MUTTONBIRDS once flew in such large flocks that they blotted out the sun and turned the ocean black when vast carpets of the seabirds settled on the waves.
In 1798, English navigator and cartographer Matthew Flinders estimated that there were at least 100 million birds within a single flock sighted in Bass Strait.
The abundance of the short-tailed shearwater – to give the species its common name used beyond Tasmanian shores – was compared at the time with the vast numbers of passenger pigeons that flew in their billions across the chestnut forests of north America.
The passenger pigeon is now extinct and although the shearwater remains Australia’s most abundant seabird, warnings are being sounded that the muttonbirds’ future is far from secure.
To suggest that the muttonbird could take the same route as the passenger pigeon might be an exaggeration but an alarming collapse in the short-tailed shearwater population, and a downturn in its breeding success, is certainly a cause for concern.
Last year the carcasses of tens of thousands of muttonbirds washed up on the shores of south-eastern Australia and Tasmania, at the time the birds were returning to their Australian breeding grounds from the northern Pacific, where they spend our winter.
On a single beach near Newcastle in New South Wales 30,000 dead or dying birds were recorded, and on another along the Sunshine Coast 10,000 sea-washed carcasses.
The total population of muttonbirds was once estimated at about 25 million birds – 18 million of which breed around Tasmania’s coasts – but researchers believe the bird has been in decline for years.
Certainly, the current evidence points to muttonbirds being in staggering decline at their breeding grounds.
On BrunyIsland alone – with an estimated 8000 breeding pairs – nesting burrow occupancy was down 17 per cent in December from 49 per cent in the previous breeding season.
When dead muttonbirds first started to appear on beaches at the start of last summer it was soon realised this would represent one of the largest shearwater “wrecks” in living memory. Wrecks of shearwaters occur occasionally, but this was the fourth reported wreck in seven years.
Speculation mounted last year over whether an oil spill, disease, overfishing or even nuclear fallout from Fukushima in Japan could explain the mass deaths. But autopsies suggested the birds were severely malnourished after the annual 18-day migration from Alaska to the southern hemisphere. Competition with salmon for fish in Canada coupled with warmer than usual waters in Australia were linked with a decrease in food for the muttonbird.
The warmer seas are a phenomenon that has also resulted in fish species not normally found in Tasmania turning up here in ever greater numbers. Marine scientists are looking at the possibly that the intrusion of the less-nutrient rich warmer waters will displace cold water fish species that are the prime source of the muttonbirds’ diet during their time in their breeding grounds.
The crisis facing the short-tailed shearwater population has already resulted in the Aboriginal community in Tasmania suspending the commercial muttonbirding season in the largest colony, on BabelIsland, which at normal times has three million burrows. As Aboriginal leader Michael Mansell put it, there were too many empty burrows.
The muttonbird is not a bird that breeds quickly and this is compounding the problem. Although birds may live for 40 years, they only produce one chick a year, and so any recovery will be a slow one.
As the muttonbirds were departing last month for their epic journey, preparations were being made by BirdLife Australia and its local associate, BirdLife Tasmania to carry out the biggest survey of muttonbirds ever undertaken when the birds return at the start of summer.