Sandbars provide refuge for water birds
Birdlife
Sandbars provide refuge for water birds
Birdlife in Western Australia's south-western estuaries is abundant and varied, from the extraordinary pelican to tiny waders which migrate 9000 kilometres to escape the Arctic winter. The birds take advantage of the rich pickings at the junction of river, land and sea, where microscopic plants and animals and fringing plants are the basis of a very productive food chain.
Many birds spend most of their life feeding in estuaries. Others converge there when inland waterbodies dry out in summer and autumn. Freshwater swamps close to estuaries let colonies of waterbirds breed near their feeding sites.
In addition to the estuaries, saltmarshes, other fringing vegetation, adjacent freshwater swamps and even flooded paddocks attract a diversity of waterfowl and other bird species.
Open deep water attracts diving birds such as the musk duck, great crested grebe and pied cormorant (which dive for bottom-dwelling animals), and those like the coot which dive after plants. Others, such as the scooping pelican and plunging caspian tern, feed on fish close to the surface.
These are rich feeding areas, particularly after high tide. A large variety of small migratory waders in dull, non-breeding plumage spend the Western Australian summer in huge flocks probing the shallows and mudflats for tiny animals. Most common are the red-necked stint, curlew sandpiper and sharp-tailed sandpiper. Some of our rarest migrants, such as the long-toed stint and wood sandpiper, prefer the freshwater swamps fringing the estuaries when water levels are receding in summer. Larger birds with long legs and variously adapted bills, sieve, scoop, probe and spear for food in the shallows. These include the avocet, stilt, pelican, spoonbill, oystercatcher, curlew, heron and egret. Shelduck and grey teal swim for their food in the shallows, while whiskered and fairy terns fly over the water and pluck their prey from above.
These outposts of land are roosts for 'loafing waders' (waterfowl and terns), particularly at high tide, when they may clump tightly together in their thousands. They are also breeding sites for some species which nest on open ground.
Reeds and samphire saltmarshes provide cover for skulking waterbirds such as the spotless crake and buff-branded rail. This sort of vegetation also attracts many wading species when it's flooded at high tide or in winter. Reed beds in freshwater swamps near estuaries are also attractive to crakes and rails and to specialised song birds such as the little grassbird and the reed warbler. These places are good nesting sites for waterfowl such as the blue-billed duck and the predatory marsh harrier.
Open, shallow marshes and paddocks around the estuaries can provide seasonally abundant food (such as crustacea, insects and frogs) for flocks of heron, ilbis, stilt and ducks.
Swamps with thickets of shrubs and trees are vital roosting and nesting sites for many species which feed in nearby estuaries. The most valuable are freshwater swamps with live plants, although dead shrubs and trees also provide loafing perches for many waterbirds and nest sites for some herons, ducks and cormorants. Individual swamps can be favoured by colonies of particular species, for example Darter Swamp and Egret Swamp near Leschenault Inlet.
This whole range of habitats must be protected to support the rich diversity of birdlife on our estuaries.
The worms, molluscs, insects and crustaceans of mudflats and shallows are snapped up by alert hunters such as small plover, or found by probing with sensitive bills as with the avocet. Add to this variety a range of leg lengths and body sizes for hunting food of different sizes in various depths of water, and you get the array of wading birds which feed side by side in estuaries. Many are trans-equatorial migrants which breed during the short Arctic summer. Then they follow the sun to the southern hemisphere where they look confusingly similar in their cryptic non-breeding plumages.
Red-necked stint are the smallest of the summer migrants. They gather on estuary mudflats in their thousands after travelling from northern Siberia. Plumage that can be seen in flight is important for distinguishing waders. The stint has a broad, white wing-bar and a dark centre to its rump. Often accompanying stints are the curlew sandpiper, with a white rump, and the sharp-tailed sandpiper, with an indistinct wing-bar.
The bar-tailed godwit is a large wader which also migrates from the Arctic. In contrast to the stint's short jabbing bill, the bar-tailed godwit's long, straight bill (with its distinctive pink base), is thrust deep into mud and sand to feel for small animals. Godwits fly in tight flocks then spread out to feed over the mudflats of estuaries. Careful observation will also reveal the closely-related black-tailed godwit, which is less common on our estuaries, and breeds in Europe and Asia. Banded stilt gather in thousands each summer to wade and swim in the shallows of the South-West's estuaries, sieving brine shrimp and other crustacea with their needle-like bills. They breed only occasionally, at inland salt lakes which only contain ample water in certain years. This happened in 1988 when 7000 chicks were counted at Lake King, north of Ravensthorpe. Black-winged stilt are smaller but similar birds which probe in estuary shallows and nearby swamps. The red-necked avocet is of the same size, but with an upturned bill used for sweeping from side to side, half opened, through water and mud.
The great egret, a brilliant white stalker of small fish, crabs and prawns, has only recently established breeding colonies in the south-west. Two of these are at Australind near the Leschenault Estuary. A much smaller (but similar) relative, the little egret, is uncommon in Western Australia but it, too, has begun to breed at Australind Swamp.
Twelve of Australia's 19 species of geese, swan and ducks occur in south-western estuaries. Estuaries are the strongholds for black swans, which graze on bank vegetation and seagrass. The large, colourful Australian shelduck is also an estuarine grazer, and many ducks such as the common Pacific black duck and grey teal dabble and dredge for a mixture of plants, seeds and small animals. The estuaries provide a summer refuge for adults and young of these and many less common species.
The musk duck, alone or in pairs, is a diver for bottom-dwelling animals in open water. The smaller blue-billed duck, distinguished by its blue bill (in breeding season) and dark head, is an accomplished diver and edge-dweller, feeding on plant material and midge larvae. Over a thousand blue-billed duck and hundreds of musk duck seek refuge on the Peel-Harvey Estuary in summer.
Up to 1500 of the distinctive, surface-feeding Australasian shoveler also seek summer refuge on the Peel-Harvey. Usually in twos and threes, these slim ducks strain water and mud through hair-like fringes to their broad bills to get surface-dwelling insects, crustacea and zooplankton. As with whales that sieve in this manner, they need water teeming with food. The zebra-striped pink-eared duck also feeds this way.
Rails and their allies stalk amongst reeds and marshes of wetlands and are a small to medium-sized relative of the domestic fowl. They commonly flick their upright tails while walking on long legs with stout, spread toes over soft ground and floating vegetation in search of plant and animal matter. They are best observed feeding at dawn and dusk, and can be heard calling at night.
The Western Australian subspecies of the eastern swamphen is a large dark-blue rail with a thick red bill. It is unusually brazen for a rail and is readily seen in dense reeds around estuaries, such as the southern end of the Harvey Estuary and adjacent swamps. It feeds on animals such as frogs and vegetable matter such as roots which are ripped out with its strong bill.
The buff-banded rail is one of a number of small, shy rails to be found in the reed margins of estuaries and adjacent wetlands. It is nomadic around coastal Australia. It breeds at Leschenault Estuary, where its harsh braying call is heard both day and night.
Only the larger raptors which soar in search of prey are regularly seen above estuaries. Marsh harriers, alone or in pairs, sweep low over swamps and estuary fringes to suddenly loom over sheltered pools from which waterbirds and other wetland vertebrates are plucked with their long talons. Well-adapted to their environment, they nest, roost and feed on the ground, but their courtships involve spectacular displays at great heights.
White-bellied sea eagles and the smaller osprey feed over the open water of estuaries, hunting for fish and smaller waterbirds. Both build large stick nests, used year after year, around some estuaries such as the Peel-Harvey. One osprey has even built its nest on an electric light pylon in Bunbury Inner Harbour.
Who doesn't know the pelican: soaring on a thermal, inscrutably watchful from a sandbank, or herding fish into the shallows for a feast? Never diving, it dips its bill into the shallows for fish and squeezes the water out through the corner of its mouth by pressing its bill-pouch to its breast. At least 100 pairs have bred on islands in Peel Inlet in recent years. Boodalan and Nirimba islands are named after south-western Aboriginal names for the pelican.
Cormorants and the darter are close relatives of the pelican and also feed on fish, supplemented by crustacea. Colonies of darters, little black, little pied and great cormorants breed in a few freshwater swamps near the estuaries. The pied cormorant breeds on offshore islands and commutes to estuaries to feed. These birds lack water-repellent plumage. They swim rapidly underwater, unhampered by trapped air, but must stand with wings out-spread to dry before they can fly. The darter stalks its prey underwater, and spears with a rapid thrust of its long neck. The pied cormorant is an agile diver. Propelled by its webbed feet, and using its wings for braking and turning, it grasps large fish in its hooked bill. Little black cormorants work cooperatively in `rafts' to herd schools of fish. The little pied, with a shorter bill, takes smaller prey, such as prawns, in shallow water. The larger of the three grebes of the south-western estuaries, the great crested grebe, dives in open water after fish and other small animals. Grebe build floating nests attached to reeds, and piggy-back their hatchlings. Great crested grebes are best known for their elaborate courtship dances in which they face each other and rise upright out of the water, necks upstretched, through vigorous paddling of their feet.
A variety of terns hover and skim over estuarine waters, plunging or dipping for their prey of fish and other aquatic animals. The smallest is the delicate fairy tern, which has nesting colonies on sandy points and islands. These colonies are vulnerable to disturbance from people and their dogs. The large red-billed caspian tern and medium-sized crested tern are commonly seen in estuaries at roosts or patrolling in search of fish. Four other species periodically appear at the estuaries, particularly the Peel-Harvey, and offer a challenge to the observer. Closely related to the terns, and much more plentiful, is the silver gull, which visits estuaries from offshore nesting islands to feed in the shallows for invertebrates and to scavenge. Thousands can be present at times in the Peel-Harvey.
Reclamation of foreshore areas has meant the loss of many habitats for waterbirds in waterways. Draining of wetlands and lakes has further reduced nesting and feeding areas for waterbirds.
Dredging to remove shallows, especially tidal flats, reduces feeding grounds for birds which feed on plants, invertebrates and fish. The increased turbidity makes it difficult for birds that fish by sight (such as cormorants). For these reasons, any proposals to dredge to improve the estuary's flushing or for recreational reasons needs thorough environmental assessment. Dredging leads to degradation of the waterway, and the release of toxins from sediments. This affects birds because they eat the plants and animals which have taken up the toxins. A degraded waterway, where living things are reduced in number and declining further, provides little for birds.
Spraying pesticides to control mosquitoes might put toxins into the food chains. Insect larvae and crustaceans are killed by pesticides. If they're not in the food chain, they can't be eaten by creatures that normally rely on them for their food. Those creatures then face starvation or must leave the area if the can.
Birds Australia (formerly the Royal Australasian Ornithologists Union) says that midge control methods should be evaluated. Block-winged stilts, which feed on midges, should be studied to see how they react to pesticide contamination.
Boating around, and other use of the foreshore by people, disturbs birds. Boating needs to be restricted on and near mudflats to stop people from walking on them and to reduce erosion caused by speedboats' wash. Waterbirds are generally very shy and will fly off when approached. A few species such as the red-necked avocet, white-headed stilt and red-capped dotterel, will settle somewhere else in the area, but many migratory birds will leave to find less disturbed locations.
Dogs are also a problem because they chase birds and destroy nests by digging in the sand. Birds Australia says that dogs harassing birds is a major problem, particularly at Como and Alfred Cove on the Swan River. Dog-owners need to be educated and regulations about leashing dogs need to be enforced to solve this problem.
Birds that fly here from the northern hemisphere (known as 'trans-equatorial migrants') can't afford to be disturbed a lot. If they are disturbed, they spend a lot of energy getting out of the way, which reduces the amount of fat they put on for their return flight to their breeding grounds. If they don't put on enough fat they may not make it back, or may not be in good condition and not be able to breed successfully.
Birds Australia also says that fishing and digging for bait in waterbird areas can be harmful. Litter such as plastic, fishing lines and hooks on the foreshore or in the water can tangle around birds legs, or be eaten by birds. Eating these sorts of things can cause a slow and painful death. If people stay away from important waterbird areas, such as Alfred Cove and Pelican Point in Perth, the amount the birds are disturbed will be reduced. Correctly sited walktrails, which allow people to watch birds without disturbing them, may be able to be built in some areas.
Each year millions of wading waterbirds leave their Artic breeding ground to follow the sun to the southern hemisphere. Stopping periodically to refuel at feeding grounds along the way, huge flocks travel down through Asia and funnel into Australia at Broome on high- and low-altitude air currents, many travelling further south. Our south-western estuaries are a principal destination for many of these travellers.
The migratory waders are protected on their journey under the Japan-Australia and China-Australia Migratory Bird Agreements (JAMB and CAMBA). Thirty-seven species named in these agreements visit south-western estuaries. Their numbers are so high in summer at Austin Bay Nature Reserve on Peel Inlet and on the Vasse-Wonerup Estuary, that these estuaries qualify as `wetlands of international importance' as defined in an international agreement known as the Ramsar Convention. Australia is responsible for managing and conserving these important sites on behalf of the entire world.
Only a few species breed in estuaries: on open, dry sand or in fringing vegetation. Islands are the safest sites from predators and from inadvertent destruction by people. Increased demand for housing, recreation sites and industrial areas around population centres, such as Mandurah, can put even island sites at risk. Fortunately, some species can take advantage of change. For example, hundreds of vulnerable fairy tern, some red-capped plover and pied oystercatcher now breed on the dredge spoils of Boundary Island in Peel Inlet.
Many of the estuarine birds that breed in Australia rely on a decreasing number of freshwater swamps with flooded vegetation that is suitable for nesting. Some of the most important of these wetlands - which support colonies of a variety of large waterbirds such as egrets, cormorants and ibis - are close to their estuary feeding grounds. Protecting these estuary and wetland breeding sites is vital to help estuarine birdlife survive.
Pressures on birdlife include destruction of their habitats by clearing, grazing and development; and alteration of their habitats (for example by raising nutrient or salt levels in the rivers). People are attracted to living close to estuaries and bring new pressures, such as the need to control insect pests like mosquitoes. Direct human disturbance around towns and cities can seriously affect waterbirds feeding and breeding.
The Water and Rivers Commission, working through waterways management authorities and the Swan River Trust, manages and maintains a number of south-western estuaries. However, the control of different regions and tasks is spread between many State Government departments - including the Environmental Protection Authority, Department of Conservation and Land Management (CALM) - local government authorities and local management committees.
The good management of the South-West's waterways relies on the goodwill and cooperation of these different bodies as well as the total community of people who live around and visit the estuaries. The continued well-being of our estuarine birdlife depends on greater understanding of what the birds need for themselves and their habitats; good management to protect and restore estuarine and wetland environments; and the strong support of the community.
CALM, in co-operation with community birdwatchers of Birds Australia, has been gathering information on waterbirds of the South-West since 1981. More observers are welcomed for regular visits to chosen sites. A good beginning is to join the many observers who spread out over south-western wetlands for the annual duck counts each spring and autumn.