Swain's Island is a raised, ring-shaped atoll with a total area of 326.34 ha, a maximum elevation of 9.1 m and a shoreline of 6.2 km. Geographically and floristically, the island is closely related to the Tokelau Islands, 160 km to the northwest. The entire central portion of the island is occupied by a large brackish lagoon, Lake Namo, which has apparently been isolated from the sea only in recent times. The lagoon is approximately 1.5 km long and 1.0 km wide. There is a small patch of marsh on the north side of the lagoon. The annual rainfall is about 2,500 mm (Volk 1993).
The Pacific Reef Heron (Egretta sacra) breeds in the coconut plantations and feeds in shallow portions of the lagoon. The Pacific Black Duck (Anas superciliosa) has been reported in the past, and could still occur as a visitor. Five species of migratory shorebirds have been recorded: the Pacific Golden Plover Pluvialis fulva, Wandering Tattler Heteroscelus incanus, Bristle-thighed Curlew Numenius tahitiensis, Ruddy Turnstone Arenaria interpres and Sanderling Calidris alba (rare). Four species of seabird breed: White-tailed Tropicbird Phaethon lepturus, Brown Noddy Anous stolidus, Black Noddy A. minutus and White Tern Gygis alba, but numbers are relatively low (Volk 1993). Previous knowledge of the avifauna of Swain's Island is scanty. The U.S. Exploring Expedition's ship Peacock surveyed the island from offshore from 1 through 4 February 1841. Titian Ramsay Peale, one of the naturalists on the expedition merely noted that "scarcely any morning birds [terns ?] were seen", and that "birds are fewer than they are even where inhabited by man" (Peale in Poesch, 1961). Charles Wilkes in his narrative of the expedition (1845) stated that "Pigeons, similar to those seen at the Samoan Group, were observed." It should be noted, however, that Wilkes, himself, did not see the island and obtained his bird information second hand. No pigeons were seen by any of the Pacific Ocean Biological Survey Program (POBSP) survey parties. Two Hawaiian-Americans, Killarney Opiopio and Abraham Piianaia, recorded their experiences on the island 24 January through 28 February, 1963 (Opiopio, 1936; Piianaia, 1936). These diaries contained references to the birds of the island, but few of the descriptions are sufficiently detailed to allow accurate identification to species. The frequency with which "gogo" (also referred to variously as "boobies" or "sootie terns") were mentioned indicates that these were the most abundant birds on the island. These "gogo" were apparently Brown Noddies (Anous stolidus) or Black Noddies (Anous tenuirostris) judging from descriptions of the birds' habits and from Donaghho's remark that the natives of Swain's Island called noddies "logo" (Donaghho, 1952). This name "logo" or "gogo" is strikingly similar to " ngongo," the name that the Ellice Islanders use for the Brown Noddy (Child, 1960) and may well refer to the same bird. The Hawaiian-Americans also make two references to white birds, one of which is further identified as a " love bird" or " akaiaki." These observations probably refer to the White Tern (Gygis alba) or possibly to the Black-naped Tern (Sterna sumatrana) which is called "akaiaki" by the Ellice Islanders and "kiakia" by the Gilbertese (Clapp 1969). Clapp (1969) recorded all birds seen during five visits to Swain's Island in 1966-1967. On 3 August POBSP personnel saw four dark-plumaged Pacific Reef Herons. Golden Plovers were seen on all visits and were present in July, 1938, as well (Donaghho, 1952). They seemed to exhibit little preference for any particular habitat on the island. Birds inhabited not only the outer beaches and the lagoon but also frequently foraged on paths through heavily forested areas. Estimated numbers present varied from about 50 birds in February to about 100 in August. Estimates on the other three visits (October, November, and April) were respectively 90, 100, and 90 birds (Clapp 1969). Ruddy Turnstones were present on all POBSP surveys except the one made in August 1966. An estimated 60 turnstones were present in February and 43 were counted in April. Nearly as many were present in November (about 30 birds). Only two turnstones were seen on the October visit but the beach was not surveyed during this visit and more could have been present. Both feeding and loafing turnstones were found primarily on the beaches and only seldom foraging along the lagoon. None were reported from forested areas. The largest concentrations were seen on the east and southeast beaches where they readily associated with plovers. On 13 April a fleck of 35 turnstones in nuptial plumage, the largest concentration seen, was found on the east beach. A single Bristle-thighed Curlew was seen 5 October 1966 on the west shore of the lagoon directly behind the village. The number of Wandering Tattler present on Swain's Island varied little from survey to survey. On visits when more complete counts were made, numbers varied from a low of about 20 birds in August to a high of 34 birds in April. In both February and November an estimated 30 tattlers were present (Clapp 1969). Most of the tattlers were observed along the outer beaches where they seemed to exhibit a preference for rocky outcroppings. Three Sanderlings were seen on Swain's Island by POBSP personnel. In 1966-1967 White-tailed Tropicbirds were seen on three of six surveys of Swain's Island but were not common (Clapp 1969). A single tropicbird was seen flying over the island in October and four were seen overhead in November. Two of the four November birds flushed from a tall Pisonia tree but no nest was found. It seems likely that a few of these tropicbirds nest on Swain's Island since there is an abundance of nest sites present. Local people stated that they occasionally saw Red-tailed Tropicbird flying over the island but that they had never seen them land (Clapp 1969). Red-footed Boobies were seen on only one of the island surveys. On 5 October 1966 about 20 were seen feeding off the northwest corner of the island. On 27 April 1967 a Black-naped Tern was seen in a flock of Brown Noddies roosting on the northeast beach. Three Sooty Terns flew near the POBSP support vessel just as it left Swain's Island on 24 February. An estimated 1,500 to 3,000 birds were breeding on Swain's Island on five visits in 1966-1967 (February, October, November, and April) but only about 40 birds were seen in August, 25 of them in a feeding flock offshore. When these noddies were numerous they were usually evenly distributed throughout the forest with perhaps slightly greater densities being encountered on the north side of the island. The number of Black Noddy on Swain's Island varied considerably from survey to survey. An estimated 200 birds were present in February; only about 25 birds were seen in August, and none were observed in October (Clapp 1969). At least 350 to 400 Black Noddies were observed in November and April and more may have been present at these times. An active colony was found in November on the east-northeast corner of the island. It contained about 125 nests about 75 feet up in two large Pisonia trees. White Tern numbers present on Swain's Island, like the numbers of noddies, varied considerably from survey to survey (Clapp 1969). An estimated 500 to 1,000 White Terns were present in October and November 1966 and an even larger number, perhaps as many as 3,000 terns, was present in February. In April 1967 an estimated 350 terns were present but in August not more than 40 individual terns were seen. In November POBSP personnel found three White Tern nests containing eggs - one egg was 30 feet up on a dead palm stub; the other two eggs about 20 feet up on horizontal branches of Pandanus trees. All four specimens collected in November had bare brood patches suggesting breeding (Clapp 1969).
Non-bird biodiversity: Seven species of reptiles occur on the island, including three species of gecko, three species of skink and the Black Turtle Chelonia (mydas) agassizi. The turtle formerly nested on the island, but now occurs only as a visitor to inshore waters. Swain's Island is the only known locality for the Micronesian Skink (Emoia adspersa) in American Samoa. The salt marsh on the north side of the lagoon is dominated by Paspalum distichum and Eleocharis geniculata. Swain's Island was originally covered with littoral forest dominated by species of Pisonia, Hernandia, Pandanus, Neisosperma, Calophyllum and possibly Barringtonia and Cordia. This original vegetation was almost totally removed and replaced with coconut plantations for the production of copra. Most of the plantations have recently been abandoned, and the coconut trees are slowly being replaced by littoral forest, chiefly Hernandia and Pandanus (Amerson et al., 1982). Scaevola is the dominant plant in the littoral scrub vegetation (Volk 1993).
BirdLife International (2021) Important Bird Areas factsheet: Swain's Atoll. Downloaded from http://www.birdlife.org on 26/01/2021.