Justification of Red List Category
Although this species's population has grown and continues to increase as a result of extensive conservation actions, it is reliant on ongoing predator control and habitat management measures, without which it would likely quickly decline again. It has a small area of occupancy and occurs at a small number of locations. Its population size remains small and is composed of small subpopulations. In the absence of continued habitat management and/or predator controls, its area of occupancy, area and quality of habitat, and population size would all likely decline. For these reasons, the species is listed as Near Threatened.
Recent population estimates have included 1,754 in 2006, 2,019 in 2007, 1,900 - 1,950 in 2008, 1,877 - 1,927 in 2009, 1,888 - 1,978 in 2010 (USFWS 2011), 2,465-2,555 in 2011 (VanderWerf 2012), 3,039 in 2015 (Amidon 2017), and 2,855 in 2016 (USFWS 2018). In 2018, the population was estimated at 3,252 individuals, including 1,104 on Hawai‘i (including 598 birds relocated from Kaua‘i), 627 on Maui, 37 on Moloka’i, 1,482 on Kaua‘i and 2 on O‘ahu (USFWS 2018).
For some time, all populations were dependent on continued releases of captive birds to persist (USFWS 2004), but releases ceased by the late 2000s (USFWS 2011). The populations on Kaua‘i, Hawai‘i Island and Maui are now considered to be self-sustaining (USFWS 2018). The population on Moloka’i is not yet successfully breeding (USFWS 2019), and so it is excluded from this assessment. In 2011-2016, 640 individuals were removed from a site on Kaua‘i to reduce the risk of bird strike at an airport, and moved to Hawai‘i and Maui (VanderWerf 2012, USFWS 2018).
The total population size of all established subpopulations is here placed in the band 2,600 - 3,300 individuals, roughly equivalent to 1,700 - 2,200 mature individuals.
Although the species is capable of flying between islands (Banko and Elder 1990), it is assumed that subpopulations on separate islands are largely isolated.
Historically, the population declined rapidly, and in 1951, the wild population was estimated at 30 individuals (Smith 1952). Captive breeding and reintroduction efforts began in the 1960s, resulting in an increasing population, although the population size declined sharply in 1981-1982 when releases temporarily ceased, indicating that wild populations were only sustained through continued releases (Black et al. 1991). In 1989 the population size was estimated at 476-555 individuals (Black et al. 1991). This grew to around 600 individuals in 1995 (Black 1995), c.885 in 1998, and c.1,249 individuals in 2004 (USFWS 2004). More recent population estimates have included 1,754 in 2006, 2,019 in 2007, 1,900 - 1,950 in 2008, 1,877 - 1,927 in 2009, 1,888 - 1,978 in 2010 (USFWS 2011), 2,465-2,555 in 2011 (VanderWerf 2012), 3,039 in 2015 (Amidon 2017), 2,855 in 2016 (USFWS 2018) and 3,252 in 2018 (USFWS 2019).
Counts since 2004 have included individuals on Moloka’i, which is not yet considered to be an established population. Nevertheless, the global population size is increasing. The population has grown rapidly on Kaua‘i, where there are no mongooses and there may be more available habitat than on other range islands (USFWS 2018). Populations on Maui and Hawai‘i have remained stable or increased slightly in recent years (VanderWerf 2012, USFWS 2018). A recent analysis of subpopulation trends found that populations at Hawai‘i Volcanoes National Park (Hawai‘i), Maui, Haleakala National Park (Maui), and Kaua‘i were all either increasing or stable (Amidon 2017).
Branta sandvicensis is endemic to the Hawaiian Islands (U.S.A.). Fossil analysis suggests that it once occurred throughout the main islands (Olson and James 1991). However, it declined due to habitat loss and alteration, hunting, and and predation by introduced predators (Olson and James 1991), and by 1951 only around 30 wild individuals remained, restricted to Hawai‘i Island (Smith 1952). Following an extensive reintroduction programme beginning in the 1960s, reintroduced populations are now also found on Maui, Kaua‘i and Moloka’i Islands. For some time, all populations were dependent on continued releases of captive birds to persist (USFWS 2004), but releases ceased by the late 2000s (USFWS 2011). The populations on Kaua‘i, Hawai‘i Island and Maui are now considered to be self-sustaining, although they continue to be reliant on predator control and habitat management (USFWS 2018). The population on Moloka’i is not yet successfully breeding (USFWS 2019), and so it is excluded from this assessment. In 2014, a pair nested on O‘ahu, having colonised the island naturally (USFWS 2014).
In 1949, the remaining populations on Hawai‘i were restricted to rocky, sparsely vegetated, high volcanic slopes. Historically, the species is likely to have used grasslands, grassy shrublands, and dryland forest (USFWS 2004). It currently occurs in a variety of habitats including golf courses, pastures, lava flows, upland grasslands and shrublands (USFWS). The optimal habitat during the breeding and moulting seasons appears to be lowland grassland, including exotic grassland, where there is an abundance of high protein food, adjacent to natural scrubland nesting areas (Black et al. 1994, Black 1995, Black et al. 1997, Leopold and Hess 2013). During the non-breeding season it prefers subalpine shrubland (Leopold and Hess 2013, 2014). The species is likely to have originally been an altitudinal migrant, nesting primarily in leeward lowlands below 700m, and moving to montane habitats above 900 meters in the non-breeding season (Black 1995, USFWS 2004). Seasonal movements are now being seen in some recovered populations (USFWS 2004, 2011, Hess et al. 2012). Although a weak flier, the species is capable of flying between islands, and there have been several records of individuals flying between Maui and Hawai‘i (Banko and Elder 1990). It feeds on a wide range of plants (Banko et al. 1999). It breeds from August to April, with most eggs hatching in December and January (Banko et al. 1999).
The species originally declined as a result of hunting by Polynesian and non-Polynesian people, habitat loss and the introduction of mammalian predators (USFWS 2004). Currently the main threats are predation by alien mammal species, habitat loss and degradation, and conflict with humans. Examination of carcasses from 1991-2013 found that emaciation, trauma from predation and road collisions, and diseases (predominantly toxoplasmosis) were the biggest causes of death (Work et al. 2015).
The introduced small Indian mongoose Herpestes auropunctatus occurs on all range islands except Kaua‘i, and is the main predator of eggs (Banko 1992, USFWS 2004). Eggs are also predated by Black, Norway and Pacific Rats (USFWS 2004). Dogs, mongooses and occasionally cats predate on goslings (Banko and Elder 1990, Banko 1992). Feral pigs trample nests and predate eggs, young and adults (USFWS 2004). Feral cats also carry the protozoan organism Toxoplasma gondii which causes toxoplasmosis, a disease that can be fatal in the species, although it is unlikely to be causing significant population-level impacts (Hess and Banko 2006, Work et al. 2015, 2016, USFWS 2018).
A lack of suitable lowland habitat, especially for rearing young, may be an important factor limiting growth (USFWS 2004). The development of agricultural systems by the Polynesians, and later by European settlers, resulted in the extensive loss and alteration of habitat (Olson and James 1991). Lowland habitat continues to be lost through urbanisation and conversion to agriculture (USFWS 2018), and is being degraded through grazing by feral ugulates (cattle, goats and sheep) and by the introduction of alien plant species such as guinea grass (Megathyrsus maximus), sword grass (Miscanthus floridulus), koa haole (Leucaena leucocephala), and lantana (Lantana camara; Banko et al. 1999, VanderWerf 2012, USFWS 2018).
Road-kills are an important cause of mortality on Hawai‘i (M. Morin in litt. 1999, Rave et al. 2005, Lepczyk et al. 2019) and probably on Maui (A. Marshall, D. Hu and K. Misajon in litt. 2007). Wind farms may also cause mortality of adults, although this is expected to be offset by habitat conservation plans at wind farm sites (USFWS 2011, 2018).
Populations have been found to have a low level of genetic diversity, which may affect the species's breeding success (Rave 1995).
Conservation Actions Underway
CITES Appendix I. The species was listed as Endangered in the USA under the Endangered Species Act from its inception until 2020, when it was downlisted to Threatened status (USFWS 2019). The species benefits from a suite of protected areas, including Hawai‘i Volcanoes and Haleakallâ (Maui) national parks, Kîlauea Point (Kaua‘i) and Hakalau Forest (Hawai‘i) national wildlife refuges, and several state sanctuaries (C. Terry in litt. 1999).
The population size is monitored regularly, with separate populations generally monitored separately (USFWS 2004).
Captive breeding began in 1949 and the release of captive-bred individuals began in the 1960s, ending in the late 2000s (USFWS 2011). Over 2,800 captive-bred individuals were released on Hawai‘i, Moloka’i, Maui and Kaua‘i (VanderWerf 2012). The populations on Kaua‘i, Hawai‘i Island and Maui are now considered to be self-sustaining, although they continue to be reliant on predator control and habitat management (USFWS 2018). Predators have been controlled at most areas where the species nests (USFWS 2004, VanderWerf 2012), and fences are used to exclude predators from breeding areas at some sites (VanderWerf 2012). Habitat has been restored at key sites through mowing, controlled grazing, control of alien plants and reintroduction of native plants (USFWS 2004). Supplementary food has been provided at some sites (VanderWerf 2012). A range of educational activities have taken place to raise awareness of the species's conservation (USFWS 2004). Press releases, posters, signs and postcards are used to raise awareness of the need for careful driving near nesting sites (USFWS 2018). Agreements have been put in place with private landowners to maintain or improve habitat, control predators and reintroduce the species to their land (USFWS 2004).
64 cm. Small, attractive, grey-brown goose. Body with scaly pattern of grey, brown and white. Black face and crown to nape. Golden-buff neck with feathers forming dark furrows. Cheeks tinged ochre. Juvenile similar but browner. Similar spp. Small subspecies of Canada Goose B. canadensis has all-black neck with white throat patch. Brent Goose B. bernicla has entirely dark head, neck and breast. Voice Two-part nasal call with accent on either first or second syllable ah-AHRK or NAY-nay in flight. Cackles in flocks. Sometimes a series of similar notes kip-kip-kip-kip- etc. Also soft, drawn-out nay calls when approached. Hints Often heard before seen.
Text account compilers
Baker, H.C., Baker, P.E., Black, J., Camp, R., Dibden-Young, A., Fretz, S., Gorresen, M., Hu, D., Marshall, A., Misajon, K., Morin, M., Telfer, T., Terry, C., VanderWerf, E., Woodworth, B., Woog, F., Sharpe, C.J., Khwaja, N., Stuart, T., Benstead, P., Butchart, S., Bird, J., Stattersfield, A., Taylor, J. & Temple, H.
BirdLife International (2022) Species factsheet: Branta sandvicensis. Downloaded from http://www.birdlife.org on 16/08/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/08/2022.