Wednesday, 9 February 2011
Recently many of us were distressed by the sight of large numbers of dead and dying birds on Main Beach. They were short tailed shearwaters often known as mutton birds. Local naturalist Michael Hines and Dave Stewart from Queensland Parks and Wildlife had been observing this event and noted carcasses every 5m for at least 5km, so there were considerable numbers of dead and dying birds.
Short tailed shearwaters are pelagic, that is, they live their life in the open ocean and are a migratory species. There are approximately 23 million in the world, breeding on the Australian islands during the warmer months mainly in Tasmania and Islands in the Bass Strait. It is the most abundant Australian seabird. There are about 285 colonies in SE Australia, 18 million birds arriving in Tasmania each year. They have adapted to life on the ocean by having webbed feet for swimming, a hooked beak for fishing, and long and narrow wings for efficient high speed gliding. Shearwaters have a wing span of 1 metre and weigh 500 g. They are one of the few birds with a well developed sense of smell. They were first recorded by members of Captain Cook’s third expedition on the Discovery sailing through the Arctic and were named as such for their graceful shearing flight.
The birds start breeding at 5 years of age and in early Sept/Oct meet with their chosen mate and begin to prepare and tidy up the old burrows or excavate new ones. They mate inside the metre long burrows , and retain that partner for life. They leave the colony in November to feed before laying a single white egg, allowing the bird to build up fat for its long journey. The distinct peak egg laying date is 27-28 Nov. Both birds incubate the egg, and the chick hatches after 53days. Both parents feed the baby and quickly it becomes twice the size of a parent. In April the adults depart leaving the downy chick behind. From this time to early May the chick does not eat, rapidly loses weight and acquires its flight feathers. It moves closer to the shore and exercises its wings. 2-3 weeks after the parents leave the young birds start their amazing migratory flight unassisted by the experienced birds. The average life span is 15-19 years but some live to 38 years.
Between June and August the birds fly north along the western Pacific to the Arctic and Bering Sea to feed. They return south between October and January along the east coast of Australia, travelling 15,000 km in each direction and incredibly some do the whole journey in 6 weeks. In some years many perish and are washed up onto the beach. This is thought to result from exhaustion, starvation the influence of storms and strong winds. By the time the birds arrive back in Australia they have expended most of their energy reserves on the journey losing half their body weight. They may meet with unusual sea surfaces temperatures which can affect their main food source which is krill, squid and fish. They can dive 10 metres to fish, but when their food supply is unavailable they become exhausted . Southerly gales make it impossible for the birds to fly on in this weakened state and so they are blown and washed ashore. Sometimes live birds are washed up but are too exhausted to head back out to sea. The elderly and young birds are the most vulnerable. They are able to cope with strong gales at sea when they are fit and well. So it is thought that this was the fate of the many birds found on our island.
The sighting of so many dead and dying birds was distressing and many people voiced their concern causing the Minister for the Environment to instigate a rescue operation. The Environment Department needed to respond cautiously in their approach to the rescue and made an order that no one should go near the birds until it had been confirmed that they were not carriers of Bird flu. There was a delay therefore of 2-3 days before 80 birds were collected , half from Main Beach and the other half from south Straddie . Wildlife carers from Straddie and DERM officers collected and took the birds to the Pelican and Seabird rescue station at Manly. The Government scientist’s testing for bird flu proved negative. It is highly unlikely that pelagic birds carry the virus. These birds are notoriously difficult to rehabilitate according to researchers at the UQ Research Station. However, of the 40 birds collected from NSI and 40 from SSI which were rescued, 18 were nursed back to health and released, regrouping to fly south. 200,000 or more shearwater chicks are harvested commercially under licence in Tasmania each year, being prized for their down, feathers, oil and flesh.
If you find shearwaters or other birds on the beach the Pelican and Seabird Rescue asks that you contact them on 0404118301. UQ Research Station is of the opinion it is best to leave shearwaters alone as they are notoriously difficult to rehabilitate. First check if they have a numbered metal band around a leg. If so, contact Australian Bird and Bat Banding Scheme as well.
A special thanks to Mike Hines for his help with information, Emma Lewis at the UQ Research station, Dunwich and to Robert Ashdown for the photos.