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It is difficult to define the Shearwaters migratory path, as they
dont come to shore during the months of the migration, with
exhausted and starved birds often found washed up on beaches of
Japan, the Aleution Islands, North America and Australia. This
originally led scientists to believe that the birds flew a figure of
eight course across the Pacific Ocean. recent studies however,
suggest the majority of birds merely fly north along the western
part of the Pacific ocean to the Artic region and return southwards
through the centre of the ocean. Whichever way they migrate, the
birds end up travelling about 15,000 kms in each direction annually. Breeding and Life Cycle
Breeding season occurs during September to April. Each year the
length of time spent by young birds at the colonies increase until
they are five years old and begin breeding themselves. Prior to
breeding, the young birds fly in with the breeding adults in
preparation for the following breeding season. On arrival in
September/October at the colony, the birds meet with their chosen
mates and begin the task of tidying up the old burrows or excavating
new ones. The burrows are about 1 metre long.
In early November the birds leave the colony to spend some time
feeding before returning to lay a single white egg in late November.
The egg hatches in January and both parents participate in feeding
the chick. The chick rapidly puts on weight and is almost twice the
weight of the parents, when the parents depart from early April,
leaving behind the young birds still covered in down. From this time
until early May the chicks do not eat. They rapidly lose weight and
acquire their flight feathers. Within two to three weeks after being
left by the parents, the yond birds begin their migratory flight,
unassisted by experienced birds.
The average lifespan is 15-19 years, although they have been
known to live up to 38 years.
Food
Shearwaters feed on krill, squid and fish. Their main methods of
feeding include plunging into the water, pursuing underwater,
surface seizing, scavenging, hydroplaning and bottom feeding. During
the breeding season the adults feed in the locality of the colony.
Whilst on migration, they feed whenever food is available.
Harvesting
A regulated bag limit and open season exist on mutton-birds each
year. In Tasmania, around 200,000 chicks are harvested and sold
annually. The Aboriginals of the Flinders Island Group are well
regarded for their expertise in capturing the young chicks. They
used the mutton bird as a major food source and the oil from the
bird was used to rub on their bodies for warmth, as well as for
medicinal purposes. Mutton
Birds are now sold as a delicacy.
Mortality
Despite the number of Short-tailed Shearwaters, they are
over-harvesting and habitat destruction. Pigs, cattle and sheep have
destroyed whole colonies, whilst feral cats find the chick easy
prey. Soil erosion after fire can destroy suitable nesting sites. In
addition, gillnet fisheries in the North Pacific accidentally drown
up to 50,000 birds annually. Birds can also ingest small plastic
particles while at sea, which may limit the birds ability to
maintain condition and contribute to deaths during migration.
Natural mortality occurs mainly during the first migration due to
exhaustion and starvation.
History
First described by a Dutch ornithologist, Jacob Temminck in 1835,
who named them Puffinus Tenuirostris (tenui: slender,
rostrum: bill). Members of Captain Cooks third expedition in 1778
also recorded the Shearwater whilst sailing in the Artic Ocean.
Places you can see Short-tailed Shearwater include: Babel Island,
Swansea,
Montague
Island. Source: from many places,
including Parks and
Wildlife Service Tasmania |
