Understanding your environment - Tasmanian birds of prey
by Mike Stevens
It is important that we enjoy and appreciate the environment around us when we go fishing. Parks and Wildlife Service have a wealth of information on our wonderful flora and fauna. This is the first in a series of Parks and Wildlife Service on what you may encounter as you spend your day sharing nature with others.
All birds of prey in Tasmania are native and wholly protected by law. They face many threats to their continued survival. Some examples of these are:
Habitat destruction
Most birds of prey rely on forests to some degree. Wedge-tailed eagles nest in large eucalypts growing in a suitably sheltered site. Clearing of forests often destroys eagle nests and disturbs the birds to such an extent that they vacate their nest. This means that the breeding population of wedge-tailed eagles in Tasmania is not producing the maximum number of young each year.
Grey goshawks require wet forest in which to hunt and nest.
Owls need old hollow trees to nest in. If the existing old trees are removed it may be hundreds of years before they are replaced. Marsh harriers prefer to nest in reedy swamps but if these are drained they will next in crops nearby. Unfortunately this means that they and their chicks are vulnerable during cropping operations.
Pesticides
Pesticides fall into two categories, persistent (such as D.D.T.) and non-persistent.
Persistent chemicals are passed through food chains and affect species other than the pests they were intended for. In birds of prey (particularly the peregrine falcon) this causes thin eggshells that break during incubation. This can mean that a breeding season will be unproductive.
Non-persistent chemicals cause problems when used improperly. For example, dead animals are sometimes "baited" with poison. Birds of prey, although not the target species, are killed when they scavenge on the carcasses.
Shooting
Birds of prey often fall victim to vandals who shoot them for "fun" or as trophies. This destructive and illegal activity must stop.
Many birds of prey are killed by land owners who incorrectly believe that they kill stock. Extensive research into lamb deaths has shown that less than 2% of healthy lambs are killed by predators. Birds of prey form only a part of this 2%. Most deaths are due to inappropriate stock management or mismothering by ewes. About 10% of the wedge-tailed eagle population falls victim to uninformed landowners and vandals each year. Remember, birds of prey scavenge and therefore have not necessarily killed an animal they are eating.
Young inexperienced goshawks occasionally kill unpenned poultry. This is a nuisance but rarely an economic problem. By keeping poultry unpenned, people are providing a self-serve supermarket for birds of prey and losses are inevitable. Chicks and other valuable birds should be penned for their protection. Up to 20% of the grey goshawk population is killed each year in revenge for unpenned stock being taken.
Peregrine falcons are sometimes killed by pigeon fanciers to try and prevent them preying on their birds. Falcons are just one of the natural hazards encountered by racing pigeons and their effect is often overstated. By their predictable racing methods, pigeon fanciers literally train falcons to catch pigeons.
Roles and values
Birds of prey are a necessary part of the environment. They are Tasmania's most important day time predators. They keep prey populations healthy by preying on sick, deformed or odd individuals. They prevent population increases in pest species such as rabbits, feral cats and even insects. They also play an important role as rubbish removers by cleaning up animal carcasses.
They help control numbers of their prey. Without such predators, prey are controlled by starvation and disease and their numbers fluctuate wildly.
Populations of birds of prey are self regulatory. When there is a lot of food they breed more, and die less, and vice versa. Thus they do not endanger the prey populations and there is no need for control by humans.
Because birds of prey occupy a similar position on the food chain to people, they act as an early warning system on environmental problems (especially toxins) that may affect us.
Birds of prey have an intrinsic value, simply as species living on our planet. This is a very important reason to protect birds of prey from the harmful effects of human activity.
What can you do to help?
Minimise habitat destruction by leaving a buffer strip of vegetation around nest sites if clearing land. The buffer should be as wide as possible. Fencing around solitary nest trees will ensure that seedlings will grow to replace dead trees, and will also provide a windbreak for stock and crops. Be conservative when using pesticides. Use poisons only as directed on the label. Report incidents of vandalism to the Parks and Wildlife Service.