Tropical Topics A n i n t e r p r e t i v e n e w s l e t t e r f o r t h e t o u r i s m i n d u s t r y Rodents of the Wet Tropics No. 46 April 1998 The cane, the rats, the trees and the owls Notes from the Cane growers do not like rats. Rodents destroy or damage up to $9 million worth of sugarcane a year, while farmers spend Editor a further $600 000 on rat bait in an attempt to control them. Rats have an image problem. Two native species, the canefield rat and the grassland Unfortunately just a few species, melomys (also known as Burton’s climbing rat) do most of the which carry disease and damage damage. Grassland dwellers and nibblers by nature, they have human property, have given the whole found the abundance of sugary cane which has replaced native family a bad name. So what use are forests on the Queensland coast very much to their liking. they? A diet of cane alone, however, is not from one area and been reduced by 80 Rodents play an important role in the enough to sustain these rats. They percent in another. environment. Primarily, they provide prefer grassy and weedy areas that good snacks, featuring on the menus provide shelter as well as protein-rich Enthusiasm for this rat control method of owls, pythons, quolls and other grass seeds, essential for breeding. is spreading. Instead of repeatedly animals. Also, although they eat large The average canefield, with its grassy spraying or slashing grasses and numbers of seeds (try to find an margins, is ideal for these rats. weeds, a one-off planting followed by unopened and unrobbed candlenut short-term maintanence provides a seed on the forest floor!) they also Traditionally, cane farmers have long-term solution. The tree species serve to disperse seeds as well as tackled their rat problems with poisons are carefully selected so as not to fungal spores. — bait in the canefields themselves shade the cane or interfere with and herbicides on the grasses which equipment. Cabinet timbers and bush From the human point of view, harbour the rats but where it is illegal foods are being planted in some places although rats and mice do not appeal for future economic reward. to everyone as pets, as laboratory to use the baits. This is costly, time animals they have played a very consuming and environmetally important role in everything from undesirable — poisoned rats become Naturally, the environment also medical to cosmetic testing. easy prey for predators such as owls, benefits. Stream health improves as pythons and goannas which in turn erosion and choking weeds are I would like to thank Steve Van ingest the toxins. Herbicides near reduced. Vegetated corridors, Dyck (Queensland Museum), Nigel water can poison frogs and aquatic particularly along connecting creeks, Tucker (DoE), Andrew Brody life. provide important cover, food and safe (BSES), Steve Comport (CSIRO) and travel routes for rainforest wildlife, Mike Trenerry (DoE) for their help In 1994, an alternative approach to the such as the cassowary. The trees also with this issue. rat problem was trialled in the Tully attract owls. Able to eat four or five and Miriwinni areas. A co-operative rats each night, an owl is a farmer’s DoE and Bureau of Sugar Research friend — but clearing and poisoning Please note Stations (BSES) project, it involved has drastically reduced their numbers. that you are welcome to photocopy planting sections of creek banks, on Now, they are being given a helping Tropical Topics. However, if the the borders of canefields, with native hand. New trees are still too young to text is reproduced separately it must trees. As the trees grew and spread provide perches and nesting hollows not be altered and must their canopies, cutting out the light, so, in the meantime, artificial ones are acknowledge the Environmental the grasses below died away. The being installed. Protection Agency as the source. results were dramatic. Illustrations must not be reused Within six This approach to the rat problem — without permission. Please contact months, the reducing their numbers by natural the editor (details on the back page) rats had methods — results in all-round if in doubt. disappeared benefits, for the farmer and the environment. What is a rodent? Rats from outside the ranks (the introduced ones) The main characteristic of The black rat (Rattus rattus) probably arrived with the First Fleet and is the a rodent is its teeth. species which carries plague (at least its fleas do), Weil’s disease* and All rodents salmonella. It is the one running rave parties in the rafters, eating holes in your have one walls, raiding your fruit basket, scuttling from your compost, sneaking in under pair of chisel- the door and sliding down your banisters. Phenomenally successful at shaped reproducing, a female can give birth to 60-100 young in one year. Fortunately this incisors (the rat, which originated in South-East Asia and was introduced to Europe in the 13th biting teeth at century, does not seem to have displaced native rat species. Instead, it has the front of the mouth) in the upper moved in where they are not present, particularly around human habitation. and lower jaws. The front surface of each is covered with a very hard Black rats differ from brown rats (R. norvegicus) which are found mainly around enamel while the back surface is softer urban centres in Australia and not in the Wet Tropics. Black rats are sleeker, with dentine, so as the animal chews on larger ears and longer tails, and are less aggressive and better climbers. hard nuts and other plant material the *Other rats, notably the canefield rat, also carry Weil’s disease. backs are worn down faster than the fronts, maintaining a constantly sharp The house mouse (Mus musculus) occurs in every part of Australia. In fact, surface. These teeth grow continually next to humans, it is the most widespread mammal species on the planet, having throughout the animal's life and must even hitched a ride and set up home in Antarctic bases. Mice can live, and breed, be continually worn down. If a rodent in refrigerators at -10deg. as well as in metal containers in 40deg. heat. is unable to gnaw, the teeth may eventually grow around into its face Every four years or so, plagues of mice occur in grain-growing areas. In northern and kill the animal. Australia, however, where there is more native competition and the wet humid climate is not especially to their liking, they are found mainly around human At the back of a rodent’s mouth, habitation. separated from the incisors by a gap, are pairs of molars which are used to grind food. Biggest and smallest What’s in a name? Vying for top position, the giant white- Perhaps our native rats would be more tailed rat, water-rat and black-footed acceptable if they were known by tree-rat can all weigh up to 1kg with other names. Melomys, which is some male water-rats tipping commonly used, sounds much more the scales above that. By attractive than ‘climbing rat’ so contrast, an adult delicate perhaps a tourist encountering a giant mouse can weigh as little as white-tailed rat for the first time is more 6g. The black rat generally likely to appreciate the unique nature weighs under 300g. of this animal if introduced to it as a The water-rat and the delicate mouse. ‘uromys’. Recent migrants In this, the land of marsupials, it is of non-marsupials into Australia, The old endemic group perhaps surprising that about one- rodents have long been considered (Hydromyinae), with over 50 members quarter of all native mammal species newcomers. They are believed to have in Australia, is the largest are rodents. Nevertheless, Australian reached first New Guinea and then of the two subfamilies. Most common rodent species comprise only about Australia, from Indonesia, on rafts of representatives in the Wet Tropics four percent of the world’s total. This vegetation or as falling sea levels are the melomys, white-tailed rats, lack of diversity in Australia is during Ice Ages presented them with prehensile-tailed rat and water-rat. undoubtedly due to their relatively land bridges. Fossil evidence indicates recent arrival (and a measure of how that one group arrived in Australia The new endemic group (Murinae), the very successful this group has been about four million years ago. Most ‘true’ rats, is considered the most elsewhere in the world). Of the 24 native rats and mice belong to this successful rodent group with over 400 rodent families in the world only one group, known as the ‘old endemics’. representatives worldwide. However, (Muridae) is found in Australia and of The ‘true’ rats — the ‘new endemics’ in Australia, where they are such the 16 subfamilies found in this family — arrived along the same route less recent arrivals, there are only 11 only two (Hydromyinae and Murinae) than one million years ago. Apart from species, seven of them native. Of are Australian. bats, marine mammals and humans, these seven, five are found in the Wet rodents were the only placental Tropics. The four introduced species Although the finding of a 115 million- representatives in Australia until the also belong to this group; two of these year-old placental fossil in Victoria dingo made its appearance 3500-5000 now inhabit the Wet Tropics (see threatens theories about the spread years ago.