Justification of Red List Category
The overall population of this species has increased from a low of perhaps just 30 birds in the mid-1900s to over 2,000 individuals in 2011. The majority of the population outside Kaua'i does not breed successfully in the wild, so the effective population size is very small and consequently the species is listed as Vulnerable.
The total population was estimated to be 1,241 individuals in 2004 (based on counts in 2003), 1,744 individuals in 2006 (A. Marshall, D. Hu and K. Misajon in litt. 2007) and c.2,500 individuals in 2011 (A. Marshall in litt. 2012). However, it is expected that fewer than 1,000 have bred successfully in the wild, and maintenance of the current population relies partly on the regular release of captive bred individuals. Hence the effective number of mature individuals falls within the band 250-999.
The total population was estimated to be 960-1,000 birds in 1999, 1,241 individuals in 2004 (USFWS 2004a), 1,744 in 2006 (A. Marshall, D. Hu and K. Misajon in litt. 2007) and 2,500 in 2011 (A. Marshall in litt. 2012). On Kaua'i, population growth from 2004-2006 can be attributed solely to natural recruitment as no releases of captive-bred birds occurred during that time period. On Maui, the population remains steady, owing in part to captive releases, as well as to predator control. On Big Island, the population has slightly increased, partly owing to natural recruitment at Hakalau National Wildlife Refuge, better recruitment at Hawai'i Volcanoes National Park post-drought, and some captive releases (A. Marshall, D. Hu and K. Misajon in litt. 2007).
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, along with other species, it declined due to habitat loss and alteration, and predation by humans and introduced predators (Olson and James 1991, A. Marshall, D. Hu and K. Misajon in litt. 2007). The species is now the focus of conservation efforts. Between 1960 and 2006, over 2,400 captive-bred individuals have been released on Big Island, Moloka'i, Maui and Kaua'i (A. Marshall, D. Hu and K. Misajon in litt. 2007). During the drought years of 1976-1983, the majority of released birds (c.1,200) perished (Black et al. 1997). Of 63 birds released between 2000-2001 and 2005-2006, 55 (87%) survived their first year (A. Marshall, D. Hu and K. Misajon in litt. 2007). On Big Island, the population has been partly dependent on continued releases, although large numbers are no longer needed to maintain a stable population (C. Terry in litt. 1999, A. Marshall in litt. 2012). This is the most genetically diverse population (F. Woog in litt. 2006). The population on Maui is considered to be more or less stable (A. Marshall, D. Hu and K. Misajon in litt. 2007). On Kaua'i, numbers had increased to c.1,400-1,600 by 2011. There is now a large population at Kaua'i Lagoons adjacent to the airport, and the state plans to move around 400 from there to sites on Maui, Big Island and Moloka'i. In 2011, the population was estimated at around 2,500 birds state-wide (A. Marshall in litt. 2012).
In 1949, the remaining populations on Big Island inhabited rocky, sparsely vegetated, high volcanic slopes. Following habitat loss and alteration for agriculture (Olson and James 1991), the optimal habitat is now apparently 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). Breeding success and productivity are currently low except on Kaua'i. In recent studies, less than 10% of all breeding-age females successfully bred (Banko et al. 1997, F. Woog in litt. 2006), although this may not be the case on Kaua'i (A. Marshall, D. Hu and K. Misajon in litt. 2007).
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). A lack of suitable habitat, especially for rearing young, is the most important limiting factor, combined with predation by the introduced small Indian mongoose Herpestes auropunctatus (except on Kaua'i), dogs, cats, pigs and rats (Black et al. 1994, Black 1995, H. C. Baker and P. E. Baker in litt. 1999, T. C. Telfer in litt. 1999, A. Marshall, D. Hu and K. Misajon in litt. 2007). Other threats include disease and parasites, inbreeding depression, loss of adaptive skills in captive-bred birds and dietary deficiencies. Feral cats carry the protozoan organism Toxoplasma gondii which causes toxoplasmosis, a disease that can be fatal in the species (Hess and Banko 2006). Road-kills are an important threat on Big Island (M. Morin in litt. 1999) and probably on Maui (A. Marshall, D. Hu and K. Misajon in litt. 2007). Indeed road-kills were found to be the most common cause of known adult mortality on Big Island from 1989-1999 (Rave et al. 2005). Recruitment is low in this species, as found in the Hawai'i Volcanoes National Park over the same period. Yearly average hatching success was only 55% (range 44-77%), probably because of introduced predators rather than inbreeding. A yearly average of only 30% (range 0-50%) of nestlings fledged, with most lost to starvation, dehydration and predation. Recruitment into the breeding population is low, with only 42% of tracked fledglings eventually attempting to breed. An average of 35% of the population breed each year, probably limited by food availability, which affects female condition. Drought is another limiting factor for this species (Rave et al. 2005).
Conservation Actions Underway
CITES Appendix I. The species benefits from a suit of protected areas, including Hawai'i Volcanoes and Haleakallâ (Maui) national parks, Kîlauea Point (Kaua'i) and Hakalau Forest (Big Island) national wildlife refuges, and several state sanctuaries (Banko et al. 1997, C. Terry in litt. 1999). Extensive research has been conducted on factors limiting population growth (e.g. Bailey and Black 1995, Rave 1995, Rojek and Conant 1996). Predators are controlled, and supplementary food and water are sometimes provided at particular sites (C. Terry in litt. 1999, A. Marshall, D. Hu and K. Misajon in litt. 2007). Despite the low average fledging success rate recorded in the Hawai'i Volcanoes National Park from 1989-1999, this was more than double the rate in the previous 15 years, owing to predator control and supplementary feeding during breeding seasons (Rave et al. 2005). Other efforts have involved habitat restoration and reducing human disturbance, especially to breeding birds (Rave et al. 2005, A. Marshall, D. Hu and K. Misajon in litt. 2007). Releases of captive birds continued until the late 2000s (A. Marshall, D. Hu and K. Misajon in litt. 2007), but have now ceased. Translocation of birds from Kaua'i to other islands is on-going, as there is a large population at Kaua'i Lagoons, near the airport (A. Marshall in litt. 2012).
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
Benstead, P., Bird, J., Butchart, S., Sharpe, C J, Stattersfield, A., Stuart, T., Taylor, J., Temple, H. & Khwaja, N.
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.
BirdLife International (2021) Species factsheet: Branta sandvicensis. Downloaded from http://www.birdlife.org on 25/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/10/2021.