Justification of Red List Category
The last two known wild individuals of this species disappeared in 2002, so the species is now classified as Extinct in the Wild. Some individuals remain in captive breeding facilities and a reintroduction plan is being developed.
In 1992, there were only 11 or 12 birds in the wild (Maxfield 1998, Banko et al. 2002, Banko 2009), and the last two individuals were last seen in June 2002. The last known wild chick fledged in 1992, and the last viable wild egg was laid in 1996 (Faike 2006). The species persists in captive breeding facilities, with development of a reintroduction programme in progress (Lieberman and Kuehler 2009, U.S. Fish and Wildlife Service 2009). Captive breeding started in the 1970s, but few fledglings were produced until eggs from wild nests were harvested and hatched in captivity during 1993-1996 (Lieberman and Kuehler 2009, Banko 2009). A total of 27 captive-reared juveniles, originating from eggs laid either in the wild or in captivity, were released during 1993-1999 (Banko 2009, U.S. Fish and Wildlife Service 2009). By 1999, 21 released birds had died and the remaining six were captured to protect them and preserve genetic diversity (Maxfield 1998, Conrow 1999, Banko 2009, U.S. Fish and Wildlife Service 2009). In 2011, the captive population stood at 94 individuals (49 at the Keauhou Bird Conservation Center, 44 at the Maui Bird Conservation Center, and 1 at the San Diego Zoo), including 39 birds used as breeders (Switzer 2011).
Corvus hawaiiensis was distributed historically on Hawai`i in the Hawaiian Islands (USA), where the last individuals were found in and around the Kona Forest Unit of Hakalau Forest National Wildlife Refuge. Bones of this or a closely related species have been found on Maui, indicating a wider distribution before Western contact (Banko et al. 2002, Banko 2009). Nesting by the last known wild birds was probably confined to higher elevations on Mauna Loa in South Kona (Faike 2006, Banko 2009).
It once inhabited dry to moist `ohi`a-koa forest and woodlands, but it later became confined to high mountain forest. It is omnivorous, but primarily feeds on the fruit of native understory plants (Maxfield 1998, USFWS and Hawai'i DLNR 1999). As well as fruits and berries, the species feeds on eggs, young birds, insects and carrion (Faike 2006). Captive-reared birds have been observed using twigs as tools to access food (Faike 2006). Nest construction usually begins in March and the first clutches are laid in April (Banko et al. 2003).
It has suffered from extensive habitat alteration, particularly reduction of understory food-plants as a result of the activities of feral ungulates, logging, agriculture and the loss of pollinators and dispersers (U.S. Fish and Wildlife Service 2009). Problematic ungulates include feral cattle, mouflon sheep, feral sheep and goats (J. Burgett in litt. 2007). The impact of shooting has probably been substantial, even in recent decades. In the late 19th Century, the species was persecuted as a pest, and it became unpopular with pig hunters for alerting animals to their presence (Faike 2006). The species was confiding and easily attracted by imitated calls, making it an easy target (Faike 2006). During breeding the species is sensitive to human disturbance (Faike 2006), including nest-monitoring operations (Banko et al. 2002, Walters 2006). Other documented threats include predation by introduced rats, the small Asian mongoose Herpestes javanicus and the native Hawaiian Hawk Buteo solitarius (classified as Near Threatened), as well as avian malaria and pox carried by introduced mosquitoes (Maxfield 1998) and Toxoplasma gondii carried by feral cats (Banko et al. 2002, J. Burgett in litt. 2007, Banko 2009, U.S. Fish and Wildlife Service 2009). Feral cats are ubiquitous in the species's habitat and are also potential predators (J. Burgett in litt. 2007). Fledged chicks remain near the ground for several days before they can fly properly and are at particular risk from predation (Faike 2006, Banko et al. 2002). Captive-reared birds have suffered from disease, with at least one dying from a bacterial infection, and diseases may have made others more vulnerable to predation (Maxfield 1998, Banko et al. 2002, Banko 2009, U.S. Fish and Wildlife Service 2009). The captive population is inbred (Faike 2006, U.S. Fish and Wildlife Service 2009), and this may be reducing reproductive success. West Nile Virus, which could potentially be introduced by migrating shorebirds and waterfowl or commercial transport, and is spread by mosquitoes (Faike 2006), could threaten reintroduction efforts in the future. West Nile Virus is presumed to be highly lethal in C. hawaiiensis, owing to a reduction in the population of the American Crow C. brachyrhynchos in mainland North America by 45% over eight years due to the virus (J. Burgett in litt. 2007).
Conservation Actions Underway
Between 1993 and 2007, over 90 birds were hatched in the captive breeding programme (Lieberman and Kuehler 2009). Captive-raised individuals were released into lightly-managed habitat and monitored (Kuehler et al. 1994, Lieberman 1997, Banko 2009), but releases were stopped after January 1999 due to increasing mortality (U.S. Fish and Wildlife Service 2009). About 75 birds need to be maintained in the captive flock for future reintroduction attempts to take place (U.S. Fish and Wildlife Service 2009). In 2011, the captive population stood at 94 individuals, including 39 birds used as breeders (Switzer 2011). Introduced mammalian predators were trapped in the Kona Forest Unit and, although this no longer takes place, predators will be managed at any future reintroduction sites (J. Burgett in litt. 2007). Some areas of its former range are now fenced and free of feral ungulates, and the exclusion of ungulates will be extended into other areas (J. Burgett in litt. 2007). Relocation of problematic B. solitarius failed because the birds homed back from over 32 km (U.S. Fish and Wildlife Service 2009). Two reintroduction sites have now been identified (Nelson in litt. 2012). Following ungulate removal, fencing and habitat restoration, reintroduction at Pu?u Maka?ala Natural Area Reserve is due to begin with the release of 6 birds hatched in 2016. Ongoing restoration effort continues at the second site. A recovery plan was prepared in 1982 and revised in 2009, outlining recovery actions including expanding the captive propagation to minimize loss of genetic diversity, protecting suitable habitat and managing threats to the species, establishing new populations in managed habitat, establishing a program to increase public support, and continuing research and adaptive management practices for species recovery (USFWS 2009). Each year, around 2,000 school children and students attend the environmental education programme and see C. hawaiiensis in captivity at the Keauhou Bird Conservation Centre (Faike 2006).
48 cm. Large crow or small raven. All dark sooty-brown with paler primaries. Heavy, black bill. Brown eyes. Juvenile has blue eyes and pink mouth lining. Voice Huge variety of squawks, screams, growls, and dissonant croaks. Hints Flies high over montane forest and ridges.
Text account compilers
Benstead, P., Capper, D., Derhé, M., Isherwood, I., Stattersfield, A., Stuart, T., Symes, A., Taylor, J., Martin, R
Nelson, J., Pimm, S., Baker, P.E., Gorresen, M., Lieberman, A., Fretz, S., VanderWerf, E., Burgett, J., Banko, P., Woodworth, B., Camp, R.
BirdLife International (2020) Species factsheet: Corvus hawaiiensis. Downloaded from http://www.birdlife.org on 27/11/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 27/11/2020.