Fig 1.
Map of the Hawaiian Islands in the Central Pacific Ocean, including Midway Atoll showing year 2011 albatross census sectors.
Table 1.
Conservation status (2015) and population status of albatrosses (Phoebastria immutabilis and P. nigripes) and Bonin petrels (Pterodroma hypoleuca) in the Northwestern Hawaiian Islands (NWHI).
Compiled from the International Union for Conservation of Nature [65], the US Fish and Wildlife Service (USFWS) Endangered Species Program [66] and its list of Birds of Conservation Concern (BCC; [67]), and the State of Hawai‘i, Department of Land and Natural Resources [68].
Table 2.
Types of nesting habitat used by seabirds and rankings of species’ sensitivity to storm-wave overwash at Midway Atoll.
Seabird behavior and nesting habitat by land cover class identified from satellite imagery at Midway Atoll (2011). Species’ sensitivity to population-level effects of storm-wave overwash were ranked from least (1) to most (3) sensitive. Nesting philopatry (natal and nest site fidelity) of species were ranked relatively as low (1), moderate (2), or high (3) and nesting frequency as annual–semi-annual (1), annual (2), annual–alternate (3; see [28] for additional details). Land cover classes beach, wetland, and infrastructure are not used as seabird nesting habitat at Midway Atoll (see [23]). Species in bold lay at most a single egg per year. Species with populations less than 100 nesting pairs at Midway Atoll were excluded.
Table 3.
The projected area inundated (in hectares as a proportion of land cover class, or total island area) at Midway Atoll for four scenarios of sea-level rise and two modeling approaches, passive (a) and wave-driven (b), with effects of rising groundwater.
Fig 2.
Breeding phenology and synchrony of select (> 100 pairs) seabird species at Midway Atoll compared with the monthly mean of the top 5% of wave heights and wind speeds.
Monthly mean of top wave heights and wind speeds (± 1 standard deviation; [27]) were derived from hindcast data for the years 1981–2004 at 28° 00’ N, 174° 00’ W (375 km east of Sand Island). Peak nesting period includes incubation and chick rearing. Species listed in descending order of nesting colony synchrony (observed at Midway Atoll).
Fig 3.
Projected inundation of Laysan albatross nests at Midway Atoll for four sea-level rise scenarios (+ 0.5, 1.0, 1.5, and 2.0 m) using passive (a) and wave-driven (b) models, including groundwater rise.
Table 4.
Projected Laysan albatross nest inundation at Midway Atoll for four sea-level rise scenarios and two inundation models, including groundwater rise.
Nest inundation based on the 2011/2012 breeding season nest census at Sand (267,978 nests), Spit (1,615 nests), and Eastern (118,424 nests) islands, totalling 388,017 nests atoll-wide.
Fig 4.
Projected inundation of black-footed albatross nests at Midway Atoll for four sea-level rise scenarios (+ 0.5, 1.0, 1.5, and 2.0 m) using passive (a) and wave-driven (b) models, including groundwater rise.
Individual nest sites with GPS locations (± < 3 m accuracy) are indicated in black, approximate site locations of nests counted within census sectors are indicated in gray (assumes uniform distribution in suitable habitat [excludes infrastructure, shrubs and wetlands]).
Table 5.
Projected black-footed albatross nest inundation at Midway Atoll for four sea-level rise scenarios and two inundation models, including groundwater rise.
Nest distribution and abundance based on the 2011/2012 breeding season nest census at Sand (15,002 nests), Spit (28 nests), and Eastern (10,413 nests) islands, totalling 25,443 atoll-wide.
Fig 5.
Projected Bonin petrel nests inundated at Sand Island, Midway Atoll for four different sea-level rise scenarios (+ 0.5, 1.0, 1.5, and 2.0 m) using passive (a) and wave-driven (b) models, including grounwater rise.
Approximate nest locations assuming uniform distribution within colonies (known active nesting areas) stratified by estimated nesting density (see Methods for details). Inundation of Bonin petrel colonies at Eastern Island is not shown (refer to Table 5 for values). Bonin petrel nesting data was collected during 2008 (see [98]).
Table 6.
Projected Bonin petrel nest inundation on Sand Island (a) and projected colony inundation on Eastern Island (b) for four sea-level rise scenarios and two inundation models, including groundwater rise.
Nest distribution and abundance based on the 2008/2009 breeding season survey at Sand (129,534 nests [95% confidence interval: 120,099–139,367]) and Eastern (1.5 ha of colony area) islands [98].