Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
Avian pox has been implicated in the deaths of wild „alalā nestlings (Jenkins at al 1989). Avian
malaria has also been detected in „alalā blood smears (Giffin et al 1987), but the lethality of avian
malaria for „alalā in the wild is unknown (Jenkins et al. 1989). Juvenile captive-reared „alalā are able
to survive malaria and pox infection with supportive care. Recent studies have shown that „alalā are
highly susceptible to toxoplasmosis, a disease caused by a parasite that is spread by cats, which now
exist throughout historical „alalā habitat (Work et al. 2000). Whether this pathogen played any role in
the decline of the wild population is unknown, but it has caused mortality of young „alalā released
into the wild (USFWS 2003).
Habitat changes that may have impacted „alalā populations include complete and partial
deforestation, selective species loss, and invasion or replacement of habitat by nonnative plants.
Because of the landscape-scale movements that allowed historical populations of „alalā to exploit
patchy food resources and escape harsh weather, alteration of small but crucial parts of their range
and reduction in some food plants (e.g., clearing low-elevation forest for agriculture and vegetation
changes throughout the species‟ range) may have reduced the ability of the „alalā to persist over large
areas. In addition, opening of the forest structure through grazing and tree cutting may have made
„alalā more vulnerable to predation by „io (USFWS 2003).
Inbreeding may also be occurring among the captive population, due to the small number of
individuals. Lethal abnormalities are occurring at a higher rate in the captive flock, suggesting
inbreeding depression (Zoological Society of San Diego, unpubl.). The mean number of clutches
produced per pair has also decreased from 2.50 ± 0.65 (SE) in 1996 to 0.87 ± 0.99 (SE) in 1999
(Harvey et al. 2002) indicating that inbreeding may also be starting to affect fertility and reproductive
outcomes of the „alalā.
4.4.6 ‘Io (Buteo solitarius)
The „io has two color morphs; dark phase birds are dark brown above and below, light phase birds
are dark above and pale below with dark streaking. Intermediates occur between the two extremes.
Females are larger than males, and often weigh approximately 25 percent more than males. The head
is dark in adults and light in immatures (Mitchell et al. 2005, HAS 2005).
The „io is endemic to the Hawaiian Islands, although historically it is known only from the Island of
Hawai„i. The first quantitative survey of „io abundance was carried out from 1980-1982 and yielded
a population estimate of about 2,700 birds (Griffin 1989). To update and address questions about the
validity of the population estimates, the Service initiated an islandwide survey that estimated the
population in 1993 at approximately 1,600 hawks (95 percent CI = 1,200 to 2,400) (Hall et al. 1997).
A subsequent study in 1998 generated a population estimate of 1,457 individuals (95 percent CI =
1,149-1,847) and a growth rate of 1.03 ± 0.04 SE, indicating a stable population (Klavitter et al.
2003).
As part of a reevaluation of the species‟ endangered status, a study conducted in 2007 estimated that
3,239 hawks (95 percent CI = 2,610 - 3,868) were present in 1998 and 3,085 hawks (95 percent CI =
2,496 to 3,680) were present in 2007. Similar to the 1998 study, no significant difference in densities
was found among years at either regional or islandwide scales, indicating a stable population. The
twofold increase in population estimates was attributed to differences among studies in (1) the
accuracy of distance estimation of „io sightings at count locations, (2) accounting for unobserved
Chapter 4. Refuge Biology and Habitats 4-29