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Branta sandvicensis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA AVES ANSERIFORMES ANATIDAE

Scientific Name: Branta sandvicensis
Species Authority: (Vigors, 1834)
Common Name(s):
English Hawaiian Goose, Nene
Spanish Barnacla Hawaiana, Barnacla Nené

Assessment Information [top]

Red List Category & Criteria: Vulnerable D1 ver 3.1
Year Published: 2012
Date Assessed: 2012-05-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S. & Symes, A.
Contributor(s): Baker, H., Baker, P., 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.
Facilitator/Compiler(s): Benstead, P., Bird, J., Butchart, S., Sharpe, C J, Stattersfield, A., Stuart, T., Taylor, J., Temple, H., Khwaja, N.
Justification:
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.

Geographic Range [top]

Range Description: 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).

Countries:
Native:
United States (Hawaiian Is.)
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: 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.
Population Trend: Increasing

Habitat and Ecology [top]

Habitat and Ecology: 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).

Systems: Terrestrial

Threats [top]

Major Threat(s): 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 [top]

Conservation Actions: 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).

Conservation Actions Proposed
Continue to monitor population trends. Carry out further research into the factors limiting breeding and causing low recruitment. Manage and restore habitat, and control predators (Black 1995, Black 1998, Rave et al. 2005). Ensure Kaua'i remains mongoose-free (H. C. Baker and P. E. Baker in litt. 2000). Optimise genetic diversity in flocks with few founders (Rave 1995). Develop community education programme, particularly with regard to road-kills (Black 1995, C. Terry in litt. 1999, Rave et al. 2005). Establish large predator-free reserves in lowland areas with better quality forage in which the above targets can be addressed (H. C. Baker and P. E. Baker in litt. 1999, H. C. Baker and P. E. Baker in litt. 2000). Expand habitat restoration efforts. In the Hawai'i Volcanoes and Haleakalâ national parks, prevent visitors from feeding the birds and speeding (Rave et al. 2005). Conduct a telemetry study to determine habitat use outside of the breeding season, as non-breeding areas have been largely unstudied (A. Marshall in litt. 2012).


Citation: BirdLife International 2012. Branta sandvicensis. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 20 October 2014.
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