Feather Moult and Migration

Feathers are essential to any bird’s survival. They are needed to keep a bird warm, keep them dry and also allow them to fly. Shorebirds must take good care to look after their feathers all throughout the year as they are essential to survival. Each day, birds will make sure that their feathers are clean and free from parasites by bathing, usually in fresh water. This is often followed by preening, the process in which feathers are kept waterproof by using their bill to work a waxy oil secreted by the preen gland into their plumage.

The colouration and patterning on feathers are part of what makes each bird species identifiable. In late summer and early autumn when shorebirds have just arrived back on the Northumberland coast from their nesting grounds, they are in their breeding plumage; brightly coloured, beautifully pattered feathers which help them attract a mate, but also enables them to remain camouflaged while incubating their eggs amongst tundra and moorland vegetation. However, shortly after arriving back, their plumage begins to change, with patterned feathers becoming plainer and colours fading to duller shades of brown and grey – much more practical for blending in with the rocky shore or muddy habitats where they will spend the rest of the autumn and winter. Come spring, the birds will again begin to change their plumage, their bold colours returning in preparation for the upcoming breading season.

This seasonal change in plumage is called moult, and the birds will do this twice every year. Body feathers are shed and replaced during each moult, allowing the birds to change their plumage ahead of the breeding or non-breeding season and replace worn, damaged feathers. Flight feathers are only replaced once a year, during post-breeding season moult. With most species being long distant migrants, it is essential that they time their second moult perfectly to ensure no impact is had on their ability to fly.

Turnstone in breeding plumage

The timing of the second moult varies between different shorebird species. Most will wait until they have arrived back to their non-breeding sites so they can focus on their migration before expending more energy on growing new feathers. For some species, moult occurs gradually at ‘stop-over’ sites during migration. Black-tailed godwit are a species which use this technique, with good numbers being seen using the Coquet Estuary during both autumn and spring migration. With so much food on offer for shorebirds at this site (see our ‘Why is mud so good for shorebirds?’ for more information about this) it is the perfect place for birds to refuel during their migration but to also build up as much energy as they can to quickly regrow their flight feathers ready for the next leg of their journey.

One species which has a slightly different approach to their second moult is golden plover. As flight is inevitably impacted while new flight feathers are growing, golden plover begin to moult when they start nesting, as the amount of flying they need to do while they are incubating eggs and raising chicks is reduced. By the time their chicks have fledged and it is ready to leave the nesting sites, adults have a lovely new set of flight feathers to carry them home, allowing them to focus on building up their energy reserves ready for colder months on the coast.

Golden plover in breeding plumage

Chicks hatch with downy feathers, which helps them to keep warm while they explore their surroundings and learn how to find food for themselves. Although warm, these feathers are not waterproof, leaving chicks vulnerable to becoming chilled during heavy rain if parent birds are unable to brood them to keep them dry. The four or five weeks following hatching, chicks are developing their first proper feathers, and as soon as their flight feathers are grown they can start to fly. Juvenile plumage is the only time in a bird’s life when all of its feathers are the same age, making it look very fresh and sharp, with body feathers often appearing textured. Along with adult birds, juveniles will also moult their first plumage in autumn, but they will keep their flight feathers until the following year’s moult.

Juvenile sanderling feeding at Boulmer

The shedding and re-growth of feathers is yet another energy-intensive process shorebirds must endure. If the birds are not fit and healthy, they risk not being able to gain their full breeding plumage which affects their ability to nest successfully or may even result in the birds not surviving migration. Migrating birds are reliant on resources being readily available to them which will allow them to feed enough to quickly replenish their energy levels ready for the next phase of their annual cycle.

Disturbance can have a huge impact on shorebirds at any time of the year as it reduces the amount of time available to the birds for feeding and wastes energy which they desperately need for moulting, migrating, breeding or simply trying to survive a cold winter day. Please help protect these birds by looking out for them during your next visit to the coast and always giving them space. Thank you.

Turnstone in non-breeding plumage

Information from the following sources was used to help compile this blog post:

• Alfaro, M., Sandercock, B.K., Liguori, L. and Arim, M. (2018), Body condition and feather molt of a migratory shorebird during the non-breeding season. J Avian Biol, 49: jav-01480. (https://doi.org/10.1111/jav.01480)
• Shorebirds in Action by Richard Chandler. Published by Whittles Publishing
• Wader Tales – www.wadertales.wordpress.com