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Site description (2012 baseline)
Rose Atoll consists of two small islets (Sand Island - 2.5 ha and Rose Island - 5.2 ha), covering six hectares of emergent land and 15,878 ha of submerged reef (Wegmann & Holzwarth 2006), and is the only uninhabited island in American Samoa. Rose is the easternmost island of Samoa and is situated 120 km east-southeast of Ta’u Island (Wegmann & Holzwarth 2006). Rose is one of the smallest atolls in the world, it is almost square with sides of approximately 1.5 miles and it encloses a lagoon of 2 km across at the widest point. Rose Island is permanently vegetated, although Sand Island is only vegetated intermittently (it is frequently cleared by hurricanes) (Rodgers et al. 1992). The reef is made mostly of coralline algae, as opposed to coral, and therefore is quite unusual (Wegmann & Holzwarth 2006). The atoll became a National Wildlife Refuge under the US Fish and Wildlife Service (USFWS) in 1973 and it is home to 11 species of migratory seabird, as well as the threatened green sea turtle. Rose Atoll receives far less precipitation than the majority of American Samoa because of its low elevation: hurricanes are frequent (Wegmann & Holzwarth 2006).

Key biodiversity
Rose Atoll is a key migratory stopover for at least seven seabird species (Wegmann & Holzwarth 2006) and approximately 97% of the seabird population of American Samoa resides on Rose (USFWS 2010). The Sooty Tern dominates population numbers on Rose Atoll. Abundances of several hundred thousand have been recorded frequently (400,000 in 1974, 300,000 in 1975 (Amerson et al. 1982)). However, little quantitative data has been documented for this species on Rose more recently. Black Noddies have usually been observed in the hundreds (235 in 1980, (Amerson et al. 1982) 292 in 1988 and 583 in 2005 (Wegmann & Holzwarth 2006)) and are most often found in nests in high up Pisonia branches (Amerson et al. 1982). Red-footed Boobies have been recorded in similar numbers, although their populations have shown greater fluctuation (3500 in 1975 (Amerson et al. 1982), 450 in 1984 and 142 in 2002 (Wegmann & Holzwarth 2006). Rose is one of only three nesting sites for Red-footed Boobies in American Samoa (Amerson et al. 1982). The activity of tree nesting seabirds such as Black Noddies and Red-footed Boobies could be adapted to significant but non-catastrophic disturbances, explaining their observed tolerance to hurricanes and the Pisonia die-off (Wegmann & Holzwarth 2006). Brown Boobies are common, and at its peak, the Brown Booby population on Rose Atoll may be the largest and densest in the Central and South Pacific (possibly with the exception of Palmyra in the Line Islands) (Amerson et al. 1982). Masked Boobies have been common on Rose Atoll (540 in 1974, 200 in 1976 (Amerson et al. 1982), although the numbers recorded more recently have been much lower (15 in 1989, 18 in 1991, 12 in 1998 (Wegmann & Holzwarth 2006)). The ground nesting Brown Noddy is also found on Rose (143 in 1982, 148 in 1991 and 111 in 2002 (Wegmann & Holzwarth 2006)). Common White Terns breed on all islands in American Samoa and although previously common, sightings have declined more recently (550 in 1975 (Amerson et al. 1982), 75 in 1984, 63 in 2002 (Wegmann & Holzwarth 2006)). Breeding of the species has been recorded mostly from September/October to February (southern summer) (Amerson et al. 1982). Rose Atoll is the Greater Frigatebird’s major nesting site in American Samoa (Amerson et al. 1982). Abundances tend to be in the hundreds (200 in 1970, 300 in 1974, 750 in 1976 (Amerson et al. 1982). Nesting has been recorded in June and October (Amerson et al. 1982). The Lesser Frigatebird is also common on Rose (200 in 1975, 425 in 1976 (Amerson et al. 1982). Grey-backed Terns are relatively uncommon across the whole of American Samoa, with the total population estimated at less than 200 (Amerson et al. 1982). A small number have been observed on Rose Atoll (14 in 1976 (Amerson et al. 1982)). Red-tailed Tropicbirds are also present in small numbers (40 in 1976 (Amerson et al. 1982), 27 in 1990 and 26 in 2005 (Wegmann & Holzwarth 2006)). Between 1976 and 1991 there were a small number of sightings of vagrant, off-course migratory birds, most commonly the Long-tailed New Zealand Cuckoo (Wegmann & Holzwarth 2006).

Non-bird biodiversity: The lagoon hosts a diverse array of marine life, including a population of rare giant clams and a number of fish species (Wegmann & Holzwarth 2006). The vegetation on Rose is dominated by the Tournefortia argentea shrub. The previously extensive Pisonia forest has significantly declined since the end of the 20th Century (Wegmann & Holzwarth 2006). Strawberry Hermitcrabs gather under vegetation during the day and forage across the island at night (Wegmann & Holzwarth 2006).

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Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Rose Atoll (American Samoa). Downloaded from https://datazone.birdlife.org/site/factsheet/rose-atoll-iba-american-samoa on 27/12/2024.