The White-breasted sea eagle in Tasmania
The edges of Macquarie Harbour, Freycinet Peninsula and Maria Island National Park are typical habitats for one of Tasmania's most spectacular birds - the white-breasted sea eagle - a bird of prey with a wing span sometimes exceeding 2 m and a weight of up to 4.5 kg.
Adults are basically black and white under, and grey over the wings, with a white belly. Immatures are mottled pale brown and take 5 years to reach adult plumage. The bare legs and feet are heavily scaled as armour. The soles have tiny spikes to aid in grasping slippery prey. Powerful talons, a large hooked beak and hazel eyes complete the picture. Their eye sight is acute. Sea eagles flap slowly and soar or glide with their wings held in a shallow V.
Sea eagles are not actually true eagles (which have feathered legs) but giant kites. The only species an adult sea eagle could be confused with is the smaller osprey (which does not occur in Tasmania). A juvernile sea eagle can be confused with a wedge-tailes eagle but look for the sea eagles short, white tail and strongly patterned underwing.
The species is widely distributed from India to Australia. Mainly coastal, it is also found in many large rivers and lakes. Tasmania's coastline with its many rivers, bays and islands provides ideal habitats.
Home range and territories
Adults are largely sedentary (not migratory) and will defend an area of about 3 km (the territory) around the nest against other adults. A larger area, up to 150 km" (the home range), is also used for hunting but is not defended. Pairs nest at least 2 - 3 km apart, much further where there is little food.
Hunting and food
Almost all hunting is done by a gliding attack from a prominent perch. Sea eagles find it very hard to take off from the water so when hunting fish, eels or penguins they snatch them from the surface or the edge of the beach as illustrated above. Objects up to about half the weight of the eagle can be carried in flight. Many types of fish are eaten, including porcupine fish which are deadly to humans. Birds, such as coots, gulls and shearwaters are also caught. Waterfowl crippled by hunters may be eaten. This may endanger the eagles with lead poisoning. Blue-tongued lizards are preyed on as are mammals as varied as water rats and young wombats. Carrion is an important food particularly for young, inexperienced hunters. Thus, when in lambing paddocks, scavenging eagles are sometimes wrongly blamed for taking lambs. Extremely few healthy lambs are attacked. Piracy by eagles is common. Typically they may pursue gannets until a fish is regurgitated. Sea eagles will often scavenge around fishing boats in rivers or near the coast.
In Tasmania most nests are in large, sheltered eucalypts. Exceptions are on small islands where rocky outcrops may be used. Each season nests are repaired and added to. Old nests may be enormous, up to 4.5 m (14 ft) deep and 2.5 m (8 ft) wide! Nests serve as breeding, feeding and sleeping platforms and act as territorial flags. Pairs mate for life. Courtship never really stops but peaks in early spring when pairs may lock talons and tumble through the air. One or two eggs are usually laid during September in a nest lined with green leaves, mainly for hygiene. Hatching takes 40 - 44 days, but often the first to hatch kills the other. Nestling life is about 95 days after which the fledglings are dependent on their parents for another month or so. Once independent - mortality is high. If the young eagles survive for a year then they will probably live to breed, at 5 years of age. Some will live for 30 years.
Status and conservation
There are about 200 pairs in Tasmania. On average each pair will produce less than. one young per year (some have none, some two). Overall, the species is secure, due mainly to its diverse breeding and feeding habits and the fact that about 20% of pairs live in reserves. In addition, the species (like all birds of prey in Tasmania) is protected by law and we are lucky, so far, that contamination by pesticides is generally low. However, there are local threats from vandals shooting, poisoning by land-owners, tree felling and excessive disturbance of breeding from development and recreational activities. Buffers of at least 250 m should be left around nests.
The Tasmanian Parks and Wildlife Service and the private Australian Raptor Association cooperate in the survey and study of these magnificent birds. For information on the ARA contact TASPAWS or the RAOV Phone (03) 98822622 or on the net: http://www.tasweb.com.au/ara/index.htm