Biology of Australia
They are believed to have possibly shared a common ancestor with red kangaroos, and in many ways the 2 species are very similar. A study of 63 collared euros found that, even in drought, none moved more than 7 km, compared with 20-30 km for red kangaroos at the same time (Croft, 1991b). The 2 species also differ in their social structure (Croft, 1981a). The most enduring social relationship among euros is that between a mother and her young. Apart from this relationship, adults sharing shelter avoid direct contact with each other, tending to live alone. Because they are sedentary, animals meet frequently when sharing shelter, and aggressive behaviour is more common than among the red kangaroo population. Much of the agonistic behaviour of euros occurs when they compete for shady places. Usually the largest animals get access to the best caves and shelters, only sharing when they are evenly matched. Females are smaller than the males, so they almost never get access to caves, but often get in parts of the caves and overhangs the large males don't fit in. The mating system is believed to be polygamous, the alpha male mating with most, if not all the females. They usually retain dominance for about a year. In a study of males that had been displaced as alpha male, it was found that 38 % did not produce sperm, apparently indicating that loss of dominance leads to declining male fertility (Sadlier, 1965).
A study in the Pilbara of Western Australia found that the availability of water was closely related to the use of caves, the caves being used when water was scarce, or forage had low moisture content, conserving water that would otherwise be expended in thermoregulation (Ealey et al, 1967b, Ealey, 1965a). When plenty of water was available, such as at stock watering sites, the caves were not used during the day, even in very hot weather, most sheltering on the shady sides of outcropping granite. The availability of caves and rainfall influenced the drinking frequency. About 1/3 of the population, mostly lactating females, used the stock water sites regularly, while 1/4 didn't drink at these sites. After rainfall of 30 mm or more, dinking at the watering sites declined, and where caves were available, was less intense.
As with the southern hairy-nosed wombats in their burrows, euros survive in arid regions by exploiting the cooler temperatures and higher humidity of caves to conserve water, obviating the need to drink, though this behaviour restricts them to the country around the caves, and forcing them to adapt to eat the green food growing in those areas. Another similarity with wombats is the high degree of nitrogen conservation they achieve, higher than that of the red kangaroo (Freudenberger & Hume, 1992), enabling them to survive on plants that have a very low nitrogen content.
A study was carried out in the Pilbara on 2 euro populations, 1 were eating mainly low-nutrient plants such as spinifex, Triodia pungens, a plant that is rarely eaten by red kangaroos, in which the mean nitrogen content is less than 0.6 % dry weight. The food of the other population consisted of a more mixed vegetation, the average nitrogen continent of which was 1.1%. A difference was found in the urea concentrations between the the 2 populations, in the population feeding on spinifex it was 1/5 of the level found in the population with a mixed diet. The reason for this difference is believed to be increased rates of urea reabsorption in the kidneys of animals in the population on the low-nitrogen diet, similar to what occurs in the tammar wallaby (Ealey & Main, 1967). The lower urine urea concentrations indicate a poorer diet with increased recycling of the urea to the forestomach, a process that occurs in all macropods.
The protein content of the food, and not the total amount, is the critical factor for euros, and this depends on the amount of rain. Nutrition is the controlling factor in euro populations. They can breed on low-protein diets, but when the protein content of the plants declines in times of prolonged drought, they enter negative protein balance and lactation fails. Where the vegetation had a low protein content in the study area in the Pilbara in 1954, it was regular mortality that kept the population low. In the area of the more nutritious vegetation the population of euros increased to levels well beyond the carrying capacity in the long term, then on the return of severe conditions, the population crashed (Ealey et al. 1965).
There are many more red kangaroos than euros in the Central Australia, where the euros are not common (Newsome, 1975). Rock holes are sparse and widely separated, and seepage sites are not common, as a result of the sandy soil in most areas. The problems are compounded for euros as there is little shelter and few watering places. It is believed the lack of heat refuges and drought fodder are the main reasons for the euros being much more common in the Pilbara than in Central Australia (Tyndale-Biscoe, 2005).
Tyndale-Biscoe, Hugh, 2005, Life of Marsupials, CSIRO Publishing.
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