Dunlins are small shorebirds that breed in the Arctic tundra and migrate long distances to wintering grounds farther south. Their plumage goes through dramatic seasonal changes, allowing them to blend in with their surroundings and avoid predators. In the breeding season, dunlins sport colorful and intricate feather patterns. But by winter, their plumage has dulled to plain gray and white. Just what colors make up the dunlin’s breeding costume, and why do they change with the seasons? Let’s take a closer look at the unique feathers of these globe-trotting birds.
Dunlin Breeding Plumage
During the spring and summer breeding season in the Arctic, dunlins acquire colorful plumage that helps the males attract mates and defend nesting territories. Their bellies become solid black, providing a stark contrast to the pure white feathers on the breast and throat. Dunlins have a distinctive black patch on either side of the belly known as the “stranded belly patch.” This black belly patch is thought to play a role in courtship displays.
The dunlin’s back and shoulders take on a warm reddish-brown hue. This rusty coloration helps provide camouflage as the birds nest on the tundra among grasses and lichens. Intricate black feather patterning emerges on the back and wing coverts. The amount of black variegation differs between individuals. Geographically isolated breeding populations tend to have unique back patterning. For example, dunlins nesting in Alaska may have different back feather markings compared to those in Siberia.
During breeding season, dunlins also sport a distinctive black bar between the eye and bill. This eye stripe along with the bold black-and-white head pattern likely helps dunlins recognize and select mates of their own species on crowded Arctic breeding grounds shared with other shorebirds. The black bill also becomes brighter at the base during breeding season.
Dunlin Wing Feathers
The wings of breeding dunlins contain colorful mixes of black, brown, and chestnut. The greater wing coverts forming the main upper part of the wing are chestnut-colored with black shaft streaks. The middle wing coverts are blackish-brown. The lesser coverts along the leading edge of the wing are also blackish-brown but have pale fringes. This variegated pattern helps camouflage dunlins against the Arctic tundra when they are sitting on nests during the breeding season.
Rump and Tail Feathers
During breeding season, dunlins have distinctive white outer tail feathers that are easily visible during flight. Their rump feathers are also bright white. This contrast between the white rump/tail and darker back likely helps dunlins keep track of others in their flock when flying over the open tundra.
Winter Plumage
After breeding, dunlins molt into a drab gray and white winter plumage. The rusty feathers on the back and wings are replaced with plain gray feathers. The black belly patch and eye stripe also disappear. The bill becomes darker gray with a black tip.
This less colorful winter plumage provides camouflage as the birds migrate and spend the winter along coastal mudflats and marshes. By being less conspicuous, dunlins reduce their risk of predation from falcons, hawks, and other predators during the long wintering period.
Juvenile Dunlin Plumage
Juvenile dunlins hatch with downy, speckled black, brown, and buff feathers. This provides camouflage from predators as the vulnerable chicks start to walk and feed themselves. After a few weeks, juveniles molt into juvenile plumage that resembles the nonbreeding adult winter plumage. Juvenile dunlins have less contrast between the pale breast and darker belly. The back feathers show some mottled black markings but lack the warm rufous tone. Young dunlins keep this subdued first winter plumage until their first breeding season spring molt.
Why Do Dunlins Change Color?
The seasonal shifts in dunlin plumage color serve different purposes at various stages of their migration cycle:
- Breeding plumage communicates identity and fitness when competing for mates on crowded Arctic breeding grounds.
- Disruptive camouflage patterns protect dunlins from predators when nesting and raising chicks.
- Cryptic winter plumage allows dunlins to blend in along coastlines and avoid predators during the nonbreeding season.
- Dull juvenile plumage helps young dunlins hide from predators and survive their first migrations.
By molting into dramatically different seasonal feathering, dunlins can best match their environments and maximize their chances of survival throughout the year.
Season | Location | Plumage Colors | Purpose |
---|---|---|---|
Breeding | Arctic tundra | Rufous back, black belly, white throat and breast, black and white head pattern | Attract mates, communicate identity, camouflage on nest |
Winter | Coastal mudflats | Plain gray back and wings, white breast and belly | Cryptic camouflage from predators |
Juvenile | Migration routes | Grayish brown back with mottling, dull buff breast and belly | Camouflage and concealment from predators |
Conclusion
The colorful breeding plumage and cryptic winter feather patterns of dunlins provide excellent examples of how birds evolve specialized feathering to match their environments throughout the year. Their ability to undergo seasonal molts gives dunlins the best camouflage and visual communication needed to breed successfully on the Arctic tundra while also avoiding predators during long migrations and wintering periods. The intricately patterned breeding feathers offer insight into the behaviors, social structures, and habitats of these widespread yet fragile Arctic shorebirds.