Australian mammals are almost all nocturnal or crepuscular and the carnivorous marsupials are no exception. Most are nocturnally active, although some diurnal foraging and basking activity has been recorded in a number of species for which detailed field observations are available, including in antech-inuses and thylacines. In some populations, spotted-tailed quolls exploit opportunities to prey upon nocturnal possum prey asleep in tree hollows, and are almost arhythmic in their activity. Three species are substantially or completely diurnal, the numbat, the speckled dasyure from New Guinea, and the southern dibbler (Parantechinus apicalis) from Western Australia.

Well developed auditory and olfactory communication could be expected in these primarily nocturnal mammals, although carnivorous marsupials use a variety of visual displays as well. Vocalizations range from hisses, growls, squeaks, barks to screeches in the low (0.1 kHz) to ultrasonic (most less than 12 kHz) frequency range. Contact calls between mother and young start while young are still living in the pouch and consist of squeaks and wheezes which are returned by the mother at a lower pitch. Aggressive calls range from hisses, to growls and screeches. The screech of spotted-tailed quolls has been described as a blast from a circular saw and that of the Tasmanian devil sufficient to "raise the devil," a trait which may have contributed to its name. Female plani-gales and quolls in estrus emit male-attracting soft clucking calls when receptive to mating. Tasmanian devil females, and to a lesser extent males, crouch mouth to open mouth and give continuous soft barks, each of which ends in a whine. Unwelcome suitors are repelled aggressively.

Scent is an important vehicle for the dissemination of social and reproductive information between individuals, such as male dominance status and the estrous state of females. In carnivores, the information-laden metabolic breakdown products of reproductive hormones are excreted mainly via the feces, although urine of male antechinus also contains sex-specific compounds. Dasyurids have well-developed par-acloacal glands from which a pungent, viscous, yellowish liquid is exuded during cloacal dragging form of scent marking. Male Tasmanian devils cloacal drag frequently in the presence of oestrous females, and both sexes mark frequently during non-breeding social interactions. This behavior is well established even in advanced pouch young before the glands have begun to produce scent. Sternal skin glands and chest rubbing are widespread primarily among males of the smaller dasyurids (antechinuses, dunnarts, phascogales), an activity which increases during the breeding season under the control of male reproductive hormones (testosterone). Female quolls and devils produce prodigious quantities of reddish oil in the pouch, the quality and quantity of which is an indicator of es-trous state, but which probably also serves to prepare the pouch for occupancy by the young. That this oil also has a function in communicating reproductive state is suggested by the intense interest that males show in sniffing the female's pouch compared with her cloaca.

Visual signals include extensive repertoires of postures, which the use of light-amplifying equipment enables humans to observe. Tasmanian devils use in excess of 20 different postures in social interactions. Visual displays that accentuate body size and weaponry (threat displays) or reproductive readiness usually prelude potentially dangerous aggressive or reproductive interactions. Open mouthed threat displays that show the teeth are common.

The Tasmanian devil (Sarcophilus laniarius) has an open-mouthed threat display. (Photo by E. & P. Bauer. Bruce Coleman, Inc. Reproduced by permission.)
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