Appearance

Descriptions of molts and plumages follow Palmer 1976, Cramp and Simmons 1977, Nelson 1978a . One plumage/cycle in both sexes.

Hatchlings

At hatching, essentially naked; skin blackish with sparse covering of short, creamy-white down with hairlike tips; bill grayish, iris dark brownish; legs and feet dark gray. Initial down replaced by a second, more wooly white down, covering all areas that are eventually feathered. Second down shed as Juvenal feathers come in; last traces of down when young gannet 11–12 wk old and nearly full grown (Palmer 1976, Nelson 1978a).

Juvenal Plumage

Prejuvenal molt generally complete by week 11–12; Juvenal feathers do not push out nestling down, but grow from separate papillae. Fully grown juvenile Northern Gannet a gray-black replica of parents, but great individual variability in overall darkness. Upperparts dark brownish slaty, speckled white, spots (white tips to feathers) larger and farther apart on back, scapulars, and wing-coverts, smaller and more dense on leading edge of wings, head, neck, and throat. Upper tail-coverts white on outer webs and tips, forming a white V-shaped area on lower rump and base of tail. Breast and flanks brown, rest of underparts similar with more white (amount variable); generally paler than upperparts, appearing finely mottled. Under tail-coverts slaty brown with white markings at tip and mostly white outer webs; rectrices blackish brown with small white tips, shafts paling toward base to straw color. Primaries and secondaries glossy, blackish brown, with bases of shafts straw colored and inner secondaries tipped white, primary-coverts lacking light tips.

Subsequent Subadult Plumages

Plumage stages between Juvenal and Definitive not well understood; birds gradually (3–4 yr) develop all-white plumage at any one time. Gannets of same age show much variation due to variable progress of molt. Known molts that involve much feathering are fairly prolonged; and, although Definitive stages include an Alternate plumage, it is as yet undescribed for earlier cycles.

Molt appears to be complete; begins in Mar–Apr before gannets are 9 mo of age, and continues through Sep when they are 15 mo of age. A dark plumage; forehead mainly dark brown with white spots, becoming white by fall, rest of head and neck white with occasional retained dark feathers. Upper mantle (back and scapulars) mainly blackish brown; dark feathers with large white areas at tips, with some white feathers; lower back and rump with small white markings. Breast with mottled dark-brown band, disappearing by autumn, rest of underparts mainly white, dark patches on thigh. Wing and tail mainly dark brown; white spots from retained juvenile wing-coverts worn off, smaller spots on new feathers; axillaries white, some marginal-coverts white.

Molt appears to be complete; begins in late summer (Jul–Sep) of third calendar year. Head, neck, upper mantle, white; crown and nape of neck with pale yellow-buff cast; remainder of upperparts dark brown, mixed with white feathers, becoming mainly white by autumn. Underparts white. Tail brown-black, 1–3 pairs of outer feathers white; primaries and their coverts brown-black, secondaries brown-black with white tips, some white; lesser wing-coverts white, median and greater-coverts a mixture of black and white. Amount of white in birds increases in autumn.

Molt appears to be complete; begins in Sep of fourth calendar year. Head and neck white with yellow-buff cast; upperparts of body white like adult. Underparts white. Primaries brown-black like adult, innermost secondaries white, some of outer secondaries blackish brown with white edges; tail largely white, with some dark central feathers. Occasional dark tail-feathers or secondaries still present in fifth-calendar-year birds.

Definitive Basic Plumage

Definitive Prebasic molt complete; postbreeding, Jul–Dec; later in some individuals. Primaries replaced sequentially from inner to outer portion of wing, with 3 active centers in wing; yellow color on crown and nape not acquired by separate partial prebreeding molt, but apparently due to oxidation of oils applied to feathers.

Almost entirely white. Crown, nape, sides of head, and hindneck pale to nearly white in autumn. Primaries blackish, paler on inner webs and shafts, primary-coverts, and alulae blackish brown, becoming brown with wear, and lesser primary-coverts along edge of wing either white or intermixed with blackish feathers; secondaries and tail white. Tail wedge shaped and pointed.

Definitive Alternate Plumage

Definitive Prealternate molt appears to be incomplete, at least flight feathers of Basic plumage retained; late winter or early spring; few details known. Almost entirely white; most of crown, nape, sides of head, and hindneck tinged pale yellow to golden brown, usually more intense in breeding males. Primaries blackish, paler on inner webs and shafts, primary-coverts, and alulae blackish brown, becoming brown with wear, and lesser primary-coverts along edge of wing either white or intermixed with blackish feathers; secondaries and tail white and same shape as in Definitive Basic plumage.

Bill

At hatching, bill grayish black in both sexes; dark horn brown in juveniles. Bill in Definitive Basic plumage, medium grayish blue, with black lines at sutures; cutting edges of both mandibles black. No seasonal change in bill color. Mouth lead-colored.

Bare Skin On Head

Bare skin at hatching black; as juvenile, bare skin and pouch brownish. In Definitive Basic plumage, bare facial skin and pouch dark blue-gray; orbital ring blue.

Iris

Dark brown at hatching; iris in Juvenal plumage gray-brown. Iris in Definitive Basic plumage pale gray with fine blackish outer ring.

Legs And Feet

At hatching, legs and feet dark gray; in Juvenal plumage, brown-black, lines on toes and tarsus barely discernible, serration on third claw undeveloped. In Definitive Basic plumage, legs and feet blackish brown with yellowish-green lines on midridge of toes in males, greenish blue in females, continuing to and fusing into a single line on tarsus; third claw curved outward and serrated on inner edge.