Each year, as summer draws to a close, you might wonder about the absence of one resident species across the Solent. Where have all the shelducks gone?
It may seem like a mysterious seasonal vanishing act, as almost all our shelducks disappear until the cooler months, but it is actually linked to their unusual moulting behaviour.
The catastrophic moult
Yes, you read that right.
While most bird species undergo a gradual moult – replacing feathers individually throughout the year – shelducks exhibit a rare phenomenon known as a catastrophic moult. This process, more commonly associated with penguins, involves the simultaneous loss of all flight and tail feathers, rendering the bird temporarily flightless and vulnerable to predation.
To successfully moult with minimal risks during this stressful period, many shelducks undertake a strategic migration. Large numbers leave their breeding grounds on a mid-summer’s night and travel to specific moulting sites where they can undergo this transformation in a safer environment.
The Wadden Sea
Although many of these sites exist across the UK and continental Europe, the Wadden Sea, spanning parts of the Netherlands and Germany, is by far the most significant moulting haven. Historical records indicate that this region can be home to nearly the entire West European population of shelducks during the moulting season – estimated at approximately 200,000 birds.
The Wadden Sea’s ecology makes it an ideal refuge. Its expansive mudflats provide abundant food resources, including invertebrates such as insects, crustaceans, and marine worms. Crucially, the open landscape offers excellent visibility, allowing shelducks to detect and evade potential predators more easily.
The moulting period in shelducks typically lasts one month and is a critical phase in the life cycle of first-year fledglings.
Observations have shown that the success of this initial moulting period is a strong predictor of long-term survival. Juveniles that get through their first moult have a greater chance of surviving to an age of 5 to 10 years.
Once the shelducks have grown their new set of feathers, they return to their wintering grounds. You’ll notice them reappearing around our coastal regions ready for the cold months, where their striking plumage – characterised by bold black, white, and red coloration – can be spotted all across the Solent.
