Short-tailed Shearwater

To: Richard Nowotny <>
Subject: Short-tailed Shearwater
From: "Jeremy O'Wheel" <>
Date: Thu, 21 Nov 2013 14:14:36 +1100
Very interesting, although I wonder about the veracity of Matthew Flinders
estimate of a single flock of 100 million birds in 1798.


On 21 November 2013 12:13, Richard Nowotny <>wrote:

> A local non-birding friend asked me some questions about the recent STSW
> wrecks, some of which I was unable to answer with any confidence (eg. how
> long do the birds normally live?) It caused me to head for Google (although
> I also have HANZAB and HBW to which I could have gone). I found the
> following from the Tasmanian Parks and Wildlife Service website. For those
> readers who would like to refresh their knowledge of this interesting, and
> currently topical, species it provides quite an interesting overview.
> Richard
> PS I have left in some colour highlighting I did for my friend - it picks
> out some interesting facts (including a reversal of the well-known "figure
> of eight" migratory path theory).
> Short-tailed Shearwater, Puffinus tenuirostris
> Description
>  <>
> Short-tailed shearwater
> Shearwaters are one of the world's
> most remarkable migratory birds
> The short-tailed shearwater, or mutton bird as it is often known, is a
> member of a group of 60 medium to large seabirds in the family
> Procellaridae. This family includes species such as petrels and prions. All
> members of the family have tube-like nostrils on the top of their upper
> beak
> and are believed to be one of the few bird families with a well-developed
> sense of smell. Almost all breed in burrows and, like the albatrosses, are
> truly impressive oceanic fliers.
> Adult birds have a wing span of about 1 metre and weigh approximately 500
> grams. Shearwaters are good swimmers and have webbed feet. Their legs are
> placed well back on their body and their wings are long and narrow for
> efficient high speed gliding. These features suit an oceanic existence so
> the shearwater has difficulty moving on land or taking flight in windless
> conditions. Shearwaters are often seen floating in large 'rafts' while
> feeding off the shores of Tasmania.
> History
> The short-tailed shearwater was first formally described by a Dutch
> ornithologist -- Jacob Temminck in 1835. He named it Puffinus tenuirostris
> (tenui -- slender, rostrum -- bill). The shearwater was recorded much
> earlier by members of Captain Cook's Third Expedition in 1778 while sailing
> in the Arctic Ocean. William Ellis, an artist on the 'Discovery' painted
> the
> bird.
> The name 'muttonbird' was first used by the early settlers on Norfolk
> Island, who each year harvested adult providence petrels (Pterodroma
> solandri) for food. The petrels were similar to but larger than the
> short-tailed shearwater. An officer in the Royal Marines called them 'the
> flying sheep'.
> Unfortunately the providence petrels became extinct following massive
> harvesting (171 000 birds one year) and the introduction of pigs to the
> island. The name 'muttonbird' has been applied to the short-tailed
> shearwater ever since. The common name, shearwater, is an apt reference to
> their graceful shearing flight moving from centimetres above the water's
> surface to high in the sky.
> Harvesting
> Tasmanian Aborigines have harvested muttonbirds and their eggs for many
> generations, and a number of families continue this important cultural
> practice. The muttonbird is one of the few Australian native birds that is
> commercially harvested. During the muttonbird season, chicks are taken for
> their feathers, flesh and oil. The industry was established by early
> European sealers and their Aboriginal families. The recreational harvesting
> of Short-tailed Shearwaters is limited to the period of the open season
> that
> is declared each year. A
> <>
> muttonbird licence must be obtained.
> Distribution and migration
> The shearwater is the most abundant Australian seabird. Approximately 23
> million short-tailed shearwaters breed in about 285 colonies in
> south-eastern Australia from September to April. Eighteen million of these
> arrive in Tasmania each year. There are known to be at least 167 colonies
> in
> Tasmania and an estimated 11.4 million burrows. The largest colony is on
> Babel Island which has three million burrows. Their colonies are usually
> found on headlands and islands covered with tussocks and succulent
> vegetation such as pigface and iceplant. Headlands allow for easy take off
> and landing.
> Early accounts suggest that the population was once considerably higher. In
> 1798, Matthew Flinders estimated that there were at least one hundred
> million birds within a single flock sighted in Bass Strait.
> Their migratory path is difficult to define because they don't come to
> shore
> during the months of the migration. Exhausted and starved birds are often
> washed up on beaches of Japan, the Aleutian Islands, North America and
> Australia. Originally this led scientists to believe that the birds flew a
> figure of eight course across the Pacific Ocean. Recent studies suggest the
> majority of birds merely fly north along the western part of the Pacific
> Ocean to the Arctic region and return southwards through the centre of the
> ocean. Either way the birds travel about 15 000 kilometres in each
> direction
> annually. They have been known to fly this remarkable distance in six
> weeks.
> Breeding
> The breeding period occurs between September and April. Each year the
> length
> of time spent at the breeding grounds increases until the birds are 5 years
> old, when they become involved in breeding. As pre-breeders, the birds fly
> in with the breeding adults in preparation for the following breeding
> season.
> On arrival in late September/early October at the colony the birds meet
> with
> their chosen mates and begin tidying up the old burrows or excavating new
> ones. The burrows are about 1 metre long. Mating takes place inside the
> burrow.
> Each bird generally remains with the same partner throughout their life,
> although the "divorce rate" does increase to nearly 25% among pairs that
> fail to produce young.
> In early November they leave the colony to spend some time feeding before
> returning to lay a single white egg in late November. This exodus period is
> important as it allows the birds to build up fat reserves to see them
> through the incubation period. There is a distinct peak in egg laying at
> 27-28 November. Males and females take turns incubating the egg. The male
> takes the first shift, which lasts for about two weeks, followed by the
> female. Usually, both sexes have two shifts. During each shift, the "duty"
> bird does not leave the burrow, nor is it fed by its mate.
> The young chicks hatch in the third week of January after an incubation
> period averaging 53 days. Both parents participate in feeding the chick.
> The
> chick quickly puts on weight and before the departure of the parents, is
> almost twice the weight of an adult. The adults depart from early April
> leaving behind the young birds still covered in down. From this time until
> early May the chicks do not eat at all. They rapidly lose weight and
> acquire
> their flight feathers. The young spend an increasing amount of time outside
> the burrow, slowly moving closer to the shore and exercising their wings.
> Two to three weeks after the parents have left, the young birds begin their
> migratory flight unassisted by experienced birds.
> The period of time spent in the breeding colonies varies with the age of
> the
> bird
> mut.JPG
> Food and feeding
> Shearwaters feed on krill, squid and fish. Their main methods of feeding
> are
> plunging into the water, pursuing underwater, surface seizing, scavenging,
> hydroplaning and bottom feeding. They are capable swimmers and are able to
> dive to 10 metres. Their hooked beak allows them to hold on to their prey.
> During the breeding season the adults generally feed in the locality of the
> colony. The chicks produce large amounts of oil in their stomach which is
> high in energy content and sustains them while the parents are away. During
> migration they feed whenever food is available.
> It is possible that krill abundance determines the migration of the
> species,
> allowing them to exploit the high concentrations of krill which occur each
> summer at both polar regions.
> Threats and mortality
> Although there appears to be a huge number of short-tailed shearwaters,
> they
> are still vulnerable to over-harvesting and habitat destruction. In places,
> pigs, cattle and sheep have destroyed whole colonies. Soil erosion after
> fire can destroy suitable sites for burrowing.
> Gillnet fisheries in the North Pacific accidentally drown up to 50 000
> birds
> annually.
> Approximately 200 000 chicks are presently harvested and sold annually in
> Tasmania by commercial operators. Birds also ingest small plastic particles
> while at sea which may limit their ability to maintain condition and
> contribute to deaths during migration.
> Feral cats are also a problem, as they find shearwater chicks easy prey.
> Trampling of burrows by humans can also cause their death. Similarly,
> erosion caused by recreational vehicles can destroy suitable sites for
> burrowing. It is important to keep off colonies.
> Natural mortality occurs mainly during the first migration due to
> exhaustion
> and starvation. The average lifespan is 15-19 years but birds can live up
> to
> 38 years.
> International treaty
> Because of the shearwater's international migratory habitats it has become
> the subject of a joint protection project between Japan and Australia --
> the
> Japan Australia Migratory Bird Treaty. Both countries monitor the
> shearwater
> population while the birds are in their area. In Tasmania harvesting limits
> are imposed to prevent over-harvesting and a number of wildlife sanctuaries
> protect shearwater colonies. Japanese and other countries are attempting to
> minimise the number of birds drowned by their fishing operations. It is
> hoped that these conservation methods will ensure the survival of one of
> the
> world's most amazing migratory birds.
> Further Information
> Lindsey, T. R. (1986). The Seabirds of Australia. Angus and Robertson.
> Marchant, S. and Higgins, P. J. (1990). Handbook of Australian, New Zealand
> and Antarctic Birds. Vol. 1. Oxford University Press, Melbourne.
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