Feral animals
Bob Salt
The arrival of Europeans in Australia and the Sydney Region introduced problems for the Aboriginal people and the native fauna. Not only did each new sailing ship bring
humans and domestic animals, it also brought their commensal companions, rats and mice, as well as the ships’ cats on board to control the vermin.Some of these animals, which found their way ashore from docked vessels or
shipwrecks, proceeded to take advantage of the new environment. In time they were joined by escaped domestic animals or later by deliberate releases of animals organised by acclimatisation societies to make Australia seem more like
Europe.
The Park, penetrating as it does into the urban fringes of Sydney, has become home to a considerable number of feral animals. These prey on, or compete for food and for
homes with the native wildlife. The feral animal population of Berowra Valley includes the following.
Cats
Felis catus
The Cat is known to have been introduced into south-eastern Australia by the early European settlers. However, it is possible that cats may have been present in Australia
for up to 500 years. It is now thought that cats arrived in the west during the sixteenth and seventeenth centuries from Portuguese and Dutch shipwrecks, and in the north from the Macassan traders on fishing trips to the Top End
(Wagner 1997, pp. 20-21). Feral cats can kill animals up to 2–3 kg. They prefer mammals up to 220 g and birds less than 200 g, but will take reptiles, amphibians, and invertebrates as well as carrion. Feral cat
predation has been linked to the disappearance of thirteen species of mammals and four species of birds from the western division of New South Wales by 1857. Current impacts on native species are most likely in modified fragmented
environments and where alternative prey such as rabbits or house mice fluctuate in abundance.1 Feral cats are wary of humans and are most active at night. They spend most of the day in a shelter such as a rabbit burrow or hollow log.
In favourable habitats the feral cat population may exceed one cat per square kilometre, but feral cat home ranges can extend up to eight kilometres. In most Australian
regions feral cat populations are now probably fairly stable (Jones 1991, p. 489). Their depredations are augmented by the activities of uncontrolled domestic and stray cats in areas like Berowra Valley.
No research has been done on the impact of feral, stray or domestic cats in the Park. However, one study of domestic-cat predation in Canberra suburbs showed that in one
twelve-month period of the study, 214 domestic cats (some of which moved up to 900 m into adjoining bushland) took some 2000 vertebrate prey items representing sixty-seven species. Their main prey consisted of house mice 50
per cent, black rats 7 per cent, and birds 27 per cent. The birds were represented by 47 species, 41 of which were native. Predation beyond suburban edges is most likely to affect birds, arboreal native marsupials (such as sugar
gliders) and small ground dwellers (like dunnarts) (Barratt 1998).
The Cat is also a carrier of toxoplasmosis — a parasitic disease — which affects humans and marsupials. The combined effects of competition and toxoplasmosis
are believed to have contributed to the decline of the Dasuryid native cats (such as the quoll).
The Companion Animals Act 1998 (NSW) requires more control and identification of domestic cats, which should reduce dumping of unwanted cats and the number of uncontrolled cats abroad at night.
Foxes
Vulpes vulpes
The Fox was introduced into Australia in the 1860s near Melbourne as a sporting animal. It has now spread to most of the continent except for the tropics and Tasmania. It
is the largest terrestrial predator in Australia after the dingo and feral dog. Basically a carnivore, the Fox is, however, an opportunistic feeder and its diet can vary from wild fruit and insects to carrion, small mammals and
garbage. Foxes normally have a home range of two to five square kilometres. They are present but seldom seen in most urban areas.
In Europe foxes are a vector for the transmission of rabies, and it would be a major problem if this disease ever took hold in Australia (Coman 1991, p. 486). Foxes are
also a vector for spreading noxious weeds including blackberries.
In 1997 Hornsby Council, in conjunction with the National Parks and Wildlife Service, began a fox control program, which in 2000 was extended to the Park as an ongoing
annual activity. The success of the program was indicated by the return of bandicoots, plovers, lyrebirds and brush turkeys to many bushland areas.
Dog owners who regularly walk their leashed dogs in the Park should be aware that the Park is closed to dogs during fox baiting periods as the baits are poisonous to all
dogs. Dog owners should refer to signage at track heads for details of times
The Fox was listed as a key threatening process under the Threatened Species Conservation Act in 1999. Unfortunately, many people feed foxes because they look cute or by
inadvertently leaving pet food outside, or food scraps on open compost mounds. This encourages foxes into gardens and supports a fox population on the urban fringe.
Rabbits
Oryctolagus cuniculus
Rabbits, common prey of foxes and cats, arrived with the First Fleet. These were most likely domesticated silver-grey meat rabbits. The Reverend Samuel Marsden tried to
set up a warren at Parramatta in 1806. In 1827 concern was expressed about rabbit populations in Tasmania. However, wild populations did not thrive on the mainland until a shipment of twenty-four genetically wild rabbits was
released by Thomas Austin at ‘Barwon Park’ near Geelong, Victoria, in 1858. By 1865 these rabbits were well established and they now occupy four million square kilometres of Australia south of the tropic of Capricorn
(Croft 1996, p. 33). Rabbits are a major pest in inland areas. Although coastal sclerophyll forests are a less suitable habitat, rabbits will harbour in sclerophyll bushland and feed out onto grassy suburban areas such as lawns,
and semi-rural areas and paddocks.
Rabbits occur around the Park, and appeared to decline with increased urbanisation (personal observation), but by 1999 there were increasing reports of sightings of both
wild and domestic rabbits in suburban areas.
Myxomatosis and calicivirus may be helping to reduce numbers in many areas, but by 2000 calicivirus had not shown any effects on rabbit populations in the Sydney region.
Genetic studies by Dr Lynton Davies have indicated that the feral rabbit populations in and around Sydney are distinctly genetically different from feral rabbit
populations in other areas of Australia (Davis 1998). The reasons for this may be attributed to escapes of pet rabbits into the wild population and Marsden’s original rabbits being of French origin. This has resulted in
Sydney rabbits having a degree of immunity to calicivirus.
Decline in the rabbit population will mean that integrated pest management measures to balance prey and predators will need to be employed to avoid increased predation on
native animals.
Carp
Cyprinus carpio
The troublesome Carp is one of a number of fishes introduced since European settlement. It has become well established in the major river systems and is blamed for
contributing to the reduction in native fish populations in the Murray-Darling basin. Its bottom-feeding habits stir up mud and undermine stream banks, increase turbidity, destroy aquatic plant beds and release nutrients into the
water that can cause algal blooms (Harris 1994 pp. 65-73). Unfortunately these fishes are now established in the upper reaches of Berowra Creek. Control measures include commercial electro-fishing, but these have not yet been
applied in Berowra Creek.
Gambusia
Gambusi holbrooki
The United States Army introduced Mosquito Fish, Gambusia or Eastern Gambusia, in many countries in the 1920s in an attempt to control malaria by reducing mosquito
populations. The gambusia were a failure at this task, but reduced native fish populations by predation and competition. Gambusia thrive in fresh or salt water and are present in most streams (Harris 1996, p. 68).
Rats
Rattus rattus & Rattus norvegicus
The Black Rat Rattus rattus and the Brown Rat Rattus norvegicus arrived with the First Fleet and have thrived near human habitation ever since. The Black Rat has been more successful and has spread around most of the coastal areas, whereas the distribution of the Brown Rat is patchier.
Black Rats can be found in bushland around Berowra Valley in the same areas as the native Bush Rats Rattus fuscipes.
Black Rats are usually found along the urban interface in the Park. Population pressures force the older, weaker and younger rats into nearby bushland to forage and nest.
Some populations are found in the same areas as the native bush rats Rattus fuscipes.
So far there is no evidence that they are having much impact on the native rodents. The Black Rat is, however, a carrier of such diseases as salmonella and leptispirosis,
and in Europe it carried the plague bacillus.
The Brown Rat is generally found around buildings and wharves and occasionally along creek banks. It is a larger and much more aggressive animal than either the Bush or
Black Rats. Fortunately for the Park, it appears to prefer proximity to human habitation rather than the bush (Watts 1991, pp. 452-54).
House Mice
Mus musculus
The well-known pest, the House Mouse Mus musculus, also arrived with the Europeans. It reaches plague proportions in wheat-growing areas. Some twenty mouse plagues
affecting twenty per cent of the land have occurred in Australia since 1960 (Newsome 1991, p. 455). In central Australia the House Mouse is believed to have replaced some native species, but apparently this does not happen in
coastal habitats. In some areas the House Mouse can become abundant about eighteen months after bushfires when native species are rare, but disappears within three to four years as native rodents become more abundant (p. 455).
Hornsby Conservation Society’s mammal survey in the 1970s collected one animal some distance from habitation in the Elouera Bushland. While Mus musculus is found in both the Park and in houses generally, so far it has become a pest only in the urban situation.
Dogs
Canis familiaris
Dingoes no longer exist in Berowra Valley and there are few if any feral dogs. However, poorly controlled domestic dogs still represent a significant threat to wildlife
in the park, particularly if they are allowed to roam free at night. Owners of such dogs should be aware that during fox baiting periods their pets share the same risks as foxes.
According to older residents, most of the original wallaby population around Hornsby was decimated by a pack of beagles owned and exercised in 1966-75 by a now-deceased
local resident. As recently as 1996 a rottweiler chased and seized a Swamp Wallaby Wallabia bicolor on Waitara Creek. A Swamp Wallaby was subsequently found dead in the vicinity and its skeleton given to the Australian
Museum. Dogs should now be better controlled under the provisions of the Companion Animals Act.
Birds
Most of the introduced birds have fortunately had limited success in the Australian bush and have affected native species only in competition for food and nest space.
The Common or Indian Myna Acridotheres tristis is one of the most troublesome in areas adjacent to urban development. It competes aggressively for nesting hollows with the smaller parrots.
Feral Mallard Anas platyryhnchos are a problem because they interbreed with the native Pacific Black Duck Anas superciliosa, threatening its genetic integrity (Slater et al. 1986, p. 64).
Bantam Hens Gallus domesticus have frequented the Galston Gorge area for years, being the result of someone irresponsibly dumping unwanted birds, rather than as an established breeding population. These birds were brought under control in 1999 and have been eradicated.
Brochures on feral cats, foxes and other threats to wildlife populations are available from Hornsby Council and the National Parks and Wildlife Service offices.
Other unwanted aliens
There are other pests that infest Australia such as pigs, goats and deer. However, there appeared to be no extant breeding populations of these in Berowra Valley in 2000.
There have been reports of feral pigs being released by misguided hunters in the Maroota area, and early in 2000 three pigs were reported from the Calna Creek area of the Park. Some goats and cattle have also been reported from
time to time, which will be eradicated as they are located.
Reporting Sightings of Feral or Native Animals
The public can help by reporting sightings or signs of any feral or stray animals to Hornsby Council and/or the National Parks and Wildlife Service. Community provision
of information on fox dens or cat lairs would likewise be particularly useful. Reports of feral animal sightings or traces are useful to the Park Managers in helping to control these pests. If possible you should accurately
note where and when you saw the animal or animals, record the date, time of day, number sighted and, if possible, the map reference or nearest track location.
Should you happen to sight rare or unusual native animals or birds, such as Koalas, Quolls, Brush Turkeys, Eagles, Powerful or Sooty Owls, Bandicoots, Platypus, or even
the Water - rat (distinguished by its white tail tip) this information is also of great assistance to the Managers.
Sightings should be reported to:
The Ranger,
Berowra Valley Regional Park
Lower Hawkesbury Area
National Parks and Wildlife Service
P.O. Box 3056, Asquith, NSW 2077
References
Barratt, D.G. 1998, ‘Predation by house cats, Felis catus (L), in Canberra, Factors affecting amount of prey caught and estimates of impact’, Wildlife Research, vol. 25, pp. 475-87.
Coman, B.J. 1991, ‘Fox’, in Strahan, p. 486.
Croft, D. 1996, ‘The Rabbit in Australia’, in Diekman, p. 33.
Davis, L. 1998, ‘Feral Animals in an Urban Environment’, unpublished paper presented to National Parks and Wildlife Service Conference, ‘Feral Animals
in an Urban Environment’.
Diekman B. (ed.) Unwanted Aliens in Australia, Nature Conservation Council of NSW, Sydney.
Harris, J.H. 1996, ‘Alien Fishes in Australia’, in Diekman, pp. 65-73.
Jones, E. 1991, ‘Feral Cat’, in Strahan, p. 489.
Newsome, A.E. 1991, ‘House Mouse’, in Strahan, p. 455.
Slater, P. et al. 1986, The Slater Field Guide to Australian Birds, Rigby, Sydney.
Strahan, R. (ed.) 1991, Complete Book of Australian Mammals, Angus & Robertson, Sydney.
Wagner, P. 1997, ‘Tracing the feral feline family tree’, Australian Geographic, no. 46, April-June, Sydney, pp. 20-21.
Watts, C.H.S. 1991, ‘Black Rat’ and ‘Brown Rat’, in Strahan, pp
|
