Breeding and moult (Shorebirds)

Migratory shorebird species breeding overseas use different habitats, some of which may be patchy, small and/or restricted. For example, broad-billed sandpiper nest on tussock islets in very shallow swamps and grey plover nest on raised dry tundra but their hatchlings have to be able to move to marshes containing short, sparse vegetation.

Shorebirds moult breeding plumage each year, mostly just prior to and during northward migration (into breeding plumage), and then during and just after southward migration (out of breeding plumage). By November, nearly all shorebirds in Australia have non-breeding plumage. These changes are caused through the moulting of body plumage, which is different to the moult of flight feathers that occurs only once a year after southward migration and after the moult into non breeding plumage. Flight feathers are moulted sequentially so as not to compromise flight efficiency.

Examples of diverse breeding requirements

There is a broad variety of habitats where migratory shorebird species breed. The Calidridinae sandpipers, the "tundra" plovers and ruddy turnstone use the arctic or sub-arctic tundra, while most of the remaining species use the more southerly region of the taiga (boreal forest), and fewer still (marsh sandpiper, greater sand plover and lesser sand plover) use the steppes and deserts of the middle latitudes. This simplistic separation of breeding zones is complicated by habitat and climatic variability introduced by the presence of coastlines, major rivers, lakes and embayments. Within an area that may be generally suitable for a species to breed, more specific requirements need to be met, for example the need for tussock islets in a shallow swamp (broad-billed sandpiper), or a dry alpine plateau (great knot), or small braided river (grey-tailed tattler), or even a gentle slope of damp moss (red-necked stint).

Timing of breeding

Shorebirds breeding at high northern latitudes mostly arrive on their breeding grounds in late May or early June. However, they may postpone their arrival due to late snow cover, which can force birds to congregate where the snow has melted (near human settlement, at the edge of cliffs, near open water). There have been instances of mass deaths of birds from starvation when snow cover has persisted late into summer. Birds will attempt to breed as early as possible after arrival and mating is often finalised within days.

A range of conditions and circumstances may influence the schedule of migration and breeding of migratory shorebirds. Some of these may include:

• availability of insects, the major food resource for the chicks
• daily temperatures, impacting the activity of prey species and food availability
• limited carrying capacity of staging areas
• shorebird migrations and breeding may be timed to avoid periods when avian predators, like falcons, are abundant.

Most of the life of migratory shorebirds is spent on the non-breeding grounds, which in many instances is within Australia.

Breeding behaviour and site fidelity

Migratory shorebirds are typically monogamous and reproduce only once a year. However, if a pair lose a clutch early (before July), they may produce a replacement clutch. Monogamous species typically exhibit high site fidelity, meaning they tend to return to the same location each year to breed. The pair share parental duties and can defend a nest against predators. The monogamous sanderling has an unusual system in which a female lays two clutches of eggs in quick succession and the first clutch is incubated by the male while the second is incubated by the female.

There are instances of polygamy in the Calidridinae sandpipers where the male mates with several females and leaves all parental duties to the female. Ruff, pectoral sandpiper, sharp-tailed sandpiper, and curlew sandpiper are polygamous species with low site fidelity and little likelihood of expending energy on defence of a nest from predators or defence of a territory from other individuals.

Polyandry is a third and less common type of mating system, an example being red-necked phalarope. The females are more brightly coloured than the males and will compete for mates. A female will mate with several males in succession and a male will incubate the eggs and rear the young either with or without, or with limited assistance from the female.

Camouflage and predation of eggs and chicks

Shorebird eggs, chicks and nests are generally well camouflaged from predators. Eggs are usually coloured and patterned to mimic the colour of local plants, dead leaves or lichen. Chicks are also cryptically patterned and will remain motionless if under threat. An adult sitting on a nest can be hard to spot, although some adult shorebirds (whimbrel, curlew sandpiper) will abandon the nest if a predator approaches. Adults will invariably offer some form of distraction display to draw predators away from their nests and free-roaming chicks also behave to minimise their risk of detection by quickly hiding or staying still where they blend into the background.

Heavy predation on shorebird eggs and chicks may occur from a range of predators when their other food sources are low due to lemming populations fluctuating in cycles of 3-4 years. At these times, arrivals to Australia of juvenile shorebirds on southward migration can be dramatically reduced. Compared to birds of similar size, shorebirds are very long lived (up to 20+ years), which is perhaps a response to the heavy predation on chicks that can periodically occur. Longevity of adults affords a degree of resilience to a population that suffers periodic, high juvenile mortality.

Local drab look

When the migratory shorebirds in the East Asian-Australasian Flyway are away from Queensland they are much more colourful.

While in Queensland, these migratory shorebirds are mostly in their non-breeding plumages of buff and grey. To the untrained eye, having lost their distinctive breeding plumages, the species now look very similar to one another and they merge perfectly with their usual background of mud and sand. In this condition, migratory shorebirds are often less noticeable than shorebirds that reside in Australia all year and certainly less obvious than many other Australian waterbirds.

Cycle of moult

A period of natural feather replacement is called a 'moult', and for migratory shorebirds occurs:

1. as a body plumage moult, twice a year (in and out of breeding plumage) and
2. as a flight feather moult which occurs once a year.

As soon as shorebirds arrive on the non-breeding grounds in Australia from August onwards, they begin to moult into their non breeding body plumage. By about November, the body moult is complete but moulting of the flight feathers begins, which lasts about three months until February.

Moulting of flight feathers is a slow process, which in some circumstances can stop and restart if it is in the best interests of the survival of an individual bird. It involves the secondary and primary flight feathers in the wing (remiges) and the tail feathers (rectrices). Individual flight feathers can take three weeks to grow and are bigger and more important than single body feathers.

After the moult of flight feathers, preparation for northward migration begins including a body moult into breeding plumage, which will extend into the time when shorebirds are migrating northward. Only certain aspects of the breeding plumage are for display, other aspects act as camouflage and helps conceal birds sitting on nests amongst the brightly coloured forbs, lichens and mosses of the tundra. Breast feathers can be for display and back feathers for camouflage.

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

• Shorebirds
• Migrations
• East Asian-Australasian Flyway
• Managing for ecological requirements - movements

Last updated: 13 November 2020