The Mutton Birds of Bass Strait (1956)
The Mutton Bird (Puffinus tenuirostris) has been the basis of a successful, if little-known, Tasmanian industry for more than a century. Each year millions of fledglings are harvested for their carcasses and oil.
In 1947, in an attempt to assess how long rookeries could withstand such losses, the Fauna Board of Tasmania joined forces with CSIRO to investigate the mutton bird”s life history. The bird”s fantastic migration was one of the most interesting facts they uncovered. The huge flocks that cross the Pacific each year to spend the northern summer in Canada and Alaska, return to their Bass Strait breeding grounds on almost the same day each year.
[Music plays, Australian Coat of Arms appears then changes to The Commonwealth Scientific and Industrial Research Organization Presents: The Mutton Birds of Bass Strait, with flock of birds flying over the ocean in background]
Narrator: A species of petrel commonly known as the Tasmanian Mutton Bird returns each spring to nest in the islands around south eastern Australia.
[Image shows map of Australia charting the mutton birds’ route of migration]
They come from the north in flocks totally many millions and migrate down the east coast of the continent to their breeding grounds in and around Bass Strait to the north of Tasmania.
[Image shows flock of birds flying over ocean]
One flock so impressed Matthew Flinders during his exploration of the Furneaux Islands in 1798 that he described it in his diary:
‘There was a stream of from 50 to 80 yards in depth and 300 yards or more in breadth and during a full hour and a half this stream of petrels continued to pass without interruption at a rate little inferior to the swiftness of a pigeon. From the lowest computation I think the number would not have been less than a hundred millions.’
[Image shows birds nesting on islands]
These birds nest in large numbers on scores of small islands in the Furneaux Group and sealers who came in the wake of Flinders were quick to exploit them for food, fat and oil.
[Image shows men carrying catch of birds]
Nowadays adult birds and eggs are protected
[Image shows a mutton bird being pulled from its burrow]
and the industry is restricted to taking fledglings between two and three and a half months old.
[Image shows man holding fledgling mutton bird, then changes to map of Furneaux Islands]
In the Furneaux Group the mutton birding industry is centred on five commercial islands.
[Image shows close up of individual islands on map]
The largest is Babel so named by Flinders from the confusion of tongues of its many kinds of bird inhabitants, penguins, gamut’s, cormorants, mutton birds and gulls. Other commercial islands in this area are Chappell, Great Dog and Little Dog and Little Green Island.
[Image shows local island people]
For the people of Flinders Island the opening of the birding on March the 23rd is the event of the year.
[Image shows aeroplane taking off]
In the weeks before visitors from the mainland arrive,
[Image shows school children]
the school closes,
[Image shows truck driving away]
islanders leave their farms.
[Image shows family outside Island Store]
They make for Lady Barron the small sea port at the south of Flinders Island.
[Image shows various people at harbour]
Cape Barren Islanders too come to take their traditional part in the harvest.
Boats are chartered and food supplies, drums for oil, boxes, salt and all the paraphernalia needed for six weeks’ stay are stowed aboard.
[Image shows Land Rover being loaded onto boat]
Even a land Rover is shipped to Babel.
[Image shows people sailing off in boat]
Small cutters are used to reach the closer islands while larger vessels make the voyages to Babel and Chappell.
[Image shows larger boat sailing across ocean. Image changes to show men loading dinghy]
The birders land their gear by dinghy on the small beaches or rocky shore platforms below their sheds.
[Image shows men unloading dinghies]
Each shed unit is double, one building for accommodation and the other for processing the mutton birds.
This is a busy time for the birders, especially if a new shed is to be built.
[Image shows shed being built]
Finally spits are sharpened
[Image shows man sharpening large sticks]
and stacked ready for the opening of the season.
[Image shows woman stacking large sticks. Image changes to show approaching dawn]
And so at dawn on March the 23rd the slaughter begins.
[Image shows man walking across grassy field with large stick]
The fledglings are removed from their burrows and killed by a sharp jerk of the arm.
[Image shows man pulling mutton bird from its burrow and shaking it]
The catchers work systematically through the rookeries and examine all likely burrows.
[Image shows birds being threaded onto large stick]
They thread the birds by their beaks on wooden spits made of Manuka the local tea tree, keeping their heads upward to maintain the crop oil, an important by-product.
[Image continues showing mutton birds being pulled from burrows and threaded onto stick]
A good man’s daily tally is very nearly a thousand birds and he carries his own catch back to the shed.
[Image shows man carrying large load of mutton birds]
His average load might be 60 birds and weighs about 120 pounds.
At the processing shed the crop oil is squeezed into a collecting drum.
[Image shows man squeezing oil into drum]
Twenty birds yield about a gallon of oil at the peak of the season but there is none in the last few weeks. After refining it will be sold for medicinal use.
[Image shows oil in bucket. Image changes to show man plucking a mutton bird]
After plucking the birds are scalded and the remaining down is rubbed off. The carcasses are left to cool before being opened up, dressed and salted.
[Image shows mutton bird carcasses hanging in a row. Image changes to man salting mutton birds]
The main part of the catch is salt cured.
[Image shows men in row boat]
Weather permitting fresh birds are sent to the freezing works at Lady Barron.
[Music plays while men transport cases of mutton birds]
Fresh birds are repacked in flat wooden cases and frozen.
[Image shows men loading flat wooden cases onto back of truck]
In recent years relatively more of the catch has been marketed in the fresh state, transported by air to the consuming centre.
[Image shows men loading wooden cases onto plane]
Tasmanians are the largest buyers, regarding the flesh of the young bird as a delicacy.
Over half a million birds were taken in 1954 and they netted over 40,000 pounds for the inhabitants of Flinders Island.
[Image shows plane taking off. Image then changes to men harvesting mutton birds]
How long can the rookery stand such intense harvesting? Little wonder that the government of Tasmania was concerned for the future of the mutton bird, so the CSIRO joined forces with the Fauna Board of Tasmania to investigate its biology and life history.
[Image shows man carrying off load of mutton birds. Image changes to show field station on small island in the distance]
In 1947 a field station was set up on Fisher Island off Lady Barron, strategically placed in the midst of three commercial islands.
[Image shows a small hut]
A hut serves as a laboratory, living quarters and store house for field equipment.
[Image shows two men inside of hut]
On Fisher the biology of the mutton bird is studied intensively,
[Image shows two men leaving hut]
supplemented by excursions to nearby islands.
Statistics compiled over a number of years will show whether the commercial rookeries are being depleted and if so what measures must be applied to maintain them.
[Image shows men walking through Tussock grass]
Tussock grass, poa pomiformis, which covers most of the island predominates in all the rookeries around Tasmania. Between the tussocks the birds scratch out their nesting burrows to a depth of about three feet.
[Image shows mutton bird burrow]
Some birds also nest in this little grove of Seaberry Saltbush
[Image shows two men walking through grassland]
and Coast Wattle on the south end of the island. About 150 pairs of mutton bird nest on Fisher but their presence is not obvious in the day time.
[Image shows close up of Tussock grass]
Even the entrances to their burrows are hidden, partly covered by tufts of grass and other debris blown there by the wind. After sunset the birds return from the sea.
[Image shows flock of birds flying at sunset]
On the larger island the air is filled with flying, wheeling forms and the caterwauling of these hundreds of thousands of birds is deafening.
[Sound of mutton birds calling. Image shows mutton bird walking on ground at night]
They land within a few feet of the entrance to their burrows and make their way below ground.
Mutton birds are particularly helpless on the ground.
[Image shows group of mutton birds walking on ground]
Birds remaining on land in the daytime do not leave the shelter of their burrows as they are easy prey for predators such as large gulls and hawks.
[Sounds of mutton birds. Image shows large group of mutton birds on ground]
Within an hour of the first arrivals the pandemonium subsides but just before dawn it rises again as the birds make their way to the take-off rocks for the communal exodus out to sea. They do not easily become airborne and usually make a running take off into the wind or plummet themselves from an eminence.
Streams of departing birds converge on rocky outcrops on the densely populated islands. Prominent rocks are marked by scratches of untold generations of birds which have used them for take-off platforms.
[Image shows mutton birds taking flight]
By dawn the birds remaining on land are safely hidden underground.
[Image shows grassland and rocky outcrops. Image changes to show man in gloves handling a mutton bird]
Here is one protesting adult occupant of the Fisher Island burrows.
[Image changes to close up of mutton bird]
The species derives its scientific name Puffinus tenuirostris from the long slender beak which is leaden grey in colour.
[Camera pans out to image of two men holding mutton bird]
The dusky appearance of the underwing coverts is also characteristic
[Image shows extended wing of mutton bird]
although on some individuals they may be almost white.
The short fan shaped tail
[Image shows tail of mutton bird]
has given the species its popular book name short tail shearwater.
[Image shows extended leg of mutton bird]
The legs are blackish grey on the outer aspect and tinged with purple on the inner.
[Image shows man pointing to mutton bird’s leg]
Notice on this bird’s leg a monel metal ring. On Fisher Island every mutton bird is banded and has it’s distinguishing number.
[Image of men undertaking mutton bird census]
A census of the Fisher Island rookeries is taken each season and to ensure that no burrow is overlooked the island is surveyed in narrow strips.
Each burrow is marked with a neat numbered peg and a detailed map of the rookery is drawn up.
Each ringed bird is recorded in the field book as the occupant of a particular burrow.
[Image shows stake being painted]
A dab of paint of distinctive colour on the stake indicates that this burrow has been inspected.
[Image shows notebook and card index]
A precis of the field notes is made in a card index with a card for every bird. Statistics from these records reveal many interesting characteristics of mutton birds. For instance they are monogamous and usually take the same mate each year. They return invariably to the same burrow site even if the burrow has been destroyed in the meantime.
[Image shows close up of card record from card index]
Female 12591 was first recorded nesting on Fisher in 1948 occupying burrow 297 to which she has returned ever since. She had the same mate til 1953 though he was not checked in during 1949. They were divorced in 1953 and each took a new mate in the same little neighbourhood.
[Image shows mutton bird being banded]
Banding experiments will eventually make it possible to calculate the mean life expectancy of mutton birds.
Many of the birds ringed in 1947 returned to Fisher Island for the eighth successive season in 1954.
[Image shows close up of man holding mutton bird]
As in most petrels both sexes have similar external features but they are easily distinguished in the breeding season. The unlaid egg in the mother bird can be felt as a hard protuberance in the belly region.
[Image shows pointing to belly of female mutton bird]
The clercal(?) opening of the male is inconspicuous,
[Image shows checking the sex of a mutton bird]
rounded and small while in the female it is a prominent transverse slit with lips swollen and tumid. After egg laying the opening becomes widely distended and the clercal(?) lips bloodshot.
[Image shows female bird nesting]
The female lays only one egg each year. The first eggs are laid about the night of November the 21st reaching a climax by November the 25th.
[Image shows researchers in the field]
The laying season ends about the second of December. These dates have not varied materially since the first observations were recorded over a century ago.
[Image shows researcher holding mutton bird egg]
The egg is disproportionately large. The adult bird weighs one pound to a pound and a half while the egg averages just over three ounces, about one sixth of the bird’s own weight.
[Image shows mutton bird nesting on egg]
Egg laying is a considerable ordeal and the female after resting in the burrow for a day or two goes out to sea to feed and recuperate.
[Image shows mutton birds flying out to sea]
The male remains sitting on the egg alone and unfed until the female returns about 13 days later. The parents continue to change over every 13 days until the egg hatches, about 54 days after laying.
[Image shows mutton bird egg hatching]
Between the 13th and the 23rd of January practically all eggs in the rookery hatch out.
[Image of baby mutton bird]
When two or three days old
[Image of person holding mutton bird chick]
the chick is left by its parents in the daytime but at night one returns to feed it a gargantuan banquet of krill and oil. If neither parent returns it must fast sometimes for as long as 15 days.
[Image shows growth of baby mutton bird]
At the peak of its growth the young bird averages a pound heavier than the adult, often scaling two and a half pounds. As the season progresses the body weight falls, feathers appear and the down is shed.
The fledglings are finally deserted by their parents in mid-April and now patrol the rookery at night exercising their wings.
[Image shows mutton bird walking on rocks]
They leave the island when about 100 days old. When ready to depart they make their way to the water’s edge or a suitable take-off point.
[Image shows bird of prey flying overhead and diving on the young birds]
With the coming of day birds of prey drop down to feast on any fledglings exposed on the ground.
[Image shows mutton bird on water]
Others take to the water and are soon on their way.
[Music plays while showing images of flocks of mutton birds flying out to sea]
The young birds feed at sea to build up their strength before following the course taken by their parents.
[Image shows flock of mutton birds feeding at sea]
The route cannot be accurately plotted
[Image shows world globe following route of the mutton birds]
but the available evidence shows their migration covers a vast circuit of The Pacific.
In late April and May many birds are reported along New Zealand beaches and in the vicinity of the Marshall Islands. In June they are seen near Japan and along the coast of Alaska. They stay in this region til the end of the northern summer, large flocks frequenting the Bering Straits.
By September the southward migration is underway, down the coast of Canada and across The Pacific. The adult birds reach the breeding grounds soon after the third week in September.
[Image shows flock of mutton birds out at sea]
The immature birds travel later and may continue to come in until December and January.
During the migration many birds die or lose their way. The greatest losses occur along the Australian coast where countless thousands may perish each year, apparently through starvation.
[Images of dead birds]
The mortality varies.
Nineteen thirty four and the years around nineteen forty were bad years. Another heavy mortality in 1954 was the largest yet recorded.
[Image shows man with dog coming across dead mutton bird on beach]
How these losses affect bird population strength is not yet known.
[Image shows researchers banding young mutton birds]
The results of exploitation by man are more easily determined. Before the yearly harvest a sample number of young birds is banded at random throughout the commercial rookeries. The catchers will retake many of these birds and from the number of rings returned after the season the intensity of harvesting can be calculated.
In 1954 1650 young birds were ringed on four commercial islands and of these 60% were retaken during the harvest. Yet despite this high rate of exploitation the records show these rookeries are not being depleted. Why then have mutton birds disappeared from large areas on some islands? Investigations have shown grazing animals to be responsible.
[Image shows animals grazing]
The natural habitat of the birds is disturbed by eating down the grassy cover, trampling in the burrows and hardening the ground.
[Image shows researcher testing soil]
Soil hardness figures determined with a penetrometer show that the harder the ground the fewer the number of burrows occurring in any given area.
[Image shows eroding sand dunes]
Erosion is another serious problem particularly on the mainland of Tasmania. This sand blow at Cape Contrariety was probably started by rabbiters digging out burrows.
[Image shows researchers inspecting sand dunes]
Similar havoc is taking place in some of the rookeries on Phillip Island in Victoria.
[Image shows flocks of mutton birds at sea]
It is comforting to know that even though commercial interests take their yearly toll this in itself does not harm the colonies. If only their natural environment can be preserved there is no reason why the mutton birds of Bass Strait should not fly for eons to come in the same thrilling abundance which amazed Flinders and delights the present day bird watcher and ocean voyager.
[Music plays while credits roll: Produced by the C.S.I.R.O Film Unit, in collaboration with The Wildlife Survey Section. Scientific Consultant D.L Serventy, Photography R.R Crispe]