Migration

Short- to medium-distance partial migrant. Banding evidence unclear, but individuals from almost any boreal S. m. maxima population south of Outer Banks of N. Carolina may winter at breeding area, while others from same area may travel short distance north or south, or thousands of kilometers to wintering grounds. Retreat from parts of North America probably governed by combination of temperature and food availability. Most immature birds summer in wintering area until first breeding, after which they undertake reasonably regular annual migrations permanently (van Velzen 1968, 1971; Buckley and Buckley 1974; Clapp et al. 1983; Cramp 1985).

Little detailed information for austral S. m. maxima (which apparently disperses north through Argentina, Uruguay, and Brazil; Escalante 1985, 1991) or for S. m. albididorsalis, which is known to disperse north to Morocco and w. (African side) Mediterranean, south to Angola (Urban et al. 1986, Malling Olsen and Larsson 1995).

Spring migration unobtrusive, boreal S. m. maxima appearing in breeding colonies and performing courtship activities late Mar–early Apr in Cape Charles, VA (Buckley and Buckley 1972a). Prebreeders or prospecting adults sometimes wander north in May (more typically, Jun) as far as Massachusetts, but immediately after juvenile fledging, adults accompany single young in dispersal northward. Such family groups routinely found as far north as Cape Cod, MA, and San Francisco Bay, CA, and have in past erroneously been responsible for reports of extralimital breeding.

Small flocks linger at favored locations, especially inlets, in s. New England into late Nov, when they abruptly depart (PAB). At Cape May, NJ, individuals remain into Dec (Sibley 1997). Normal northern limit of winter flocks is Outer Banks of N. Carolina (CBC data). On Pacific Coast, species is year-round resident south of Orange Co., CA (Small 1994, Howell and Webb 1995), and where not breeding, numbers drop off abruptly in Feb–Mar as more northerly breeders return north.

Throughout wintering area, Royal Tern a conspicuous coastal bird. Numbers increase greatly beginning in Oct, probably peak in Jan, and begin to decline in late Feb. By May only nonbreeders remain (except at few known West Indian and Mexican breeding sites), mostly 1-yr-olds, with increasingly fewer in each sub-sequent year class. As species lives along sandy coasts and offshore islands, maximum counts on tropical wintering areas surely vastly underestimated: Haverschmidt and Mees (1995) found no more than 1,000 occur at any one time in Suriname, an estimate likely low by perhaps a factor of 4–5.

Moves coastwise; but, unexpectedly, many Atlantic Coast breeders cross Central America somewhere (perhaps in Isthmus of Panama, where known from Gatun Lake in heart of Panama Canal; Ridgely and Gwynne 1989), then move south along Pacific Coast to Peru (Ashmole and Tovar 1968, van Velzen 1971). Thus, Atlantic and Pacific coast breeders mix in winter, but unknown if this leads to exchange of breeders (and genes). Although some birds banded in Florida have been recovered in West Indies and Middle America, many U.S. breeders winter in or migrate through Florida, and birds have been recovered in Florida that were banded in Maryland, Virginia, N. Carolina, S. Carolina, Texas, Louisiana, and Mississippi (Stevenson and Anderson 1994). No information on austral S. m. maxima or S. m. albididorsalis .

Selected regional dates for migratory movements are Sep–Dec and Apr–early Jun in Costa Rica (Stiles and Skutch 1989); (suspected) Mar–May in Florida (Stevenson and Anderson 1994); as early as late Mar in Maryland (Brinker 1996). In California, wintering birds present Aug–late Feb or occasionally May (Small 1994). North of breeding range on East Coast, individuals move through Cape May, NJ, early Apr–May, but most observed beginning early Jul, with another strong movement during late Oct, and most have departed by early Dec (Sibley 1997). In Massachusetts, small numbers observed late May but most observed late Jun to mid-Aug, with stragglers through Nov (Veit and Petersen 1993).

No published information.

No published information.