Migration

In North America, tendency to vacate seas around breeding colonies in winter more marked than in Western Palearctic; initial dispersal of fledglings from nest site not clearly separable from start of southward migration, and difficult to discern extensive postbreeding foraging excursions of adults and subadults from start of their fall migration (Nelson 1978a). Gannets remain at sea all year during their first 3 yr; southward movement more pronounced in juveniles during first winter than for older birds, with first-year birds moving on average farther south; ratio of immatures to adults and subadults 12:1 in Gulf of Mexico during Dec–Feb (Palmer 1976, Cramp and Simmons 1977).

In autumn, all age classes move southward along Atlantic Coast, at about 24–32 km/d (Brewer et al. in press). Southward movement begins in late Sep with departure of juveniles; by early Oct, most juveniles depart breeding area and move southward off New England coast; by early to mid-Oct, large numbers of juveniles off Georges Bank and its adjacent shelf waters (Perkins 1979, Veit and Petersen 1993). Adult and older immatures may travel north of breeding colonies on foraging trips off Labrador coast, before migrating south; peak departure of adult and subadult birds from breeding area mid- to late Oct; last birds gone by early Nov (Palmer 1976). By Nov, juveniles common off Long Island and New Jersey coasts, and by Dec have reached east coast of Florida; juveniles common in e. Gulf of Mexico Jan–May (Palmer 1976, Nelson 1978a); most band recoveries of juveniles in Gulf of Mexico Mar–May (Brewer et al. in press). Adult and older immature birds also migrate south from breeding colonies, but generally travel shorter distances; large concentrations of adults observed during winter months near continental slope, off coast of Massachusetts (Veit and Petersen 1993), and off Outer Banks of North Carolina (Potter et al. 1980); no band recoveries of adult birds (≥5 yr) reported beyond Atlantic coast of Florida (Brewer et al. in press).

Spring migration for adults begins in Feb; adult-plumaged birds begin to move earlier than subadults (early Mar) and immatures (Apr), with a mix of age classes by late Apr (Brewer et al. in press); birds tend to follow offshore reef edges and avoid deep water (Maxwell 1972, Palmer 1976, Stevenson and Anderson 1994). Peak northward migration of adults and subadults off coasts of New Jersey and New York early Mar through early Apr, and of immatures late Apr to mid-May (Askildsen 1998, Walsh et al. 1999); peak off New England coast late Mar to mid-Apr, and continuing into early May (Veit and Petersen 1993). Of the Northern Gannets migrating north off Georges Bank and adjacent continental-shelf waters, juveniles represent <1% during early spring migration (Mar–Apr), 25% in early May, and by late May 43%; northbound migrants appear to remain farther from coast than southbound migrants (Perkins 1979). Adults arrive at breeding grounds in mid-Apr, before favorable weather and plentiful fish supplies have arrived, younger age classes correspondingly later; spring return at 56–112 km/d somewhat faster than fall migration (Brewer et al. in press).

Little information on fall migration of fledglings following initial departure from nesting colonies; once in the water, apparently unable to takeoff again for 3 d–2 wk (Bent 1922, Nelson 1978a, Wanless 1984); thus likely begin southward migration to subtropical waters of Atlantic and Gulf of Mexico by swimming. Based on band-recovery data, speed of migration, and distance covered for North American gannets, about 24–32 km/d (Brewer et al. in press). In Western Palearctic, gannets banded as nestlings on Bass Rock, e. Scotland, in Jun occurred off coast of Morocco, nw. Africa, in <2 wk, suggesting rapid migration (Nelson 1978a). Some first-year individuals may remain in tropical waters during first breeding season (Palmer 1976, Nelson 1978a).

Motivation to migrate apparently wanes slightly in older birds. Following their extensive first-year migration, many immatures tend to remain closer to breeding areas during subsequent winters; with maturation, subadults tend to depart breeding waters later, travel shorter distances southward, and return to breeding sites earlier, with breeding adults migrating the shortest distances and returning back to breeding colonies earliest (Nelson 1978a, Brewer et al. in press).

No information available.