Tasmania is home to 13 species of birds of prey, all of which are native. These include some of Australia's most spectacular species, such as the majestic wedge-tailed eagle and the white-bellied sea eagle. Several of our birds of prey are threatened with extinction. Some also occasionally come into conflict with landowners. It is vital that any protective measures that landowners take do not place these birds at risk. Remember, all of our birds of prey are wholly protected by law.
The following notes are provided to identify ways of overcoming these problems and ensuring that these magnificent birds continue to survive.
Roles and Values
Birds of prey are among the most important forest predators. They:
- are a stabilising influence. Without such predators prey populations fluctuate, in effect controlling themselves by overpopulation, starvation and disease.
- promote survival of the fittest by selectively preying on deformed, weak or sick animals. Thus, they assist with bush hygiene.
- eat many introduced pests.
- are indicators of environmental health. Because they are predators at the top of the food chain they accumulate certain agricultural chemicals from their food and can act as an early warning system for pollution.
- provide enjoyment for many people who find them a source of pleasure and inspiration.
- Like all native species they have the right to exist in the wild.
Ever since Europeans settled in Australia, wedge-tailed eagles have been accused of attacking and killing almost anything from horses to honey-eaters. In some States bounties were paid for their destruction and a total of about 20 000 were slaughtered per year in the mid 1960's.
Today, despite legal protection and changing attitudes, the wedge-tailed eagle remains vulnerable to extinction. Some landowners believe that wedge-tailed eagles pose a threat to lambs and kids. However, studies have shown these fears to be unwarranted. In 1970, for example, the CSIRO published an analysis of the cause of death of over 12 000 lambs in several States. Although up to 34% of dead lambs had been at least partly eaten, only 2% of lambs born had been actually killed by predators such as eagles. More importantly, only 2.7% of dead lambs would have survived if a predator had not attacked. Exposure to bad weather and miss-mothering were the most important causes of death.
Studies in Tasmania show that in sheep grazing areas, rabbits, hares, brushtail possums and wallabies are the most important prey, although a great variety of animals are eaten dead or alive, from cormorants and echidnas to snakes. With rare exceptions, eagles simply do not create an economic problem.
Why there is concern for the eagle's survival
Our wedge-tailed eagles have been isolated for 10 000 years from their mainland counterparts and have become a separate subspecies. With naturally low numbers they have little genetic insurance, and continued pressure means they have been declared endangered.
There are a number of problems facing eagles in Tasmania. One is habitat destruction through forestry operations and land clearing which is removing the type of forest eagles need for nesting. Needless persecution, mainly by vandals, is also a problem as is accidental collisions and electrocution by power lines.
There are only about 100 pairs of wedge-tailed eagles successfully breeding each year in Tasmania. They use very traditional nests almost always in very large eucalypts sheltered from the wind. They are very shy nesters and will often desert their nests if disturbed by land clearing, particularly early on in the breeding season, which is August to December. Breeding eagles need over 10 ha of surrounding forest especially uphill of a nest tree. Try and leave this amount, try to postpone development until the breeding season is over and follow Forestry Tasmania's 'Forest Practices Code'.
Shooting, poisoning and trapping are also serious threats. About 8% of adult eagles are illegally killed each year. This is critical considering that the total adult mortality should be only 5%. The illegal poisoning of scavengers can easily kill eagles and other wildlife. Fortunately, eagles are quite resistant to 1080 poisoning and should not be harmed if the prescribed mixing procedures are followed during legal poisoning operations.
In Tasmania about 40% of pairs are on private land, 40% in State Forest and only about 20% on reserved or Crown land. Obviously a large proportion of the population are at risk from the threats mentioned.
Problems with Hawks
Once juvenile hawks have left the care of their parents in summer/autumn they enter a period where they must quickly perfect their hunting skills or starve. During this time domestic birds can seem very attractive. Free-range chickens can be like a neon 'take-away' sign for these inexperienced hawks. Once hawks discover such an easy supply of food they can be very persistent.
What to Do?
- Chickens have natural defences at the sight of a hawk and will squeeze under shelter such as buildings, old cars, bushes etc. Special shelters can be made of planks on logs or bricks. They should be at least 2 m x 2 m and 15 cm off the ground.
- Dogs, broody hens and some roosters can also be good defenders of chickens.
- By far the best defence is to enclose the poultry. Provide at least 1/4 of the pen as solid cover and arrange the entrance such so that poultry can get out of sight. Obviously smaller chickens are more vulnerable, keep penned until well grown. Although aviary birds are rarely directly harmed they can injure, even kill, themselves in panic when attacked. Problems mainly occur when there is a large flight and small shelter. If a hawk lands near the shelter the birds can feel trapped in the exposed end and panic.
- Cover most of the flight or have a roll-on cover handy. If the hawks cannot catch or at least see food they will not stay for long.
- Two layers of mesh 5 cm apart, can help.
- Low power ( 0.5 or 1 Joule) electric fence wires on prominent perches or around the rim of an aviary can deter hawks and owls from landing (see diagram). Small birds do not earth this wiring and will not get a shock. These wires can repel cats and possums.
- Pigeons can usually outfly hawks so let them take to the air. If they are in the loft lock it - goshawks have been known to enter the loft after pigeons.
Birds of prey other than hawks are not nearly so bold near humans and are rarely such a problem with domestic birds. Often they can be frightened off with loud noises.