[Music playing]
(Narrator) A species of petrel commonly known as
the Tasmanian Mutton Bird
returns each spring to nest in the islands
around south eastern Australia.
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.
[Music playing]
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.’
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.
Nowadays adult birds and eggs are protected
and the industry is restricted to taking fledglings
between two and three and a half months old.
[Music playing]
In the Furneaux Group
the mutton birding industry is centred on five commercial islands.
The largest is Babel
so named by Flinders from the confusion of
tongues of its many kinds of bird inhabitants,
penguins, gannets, cormorants, mutton birds and gulls.
Other commercial islands in this area are Chappell,
Great Dog and Little Dog and Little Green Island.
[Music playing]
For the people of Flinders Island the opening of the birding
on March the 23rd is the event of the year.
In the weeks before visitors from the mainland arrive,
the school closes, islanders leave their farms.
They make for Lady Barron the small sea port
at the south of Flinders Island.
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.
Even a land Rover is shipped to Babel.
[Music playing]
Small cutters are used to reach the closer islands
while larger vessels make the voyages to Babel and Chappell.
[Music playing]
The birders land their gear by dinghy on the small
beaches or rocky shore platforms below their sheds.
Each shed unit is double, one building for accommodation
and the other for processing the mutton birds.
[Music playing]
This is a busy time for the birders,
especially if a new shed has to be built.
Finally spits are sharpened
and stacked ready for the opening of the season.
[Music playing]
And so at dawn on March the 23rd the slaughter begins.
The fledglings are removed from their burrows
and killed by a sharp jerk of the arm.
The catchers work systematically through the rookeries
and examine all likely burrows.
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.
[Music playing]
A good man’s daily tally is very nearly a thousand birds
and he carries his own catch back to the shed.
His average load might be 60 birds and weighs about 120 pounds.
[Music playing]
At the processing shed the crop oil is squeezed into a collecting 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.
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.
The main part of the catch is salt cured.
Weather permitting
fresh birds are sent to the freezing works at Lady Barron.
[Music playing]
Fresh birds are repacked in flat wooden cases and frozen.
In recent years
relatively more of the catch has been marketed in the fresh state,
transported by air to the consuming centre.
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.
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.
In 1947 a field station was set up on Fisher Island off Lady Barron,
strategically placed in the midst of three commercial islands.
A hut serves as a laboratory,
living quarters and store house for field equipment.
On Fisher the biology of the mutton bird is studied intensively,
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.
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.
Some birds also nest in this little grove of Seaberry Saltbush
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.
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.
On the larger island the air is filled with flying, wheeling forms
and the caterwauling of these hundreds of thousands of birds is deafening.
[Sounds of mutton birds]
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.
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]
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.
[Sounds of mutton birds]
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.
[Sounds of mutton birds]
By dawn the birds remaining on land are safely hidden underground.
Here is one protesting adult occupant of the Fisher Island burrows.
The species derives its scientific name Puffinus tenuirostris
from the long slender beak which is leaden grey in colour.
The dusky appearance of the underwing coverts is also characteristic
although on some individuals they may be almost white.
The short fan shaped tail has given the species its popular book name
short tail shearwater.
The legs are blackish grey on the outer aspect
and tinged with purple on the inner.
Notice on this bird’s leg a monel metal ring.
On Fisher Island every mutton bird is banded
and has it’s distinguishing number.
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.
A dab of paint of distinctive colour on the stake
indicates that this burrow has been inspected.
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.
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.
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.
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.
The clercal(?) opening of the male is inconspicuous, 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.
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.
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.
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.
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.
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.
Between the 13th and the 23rd of January
practically all eggs in the rookery hatch out.
When two or three days old
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.
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.
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.
With the coming of day birds of prey drop down to
feast on any fledglings exposed on the ground.
Others take to the water and are soon on their way.
[Music playing]
The young birds feed at sea to build up their strength
before following the course taken by their parents.
The route cannot be accurately plotted
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.
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.
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.
How these losses affect bird population strength is not yet known.
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.
The natural habitat of the birds is
disturbed by eating down the grassy cover,
trampling in the burrows and hardening the ground.
Soil hardness figures determined with a penetrometer
show that the harder the ground
the fewer the number of burrows occurring in any given area.
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.
Similar havoc is taking place in some of the rookeries
on Phillip Island in Victoria.
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 playing]