subgenus Notamacropus as well as the swamp wallaby have an unusual oesophagus lined with numerous elongate papillae (Obendorf 1984).
Macropods are foregut fermenters and the advantages of foregut fermentation are the same as those for ruminants. However, the anatomy of the macropod stomach is quite different from that of ruminants (Freudenberger et al. 1989; Hume 1999; Tyndale-Biscoe 2005). It is large and sacculated (Fig. 7.2). There are four parts that each have distinct functions. The oesophagus opens into a funnel-shaped region, which extends along the inner curvature of the stomach as a partly closed spiral groove and, like the oesophagus, is lined by squamous epithelium. It separates fine from coarse plant material and directs the fine material to the hindstomach, which is lined with an epithelium that secretes hydrochloric acid and proteolytic enzymes. Coarse plant material is directed to the forestomach, where bacterial fermentation takes place. This is the largest part of the macropod stomach and is divided into the sacciform and the tubiform forestomachs (Fig. 7.2). Both are lined with glandular epithelium that only secretes mucus. The pH in the sacciform region is maintained between 4.6 and 8.0 by the buffering action of the mucus and saliva from the parotid salivary glands, which is released during chewing. Bicarbonate, phosphate and sodium ions maintain the alkaline pH and support bacterial growth in the forestomach, which contains large populations of bacteria and ciliated protozoa. The bacteria digest the cellulose of the plant cell walls anaerobically, forming short-chain fatty acids that provide a rich source of energy (Tyndale-Biscoe 2005). Forestomach fermentation may further benefit the host by detoxifying plant chemicals and producing B vitamins. The musculature of the forestomach wall is organised into three longitudinal taeniae. Semi-lunar folds between the taeniae form haustrations that give the stomach a colon-like appearance (Freudenberger et al. 1989).
The musky rat-kangaroo has a simple stomach with low pH, no forestomach regions and no bacterial fermentation. In the Potoroidae, tree-kangaroos and pademelons, the sacciform forestomach is larger than the tubiform forestomach, which reflects their more digestible diet and lower requirement for fermentation to break down cellulose (Hume 1999) (Fig. 7.2 iii).
There is also a trend toward increasing relative size of the tubiform forestomach with increasing body size. Consequently, the browsers, which are relatively smaller in body size than the grazers, have a larger sacciform region of the forestomach (Fig. 7.2 ii). In grazers the tubiform region is larger. The forestomach contents of kangaroos can be 9–15% of total body weight (Dawson 1995).
The caecum and proximal colon of macropods is relatively small and although they contain some fermentative bacteria, they contribute little to digestion. The distal colon is an important site for the absorption of water from the faeces. The length of the colon varies with the types of habitat of the species. In the forest-welling species the distal colon is short and their faecal pellets have high water content, while arid zone species have a long colon and faecal pellets with low water content (Tyndale-Biscoe 2005).
Figure 7.2 Gastric morphology of macropod species. i) Grazer. ii) Browser. iii) Potoroidae, tree-kangaroo and pademelon. a) Tubiform forestomach. b) Oesophagus. c) Sacciform forestomach. d) Taenia. e) Hindstomach. f) Pylorus. (Source: After Hume (1999) and Tyndale-Biscoe (2005).)
In a process known as merycism, macropods, particularly the browsers and grazers, occasionally regurgitate food into their mouths. Merycism involves a rather violent heaving motion with vigorous movements of the fore limbs and thorax. Occasionally the bolus of ingesta may spill out of the mouth. The bolus is not generally re-chewed, unlike ruminants, and is quickly re-swallowed. The function of merycism is unknown (Dawson 1995).
In pouch young, before they start to eat herbage all regions of the stomach have a low pH and are proteolytic. It is only when the PY leaves the pouch permanently that the forestomach becomes a functional fermentation chamber with neutral pH. It also becomes colonised by bacteria and protozoa, which are presumed to come from the mother. At this time the PY is frequently seen to contact the mother’s mouth, and stomach contents may be passed to the PY during merycism. This behaviour resembles and serves the same function as pap feeding of koalas and wombats and coprophagy in some possums (Dawson 1995; Jackson 2003; Tyndale-Biscoe 2005).
Macropods generally have thin skin, particularly in the inner surfaces of the limbs. This is particularly pronounced in the fore limbs, where there is significantly increased vascularity of the subcutis. This allows the animals to lose heat by evaporation of saliva, which they lick onto their forearms. The skin of the neck, shoulders, chest and abdomen tends to be thicker in males than in females. The skin on the ventral surface of the tail is also thickened.
Female macropods have four teats on the abdominal wall within the pouch. Teats are a few millimetres in length in the nulliparous animal. The teat enlarges when being suckled by a PY. At weaning it is about the length of the palate of the young-at-foot. It can be pulled out of the pouch to enable suckling by the emerging young while standing outside the pouch. After weaning the teat regresses, but it remains longer than an unsucked teat. The pouch of a multiparous female typically contains teats of different sizes. Each PY sucks on only one teat. Males lack teats.
Eccrine sweat glands are present on the hairless surfaces of the paws and feet and apocrine sweat glands are distributed over the rest of the body surface. The most developed apocrine sweat glands occur in the axillary and sternal regions. Aggregations of large apocrine glands are found around the scrotum in males and the cloaca and pouch area in females. The sternal glands are larger in males. Sebaceous glands are associated with hairs and these are particularly abundant in the sternal and axillary region in males, and around the cloaca and in the pouch of females. The oily secretions from these glands can be odorous and pigmented, particularly in males. The characteristic reddish-brown pigment of the sternal patch results from tryptophan derivatives in the apocrine secretion, which cause internal pigmentation of the hair and produce a pigment which adheres externally to the hair shafts. There are seasonal fluctuations in the amount of sternal gland secretion in some species (Hume et al. 1989; Dawson et al. 1989).
Two types of paracloacal glands are found within the cloaca: a holocrine sebaceous type and a cell-secreting type. These lie in pairs along the lateral cloacal walls and drain into the cloaca by single thin-walled ducts. These glands are small and cyst-like, and are invested in a thin striated muscle capsule. The sebaceous glands produce a pale yellow pungent secretion. The cell-secreting glands secrete an odourless cell suspension in an aqueous phase. These secretions are often released during handling and are a component of urine, are coated on faeces and used for marking (Hume et al. 1989; Dawson et al. 1989).
The two gaits used by macropods are pentapedal locomotion and bipedal hopping. In pentapedal locomotion the tail is used, with the fore limbs, as the third leg of a tripod to support the animal while the large hind limbs are moved forward together. This form of locomotion is used at speeds below 6 km/hr and is ungainly and energy-inefficient. Smaller macropods are able to hop even at low speeds. When hopping, the tail assists balance, but neither the tail nor the fore limbs provide support. Hopping is an economical way to travel for a large mammal, but there is less mechanical and physiological advantage for species of less than 5 kg body weight. Kangaroos can swim and when doing so the hind limbs are moved independently and alternatively (Hume et al. 1989).
At speeds of over 15 km/hr, hopping is more energetically efficient than running for similar sized species. The most economical speed for kangaroos to travel is around 20–25 km/hr. Large kangaroos can reach speeds of up to 70 km/hr (Tyndale-Biscoe 2005). Hopping rate remains constant up to about 40 km/hr with the increase in speed achieved by increasing length of stride. At speeds of 60–70 km/hr there is a noticeable increase in stride frequency and stride length, probably accompanied by a marked increase in energy consumption (Dawson et al. 1989).
2.6 Metabolism and thermoregulation
As a generalisation, macropods have a metabolic rate that is about 25% lower than that of comparably sized eutherian mammals. While this relatively lower basal metabolism impacts on macropod (and most other marsupials) physiology it does not mean that macropods are not capable of expending large amounts of energy. To compensate for the lower metabolic rate, the larger macropods have hearts one-third larger than those of comparably sized eutherian mammals. They can also move more air through their lungs with each breath (Dawson 1995).
Macropods, like most marsupials, have a resting body temperature of around 36°C. When faced with high ambient temperatures the first thing a macropod will do is try to avoid it by seeking shade (Hume et al. 1989). They may also adopt particular postures (e.g. crouching) to expose a smaller surface area for radiant heat inflow (Dawson 1995). Similarly, in cold windy conditions macropods will seek shelter. In winter some species have thicker pelts. Macropods also shiver to generate heat.
Once ambient temperatures approach or exceed body temperature, thermoregulation is by evaporative mechanisms. These mechanisms are also used to dissipate heat after exertion. This may be the result of obvious physical activity or increased muscle activity as a result of severe anxiety. Three mechanisms of evaporative heat loss are used: panting, sweating and licking. The mechanism of cooling by panting is no different from other mammalian species. Macropods also sweat. A unique feature of kangaroos is that sweating stops as soon as exercise stops, even if body temperature is still elevated and the animal is still panting rapidly. This may be related to economy in water loss (Dawson 1995; Tyndale-Biscoe 2005). The third method of evaporative heat loss is spreading saliva on the forearms. This saliva is produced by the maxillary salivary glands and has a different composition from the parotid saliva secreted during feeding. The area under the thin skin of the forearms has a dense superficial network of fine blood vessels and as the saliva evaporates it cools the blood in the veins. There is a marked increase in blood flow to the forearms in hot conditions. Antilopine kangaroos salivate on the inner thigh and this region is also highly vascularised. Males of all species also lick the scrotal region when hot. Salivating on the forearms is a common method of cooling in macropods that have undergone a period of exertion or anxiety. This can be used by the clinician as a guide to when an animal is stressed or overheating. Procedures should be aborted or cooling applied to avoid capture myopathy (see 9.10.3a).
2.7 Sensory systems
Macropod eyes are positioned high in the skull, giving them a wide field of vision, but at the same time the forward field of each eye overlaps that of the other by about 25°. This wide field of peripheral vision enables them to see movement in almost every direction, and the binocular vision enables them to have more precise close vision (Tyndale-Biscoe 2005). They have good vision both day and night. Despite this, they appear to have difficulty navigating obstacles and barriers that are not solid (e.g. wire fences), especially when alarmed and fleeing. Under these circumstances collisions are common. Colour vision has been demonstrated in the tammar wallaby (M. eugenii), particularly in the blue to green spectrum (Hemmi 1999).
The macropod iris is thick and uniformly brown. The pupil is circular and can be dilated easily with one drop of tropicamide. The fundus is heavily pigmented ventrally and is usually dark brown. The dorsal area of the fundus is usually lighter in colour and in some animals the choroidal blood vessels can be seen through the pigment. The optic disc sits on the junction between these two zones. The optic disc is well vascularised. Retinal vessels are not prominent and the macropod retina appears relatively avascular. All macropods have persistent hyaloid vessels. These are seen as a tuft of vessels arising from the centre of the optic disc and extending anteriorly into the vitreous toward the posterior capsule of the lens but not touching it. The prominence of the vessels varies between individuals and species. The vessels are thin-walled capillaries. In most macropods the plexus is fixed anteriorly and is not easily visualised on ophthalmoscopic examination. If not fixed, the plexus may be seen moving within the vitreous. In many kangaroos, myelination of the nerve fibre layer can be seen extending 2–3 disc diameters from around the optic disc. This myelination is generally most obvious in the lateral and medial aspects (Stanley 2002).
Most kangaroos and wallabies have large ears which can move independently through 180°. In contrast, tree-kangaroos have short rounded ears, which are not mobile.
2.8 Immune system
Passive transfer of immunity and the development of the marsupial immune system are reviewed in Chapter 2. The macropod thymus is a paired structure found SC on the ventral side of the neck. The shape and extent vary with species. In the healthy PY they are firm bulging structures with the caudal border level with or just beyond the clavicles. The medial border is close to the midline but separate from the opposite thymus. The lateral border does not extend beyond the ventral surface of the neck and the cranial limit is close to the angle of the jaw. In most species they are pear-shaped structures with the narrow part cranially In unfurred or early furred PY the thymi can be visualised. The thymi regress fully by sexual maturity (Speare 1988; Tyndale-Biscoe 2005).
Superficial lymphnodes are not palpable in the healthy macropod. The spleen is Y-shaped and straplike.
2.9 Reproductive system
The anatomy of the female macropod reproductive tract is similar to that of other marsupials (Fig. 7.3). The completely separate uteri (no marsupials have a single chambered uterus) open by separate cervices into the vaginal cul de sac which is divided by a median septum (Dawson et al. 1989). Two separate lateral vaginae arise from the vaginal cul de sac. The caudal ends of the lateral vaginae open into the urogenital sinus, which also receives the urethra. Caudally, the two lateral vaginae may unite for a short distance before joining the urogenital sinus. The two lateral vaginae are separated by a mass of fibrous connective tissue called the urogenital strand. Prior to each parturition a pseudovaginal canal forms within the urogenital strand, connecting the vaginal cul de sac cranially with the urogenital sinus caudally to permit the passage of the foetus (Tyndale-Biscoe & Renfree 1987; Dawson et al.1989). The urogenital sinus, together with the rectum, opens into the common vestibule or cloaca.
Figure 7.3 The female macropod urogenital tract. a) Kidney. b) Ovary. c) Uterus. d) Cervix. e) Vaginal cul de sac. f) Ureter. g) Median vagina. h) Lateral vagina. i) Bladder. j) Urogenital sinus.
In most species of Macropodidae the pseudovaginal canal becomes epithelialised after the first parturition with cuboidal epithelium of the vaginal cul de sac and merges with the stratified squamous epithelium of the urogenital sinus. This remains patent as a permanent median vagina. However, as is the case in most marsupials, the musky rat-kangaroo, the Potoroidea, banded hare-wallaby and the eastern grey kangaroo, the pseudovaginal canal closes rapidly after the passage of the foetus and reforms with each subsequent parturition (Tyndale-Biscoe & Renfree 1987; Dawson et al.1989). After copulation, semen is deposited in the lateral vaginae and sperm travel up the lateral vaginae, through the two cervices and uteri to the oviducts where fertilisation occurs.
The anatomy of the male macropod reproductive tract is similar to that of other marsupials. Paired testes and epididymides are located externally in a pendulous, pedunculated prepenile scrotum. A strong active cremaster muscle encloses the spermatic cord and retracts the scrotal contents tightly against the pelvic body wall in cold weather or when stressed. When relaxed and in hot weather the scrotum hangs very low. The incidence of scrotal pigmentation is variable in adult macropods, with some heavily pigmented and others not at all. There is a 2.5–5°C temperature differential between body and testicular temperature. Kangaroos are able to maintain normal spermatogenesis at much higher ambient temperatures than eutherians of similar size. The vas deferentia join the prostatic urethra close to the neck of the bladder. Seminal vesicles and ampullae are lacking in marsupials. In macropods, three pairs of bulbourethral glands and a relatively large carrot-shaped disseminate prostate are the only accessory sex glands (Dawson et al. 1989; Hume et al. 1989). The Macropodidae are the only Australian marsupials to produce semen which coagulates to form a seminal or copulatory plug in the female’s urogenital sinus and vaginae after ejaculation (Jones 1989; Dawson 1995; Paris et al. 2004). If protruding from the cloaca, the copulatory plug can be mistaken for a prolapse. Unlike a prolapse, which is rare in macropods, the plug usually disappears after a day or so.
When relaxed, the penis is sigmoid-shaped in a preputial sac in the common vestibule. The penis is rarely exposed other than during urination and erection. Unlike most other marsupials, the macropod penis is not bifid and the tip is sharply tapered.
The scrotum is discernible shortly after birth and the testes have descended completely by about 90 d in the parma wallaby (M. parma) and 70 d in the tammar wallaby. There is no seasonal variation in the size of the testicles or sperm production in male macropods. In prolonged severe droughts sperm production is reduced. Macropod sperm are short-lived, surviving no more than 24 hr in the female reproductive tract (Tyndale-Biscoe & Renfree 1987; Dawson et al.1989).
2.10 Urinary System
The urinary system is not significantly different from that of other marsupials. The urethra of male macropods has paired valve-like cusps approximately 2–3 cm proximal to the external orifice. Each cusp is approximately 5 mm long, with its free margin directed toward the external urethral orifice. Histologically, each cusp consists of transitional epithelium overlying a submucosa of poorly vascularised fibrous connective tissue. The epithelium and submucosa is continuous with the corresponding layer in the remainder of the urethra. A similar but larger pair of cusps lies immediately distal to the urinary bladder sphincter. The distal pair of cusps are on the lateral aspects of the urethra, are not near the ischial arch and are not associated with the bulbourethral gland. Although the functional role of these cusps is unclear, they may inhibit the retrograde movement of microorganisms that gain access to the urethra (Hatkin & Janssen 1979). These cusps can make urethral catheterisation difficult (see 9.4.1).
Tintibulation is an apparent expression of anxiety or excitement in macropods. It is manifest by a wide-eyed expression and trembling of the head, neck and upper body. It is frequently seen in hand-reared animals that have a tendency for a nervous temperament. It is of no clinical significance.
3.1 Oestrous cycle and pregnancy
All macropodid species that have been studied are monovular and polyoestrus with cycles ranging from 22–46 d (Table 7.1). There is a clearly defined pro-oestrus during follicular development. Ovulation is spontaneous and alternate and occurs within 2 d of oestrus. The resulting CL secretes progesterone which controls the development of the luteal phase. A rather poorly defined post-luteal phase follows as the CL regresses. In an unmated female this phase merges with the next pro-oestrus phase and ovulation. Since macropodids are monovular with alternate ovulation, in each pregnancy there is one gravid uterus ipsilateral to the CL and one non-gravid uterus ipsilateral to the developing follicle. The life-span of the CL does not extend much beyond the length of the oestrous cycle. Gestation therefore extends into the post-luteal and pro-oestrus phases without suppressing follicular growth, so that ovulation occurs within a few days before or after parturition—the post partum oestrus (Tyndale-Biscoe & Renfree 1987). If conception occurs, the resulting zygote develops to blastocyst stage where it remains in diapause as long as lactation occurs, i.e. until the first PY’s final emergence from the pouch or loss of the PY. Therefore, as in all marsupials and unlike eutherian mammals, conception does not interrupt the oestrous cycle. Lactation does. The release of prolactin suppresses full development of the new CL and the next luteal phase does not occur. In tammar and red-necked (Tasmanian subspecies only) wallabies this persists for several months after weaning due to seasonality of breeding (Hume et al. 1989).
Embryonic diapause is characteristic of macropod reproduction, with the exception of the western grey kangaroo (M. fuliginosus), Lumholtz’s tree-kangaroo (Dendrolagus lumholtzi) and musky rat-kangaroo, in which it does not occur. In the eastern grey kangaroo, parma wallaby and whiptail wallaby, post partum oestrus does not occur, but the females may come into oestrus and mate when the PY is older. Under favourable conditions female eastern grey kangaroos may mate when the PY is greater than 5–6 mo old, with the resulting embryo remaining in diapause due to lactational inhibition. In the swamp wallaby oestrus always occurs about 7 d prepartum.
The CL holds a central position in the control of reproduction in the Macropodidae. However, unlike other marsupials the CL does not provide the sole stimulus to the uterus to maintain gestation; the foeto-placental unit assumes this function in the second half of gestation and determines the length of gestation. The length of the luteal phase, the follicular phase and the placental influence determine whether ovulation is prepartum, post partum or absent in the different macropod species (Hume et al. 1989). The reproductive cycle of macropods differs from other marsupials in that gestation is extended from about half the oestrous cycle to occupy almost all of it, with birth occurring 1–2 d before the next oestrus (Dawson 1995). The gestation period for most macropods is 25–35 d and is shorter than the oestrous cycle in all species other than the swamp wallaby (Table 7.1).
The gestation period of macropods is considerably longer than most other marsupials. As a result, the newborn PY is relatively larger and more developed than non-macropod marsupials. This more advanced development, particularly in neurological organisation, is significant in that it reduces the risk of the single PY going astray on its journey to the pouch and attachment to the teat (Dawson 1995; Tyndale-Biscoe 2005).
In marsupials the foetus develops within an egg. The egg has a full set of shell membranes but they are much reduced compared to reptiles and birds. The yolk is also very small. In macropods the shell membranes persist for much of pregnancy, rupturing only in the last third of gestation. In macropods (and some other marsupials) there is complete loss of the allantois as the placental attachment, but it remains as a small intact vascular sac and probably functions only as an excretory store. The allantois expands rapidly near full term. The yolk sac is well developed and vascularised and is the only connection between mother and foetus. This choriovitelline placenta fulfils all the nutritive and respiratory requirements of the foetus (Dawson et al. 1989; Hume et al. 1989; Tyndale-Biscoe 2005).
Macropods are either continuous breeders or seasonal (Table 7.1). The basic reproductive pattern of macropods is controlled by lactation. However, under adverse conditions animals may become anoestrus. True seasonality, as seen in the tammar wallaby, quokka and red-necked wallaby (Tasmanian subspecies only), is controlled by day length. This occurs by either prolonging diapause until after the summer solstice, called seasonal quiescence, or by undergoing seasonal anoestrus (Tyndale-Biscoe 2005).
Table 7.1 Reproductive parameters of selected macropod species
Reproduction in the tammar wallaby has been studied more than any other species. They have a strictly seasonal breeding pattern. Female tammars mate approximately 1 hr after giving birth and the resulting conceptus grows to a 100-cell unilaminar blastocyst, which normally remains in diapause for 11 mo. Diapause is initially maintained by the sucking stimulus of the PY (lactational diapause) between January and late May, and by photoperiod control (seasonal diapause) between June and December. Soon after the summer solstice (22 December) the photoperiod inhibition ceases, the CL is reactivated and the blastocyst resumes development, with birth occurring in late January (Tyndale-Biscoe 2005).
3.2 Parturition, lactation and neonatal development
Maternal responsibilities in marsupials can be divided into five stages: parturition; parturition to first emergence from the pouch; first emergence to permanent emergence; permanent emergence to weaning; and the post-weaning period. Macropods typically have a reproductive sequence consisting of vacation of the pouch by one PY, birth within a couple of days, a post partum oestrus, conception and brief development of the embryo, then diapause of the embryo until the PY is within about 4 wk of permanently vacating the pouch. Embryonic development then recommences.
As the marsupial neonate is so small and fragile the mother must ensure the best chance of it reaching the pouch and attaching to a teat. One of the first signs of impending parturition is intense cleaning of the pouch. This starts 1–2 d before birth and is most intensive 1–2 hr before birth. Licking of the urogenital area also increases in intensity prior to birth. The female also adopts a birth position which is characteristic for the different species of macropod (Renfree et al. 1989). Parturition and maternal behaviour is under precise hormonal control. These include prolactin, oxytocin and prostaglandin. Progesterone declines rapidly prior to birth. The neonate climbs through the fur, taking about 3 min to reach the pouch in kangaroos. Once in the pouch the neonate attaches to a teat within a few minutes. Throughout pouch life the mother continues to clean her pouch and consumes the PY’s urine and faeces. Licking of the PY’s cloaca stimulates urination and defecation. Growth rate of the PY is variable between species, as is the time to permanent emergence (Table 7.1). Typical length of pouch life ranges from 150–320 d and varies between species. The PY remains permanently attached to the teat for about the first half of pouch life (Hume et al. 1989; Tyndale-Biscoe 2005).
The majority of macropods have only one young. Twins have been reported rarely in some species. The only species of macropod that routinely produces twins and even triplets is the musky rat-kangaroo (Jackson 2003). As the interval between young in the Potoroidae is short they can produce up to three young a year. All other macropods are not able to fully raise more than one young in a year. They can, however, have three young at different stages of development: one in embryonic diapause; one in the pouch attached to a teat; and one that has vacated the pouch permanently but occasionally suckles (a young-at-foot).
Lactation in marsupials is unique in that it sustains the neonate from an almost embryonic form after birth to a young-at-foot prior to weaning. This period may last over a year in some species. In all macropods there is a choice of four teats for the single young. Once attached, the PY remains on the same teat throughout pouch life. The mammary glands do not reach maximal milk production until some months after birth.
There are marked changes in milk composition throughout lactation, corresponding with changes in the sucking regime of the PY from continuous to intermittent. The most marked changes in milk composition appear to be associated with increased secretion of prolactin (at 20–24 wk in the tammar wallaby). This change in milk composition is also associated with a marked acceleration in PY growth rate. As macropods can have two young at different stages of development (a PY and young-at-foot), they can produce milk of two different kinds from adjacent mammary glands simultaneously. As there is also variable sensitivity of the mammary gland to oxytocin at different stages of lactation, milk ejection can occur semi-independently in adjacent glands in response to suckling by a tiny PY or a young-at-foot (Hume et al. 1989; Tyndale-Biscoe 2005).
Following permanent emergence from the pouch, the PEY (pouch emergent young) may spend many months getting in and out of the pouch. Once denied re-entry into the pouch (usually just before birth of the next young), the PEY still follows its mother and continues to suckle by putting its head into the pouch. This is a typical pattern for the larger species of macropod. In contrast, in the smaller species the period of getting in and out of the pouch is much shorter (a few days to weeks). Once permanently out, the PEY is often left alone under cover while the mother goes away to feed (Hume et al. 1989).
Hybridisation, both within Genera and between different Genera of macropods, can occur. Most hybrids are sterile, and may have reproductive organ and pouch abnormalities and physiological and behavioural incompatibilities between mother and PY. For example, the genetically determined length of pouch life and duration of weaning and milk production and milk composition may be asynchronous between mother and PY, resulting in rejection of the PY or incompatibility with the PY’s needs for growth and development. Great care needs to be taken to prevent hybridisation. It rarely occurs in the wild but may occur in captivity where macropods are held in mixed facilities with small mobs of different species. Animals preferentially choose the same species with which to breed (Jackson 2003; McCauley 2003).
The husbandry of macropods requires an understanding of spatial, social and behavioural requirements and responses to stressors and disease. The veterinary management of sick or injured macropods must also take these factors into consideration as not doing so may compound the animal’s problem, primarily through stress. The husbandry requirements of macropods are covered in detail by Jackson (2003) and in the Exhibited Animals Protection Act 1995; readers are referred to these sources for detailed information.
4.1 Housing and husbandry
Macropods are a diverse group of animals that have adapted to a wide range of habitats. Consequently, their housing and husbandry requirements are equally diverse.
Enclosures for macropods must take into account the unique requirements of the species and wherever possible mimic the natural environment for the species. Both the physical and psychological needs must be met. Many macropods are prone to stress and stress-related disease. Enclosures should provide a stress-free environment that includes adequate shelter, privacy, elevation, climbing structures and other furniture. All animals should be provided with a means of sheltering from wind, rain and extremes of sunlight and temperature. Although many macropods live in arid environments they do not necessarily cope well with high ambient temperatures. Most species seek refuge from heat during the day. Conversely, heating may be required for some species in cold climates. Many macropod species are nocturnal and are better suited to nocturnal displays.
Where possible, enclosures should allow for easy observation of animals from a distance (for public and staff) to minimise stress from being approached too closely. Where visitors are permitted to go into an enclosure, areas should be provided where the animals can seek refuge from unwanted visitor attention. Areas should also be provided where animals can have privacy and seek refuge and hide from other animals in the enclosure. Enclosures should be large enough to allow for the normal activity of the species and prevent overcrowding and for animals to get away from each other. Most macropods require a relatively larger area than other marsupials (Jackson 2003).
Macropod enclosures are best kept simple and free of obstacles. Fencing and other enclosing structures must be carefully designed. Macropods are prone to fence-running when stressed or being pursued and will collide with the fence or obstacles protruding from it. Fence posts should be outside the enclosure so the inside fence line is smooth and free of obstacles. Where possible, fence lines should be relatively straight and without corners. The height of the fence will depend on the species with the highest fences, about 1.8–2.4 m high, required for kangaroos at. Fences should be made of chainlink or similar mesh or solid material. Mesh size should be small enough to prevent the animals getting their heads and arms through if there are other macropods in an adjacent enclosure. Males often fight through fences, causing abrasions and even severe bite wounds on the arms (C Herbert pers. comm.). The fence should also prevent entry of predators such as foxes and dogs by preventing access to the enclosure through, under and over the fence. If climbing species (musky rat-kangaroo, rock-wallabies, tree-kangaroos, bettongs) are to be held in unroofed enclosures, the fences should be made of material (smooth tin, corrugated iron, timber or brick) that is unclimbable or is rimmed by a 45° outrigger 0.5 m wide facing into the enclosure. When alarmed, macropods are prone to colliding with fences if they are not clearly visible. Shadecloth or hessian attached to the fence is useful as a site barrier and should always be in place when introducing animals to new enclosures (Williams 1990; McCauley 2003; Jackson 2003).
Enclosure furniture and planting should be appropriate for the species. Arboreal species such as tree-kangaroos should be provided with adequate climbing structures and thick shade. Rock-wallabies require a rocky mound with crevices for hiding. Macropods can be very destructive to vegetation and plants within an enclosure. Plants need to be chosen carefully for resilience and toxicity. Most plants will need protection from the animals, with barriers. Many macropods use grass tussocks, bushes and shrubs to hide or nest in (Williams 1990).
Substrates should be readily cleanable to allow regular removal of faecal material. They should be well-drained and not remain damp, to prevent the build-up of parasite oocysts and larvae, and bacteria. This is particularly important around feed and water points where animals congregate. Uneaten food must be removed daily to prevent build-up of bacteria and fungi and not attract pests. Grass, sand, soil or leaf litter are suitable substrates for most macropod species.
Feed and water containers should prevent contamination with faeces and urine, prevent access by pests and be readily cleaned and disinfected. This will aid in preventing build-up and spread of parasitic and bacterial infections and attracting pests. Feed areas should be under cover. Feed dishes, troughs, pellet hoppers and hay racks should be kept off the ground. This reduces the risk of food contamination with faeces and urine by preventing animals sitting in them. Feed areas should ideally have a concrete slab so that spilled feed and faeces can easily be picked up. Several feed areas may be required if there are a large number of animals in the enclosure. Fresh clean water should be provided in ponds, troughs or self-filling waterers. These should be cleaned regularly.
Enclosures must include suitable facilities to allow for capture, restraint and holding (off-exhibit) for sick or injured animals and for a recovery area after anaesthesia. Macropods are readily stressed and prone to trauma during capture, and to developing capture myopathy. All macropod enclosures should have a small area into which animals can be moved. This area should be away from people, enclosed with mesh fencing covered with hessian or shadecloth, have no sharp corners and have 2–3 separate yards. Animals should be allowed access to this area on a regular basis, possibly even fed in it daily so that moving animals into it is not difficult. Feed and water stations and shelter should be available.
Macropods that require hospitalisation must be housed in a quiet area away from noise, people, dogs, cats and other animals. Enclosures should be simple, solid-walled with no objects protruding from the walls and with appropriate substrate (rubber matting, wood shavings, straw). Shelter and structures in which the animal can hide and seek refuge should be provided. Rock-wallabies and tree-kangaroos should be provided with structures they can sit on top of or climb, as they generally feel more comfortable off the ground. Branches with leaves placed upside down in corners provide suitable privacy for some animals. Small species may be housed in hospital cages while larger species require a den or stall-type accommodation. Consideration should be given to the use of long-acting neuroleptic drugs in hospitalised animals (see 6.2.1).
4.2 Pest prevention and control
Pest species (rodents, foxes, dogs, cats) are known to transmit and harbour pathogens and can prey on macropods. The exclusion of cats from macropod enclosures and preventing their access to bedding and feed storage areas is essential to prevent exposure to the oocysts of Toxoplasma gondii. Rodents may carry Salmonella, Leptospira, encephalomyocarditis virus and parasites. Pests also disturb animals, particularly at night, causing stress or injuries associated with alarm and collision. Shelter and food are the primary attractants for pests. Food should be stored in pest-proof containers and food scraps should be cleaned up regularly. Pellet hoppers are useful in that they restrict bird and rodent access to the food. The judicious use of traps and baits to control pests is important, however, exposure of non-target species must be prevented. Enclosures should be built to exclude pests.
4.3 Individual marking and identification techniques
Accurate record-keeping is crucial to the effective management of any animals in captivity. Where possible, animals must be individually marked with a unique identifier (Jackson 2003). Techniques such as keeper familiarity are unreliable for macropods as they rarely display unique physical or behavioural characteristics that allow differentiation. Identification techniques that have been used in macropods include eartags, earmarks (notches, punches), tattoos, collars and passive integrated transponders (PIT tags) or microchips. Eartags and microchips are most commonly used. The standard site for insertion of microchips is SC on the dorsal midline between the scapulae. The point of the needle should be directed caudally The hole should be closed with tissue glue. This, together with the caudal direction of implantation, prevents the likelihood of the microchip falling out soon after insertion.
Macropods can be transported in specially constructed boxes, pet packs or sacks (Jackson 2003; Exhibited Animals Protection Act 1995). A box or pet pack should be large enough for the animal to turn around, lie down and stand comfortably. A layer of thick cardboard or plywood should be attached to the inside of the wire door and the inside of the roof should be padded. There should be no objects or frames protruding into the box or pet pack, and feed and water bowls should be secured inside the box. Only one animal should be placed inside a box.
Figure 7.4 Suspension of a macropod in a sack for transport. Photo: Larry Vogelnest.
It is now considered preferable to transport macropods suspended in sacks. The sack should be suspended securely from a beam in a vehicle or box so that it is not touching the sides or floor. It must be large enough so that the animal can lie comfortably in it, and should be prevented from swinging by rope tied to the corners and secured to the sides of the vehicle or box (Fig. 7.4).
Females with PY still permanently attached to the teat (essentially while furless) are usually safe to transport as there is less risk of the PY being thrown from the pouch. The risk of being thrown is greater once the PY detaches from the teat. If it is necessary to transport a female macropod at this stage, the pouch may be taped closed and the tape removed prior to release. Animals should not be transported when ambient temperatures are high. All vehicles must be well-ventilated and cool. Care should be taken when releasing animals from boxes, pet packs or sacks to avoid alarming them in an unfamiliar environment (Jackson 2003). The judicious use of sedatives and tranquillisers will ensure that the animals are calm when released (see 6.2.1).
The wild diets of macropods are diverse. Although generally considered herbivorous, many of the smaller species also eat invertebrates, roots and tubers, bulbs, fruits, seeds and fungi. Vegetation consumed by macropods is of two general types: monocotyledons, including mainly grasses and sedges; and dicotyledons such as forbs, shrubs and trees. Ferns may also be consumed by some species (Dawson 1989; Sanson 1989). Nutrition of macropods has been reviewed by Hume (1999); readers are referred to this source for detailed information.
5.1 Wild and captive diets of groups of macropods
The diets of macropods can be correlated with their dentition and gastrointestinal anatomy. The various macropod species have been categorised in groups according to dietary preferences and dentition (see 2.2) (Sanson 1989). There is also a correlation between body size and type of diet. The smaller species tend to be more specialised, feeding on more digestible energy-rich food items. The medium sized species are more generalist feeders and select a wide variety of vegetation types. These generally have relatively low fibre content. The large species, especially the kangaroos, are specialist grass-eaters. These diets are high in fibre and less digestible.
Captive diets should mimic as closely as possible the wild diet. This can be difficult, particularly when a regular supply of fresh grasses and browse is required. Most captive diets for macropods are therefore made up of various types of hay, fruits, green leafy and hard vegetables, dried corn, commercial dairy or macropod pellets and dog kibble. Lucerne and grass hays are most commonly used. Hay with a high proportion of stalk, grass awns and contamination with thistle should be avoided as these may pierce the gums, increasing susceptibility to lumpy jaw (see 9.2.2 and 9.9.26). Omnivorous species should be offered animal-based protein and insects. Most of these items are more easily digestible, and have a higher protein and energy content than the wild diet. They are also often fed in excessive quantities. Consequently, obesity is common in captive macropods. Specific captive diets for various macropod species are presented by Jackson (2003).
The diets of captive animals should not only provide for the nutrient requirements of the species but also the psychological and physical needs. Behavioural enrichment with macropods is as important as for any other species. Food and the way it is presented and the frequency of feeding can be important enrichment for captive macropods. Diet also plays an important role in dental health—food items such as bread and hard stalky items should be avoided as these promote plaque and calculus formation and gingival damage. This leads to periodontal disease, which may then progress to osteomyelitis or lumpy jaw.
5.1.1 Rat-kangaroos (Hysiprymnodon and the Potoroidae)
These species seek diets that are more easily digestible and energy-rich. These food items include young grasses, forbs, grass seeds, rhizomes, bulbs, tubers, swollen taproots, hypogeous fungi, plant exudates (Acacia gums) and invertebrates (Seebeck et al.1989). Hypogenous fungi (underground fungal fruiting bodies) are a principal food source for some of these species (Dawson 1989; Hume 1999).
Although there are no detailed studies on the diets of these species in the wild, these small wallabies seem to feed on forbs, especially succulents, some green grass and grass seed heads (Dawson 1989; Hume 1999).
The wild diets of these species have not been examined in detail other than the yellow-footed rock-wallaby (Petrogale xanthopus). Herbaceous forbs, young grasses and leaves of woody shrubs are all consumed. The diets of other rock-wallabies appear to be similar. An exception is the nabarlek. Their diet in the wet season is largely sedges and grasses and in the dry season they forage on ferns (Dawson 1989; Hume 1999).
These species eat succulent short grasses and herbage, fruits, ferns and browse (sometimes as fallen leaves). The rainforest-dwelling red-legged pademelon has a large intake of fallen fruits and leaves (Dawson 1989; Hume 1999).
5.1.5 Nail-tailed wallabies
These species primarily eat forbs, seeds, grasses and browse including fallen leaves. They particularly enjoy Portulaca