Justification of Red List Category
This species has a very small breeding range, known from five locations in the main Hawaiian islands, and the future of at least two are in jeopardy (Mauna Loa and West Maui). Radar surveys show that the species is declining rapidly on at least one of the other islands where it breeds (Kaua'i), and declines are probable on other islands too. Therefore, it is assessed as Endangered.
Spear et al. (1995) give a best estimate of 3,750-4,500 breeding pairs based on at-sea surveys. This roughly equates to 7,500-9,000 mature individuals, and 11,250-13,500 individuals in total. The discovery of possibly several thousand birds breeding on Lana'i during terrestrial surveys in 2006-2007 and two small colonies on West Maui (J. Penniman in litt. 2007), probably in the tens or low hundreds of birds (D. Ainley in litt. 2007), may bring the estimated breeding population close to the upper estimate of 6,500-8,300 pairs calculated by Spear et al. (1995). However, the rapid decline in at least the population on Kaua'i would suggest that the population size may now in fact be smaller than this. Given uncertainty regarding overall trends, the upper and lower bounds from Spear et al. (1995) are used here, i.e. 3,750-8,300 pairs, or 7,500-16,600 mature individuals.
A standard population monitoring technique has not yet been fully developed for use across colonies and survey sites. However, efforts are underway among collaborating scientists to standardize metrics and procedures, so that population trends can be monitored more effectively on each of the islands. Pterodroma sandwichensis is suspected to have declined severely for the past few centuries, owing primarily to predation by introduced species at nesting colonies and urbanization (D. Ainley in litt. 2007), as well as collisions with utility structures and power lines. On Kaua'i, the population has declined by as much as 78% between 1993 and 2013 (Raine et al. 2017), but the rate of subpopulation decline probably varies considerably, and as such the overall trend is difficult to quantify. Assuming that, apart from the population on Kaua'i, all other subpopulations are overall stable, the ongoing global rate of decline would be c.19-42.5% over three generations (59.4 years), depending on the proportion of the overall population previously found on Kaua'i. Terrestrial and at-sea threats are likely to impact all subpopulations though, so they are all likely in decline (A. Raine in litt. 2018). If all subpopulations were declining at the same rate as on Kaua'i, the reduction over three generations could even reach as high as 99%. In the absence of evidence from other subpopulations, the overall ongoing rate of decline is tentatively placed here in the range 50-79% over three generations, and is suspected to continue into the future.
Pterodroma sandwichensis ranges in the central Pacific and breeds on the Hawaiian Islands (U.S.A.). There are approximately 2,547 known burrows within Haleakalā National Park (Haleakalā National Park 2015 unpubl. data). Two small colonies are present in the West Maui Mountains, but they are so far unquantified (Cooper and Day 2003, J. Penniman in litt. 2007), with numbers perhaps in the tens or low hundreds (D. Ainley in litt. 2007). On Hawai'i, small numbers breed on Mauna Kea and 40-50 pairs were present on Mauna Loa prior to 1995 (Ainley et al. 1997, Simons and Hodges 1998). On Kaua'i, 1,600 pairs are indicated by observations of birds at a rafting site (Ainley et al. 1997). On Moloka'i, 5-10 birds were heard calling in 1980, suggesting small numbers (Simons and Hodges 1998), but there has not been a concerted effort to estimate numbers on this island (D. Ainley in litt. 2007). Surveys in 2006-2007 located a colony in the cloud forests of Lana'ihale on the north side of Lana'i (P. Baicich in litt. 2007, A. Wilson in litt. 2007). This population probably numbers several thousand birds, based on the volume of calling during night time listening surveys in April and May along the Lana'ihale ridge at the highest point in the uplands, although only 14 burrows had been found by October 2007 (J. Penniman in litt. 2007). Surveys have so far been hampered by weather conditions and the risk of habitat disturbance (J. Penniman in litt. 2007).
On Maui, Mauna Kea and Mauna Loa, nesting takes place mainly between 2,000 and 3,000 m, in lava cavities with little vegetation nearby (D. Ainley in litt. 2007). Elsewhere, for example West Maui (J. Penniman in litt. 2007) and Kaua'i (N. Holmes in litt. 2007), it nests at lower elevations, amongst dense shrubs and ferns or in native grasslands with bracken (Ainley et al. 1997, Simons and Hodges 1998, P. Baker in litt. 1999, D. Ainley in litt. 2007). On Haleakalā, Maui, birds nest in rock crevices and tunnels that are over 0.5 m deep, often exceeding two metres (Simons and Hodges 1998, J. Penniman in litt. 2007). Pairs nest in cavities in the volcanic terrain, in burrows beneath rocks or at the base of clay cliffs (N. Holmes in litt. 2007). At lower altitudes, they excavate burrows or nest in cavities often at the base of trees (Simons and Hodges 1998, P. Baker in litt. 1999, N. Holmes in litt. 2007), although many burrows on Lana'i are not at the base of trees (J. Penniman in litt. 2007). On Lana'i, birds breed in dense uluhe fern habitat (Dicranopteris linearis and Diplopterygium pinnatum) and start breeding in March, whereas in Haleakalā, Maui, birds begin breeding in mid-February (Penniman et al. 2008). On Kaua'i, birds breed in montane wet forests, where burrows are located along ridgelines in predominantly native forest, often at the base of large trees. On average, birds take five to six years to reach maturity but begin visiting colonies to establish pair bonds and prospect nesting sites at 2-3 years (Hess and Banko 2006). Most eggs are laid in May and June, with most young fledging by December (Mitchell et al. 2005). Birds nesting at higher elevations appear to finish provisioning chicks earlier, with most birds having departed the colony at Haleakalā by the end of October. The diet comprises mostly fish and squid, with squid constituting c.50-75% of the food ingested (Simons and Hodges 1998). It has been found that at least some birds nesting on Lana'i feed in waters around the Aleutian Islands, as shown through the use of tracking devices on several breeding individuals (P. Baicich in litt. 2007). P. sandwichensis regularly is observed foraging in mixed species flocks in association with predatory fish species (Mitchell et al. 2005).
Historically the species suffered declines through harvesting by early Polynesians and during the period of Hawaiian settlement beginning c.1,800 years ago (Carlile et al. 2003). The species may have been restricted to its current breeding range since the arrival of Europeans (Carlile et al. 2003). The most serious current threat is predation by introduced vertebrates including Indian mongoose Herpestes javanicus, feral cats, Common Barn-owls Tyto alba, rats, dogs, and pigs. Although not yet established on Kaua'i and Lana'i islands, mongooses represent an ongoing major threat to nestling and adult birds at breeding colonies on the other islands within the Hawaiian Petrel’s range. Feral cat and rat depredation, where unmanaged on other islands, continues to limit recovery capacity. Considerable efforts are ongoing to reduce the impact of cat predation on the species with cat-proof fences erected on Maui and Mauna Loa. Adults and nestlings are very susceptible to predation, as nests are on the ground, and they are naïve to predators.
A significantly lower percentage of birds come ashore to nest during El Niño years (c.40% compared to c.65% normally) (C.N. Hodges per Carlile et al. 2003), suggesting that the species is sensitive to such disturbances in environmental conditions (Carlile et al. 2003).
Each autumn during the fledging season, some of the fledgling birds become grounded as a result of light attraction and disorientation. Occassionally, birds collide with sources of light, and mortality sometimes occurs as a result of collisions with fences and power-lines mostly on Kaua'i and Maui (Simons 1985, Cooper and Day 1998, Simons and Hodges 1998). Once on the ground, fledglings are unable to fly and are killed by cars, cats and dogs, die from environmental exposure or injuries, or are recovered by the public. The siting of the Kaheawa wind farm on Lana'i also appears to be causing ongoing mortality at a potentially significant rate.Some areas of nesting habitat have been lost to the pressures of modern urbanisation and degraded by feral goats and pigs and weeds. Nest burrows are trampled by feral goats, mouflon sheep and Chital Deer Axis axis (Mitchell et al. 2005, H. T. Harvey and Associates 2015) however, these are now excluded from the largest colony and deer are not present at the majority of sites. On Lana'i, habitat degradation caused by the invasive tree, Strawberry Guava Psidium cattleianum, is considered to be the biggest threat to the long term survival of the colony (J. Penniman in litt. 2007). In the past, considerable amounts of the Hawaiian Petrel’s habitat were converted for livestock, however as the majority of colonies are now protected, this represents a much reduced threat.
Conservation Actions Underway
CMS Appendix I. On Maui, there is a long-term monitoring programme in the Haleakala National Park (Simons and Hodges 1998) and efforts are made to control introduced mammals. In 1976, a perimeter fence was put up around the main colony to exclude feral goats and pigs from the habitat (Carlile et al. 2003). The predator exclosures placed around the national park may have facilitated an increase in the number of birds in eastern Maui (Cooper and Day 2003). The trapping of rats started in 1968, and since 1997 rodenticides have been used (Carlile et al. 2003). Cats and mongooses have been controlled since 1981, and trapping of these species and rats continues to be carried out year-round (Carlile et al. 2003). On Lana'i: colony delineation surveys are continuing (J. Penniman in litt. 2007), and as burrows are found they are included in basic breeding biology study; feral cats are being trapped and removed; studies on Common Barn-owl Tyto alba are being designed; a rat population assessment was due to begin in 2007, with control by rodenticide to be carried out subsequently; habitat restoration work may begin in January 2008; and public education projects will be implemented in 2008 (J. Penniman in litt. 2007). In 2006, a fence was completed to encircle a large portion of the breeding habitat on Lana'i; the purpose was to exclude ungulates that damage the vegetation thus impacting the island's water supply (D. Ainley in litt. 2007). Simultaneously, a limited cat-trapping programme has been initiated in the fenced area (D. Ainley in litt. 2007). On Maui, Lana'i, and Kaua'i, grounded fledglings are collected and released, although the benefit of doing this has yet to be confirmed as very few banded individuals have subsequently been encountered (D. Ainley in litt. 2007). Fencing erected for forest conservation has been modified to reduce collisions (Simons and Hodges 1998). On Kaua'i, auditory surveys to detect colonies are ongoing, and have included documenting the first known nesting sites on Kaua'i in the Upper Limahuli Preserve (N. Holmes in litt. 2007). Also on Kaua'i, street lighting is shielded in critical areas and lighting on some buildings has been modified to reduce collisions (Ainley et al. 1997, Simons and Hodges 1998). A ruling brought by the U.S. Fish and Wildlife Service in 2006, under the U.S. Endangered Species Act, has enforced a campaign running since 2005, in which all non-essential lights on Kaua'i are required to be turned off or shielded between 15 September and 15 December when young birds leave their nests (Appel 2006). The island's electricity company is helping by darkening all of its 3,000 street lights, and shielding or turning some of them off. The company has also fitted large balls to power lines in an effort to reduce the number of birds that collide with the cables (Appel 2006). Significant improvements have beem made in reducing light attraction and collision, although there is still a considerable amount of new and existing infrastructure that requires modification (N. Holmes in litt. 2007). Methods are currently being developed to quantify the population on each island; surveys for colonies on West Maui are being carried out and surveys on Moloka`i were planned to begin in Spring 2008 (J. Penniman in litt. 2007).
43 cm. Large, dark grey-brown and white petrel. Dark black-brown cap extends below eye and also forms half collar across upper breast. Remainder of head white, forehead conspicuously so. Upperparts, including upperwing and tail, darkish grey-brown without M pattern. Many, but not all, show white patches on side of rump. White underwing with narrow black trailing edge, black tip, broad black edge between primaries and carpal joint. Band extends weakly towards centre of wing from joint. Similar spp. Compared to Juan Fernandez Petrel P. externa and White-necked Petrel P. cervicalis darker, with more extensive cap, darker back, lacking M, and different underwing. Compared to Galápagos Petrel P. phaeopygia lacks black forehead markings. Voice Low-pitched, gurgling goo-oooo-gouih-gouih-gooo-o. On L`i, approximately 12 different vocalizations are known through the Hawaiian language, `ua`u, including u-u-u, ur-ur-ur, e-che-che-che and ur-ur-ah-ah-ah (J. Penniman in litt. 2007). During pair flying behaviour, one bird may give an u-u-u call, followed immediately by a rapid ch-ch-ch from the other bird (J. Penniman in litt. 2007).
Text account compilers
Stuart, T., Taylor, J., Temple, H., Westrip, J., Fjagesund, T., Hermes, C., Benstead, P., Anderson, O., Isherwood, I., Martin, R., Stattersfield, A., Stuart, A.
Baicich, P., Holmes, T., Baker, P.E., Morin, M., Ainley, D., Penniman, J., Raine, A., Wilson, A.
BirdLife International (2021) Species factsheet: Pterodroma sandwichensis. Downloaded from http://www.birdlife.org on 23/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/10/2021.