Black-footed albatross (Phoebastria nigripes) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

Nesting habitat

Black-footed Albatrosses typically nest on exposed sandy beaches or on the adjacent, sparsely vegetated fringes of low-lying coral and sand islands in the low-latitude Pacific (Fisher 1972; Whittow 1993; Tickell 2000). Birds may also breed in altered habitat: for example, at Midway Island, Black-footed Albatrosses nest on the grassy borders of an aircraft runway, and in the open areas among introduced ironwood trees (Casuarina equisetifolia; Whittow 1993). In this species, a breeding territory is confined to the nest site and its immediate vicinity, and is active only during mating and nesting periods (Rice and Kenyon 1962a).

Marine habitat

Life history stage constrains and influences the marine habitats used by Black-footed Albatrosses. At Tern Island in the Central Pacific, birds brooding chicks made restricted foraging trips over the warm, pelagic, oligotrophic waters (>20°C sea surface temperature (SST); >3000 m depth; <0.3 mg/m³ chlorophyll a; respectively) in the vicinity of the colony. After chicks reached 18 days old, breeding albatrosses expanded their foraging range to access the cold, coastal, productive coastal waters (<15°C SST, <200 m depth; >0.3 mg/m³ chlorophyll a) along the continental shelf of North America, from central California to British Columbia (Fernández et al. 2001; Hyrenbach et al. 2002). With the onset of the post-breeding period, Black-footed Albatross dispersed across the North Pacific, where they used a broad range of oceanic domains (7.1° to 24.9°C SST) characteristic of tropical, sub-tropical, transition zone and sub-arctic waters (Wahl et al. 1989; McKinnell and Waddell 1993; Hyrenbach and Dotson 2001; Hyrenbach and Dotson 2003). Four female Black-footed Albatrosses tagged and tracked at sea during their post-breeding dispersal foraged largely along the transition zone between the California Current and the Central Pacific Gyre (Hyrenbach and Dotson 2003).

In general, albatross marine habitat use is mediated by wind patterns and food distribution (with the latter largely determined by bathymetric and hydrographic features; cf. Croxall et al. 2005). Different physical processes influence the marine distribution of seabirds at different scales (Hunt and Schneider 1987): over meso-scales of 10 to 100 km, processes that aggregate prey, e.g., convergence or frontal zones, likely influence the distribution of the Black-footed Albatross (Hyrenbach et al. 2002). At-sea survey data from Canadian and US pelagic studies show that Black-footed Albatrosses are most abundant over the outer continental shelf (in waters >100 m deep; Harfenist et al. 2002), particularly at the shelf break (Morgan et al. 1991; Whittow 1993; McDermond and Morgan 1993),. This species frequents boundaries between water masses and areas of strong and persistent upwelling (Wahl et al. 1989; McDermond and Morgan 1993; Whittow 1993; Hyrenbach and Dotson 2001). Telemetry-tracked birds travelled more slowly in the vicinity of the continental shelf and at hydrographic fronts, indicating that they were foraging in these areas (Hyrenbach et al. 2002). Seamounts may also be important oceanic features for albatrosses: two pelagic surveys found significantly higher densities of Black-footed Albatrosses over Cobb Seamount, BC than in waters beyond one seamount diameter away (K. Morgan, unpublished data). As well, the highest bycatch of Black-footed Albatross occurred at Bowie Seamount, indicating unusual densities at this location (Smith and Morgan 2005).

Habitat trends

Ironwood was introduced to Midway Atoll in the early 1900s, leading to ongoing loss of open nesting habitat through conversion to forested areas. In 1940 US preparations for WW II began and these resulted in substantial physical alteration to Midway and other islands in the Northwestern Hawaiian chain (McDermond and Morgan 1993; USFWS 2005a). More recently, introduced golden crown-beard (Verbesina encelioides) has significantly degraded breeding habitat at Midway, Pearl and Hermes and Kure Atolls, with areas of thick infestation uninhabitable by nesting birds (Shluker 2002). Active control programs now manage non-native plant species at albatross colonies but these are costly and much work remains to be done (USFWS 2005a). Midway Atoll National Wildlife Refuge (NWR) was established in 1988 as an overlay refuge of the Naval Air Station. In 1997, the Naval Air Station at Midway Atoll was decommissioned and operation of the atoll was transferred from the US Department of Defense to the Department of the Interior (i.e., the US Fish & Wildlife Service) for management as an NWR. Although the airstrip at Midway is still operational, airfield operations are now conducted to minimize and document albatross mortality via air strikes, and many obstacles such as overhead wires and traffic signs have been removed, reducing risk of bird collision (Cousins and Cooper 2000; USFWS 2005c). Military operations at Midway created as well as destroyed nesting habitat, e.g., dredged fill material substantially increased the area of Sand Island (Cousins and Cooper 2000).

Volcanic activity may lead to future habitat alteration or loss at some of the minor colonies, e.g., San Benedicto Island, Mexico (Pitman and Ballance 2002) and at Torishima Island, Japan (Whittow 1993; USFWS 2005c); an eruption at Torishima in 1939 reduced the population breeding there to just a few birds (Cousins and Cooper 2000). Longer-term habitat loss can be predicted to occur at low-lying atolls – some of which are a maximum elevation of only three or four metres above sea level (Herbst and Wagner 1992) – as a result of climate change and an associated rise in sea level (Baker et al. 2006). Climate change and related perturbations in marine ecosystems (e.g., intensification of El Niño events), in conjunction with natural longer-term cycles such as the Pacific Decadal Oscillation (PDO), are also affecting marine habitat through altering distribution, abundance and quality of prey (Robinson et al. 2005; USFWS 2005a). For example, a warm PDO regime since 1976 has resulted in prey declines and increased SST in the California Current system, a body of water that extends to the northern end of Vancouver Island. These factors have in turn been implicated in a 90% decline of Sooty Shearwaters (Puffinus griseus) in the region, and the number of Black-footed Albatrosses in the California Current also declined over the past 20 years. Sooty Shearwaters may have simply redistributed themselves in the Pacific basin by moving to the central North Pacific transition zone, where waters have been cooling and increasing in productivity (Ainley and Divoky 2001; Bertram et al. 2005; Robinson et al. 2005). It is not known whether the same pattern holds true for Black-footed Albatross, but a recent rapid increase in California Current Black-footed Albatross numbers in response to PDO-related SST cooling indicates that this may be the case (Ainley pers. comm. 2006). Sea surface temperatures off northern Mexico are now similar to those around the Hawaiian archipelago, and this change in SST may be involved in the establishment of new albatross colonies on Mexican offshore islands (Ainley and Divoky 2001).

Habitat protection/ownership

Approximately 35% of the global Black-footed Albatross population breeds at Midway Atoll, a US National Wildlife Refuge, while similar numbers of birds nest at Laysan Island in the Hawaiian Islands NWR. Most of the remaining US Black-footed Albatross colonies occur on other islands and atolls also within the Hawaiian Islands NWR or on Hawaii state seabird sanctuaries (Kure Atoll; Anon. 2004, USFWS 2005a,b). Over 95% of the total population breeds in the Hawaiian archipelago, and thus the vast majority of the world’s Black-footed Albatrosses nest at protected sites. Except for field stations on Tern and Laysan Islands, and USFWS workers at Midway Atoll, the Hawaiian Islands NWR is uninhabited by humans. Entry to the refuge is by USFWS Special Use Permit only and even scientific research is limited and reviewed in order to minimize unnecessary disturbance (USFWS 2005b).

San Benedicto and Guadalupe Islands fall under the jurisdiction of Mexico; the former is not protected, but is uninhabited and free of introduced predators. Military personnel are stationed at Guadalupe Island year round (Pitman and Ballance 2002). A Biosphere Preserve was proposed for Guadalupe in 2003 (Aguirre Muñoz et al. 2003), and was declared in April 2005 (Comisión Nacional de Áreas Naturales Protegidas, no date; Tershy pers. comm. 2006). Torishima Island is a Japanese National Monument, i.e., is under the ownership of the Japanese government, and is managed for wildlife conservation. Japan’s jurisdiction over the Senkaku Islands is in dispute, and the archipelago may be subject to future oil development (USFWS 2005c).

There is little protection in place for the marine habitat of the Black-footed Albatross, in part because birds use high seas waters outside of national jurisdictions. In Canada, Parks Canada Agency has proposed the Gwaii Haanas National Marine Conservation Area (NMCA) for the waters around Gwaii Haanas National Park Reserve (Queen Charlotte Islands/Haida Gwaii). However, this proposal is in the consultation stage and although species at risk are already managed by Parks Canada within the proposed NMCA, the timelines for the establishment of this protected area are unknown (Shepherd pers. comm. 2005; Achuff pers. comm. 2006). In addition, Environment Canada is working towards the establishment of a Marine Wildlife Area (MWA) around the Scott Islands. If the boundary of the proposed study area becomes the boundary for the MWA, approximately 25,800 km² of marine habitat would be under some level of protection (Dunn pers. comm 2006).  In 1991 a 50 nautical mile Protected Species Zone was established around the Northwestern Hawaiian Islands, largely to protect endangered Hawaiian monk seals (Monachus schauinslandi; BirdLife International 2004a). Three US National Marine Sanctuaries created in the California Current System off coastal California (Gulf of the Farallones, Cordell Bank, Monterey Bay; Ford et al. 2004) appear to encompass foraging areas important for Black-footed Albatross during the breeding season (Hyrenbach et al. 2006). In the eastern North Pacific Ocean Black-footed Albatrosses pass through the EEZs of Mexico, the USA and Canada (Figure 3). Hyrenbach and Dotson (2003) used satellite transmitters to track four female Black-footed Albatrosses off the coast of California during their post-breeding dispersal and found that these birds spent 25%, 24% and 51% of their time in the EEZs of the USA and Mexico and in international waters, respectively. Throughout their known range, Black-footed Albatrosses also occur within the territorial waters of China, Guam, Japan, the Republic of Korea, the Marshall Islands, the Federated States of Micronesia, New Zealand (as a vagrant), the Northern Mariana Islands, Russia, and Taiwan (BirdLife International 2004b).