Colophon

The animal on the cover of Functional JavaScript is an eider duck (Somateria mollissima), a sea-duck that ranges between 50−70 cm in length. Eider ducks can be found along the coast of Europe, North America, and the east coast of Siberia. They spend their winters in temperate zones after breeding in the Arctic and other northern temperate regions. In flight, eider ducks have been clocked at speeds of 113 km/h (70 mph).

Eider nests are often built close to the ocean and are lined with eiderdown—plucked from the breast of a female eider. The lining has been harvested for use as pillow and quilt fillers, a sustainable practice that happens after the ducklings have left the nest without harm to the birds. Eiderdown has been replaced in more recent years by synthetic alternatives and down from domestic farm geese.

Male eider ducks are characterized by their black and white plumage and green nape; the female is brown. In general, eiders are bulky and large with a wedge-shaped bill. They feed on crustaceans and mollusks. Their favored food, mussels, are swallowed whole, the shells crushed in the gizzard and excreted.

This species has populations of between 1.5 and 2 million in North America and Europe; the numbers in eastern Siberia are large but unknown. One colony of eiders—about 1,000 pairs of ducks—on the Farne Islands in Northumberland, England, enjoys a bit of fame for being the subject of one of the first bird protection laws in the year 676. The law was established by Saint Cuthbert, patron saint of Northumberland, giving the ducks a local nickname of “Cuddy’s ducks” (“Cuddy” being short for “Cutherbert”).

In the 1990s, there were eider die-offs in Canada’s Hudson Bay that were attributed to changing ice flow patterns. According to data gathered by the Canadian Wildlife Services, the population has shown recovery in the years since.

The cover image is from Wood’s Animate Creation. The cover font is Adobe ITC Garamond. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.