Social ethology of the whiptail wallaby, Macropus parryi, in northeastern New South Wales

Summary The Macropodiae are the most social marsupials, and the whiptail wallaby is the most social macropod. This report describes the behaviour of whiptails and compares it with that of other macropods and of grazing ungulates, the macropods' colsest ecological equivalents elsewhere. The whiptails were studied in northeastern New South Wales from October 1966 to November 1967. This is an area of ridges and valleys, partly cleared, and grazed by cattle. The whiptails were found in open Eucalyptus forest and adjoining pasture. Field observations were made of three discrete mobs of up to fifty members each. The East end mob was studied intensively: each member was named, aged and sexed, and all gains and losses were recorded throughout the year. Less intensive observations were made of the Tank 1 and Ringbark hill mobs. Whiptails share a variety of postures and gaits, including bipedal hopping, with other macropods. Autogrooming with the mouth and feet was conspicuous, both as a utilitarian activity and as a conflict act in social situations. These whiptails were strictly grazers and did not drink. They were most active at dawn and dusk, and of all the macropods yet studied, whiptails are the most diurnal. Whiptails are alert animals with excellent vision and hearing. When alarmed they panicked easily and dashed wildly off in erratic, criss-crossing courses. During flight the hind feet produced a loud thump on the first few hops, an alarm signal shared with most other macropods. The principal predators on wallabies today are the introduced dingo and fox, which have replaced the marsupial wolf on the Australian mainland. The whiptails shared their grazing areas peacefully with several other species of macropods, but were occasionally displaced by cattle. The mobs contained all ages and sexes throughout the year, but seldom if ever were all members of a mob together at one time. Typically, they were split into continually changing subgroups of fewer than ten animals. Emigration of sub-adult males was observed, and there was evidence of emigration or differential mortality of adult males. Communication was primarily through visual signals, and an analysis of these shows remarkable convergence with the displays of ungulates. In accordance with the whiptail's unaggressive nature, threat and submissive displays were less well developed than superiority and courtship displays and conflict activities. Olfaction was primarily used for individual recognition and for sexual checking. Auditory signals are poorly developed in macropods generally. Whiptails show a positive gregarious tendency and a significant lack of overt interaction at close quarters. Social grooming was mostly restricted to mothers and their offspring. Fights between males consisted of ritualized pawing bouts. These bouts established a dominance hierarchy which functioned only to determine access to oestrous females. Recognizable social roles and co-operation were virtually absent. Breeding occurred throughout the year. Whiptails become sexually mature at about 18 to 24 months, but males probably had no opportunity to mate until they were 2 to 3 years old because of the sub-adults' inferior social status. Females typically mated late in their joey's pouch life. Fertilization was apparently followed by two months of embryonic diapause. Then gestation resumed for about one month so that the next young was born as soon as the previous joey vacated the pouch permanently at the age of 9 months. This pattern is similar to that of the Eastern grey kangaroo but differs from most other macropods, which have a postpartum oestrus and a longer embryonic diapause. The origin and function of embryonic diapause in macropods are poorly understood. Sexual checking of females and anoestrous courting were the most conspicuous interactions between adults. Oestrous courting was limited to a few days around the female's receptive period, which lasted only a few hours. Persistent following by the alpha male and several secondary males, wild mating chases, and copulation were diagnostic of oestrous courtship. Joeys typically began leaving the pouch late in the 8th month, became young-at-foot a month later, and were weaned by the 15th month. Mothers were not very solicitous or protective of their young. Females might remain loosely associated with their mothers for years, but males left the mob or became completely independent within it by their 21st month. Play consisted mostly of solitary chasing; social play except with the mother was almost non-existent. All types of play were less common than in other social mammals. Each mob had a home range of about 100 ha, which overlapped slightly the ranges of other mobs. All of the mob's range was occupied by all sexes and ages, but probably no individual occupied 100 per cent of the mob range. Males were generally wide ranging, while some females were sedentary. Females occupied smaller areas when their joeys were vacating the pouch. The most heavily used areas were flats with grass, close to woods or ridges. Whiptails probably benefit from limited clearing and pasture development, but large-scale habitat destruction has reduced their numbers overall. Members of adjacent mobs mingled peacefully in the overlap zones, but mostly kept to their own undefended ranges. Thus most of each mob's range qualified as a monopolized zone, or functional territory. Individuals of one mob occasionally visited in another mob's range, and several sub-adult males changed mobs. Field studies of mammalian societies have revealed a number of correlations between social organization and adaptations such as habitat preferences, activity cycles, and food. These generalizations seem to apply to macropods as well, but most macropods have never achieved either the other adaptations which encourage sociality, or an advanced stage of sociality itself. As diurnal, grazing inhabitants of rather open cover, whiptails are apparently at the peak of macropod social development. Their chief benefits from group behaviour are probably facilitation of mating and especially group vigilance and warning. Their social system also keeps the number of conspecifics regularly encountered to a manageable, recognizable level. The first macropods were probably solitary, nocturnal forest dwellers; the evolution of social organization in the family is obscure, but probable progressive stages are represented by the musk kangaroo, the quokka, and the whiptail.