The purple sandpiper, with its distinctively colored plumage, is a shorebird that breeds in the high Arctic and migrates along the coasts of the North Atlantic and North Pacific Oceans. But why is this sandpiper named for its purplish coloration? The answer lies in the details of its unique appearance.
Description of the Purple Sandpiper
The purple sandpiper (Calidris maritima) is a medium-sized shorebird, measuring about 20–24 cm (8–10 in) long with a wingspan of 39–45 cm (15–18 in). Its stout body and short legs give it a plump appearance compared to other sandpipers. Its bill is orange with a black tip and its legs and feet are yellowish.
The purple sandpiper’s most distinctive feature is its coloration. In its breeding plumage, it has grayish-brown upperparts with a slight purplish iridescence. Its underparts are white with variable gray mottling on its breast. But it’s during the nonbreeding season when the purple sandpiper earns its colorful name. Its breast becomes extensively suffused with a rich purple-gray color while its belly remains white. The contrast makes the purplish breast particularly eye-catching. When seen against an icy backdrop of snow and sea, the purple stands out vividly.
Range and Habitat
The purple sandpiper breeds in the high Arctic tundra of North America, Greenland, Svalbard, and Eurasia. It nests near water, laying its eggs on the ground lined with vegetation. After breeding, it migrates south along the Atlantic coast of North America and Western Europe. Some birds continue down the coast of West Africa. In the Pacific, it is found along the coasts of Russia and Alaska, migrating down the west coast of North America into California.
During migration and winter, purple sandpipers are almost exclusively found on rocky intertidal habitats, especially on wave-splashed rock ledges and rock platforms. They forage on invertebrates picked from rock crevices and among seaweed. Their short legs and sturdy build are adaptations for maintaining balance on slippery, spray-drenched rocks while hunting for food.
Taxonomy and Relationships
The purple sandpiper is one of nine species in the genus Calidris, a group of small sandpipers commonly known as stints. Its closest relative is the rock sandpiper (C. ptilocnemis) of northeastern Asia and North America. Both species have similar plumage patterns and preference for rocky coasts in winter.
The genus name Calidris is from Ancient Greek kalidris or skalidris, a term used by Aristotle for some kind of waterside bird. The specific epithet maritima is Latin for “of the sea”, referring to this species’ coastal habitat.
There are two recognized subspecies of purple sandpiper:
- C. m. maritima breeds in northern Eurasia
- C. m. belcheri breeds in North America
The North American subspecies C. m. belcheri is slightly smaller and paler in color compared to the Eurasian nominate race C. m. maritima.
Theories on the Purple Plumage
What evolutionary factors gave rise to the striking purple breast plumage of this sandpiper? Scientists have proposed various hypotheses:
Camouflage
One theory is that the mottled purple-gray coloration helps provide camouflage as the birds roost among the dark, seaweed-covered rocky coasts. The muted purple blends in along these shores. However, this seems unlikely to be the main driver since the purplish breast is such a noticeable feature compared to its more cryptically patterned back.
Social Status Signal
Another idea is that the vibrant plumage signals social status. Birds with the deepest, most intense purple color may attract the best mates and maintain prime feeding territories. However, there is not much evidence yet that purple brightness correlates strongly with measures of fitness in these birds.
Prey Detection
One of the more plausible theories is that the purple breast color enhances the sandpiper’s ability to detect cryptic prey along the rocky shoreline. The contrast between the purple breast and white belly may improve their ability to spot small dark invertebrates along the intertidal zone. The high visibility of purple against the coastal backdrop may have selective advantages. Experiments testing prey detection ability relative to plumage color could help evaluate this hypothesis.
Thermoregulation
Finally, the dark purplish color may aid in heat absorption. The rich color could help the sandpipers maintain body temperature as they endure freezing conditions along northern shorelines. Shorebirds can conserve heat by redirecting blood flow to their chilly legs. Dark plumage may help compensate for heat loss.
In reality, the purple sandpiper’s colorful namesake is likely influenced by a combination of these factors. But the striking hue probably aids prey detection and thermoregulation while roosting on cold, wave-swept rocks during the nonbreeding season. This illustrates how the functional needs of different environments shape a species’ appearance.
Conclusion
With its stout build, short legs, and handsome purplish-gray plumage, the purple sandpiper is exquisitely adapted to its ecological niche. As a high Arctic breeder that migrates huge distances along rocky intertidal areas, it requires characteristics that aid survival in these extreme environments. The purple sandpiper’s distinctive coloration enables it to blend in, maintain body heat, and spot prey along icy shores. Its name accurately reflects one of its most obvious traits – that beautiful violet breast that stands out against the neutral shades of the northern coastline.