Justification of Red List Category
This species is classified as Near Threatened because it has a very small population and a small range, for which there is currently no evidence of a decline. If the population was found to be declining, it would warrant uplisting to a higher threat category.
Using a mean density of 0.004 birds/ha observed in 1993, and an estimate of 400,000 ha of suitable habitat on Hawai`i, an estimate of 1,600 birds, including 1,120 adults (560 pairs), was calculated by Hall et al. (1997). A similar estimate of 1,457 individuals was obtained from surveys in 1998-1999. The breeding population calculated by Hall et al. (1997) is rounded to 1,100 mature individuals.
The population is thought to be fairly stable and may be at or near the carrying capacity of remaining habitat (J. Nelson in litt. 2007).
Buteo solitarius breeds on Hawai`i in the Hawaiian Islands (USA), with vagrants recorded on Maui, O'ahu and Kaua'i. The population is thought to be fairly stable (J. Nelson in litt. 2007), and estimates range from 1,457 (Klavitter et al. 2003) and 1,600 (1,120 adults) to 2,700 birds (Hall et al 1997, Griffin et al. 1998). The lack of information on historical numbers makes an assessment of this species difficult, and the underlying trend may be of gradual decline as nesting habitat disappears (J. Klavitter in litt. 1999). The rapid occupation of abandoned breeding territories suggests that the species may now be at or near the carrying capacity of remaining habitat (J. Nelson in litt. 2007).
It occurs in a broad range of habitats up to 2,700 m, from lowland agricultural areas to all types of forest (Thiollay 1994, Hall et al 1997). However, most successful nesting is restricted to native `ohi`a trees Metrosideros polymorpha (which are slow growing and generally in decline) (J. Klavitter in litt. 1999). It benefits from some anthropogenic changes, for example, it feeds on introduced game-birds, passerines and rodents, and uses edge habitat around sugar-cane fields and orchards for hunting (Hall et al 1997, J. Klavitter in litt. 1999). The species reproduces at a slow rate, and there are observations that incubation lasts for 38 days, nestlings fledge after 59-63 days, and parents care for fledglings for an average of 30.2 weeks (Griffin et al. 1998). Parents feed nestlings with mostly mammalian and avian prey.
Continuing threats include forest clearance for agricultural and other developments, logging, the actions of introduced ungulates that degrade native forests and inhibit their regeneration, repeated nest disturbance, and perhaps road-kills (Scott et al. 1986, Thiollay 1994, J. Klavitter in litt. 1999). Nesting habitat in particular has been reduced, with recruitment of M. polymorpha restricted by competition from exotic plants in some areas (M. Gorresen in litt. 2007). The species is threatened by the conversion of land used for pasture and sugar-cane to eucalyptus plantations, and residential development in extensive areas of subdivided land, mainly in Puna District (T. Pratt in litt. 2007). It formerly suffered extensively from shooting and may come into conflict with future efforts to reintroduce the Critically Endangered Hawaiian Crow Corvus hawaiiensis, which it preys upon.
Conservation Actions Underway
CITES Appendix II. Following surveys in 1998-1999, an island-wide survey for the species was carried out in 2007 (M. Gorresen in litt. 2007). A plan for the monitoring of the species's population is being developed (T. Pratt in litt. 2007). Ungulates are locally excluded from regenerating habitat (M. Gorresen in litt. 2007).
Text account compilers
Benstead, P., Capper, D., Sharpe, C J, Stuart, T., Taylor, J.
Pratt, T., Gorresen, M., Klavitter, J., Nelson, J.
BirdLife International (2018) Species factsheet: Buteo solitarius. Downloaded from http://www.birdlife.org on 22/10/2018. Recommended citation for factsheets for more than one species: BirdLife International (2018) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/10/2018.