Migration (Shorebirds)

The majority of migratory shorebirds found in Australia use the East Asian-Australasian Flyway, spanning migratory routes from New Zealand and Australia to Asia or Alaska, including important staging sites such as the mudflats around the Yellow Sea in China and Korea. However, some of the migratory shorebirds that are too young to breed or adults that are not strong enough for the journey north, stay in Australia the whole year.

Most migratory species breed in northern China, Mongolia, Siberia and Alaska during June and July and then migrate to Australia for the non-breeding season. One exception to this is the double-banded plover, that breeds on the pebble beds of the rivers of New Zealand's South Island in the summer months from September to March. It then flies trans-Tasman to spend the southern winter in the comparatively warm conditions of Australia's east coast, arriving in Queensland in March/April when all other migratory shorebirds are leaving for Siberia.

Timing

Migratory shorebirds leave the northern hemisphere around July and arrive in Australia from late August onwards, with adults of the more southerly breeding species arriving first. Adults from farther north follow and then juveniles begin to turn up. Once adult birds have arrived back in Australia, they will move to familiar locations where they have lived for the greater part of the austral summer in previous years. This re-location within Australia may take several weeks and include a number of locations not very far apart before arriving at their final destinations. The initial flights at the beginning of either the northward or the southward migration, are typically longer than flights when birds are closer to their final destinations on either the breeding grounds or back in Australia.

Birds are in non-breeding plumage in Australia between mid-November and mid-February. However, by late February many species begin to gain weight and to moult their body plumage in preparation for migration and breeding in the northern hemisphere. Depending on the species, over a period of as little as 6 weeks birds can almost double their weight and transform their appearance.

After departing Australia, birds often stopover in central parts of the flyway, such as the Yellow Sea, for several weeks until they have regained some of their lost body weight and are primed for breeding. They must arrive in their northern breeding grounds at the right time to make the best use of a proliferation of plant and insect life that is available over the short northern summer. Arriving too early could mean bad weather or cold conditions that prevent any chance of breeding success or even death of the adult birds.

Many adult shorebirds arrive back in Australia by late August. Juveniles start arriving back at least two weeks later. Juveniles leave the breeding grounds later than the adults and will have travelled without adult guidance. They then establish on a suitable intertidal flat or freshwater wetland for the coming months. First-year birds do not migrate and remain in Australia over the austral winter and for many species, especially the larger ones, the young may not migrate and breed until they are in their 3rd or 4th year.

Energy Budget

Shorebirds need to markedly increase their food intake rates in order to store fat as fuel for migration. More energy can be stored per unit of weight in fat than in other types of tissue and birds can metabolise fat in unmodified form, making it ideal fuel for migration. The next best energy source is their own muscle tissue, although it is eight times less dense in energy than fat. Flight muscles increase in size before migration in preparation for the extra weight that will be carried as fat, but as the migration proceeds and fat is shed, large muscle is metabolised to fuel the muscle that remains.

A bird that doubles its weight before migration can use the stored energy in a matter of days of constant flying. The fat is stored as a subcutaneous layer of tissue but also as abdominal fat. Shorebirds are able to reduce the size of digestive organs such as the liver, which are not necessary during flight. Protein to repair muscle damaged during flight can be stored as a thick skin layer before departure.

Shorebirds can fly higher than 5,000 m to find favourable winds to assist in their flights and/or to achieve a direct flight pat[2]. Departure times are often linked to favourable prevailing winds, which can make dramatic differences to flight times as air speed of shorebirds is around 50 km per hour, meaning wind direction is of major importance.

A demanding lifestyle

During their “over-wintering” time throughout the Australian summer, shorebirds are not involved in breeding and migrating and simply travel locally between where they roost and where they feed. Their daily routine is determined by the tide and they also moult their flight feathers which leaves them vulnerable to predation. Once the moult is complete, feeding must increase for birds to gain weight to migrate.

Migratory shorebirds are locked in a cycle of migration and breeding with intervening times of preparing for, or recovering from, their extraordinary flights across the world. They must be capable of living in totally different environments, that requires a shift between an isolated, terrestrial lifestyle to living in flocks in a marine environment, driven by the tide. They are able to drink salt water because they have the ability to extract the salt with special glands in the head, an energy intensive process[1]. They need to be able to survive extremely cold environments but also be able to keep cool while living in the tropics. They keep cool by lifting feathers for better ventilation, standing in pools of water, or directing blood to the base of their bills where it has a chance to cool down through a layer of thin skin.

Acknowledgements

Information was compiled using a number of sources including the following:

• Rogers, D. I., T. Piersma, M. Lavaleye, G. B. Pearson, and P. de Goeij (2003) Life Along Land’s Edge, Wildlife on the shores of Roebuck Bay. Department of Conservation and Land Management, Western Australia.
• Geering, A., L. Agnew, and S. Harding (2007) Shorebirds of Australia. CSIRO Publishing, Victoria.
• Paulson, D. (1994) Shorebirds of the Pacific Northwest. University of British Columbia Press, Vancouver.
• Marchant, S., and Higgins, P. J. (1993) Handbook of Australian, New Zealand and Antarctic Birds. Vol. 2: Raptors to Lapwings. Melbourne Univ. Press, Melbourne.

Additional information

• Australian Migratory Shorebird Habitat Directory
• National Directory of Important Migratory Shorebird Habitat

References

1. ^ Gutierrez, JS, Masero, JA, Abad-Gomez, JM, Villegas, A & Sanchez-Guzman, JM (1 March 2011), 'Understanding the energetic costs of living in saline environments: effects of salinity on basal metabolic rate, body mass and daily energy consumption of a long-distance migratory shorebird', Journal of Experimental Biology. [online], vol. 214, no. 5, pp. 829-835. Available at: http://jeb.biologists.org/cgi/doi/10.1242/jeb.048223 [Accessed 21 January 2021].
2. ^ Senner, NR, Stager, M, Verhoeven, MA, Cheviron, ZA, Piersma, T & Bouten, W (27 June 2018), 'High-altitude shorebird migration in the absence of topographical barriers: avoiding high air temperatures and searching for profitable winds', Proceedings of the Royal Society B: Biological Sciences. [online], vol. 285, no. 1881, p. 20180569. Available at: https://royalsocietypublishing.org/doi/10.1098/rspb.2018.0569 [Accessed 21 January 2021].

Last updated: 27 October 2023