Habitat

Figure 2 . Northern Gannet almost exclusively marine, in subarctic and temperate continental-shelf waters of North Atlantic from 46°50’N to arctic fringe at 70°35’N; comes to land only to breed, where it occurs in dense colonies on isolated stacks or small uninhabited islands, or less frequently on precipitous inaccessible cliffs of mainland or large islands; occasionally on gently sloping or flattish ground. Nests on ledges of cliffs, in the direction of prevailing winds, from just above splash zone to >200 m; prefers bare rock surfaces, and when spilling onto vegetated areas, nesting quickly strips away plants and soil. Prefers igneous to sedimentary rocks, and ideally selects long, fairly broad, flat ledges where several pairs can nest and nest materials can easily accumulate; will, however, use narrow (15 cm wide), sloping ledges and faces (Nelson 1978a). Suitability of islands as breeding sites dependent upon proximity to foraging sites, degree of protection birds afforded from mammalian predators, and favorability of winds and updrafts for landing and taking off (Cramp and Simmons 1977, Nelson 1978a).

Post-breeding Northern Gannets generally forage extensively throughout the Gulf of St. Lawrence, Strait of Belle Isle, nearshore waters off Labrador, and North Atlantic off the coast of Newfoundland before migrating southwest from breeding areas; migrate largely in waters of continental shelf, and along continental slope; come to land only in pursuit of shoals of fish or in unusual weather conditions; even more infrequent as a pelagic wanderer >200 km from land. Hatch-year juveniles, initially unable to fly, move south to subtropical waters of s. Florida and the Gulf of Mexico. Adults and older immatures fly south utilizing a wide range of airspace (Brewer et al. in press), from low over waves, to soaring at high altitudes; adjust rapidly to good opportunities and sometimes form substantial local concentrations in areas with ample resources of fish concentrated within 10–15 m of surface, and accessible by plunge-diving from a cruising height of 10–40 m; avoid unproductive areas (Palmer 1976, Cramp and Simmons 1977, Nelson 1978a).

Adults appear to winter off New England coast, with large concentrations often observed near continental slope off Massachusetts (Veit and Petersen 1993). Immatures scattered in continental-shelf waters along coast from Massachusetts south to Florida and Gulf of Mexico (Kain 1987, Rappole and Blacklock 1994, Stevenson and Anderson 1994, Turcotte and Watts 1999, Brewer et al. in press), with significant concentrations in mixing currents off Outer Banks of N. Carolina (Potter et al. 1980).