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Figure 1 . Breeds Apr–Jul in large colonies on barrier islands and other isolated locations along immediate coastlines. Some smaller colonies also may be located within those of other tern or gull species. Colony locations often widely scattered.
In e. U.S., breeds from Virginia (irregularly from se. Maryland; Brinker 1996) south along Atlantic Coast to Florida, thence west along Gulf Coast to s. Texas. Within this region, breeding confirmed in Accomack and Southampton Cos., VA; Dare (Cape Hatteras), Carteret (Cape Lookout), and Brunswick (Cape Fear) Cos., NC; Charleston Co., SC; McIntosh Co., GA; Nassau, Duval, Brevard, Indian River, Lee, Charlotte, Citrus, and Wakula Cos., FL; Baldwin Co. (Gulf Shores), AL; Jackson Co. (Gulf Is. Natl. Seashore), MS; St. Bernard (Chandeleur Is.), Plaquemines, Lafourche, Terrebonne, and Vermillion Parishes, LA; and at numerous locations along Texas coast, especially in Laguna Madre (Buckley and Buckley 1984a, Clapp and Buckley 1984, Post and Gauthreaux 1989, Wiedenfeld and Swan 2000, Georgia Breeding Bird Atlas [BBA] unpubl., Florida BBA unpubl., Texas BBA 1987–1992 unpubl., Virginia BBA unpubl.).
Along Pacific coast of s. U.S. and n. Mexico, breeds irregularly in extreme s. California (Orange, San Diego Cos., where breeding occurs within Elegant Tern [S. elegans] colonies) and locally in Baja California Norte (Laguna Ojo de Liebre, I. San Roque, I. Raza, mouth of Colorado River), n. Sinaloa, and Is. Tres Marias (Wilbur 1987, Small 1994, Howell and Webb 1995, Am. Ornithol. Union 1998). Breeding formerly suspected in Sonora but never confirmed (Russell and Monson 1998).
Along Gulf coast of Mexico, breeds on islets in Campeche Bank off Yucatán (Cayo Arcas and Alacrán Reef), and possibly off coast of Belize (Howell and Webb 1995).
In West Indies and n. South America, very local breeding occurs/has occurred in Bahamas, Cuba, Jamaica, Culebra, U.S. Virgin Is., and Anguilla, as well as on Las Aves, Venezuela; Battures des Malmanoury, French Guiana; also on Aruba, Curaçao, and Bonaire (erratic), and Tobago (regular? Voous 1983, Chardine et al. 2000). Not known to breed east of French Guiana or in Suriname (Haverschmidt and Mees 1994).
Austral-breeding population barely hinted at until Escalante (1968, 1985), and breeding sites not discovered until 1970s. Escalante (1985) noted austral breeding proven only from Argentina (Buenos Aires and Chubut Provinces), even though suspected/likely from Uruguay and Brazil, but then Olmos et al. (1995) reported Brazil’s first colony at Laje de Santos in São Paulo. Colonies occupied Aug–Feb, and austral Royal Terns usually nest with endangered Olrog’s Gull (Larus atlanticus), Dolphin Gull (L. scoresbii), and Cayenne (S. [sandvicensis ?] eurygnatha) and South American (S. hirundinacea) terns.
Figure 1 . Boreal S. m. maxima winters along most of Pacific coast from s. California (north to about San Luis Obispo Co.) south to Peru, along Atlantic and Gulf coasts from n. North Carolina south to Panama and the Guianas, and through-out West Indies, including San Andres (Ridgely and Gwynne 1989, Stiles and Skutch 1989, Small 1994, Howell and Webb 1995, Raffaele et al. 1998, Christmas Bird Count [CBC] data). Also occasional during winter (mostly Dec) in Bermuda (Amos 1991) and occurs very locally in interior of s. Florida (Stevenson and Anderson 1994). Prebreeding adults remain on southern portion of winter range until first-breeding, probably moving farther northward each successive year. Boreal breeders unknown from band recoveries south of the Guianas, although summering prebreeders from ne. coastal Brazil suspected of coming from north (Escalante 1985, Sick 1993).
Austral S. m. maxima disperses north postbreeding, and presumably winter and summer, prebreeding, as far north as Brazil (Sick 1993). Without band recoveries, morphometric discrimination, and molecular data, impossible to say how far north such birds routinely move, or if they mix with or exchange individuals with boreal populations (unlikely).
After breeding, disperses northward along Pacific coast to central California, and casually to n. California; along the Atlantic coast to Massachusetts, occasionally Maine, and rarely to New Brunswick, Nova Scotia, and Newfoundland; and north from the West Indies (as indicated by band returns) to Bermuda (Amos 1991, Am. Ornithol. Union 1998). Although normally strictly coastal, boreal S. m. maxima has been found at various inland locations in North and Middle America, especially, but not only, after tropical storms and hurricanes. Inland records include s. California (Salton Sea), Wisconsin (Manitowoc), Illinois (Chicago and Lake Calumet), Ohio (Lorain), Ontario (Kingsville), New York (Rochester), Oklahoma, Arkansas, and e. Tennessee, as well as Distrito Federal, Mexico (sight report), and n. Guatemala (Beavers et al. 1991, Howell and Webb 1995, Am. Ornithol. Union 1998).
Outside The Americas
S. m. albididorsalis known from only 5 breeding (Apr–Jul) locations in w. Africa on islands off Mauritania (Banc d’Arguin) and Senegambia (Saloum, Casamance, and Senegal deltas; Bijolo Is.), but likely undiscovered sites and populations on isolated parts of w. African coast, notably Nigeria (cf. Elgood et al. 1994). [N.B.: Malling Olsen and Larsson (1995: 33) refer to South African breeding population of Royal Tern, typographical error for South American .] Disperses widely postbreeding, in winter north to Morocco, south to Namibia; most frequent between Mauritania and n. Angola, most probably wintering in Gulf of Guinea (Urban et al. 1986).
Royal Terns, most probably S. m. albididorsalis, have occurred several times in w. Europe, most often Spain and Gibraltar (at least 9 records to date). But others (Ireland, United Kingdom, Norway, Portugal), probably S. m. maxima, on occasion assisted by hurricanes: 2 banded in North America recovered in Wales (Lewington et al. 1991) and Spain (A. van den Berg pers. comm.). Vagrant to Mozambique (Am. Ornithol. Union 1998).
In Audubon’s time (1830s–1840s), Royal Tern described as breeding sporadically along Gulf Coast, mostly in Texas, Louisiana, and extreme s. Florida, occasionally up to N. and S. Carolina. By Bent’s time (1921), range given as “s. Atlantic and Gulf coasts from Virginia (Northampton Co.) to s. Texas (Cameron Co.) . . . some of Bahamas . . . and many of West Indies . . . [plus] Pacific Coast of Lower [= Baja] California and Mexico.” In general terms, this not far from current distribution and perhaps also from Audubon’s time (see Demography and populations: population status, below).
First modern Royal Terns began to appear in Northeast after 1933 hurricane (New Jersey), but it was not until 1944 storm that numbers were recorded from Cape May, NJ, to Cape Cod, MA. Odd individuals seen postbreeding north to Cape Cod in following 10 yr, but not until 1954–1955 hurricanes did large numbers (up to hundreds) appear, peaking with thousands after Hurricane Donna in 1960. From that year on, Royal Terns have appeared in large numbers even up to Gulf of Maine without storms, remaining increasingly late in autumn, routinely to late Nov as far north as Long Island, NY. In New Jersey, one-day highs at Cape May reached 350 by Oct 1956, and 1,600 in Oct 1996 (Sibley 1997).
Predictably, breeding advanced northeast in same period, albeit slowly, reaching Maryland in 1950 (Stewart and Robbins 1957), and then apparently backfilling south toward Cape Charles, VA. North of Maryland, only known instance is 1 pair once in New Jersey (1988; Walsh et al. 1999). Absence of suitable colony sites free of mammalian predators probably limiting north of Delmarva Peninsula.
In California (unknown further north on Pacific coast), Unitt (1984: 93) succinctly reported historical status as follows: “declined in numbers in California during 1900s. [In 1930s] commonest large tern, [but by 1984] vastly outnumbered by Caspian and Elegant.” Remains rare north of Morro Bay, where absence of sandy shores plus cooler waters appear restrictive (P. Lehman, S. Finnegan, and K. Garrett pers. comm.).
After first Maryland breeding record in 1950 (a previous nest there in 1945 had been collected), several hundred pairs (occasionally >1,000) bred through late 1980s, but suitable habitat has since been lost or degraded so that subsequent nesting attempts few and typically unsuccessful (Brinker 1996).
In Florida, Royal Tern apparently a widespread breeder only until late 1800s, then not reported breeding until 1951, when 1 pair nested at Port St. Joe, Gulf Co. Has since increased (especially since 1970) to occupy Florida breeding distribution described above (Stevenson and Anderson 1994). During mid-1950s (shortly after Florida breeding had resumed in 1951), breeding range (and records of postbreeders) began dramatic northward expansion along Atlantic Coast.
Detailed historical data unavailable for central and w. Gulf Coast (where species’ status appears to have changed little in last 175 yr), or for Mexico, Bahamas, and West Indies. Breeding sites for austral S. m. maxima still being discovered; likewise, no firm data available on historical change in albididorsalis ’s w. African breeding range.
Wetmore (1937, 1938) described fossils (apparently Late Holocene) from Puerto Rico and St. Croix (U.S. Virgin Is.), and Olson and Rasmussen (2001) report ancestral Royal Tern (“ Sterna aff. maxima ”) fossils from mine on Pamlico River in ne. North Carolina, part of rich marine ecosystem offshore during Pliocene. No others known.