Mutton Bird Existence Cycle

Mutton Bird Life Cycle

The mutton bird, also known as the short tailed shearwater, is a migratory seabird whose range extends throughout the Pacific, but whose nesting grounds are located in the extreme South Pacific in Tasmania, New Zealand, and adjacent islands. A long-flight bird ill suited to land but beautifully adapted to life in the air and on the ocean, it is New Zealand's most populous sea bird.

Related to the Petrel, it is slim with trim, arched wings. Its legs are placed well back on the body to reduce wind resistance. The beak is more slender than that of a gull, with narrow, tubular nostrils high up the beak. It is believed to have a strong sense of smell, unlike most birds.

The name "mutton bird" was given it by European colonists coming to the South Pacific. They hunted several species of shearwater for their meat, which they felt tasted similar to mutton.

Adult Life

The adult mutton bird spends the majority of the year in migration between Japan and the Aleutian Islands in the north, and Tasmania and New Zealand in the south. The migratory pattern forms a rough figure 8, following the trade winds up the coast of Asia, arching across the Bering Straights, coming down the western coast of the Americas, and returning to the southern nesting grounds in the southern hemisphere's spring in September.

Mutton birds primarily feed on small marine life, including squid and fish. They are an acrobatic hunter, diving to pursue prey, cutting the surface of the water with the edge of their wings, and actively "flying" through the water as they hunt.

The birds are believed to live as much as 30 years.

Mating

Mutton birds are comparatively long in maturing, not mating until their third to fifth year, if then. The youngest birds, only a year or two from hatching, spend the least amount of time in the hatcheries, returning only for a brief stay in midsummer. Over the next years the birds will extend their stays, remaining longer and longer among birds of the breeding colony. By their sixth year they will have become active breeders.

As breeders they will spend the first weeks after their return to the breeding grounds preparing nest burrows. Burrows are dug in soft sand or soil, and are over a yard long, but not very deep. The combination of soft soil with the tunnels running near the surface makes a nesting ground vulnerable to walkers, who can easily crush the hidden nests. Birds appear to be monogamous over their mating lives. Burrows and crevices appear to be reused regularly by returning birds year after year.

After preparing the nesting ground, the entire colony will return to the oceans for about three weeks on a "honeymoon flight." During this period they will regain weight lost on the migration, and then add more weight to see them through the long stretches without food during incubation. At the end of the period the female will return first, with the entire colony laying their eggs within a period between the 20th of November to the 2nd of December with peak production over a mere two day period in late November--on or around the 24th to 26th. The result ensures chicks will all be hatched and reach full development at the same time, enabling them to start their own migration in unison.

Incubation

Female birds lay only one egg per year. The egg will be large, taking up "a high proportion of female weight," according to the Victorian Ornithological Research Group, Inc. (Vorg). After laying the egg, the female will transfer responsibility to the male, who will sit the first round of incubation while the female returns to the feeding grounds to recover weight and strength. The incubation period takes 52 to 53 days, and the parent birds sit alternating shifts of 10 to 13 days. During these incubation periods parent birds in the burrows do not eat at all, feeding only when they return to the ocean after being relieved of duty by a returning mate.

Chicks

Chicks are large and downy on hatching. For the first week of their lives they are fed nightly, with parents alternating feeding shifts. Food is regurgitated by the parents. After the first three days parents leave the chick unattended for increasing periods of time. Feedings are very large, but irregular, with baby chicks gorging massively when fed, then slowly losing weight again until the next feeding. In spite of the fluctuation, the feedings are still quite regular enough for the babies to gain weight. They will weigh more than their parents by the end of summer.

The babies have fledged (grown in their mature feathers, including flight feathers) at 94 days. They will, by then, be able to comfortably go two weeks without food or supervision. They will weigh as much as 40 percent more than their parents. At this time the parent birds will leave them completely, returning to the migratory loop. The now mature chicks will remain on the breeding grounds for another two weeks before following their parents.

Life Away From the Breeding Ground

Relatively little is known about the life of mutton birds when they are far from land. As much of their lives are lived at sea in their constant round of migration, that means there is much not yet discovered about the species. Some, sickened, old, injured or made ill by ingestion of pollutants or plastics, will wash ashore on the currents along their migration patterns. Overall, however, they are mysterious birds of passage: graceful, powerful fliers who come for a short time and are gone along the coasts of their route.

Considerations

Mutton birds are among the few wild birds commercially harvested. Each year in Australia and New Zealand commercial and non-commercial mutton licensed chick harvests occur. For some of Maori aboriginal roots the annual hunt is a critical element in maintaining cultural patterns and history. For commercial groups it is a chance to harvest a resource valued for a specific set of rewards: oil used as an additive in race horse feed, feathers for stuffing down pillows, and preserved meat for those who are passionately fond of the commodity (a limited market).

According to the Australian Parliament the breeding grounds have succeeded well as managed populations, with the breeding grounds used by non-commercial hunters suffering more than those used by commercial groups. There are concerns, however, for the humane killing of the chicks, and for the true sustainability of a species that produces only one chick per year. A related petrel species, the providence petrel, was hunted to extinction.

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Monday, February 25, 2013