Eclipse plumage refers to the distinct plumage of some bird species that is adopted briefly prior to their annual molt. Many species develop drab, cryptic eclipse plumages that allow them to blend into their surroundings and evade predators during the flightless molting period. Understanding the purpose and function of eclipse plumages can provide insight into avian biology and evolution.
What is eclipse plumage?
Eclipse plumage is a special type of plumage that is present only for a limited period of time in some bird species. It typically refers to the dull or drab plumage that replaces colorful breeding plumages in ducks, geese, and other waterfowl species prior to molting. The term “eclipse” refers to the plumage being eclipsed or covered over by the dull feathers.
Eclipse plumage provides camouflage and conceals birds during the molting period when they are vulnerable due to reduced mobility. It allows them to blend into their surroundings and avoid predation during this time. The eclipse plumage replaces the bright breeding plumage after nesting duties are completed. It is then replaced by fresh breeding plumage during the next molt.
When does eclipse plumage occur?
The timing of eclipse plumages is precisely aligned with the molting cycle in birds. It occurs after breeding duties are completed, just prior to the annual molt when flight feathers are shed. In ducks and geese, eclipse plumage generally occurs from late June through September, although the exact timing varies by species. The drab eclipse plumage is present only temporarily until colorful breeding plumage returns, typically in the fall.
What causes the plumage change?
Hormonal changes are the trigger for eclipse plumage in birds. As breeding hormones decline after nesting duties are complete, the eclipse plumage emerges. Lower levels of androgens, estrogens, and other hormones cause growth of the dull eclipse feathers. The timing ensures camouflage is present precisely when it is most needed, during the flightless wing molt.
What are the characteristics of eclipse plumage?
There are several distinct characteristics of eclipse plumages in birds:
- Dull, cryptic coloration – Browns, grays, and blacks replace bright breeding colors
- Mottled patterning – Disruptive patterns aid camouflage
- Reduced or absent ornamentation – Loss of decorative feathers like crests
- Similar between sexes – Males lose distinct breeding plumage traits
- Rapid transition – Occurs in just weeks or months
These changes all facilitate crypsis or the ability to avoid detection. Without colorful breeding plumage or conspicuous markings, birds blend into their surroundings much better during molting.
Example species
Some examples of species with eclipse plumages include:
- Mallard ducks – Males transition from green heads to dull brown
- Wood ducks – Males lose ornate crests and bright plumage
- Canvasbacks – Red heads fade to black
- Scaup – White wing patches and head markings disappear
- Eiders – White and black patterns camouflage well
- Oldsquaw ducks – Striking black and white breeding plumage dulled
In most waterfowl species, eclipse plumage is much more pronounced in males, allowing them to lose bright breeding colors. Some female ducks show minimal changes.
What is the purpose of eclipse plumage?
The main purpose of eclipse plumage is camouflage. By adopting cryptic plumage, birds reduce their risk of predation during the flightless wing molt period. Eclipse plumage allows birds to hide in plain sight and avoid detection by predators.
Specifically, the dull colors and disruptive patterns provide:
- Camouflage and crypsis – Avoid visual detection in surroundings
- Concealment near nests – Hide vulnerable flightless young
- Reduce conspicuous signals – Lose bright colors that attract attention
- Increase survivability – Avoid predation during molting period
The plumage change is precisely timed to provide maximum protection when it is most critically needed, during the metabolically stressful and energy-intensive molting period.
Why is camouflage important during molting?
Molting is an extremely vulnerable time for birds as they lose old feathers and regrow new ones. Shedding large wing feathers impairs flight capabilities, reducing mobility and escape from predators. Birds undergoing molt must evade threats on the ground or water. Camouflage helps them go undetected.
Molting is also metabolically costly as resources are invested in rapidly growing new feathers. Avoiding danger allows birds to devote more energy solely to this process. Eclipse plumages therefore provide protective coloration when it is most vitally needed.
How do eclipse plumages provide camouflage?
Eclipse plumages use several methods to provide effective camouflage while birds are flightless:
Disruptive coloration
Mottled blacks, browns, and grays act as disruptive coloration by breaking up the bird’s outline. This makes it harder for predators to recognize the shape of a hiding bird.
Background matching
Drab colors match the ground, water, and vegetation that birds take cover in. This background matching helps avoid visual detection.
Countershading
Dark upperparts and pale underparts create countershading. This gradation makes birds appear flat when seen from above or below.
Loss of ornamentation
Breeding plumage markings like bright colors, crests, and elaborate patterns attract attention. Losing these reduces conspicuous signals that can betray hiding birds.
Together, these mechanisms allow birds to exploit their surroundings and avoid predation during the energetically expensive and mobility limiting molting period.
How does eclipse plumage change throughout molting?
The transition in and out of eclipse plumage is gradual and follows a predictable pattern aligned with the molting sequence of feather groups:
- Wing and tail feathers are replaced first, impairing flight
- Body feather molt begins next, with eclipse plumage growing in
- Lastly, head and neck feathers molt to eclipse colors
- Fresh breeding plumage returns in reverse order
This staggered sequence ensures camouflage emerges right as flight abilities are lost. It is sustained throughout the molt and until new breeding feathers return. The timing ensures maximal crypsis is present during the bird’s greatest vulnerability.
Do juvenile birds have eclipse plumage?
Unlike adults, juvenile birds generally do not go through eclipse plumage changes. Juvenile plumage in young birds functions similarly to eclipse plumage in providing camouflage:
- Dull, cryptic colors aid hiding
- Disruptive patterns conceal shape
- Reduced ornamentation compared to adults
Because juveniles do not breed, they have no bright breeding plumage to replace. Their dull juvenile plumage serves as effective camouflage year-round prior to reaching maturity.
How does eclipse plumage return to breeding colors?
The return to colorful breeding plumage occurs as hormone levels rise outside of breeding season. Androgens increase and stimulate growth of brightly colored feathers. The transition occurs in the opposite order it emerged:
- Head and neck breeding feathers grow first
- Bright body plumage replaces drab feathers
- Finally, wing and tail feathers molt back to breeding colors
This staggered sequence ensures birds have regained flight capabilities before conspicuous breeding plumage returns. It also aligns with courtship displays, ensuring birds advertise for mates only when ready to breed again.
Why don’t all birds have eclipse plumage?
Eclipse plumage appears to be most common in waterfowl that undergo simultaneous molting of all flight feathers. This leaves them fully flightless, favoring cryptic coloration. In contrast, passerines and other birds molt feathers gradually, retaining some flight ability throughout.
Also, male waterfowl tend to have elaborate breeding plumage that attracts attention. Hiding these conspicuous signals during molting provides an advantage. Some birds lack pronounced breeding color differences between sexes or molt more gradually, reducing selection for eclipse plumages.
Conclusion
Eclipse plumages serve an important role in bird biology. The dramatic but temporary plumage transformation provides protective coloration vital for survival during the metabolically taxing and mobility limiting molting period. Dull colors, disruptive patterns, and reduced ornamentation allow vulnerable birds to hide in plain sight from predators throughout the wing molt. The precisely timed changes are an elegant evolutionary adaptation to a critical life history stage, ensuring birds can molt successfully and return to bright breeding colors when needed for attracting mates and defending territories.