Eclipse Plumage in Ducks: Nature’s Camouflage Strategy

Every summer, the vibrant plumage of male ducks, fades from Yorkshire’s wetlands, replaced by a drab, female-like appearance. This transformation, called eclipse plumage, is a fascinating adaptation in many duck species. In this blog post, we’ll explore what eclipse plumage is, its purpose, the phenology and moult timings of common duck species in Yorkshire, and the scientific insights behind this phenomenon.

What is Eclipse Plumage?

Eclipse plumage is the cryptic, mottled brown plumage that male ducks adopt after the breeding season, closely resembling the appearance of females. Unlike the bright nuptial plumage used to attract mates during breeding, eclipse plumage is temporary and coincides with a full moult of flight feathers. During this period, ducks shed all their flight feathers simultaneously, becoming flightless for three to four weeks. This subdued plumage helps them blend into their surroundings, reducing predation risk during this vulnerable time. The term "eclipse" aptly describes this temporary dimming of the drake’s brilliance, akin to a celestial eclipse. After regrowing their flight feathers, drakes undergo a second moult to regain their vibrant breeding colours for the next courtship season.

A male mallard in eclipse plumage, whilst it may look quite female like in appearance note its yellow bill, hint of green on the head and chestnut in the breast. This is quite late in its moult cycle (photo taken in August) as can be seen by the well developed primary feathers.

Why Do Ducks Have Eclipse Plumage?

The primary function of eclipse plumage is camouflage for protection. Ducks undergo an explosive moult, losing all primary wing feathers at once, which leaves them unable to fly and vulnerable to predators like foxes or birds of prey. The female-like, mottled brown eclipse plumage allows drakes to blend into reeds, marshes, or open water, making them less conspicuous. Evolutionarily, this adaptation balances sexual selection and survival. During the breeding season, females choose mates based on bright plumage, which signals genetic fitness. Post-breeding, when mating is no longer a priority, survival takes precedence, and eclipse plumage helps drakes avoid detection.

Eclipse plumage also supports feather maintenance. Feathers wear out over time, and the simultaneous moult ensures efficient replacement, maintaining waterproofing and flight capability. The preening fluid from an oil gland at the tail base keeps feathers pliable and waterproof during this transition.

Phenology and Moult Timings in Yorkshire’s Ducks

In Yorkshire’s wetlands, the timing of eclipse plumage and the associated moult is intricately tied to the life cycles in the common duck species like the Mallard Anas platyrhynchos, Gadwall Mareca strepera, Teal Anas crecca, and Tufted Duck Aythya fuligula. These species follow distinct schedules influenced by breeding, migration, and environmental cues like day length. For example, Mallards, one of Yorkshire’s most abundant ducks, typically breed from March to June, with females incubating eggs and raising ducklings. By late June or July, Mallard drakes begin their eclipse moult, shedding flight feathers and adopting a female-like plumage with a yellow bill and rufous-tinged breast. This flightless period lasts three to four weeks, often peaking in August, during which they seek dense cover in marshes or open water to evade predators. By September, Mallards start their nuptial moult, regaining their iconic green heads and chestnut breasts by October for courtship. A 1937 study in the Journal of Experimental Biology found that artificial light could trigger early eclipse moult in Mallards, suggesting photoperiod’s role, while castration experiments indicated that moult timing is influenced by endocrine factors beyond testicular hormones.

Similarly, Gadwalls breed slightly later, from April to June, and their eclipse moult occurs from July to August. During this time, Gadwall drakes adopt a greyish, female-like plumage with a distinctive white speculum on the wing, becoming flightless for about three weeks in August. While less common in Yorkshire during summer, some Gadwalls moult locally, and by September, they begin transitioning back to their subtle yet elegant breeding plumage. Research in The Birds of North America (Drilling et al., 2002) notes that Gadwalls’ eclipse plumage is less pronounced than Mallards’, reflecting their naturally understated breeding colours.

Teal, often winter visitors to Yorkshire but with some breeding in the region’s uplands from May to July, follow a similar pattern. Their eclipse moult occurs from July to August, with drakes adopting a mottled brown plumage resembling females. The flightless period, lasting three to four weeks in August, sees Teal hiding in dense vegetation. As migratory birds, some Teal may moult in northern Europe before arriving in Yorkshire’s wetlands, with their nuptial moult starting in September to restore their striking chestnut and green heads by October. Studies in Wildfowl (Boyd, 1961) highlight that Teal synchronize their moult with migration to ensure flight capability for autumn movements.

Tufted Ducks, which breed in Yorkshire’s lakes and reservoirs from May to July, undergo their eclipse moult from July to August, adopting a brownish tinge to their black plumage with a faint crest. Their flightless period, also about three to four weeks in August, often sees them gathering in flocks on large water bodies like Fairburn Ings. By September, they begin their nuptial moult, regaining their glossy black plumage and white flanks by October. Research in British Birds (Ogilvie, 1975) suggests that diving ducks like Tufted Ducks may delay their moult slightly compared to dabbling ducks, aligning with their deeper-water habitats and differing predation pressures. Across these species, the eclipse moult’s timing ensures that drakes are flightless when predation risk is high but can recover their breeding plumage in time for autumn courtship, seamlessly integrating with Yorkshire’s seasonal rhythms.

Ecological and Evolutionary Context

The eclipse moult’s timing is closely linked to ducks’ reproductive cycles. After breeding, females focus on raising ducklings and moult later, once their young fledge. Drakes, free from parental duties, moult earlier, often retreating to specific moulting areas, sometimes distant from breeding grounds, to undergo their flightless period safely. For instance, Mallards may gather in Yorkshire’s marshes, while Teal might moult in northern Europe before migrating south. Ecologically, eclipse plumage reduces predation risk, with predatory species like Red Foxes Vulpes vulpes and Sparrowhawk Accipiter nisus relying on visual cues. Evolutionarily, eclipse plumage reflects a trade-off between sexual selection and survival, allowing drakes to prioritise camouflage when mating displays are unnecessary. Species lacking eclipse plumage, like the Ruddy Duck Oxyura jamaicensis, face different evolutionary pressures, such as prolonged breeding seasons.

Observing Eclipse Plumage in Yorkshire

For birdwatchers, summer in Yorkshire offers a chance to spot eclipse plumage, though it requires careful observation. Male Mallards in eclipse have a yellow bill, unlike females’ orange and black bills, while Gadwall drakes show a white speculum, and Tufted Ducks retain a faint crest. Visit wetlands in July and August to see moulting ducks, with drakes transitioning back to nuptial plumage by September. Use binoculars and a field guide like Collins Bird Guide (Svensson et al., 2010) to distinguish eclipse drakes from juveniles or females based on bill colour, body size, or faint breeding plumage traces.

Conclusion

Eclipse plumage is a remarkable adaptation that allows male ducks to balance reproduction and survival. By adopting cryptic, female-like plumage during their flightless moult, species like Mallards, Gadwalls, Teal, and Tufted Ducks evade predators in wetlands. The moult’s timing, peaking in July and August, aligns with post-breeding recovery, ensuring drakes are ready for autumn courtship. Scientific studies reveal the complex interplay of hormones, photoperiod, and evolutionary pressures behind this phenomenon. Next time you visit a Yorkshire wetland in summer, look closely at those “female” ducks—some may be drakes in their eclipse disguise, showcasing nature’s clever survival strategy.

References

• Boyd, H. (1961). The flightless period of the Teal Anas crecca in Britain. Wildfowl, 12, 76–80.

• Drilling, N., Titman, R., & McKinney, F. (2002). Mallard (Anas platyrhynchos). In The Birds of North America, No. 658.

• Ogilvie, M. A. (1975). Moults and plumages of diving ducks in Britain. British Birds, 68, 298–305.

• Svensson, L., Mullarney, K., & Zetterström, D. (2010). Collins Bird Guide (2nd ed.). HarperCollins.

• Walton, G. A. (1937). On the eclipse plumage of the Mallard (Anas platyrhyncha platyrhyncha). Journal of Experimental Biology, 14, 440–447.