DESCRIPTION AND TAXONOMY
The po`ouli is a medium-sized, 26 gram (0.9 ounce), stocky Hawaiian
honeycreeper easily recognized by its brown plumage and characteristic black
mask framed by a gray crown and white cheek patch. Robust birds, they have
short wings and tail, stout legs and feet, and a conical finch-like bill. Plumages of
the po`ouli are not well known (Engilis et al. 1996, Baker 1998), but observations
at two nests revealed that adults of both sexes and young differ subtly in
coloration. Males have whitish under parts, whereas females (and perhaps young
males) have a grayish throat and breast. Fledglings have whitish under parts, a
mask smaller than that of the adults, and a pale tip to the mandible. The original
species description (Casey and Jacobi 1974) was based on two specimens now
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believed to be in immature (first basic) plumage, because they look like females
but retain a pale tip to the mandible. There is no information on molt.
The po`ouli comprises a monotypic genus and species that, remarkably,
was discovered in 1973 (Casey and Jacobi 1974). Morphological and genetic
studies agree that the po`ouli forms a unique lineage within the Hawaiian
honeycreepers (Casey and Jacobi 1974, James and Olson 1991, Fleischer et al.
2001). Pratt (1992a) suggested that the po`ouli may not be a Hawaiian
honeycreeper, but also noted the similarity in tongue morphology with another
honeycreeper, the Maui creeper (Paroreomyza montana).
LIFE HISTORY
Po`ouli have been observed singly, in pairs, and in family groups with a
single young (Pratt et al. 1997b). It is unknown whether po`ouli pairs defend
territories like the other bark-foraging honeycreepers, the `akiapôlâ`au and Maui
parrotbill. In studies of a nesting pair, territorial behavior, such as singing in
vicinity of the nest after eggs were laid or consistent chasing of birds of other
species that approached the nest, were not observed (Kepler et al. 1996).
However, no other po`ouli occurred in the vicinity of the nest.
Our knowledge of the po`ouli breeding biology is based on two sequential
nestings by the same pair in 1986 (Kepler et al. 1996). Egg-laying took place on
about March 10, and about April 26 and 27, for the first and second nests,
respectively. Clutch size was probably two eggs. The second, successful nest
fledged only one of the two young, which spent 21 days in the nest. The female
alone incubated the eggs and brooded the chicks, but both parents fed the chicks.
Throughout nesting, the male fed the female at or away from the nest. This
provisioning became important in poor weather -- either wind or rain -- when the
female spent more time on the nest. Both po`ouli nests were typical of the nests
of other honeycreepers; an open cup composed of pûkiawe twigs and mosses and
lined with thin fern rootlets (Engilis et al. 1996). The nests were 8 meters (26
feet) high in tall `ôhi`a trees and were hidden among leaf-bearing twigs (Kepler et
al. 1996). Both nests are stored at the Bishop Museum in Honolulu.
Po`ouli forage primarily on tree branches, making extensive use of the
subcanopy and understory. They seem to prefer the native hydrangea, kanawao
(Broussaisia arguta), the native holly, kawa`u (Ilex anomola), and `ôhi`a
(Mountainspring et al. 1990, Pratt et al. 1997b). Po`ouli glean from, probe, and
excavate moss mats, lichen, and bark for small invertebrate prey. Detailed
examination of stomach contents from the two type specimens revealed a diet of
tiny native snails, beetles, and proportionately few other arthropods (Baldwin and
Casey 1983). Based on foraging observations, Mountainspring et al. (1990)
believed that po`ouli took proportionately more Lepidoptera and Coleoptera
larvae. The most common food items seen delivered to po`ouli chicks were these
larvae and succineid snails (Kepler et al. 1996).
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Po`ouli often associate with mixed species foraging flocks of other
insectivorous honeycreepers, especially Maui `alauahio (Paroreomyza montana)
and Maui parrotbill, gleaning insects from branches and foliage. Observers
searching such flocks increase their chances of locating po`ouli.
Po`ouli are unusually quiet, and surveys or variable circular plot counts
that depend on vocal detections are not appropriate for po`ouli. Males rarely sing
and do so mostly as part of courtship prior to egg-laying. The song is a series of
chip notes alternating in pitch. The infrequent chip notes are similar to those of
Maui `alauahio, but often characteristically paired or given in rapid succession.
Interestingly, most of the more recently observed po`ouli calls have been very
similar to those of the Maui parrotbill, with which po`ouli often associate,
including an up-slurred "chu-wee" and a soft "whit" contact call (Jamie Bruch,
pers. comm.).
HABITAT DESCRIPTION
Po`ouli currently occur in montane wet forests from timberline at 2,100
meters (7,000 feet) elevation down to a lower limit of 1,440 meters (4,750 feet).
The terrain is steep and dissected by numerous stream gulches. Rainfall,
delivered mostly by the trade wind weather system, exceeds 5 meters (200 inches)
annually. The vegetation is mixed shrub montane wet forest (Jacobi 1985) with a
canopy averaging 13 meters (43 feet) height and 60 percent crown cover,
dominated by `ôhi`a (Metrosideros polymorpha). Areas of similar habitat remain
unoccupied to the southeast and west. The range of the po`ouli coincides with
high population densities of other honeycreeper species, a distribution believed to
be delimited by disease-bearing mosquitoes prevalent at elevations below 1,500
meters (5,000 feet; Scott et al. 1986). Po`ouli are associated with low levels of
disturbance to soil and vegetation by feral pigs (Mountainspring et al. 1990).
Po`ouli are believed to require an intact subcanopy and understory for foraging
and cover and as such are intolerant of habitat alteration by feral pigs.
HISTORICAL AND CURRENT RANGE AND STATUS
The po`ouli apparently was unknown to the Hawaiians; it eluded western
naturalists during the discovery period of Hawaiian ornithology at the end of the
19th century, and was discovered by a team of university students in 1973 (Casey
and Jacobi 1974). Historically, po`ouli have been confined to a 1,300-hectare
(3,200 acres) section of forest on the northern and eastern slopes of Haleakalâ
Volcano, Maui (Figure 14; Mountainspring et al. 1990). The type locality was
between the eastern and western forks of Hanawî Stream. Fossil evidence shows
that the po`ouli once inhabited drier forests at lower elevation on the leeward
slope of Haleakalâ, implicating a much broader geographic and habitat range
(James and Olson 1991).
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Po`ouli numbers and range have declined to a tiny population difficult to
detect over at most a few hundred hectares. Attempts to estimate population size
and density have met with frustration because of the bird’s poor delectability.
Mountainspring et al. (1990) reported densities at the type locality of 76 ± 8 (SE)
birds/square kilometers in 1976, 15 ± 7 birds/square kilometers in 1981, and 8 ± 4
birds/square kilometers in 1985 (30.8 ± 3.2 birds/100 acres in 1976, 6.1 ± 2.8
birds/100 acres 1981, and 3.2 ± 1.6 birds/100 acres in 1985). No birds were
found in the type locality in 1993 to 1995 (J. Simon/U.S. Geological Survey
unpubl. data). Surveys in 1994 to 1995 found perhaps as many as six po`ouli at
four locations, from the west rim of Kûhiwa Valley at 1,880 meters (6,200 feet)
east to the upper reaches of Helele`ike`ôhâ Stream at 1,570 meters (5,200 feet);
(Reynolds and Snetsinger 2001, Baker 2001). Thorough surveys of the historical
range in 1997 to 2000 located only three birds, all in Hanawî Natural Area
Reserve, and no others have been located since these birds were color-banded in
1996 and 1997 (Hawai’i Department of Land and Natural Resources unpubl.
data). These last three birds, now known to consist of one male and two females,
occur in separate, non-overlapping home ranges, so there are no known breeding
pairs.
REASONS FOR DECLINE AND CURRENT THREATS
Habitat damage by feral pigs is thought to be an important cause of the
decline in po`ouli numbers (Mountainspring et al. 1990). Other threats have not
been directly linked to the po`ouli, but the species can be assumed vulnerable to
the same threats that impact other honeycreepers. Of these factors, the most
important are presumed to be nest predation by rats and mortality from mosquitoborne
diseases. Both black and Polynesian rats are abundant in po`ouli habitat
(Sugihara 1997). These animals feed largely on invertebrates (Sugihara 1997)
and have been blamed for the decline of native land snails, which are an important
food for the po`ouli (Hadfield et al. 1993). Another predator of the native land
snails in po`ouli habitat is the abundant, nonnative garlic snail (Oxychilus
alliarius).
CONSERVATION EFFORTS
The po`ouli was federally listed as an endangered species on September
25, 1975 (U.S. Fish and Wildlife Service 1975), and was included in the Maui-
Moloka`i Forest Bird Recovery Plan (U.S. Fish and Wildlife Service 1984a).
Decline of the po`ouli prompted conservation agencies to protect its entire
historical range, as it was known at the time, by creation of the State of Hanawî
Natural Area Reserve. Through fencing and control efforts, the State has
removed feral pigs from sections of Hanawî Natural Area Reserve and State
Forest Reserve that harbor po`ouli immediately to the east. These actions have
stabilized soil erosion and stimulated vegetation recovery, improvements that
should benefit the po`ouli. To the south, in habitat that appears suitable for
po`ouli, the National Park Service has also erected fences and removed pigs.
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Portions of The Nature Conservancy’s Waikamoi Preserve are managed as native
ecosystems and could also serve as habitat for po`ouli. Habitat downhill from the
fenced portions of Hanawî Natural Area Reserve is proposed for fencing.
Several agencies and groups have initiated research and recovery. The
East Maui Watershed Partnership, a consortium of government agencies,
nongovernmental agencies, and private landowners seeks to protect 40,000
hectares (100,000 acres) of rainforest, of which the higher elevations contain the
last population of po`ouli. The Hawai’i Department of Land and Natural
Resources and the U.S. Geological survey Biological Resources Division are
continuing searches for the po`ouli in the Hanawî Natural Area Reserves and
adjacent habitat. The Hawai’i Department of Land and Natural Resources and the
U.S. Fish and Wildlife Service have entered into a cooperative agreement to
jointly fund the Maui Forest Bird Recovery Project. Activities of this project
include control of small mammals in an attempt to reduce the threat of predation
on adults and nests and competition for invertebrate prey, research on optimizing
rodent control methods, surveys for native land snails, and mist netting, banding,
and collecting blood samples to monitor demography and disease prevalence in
native bird populations, including the po`ouli. The same program has included an
attempt to translocate one po`ouli into the home range of another to encourage
breeding (see Recovery Strategy for more detail).
RECOVERY STRATEGY
Fundamental to the long-term strategy for recovery of the po`ouli is
protection and management of high elevation rainforests on East Maui. While the
canopy of this forest remains relatively intact, the understory has been severely
degraded by feral pigs in places, and subcanopy trees have died as a result of soil
loss and disturbance to roots. Recovery of vegetation should proceed rapidly at
first as ferns and native shrubs move into disturbed areas. Regeneration of
subcanopy trees will be slower, but within a few decades should return the forest
to a restored condition. Forested lands below the lower boundary of Hanawî
Natural Area Reserve should be fenced, and feral pigs removed, to provide a
buffer for current po`ouli home ranges and to protect any po`ouli that have not
been detected.
Alternative strategies for recovery of the po`ouli were outlined in The
Environmental Assessment for Proposed Management Actions to Save the po`ouli
(U.S. Fish and Wildlife Service and Hawai’i Department of Land and Natural
Resources 1999). This document included solicitation for public input on
recovery strategies, including continued habitat management only, field
translocation with "hard" release to create a breeding pair, field translocation with
"soft" release by temporarily holding birds in a field aviary, and bringing all three
remaining birds into captivity for propagation. Based on the Environmental
Assessment and subsequent public comments, it was decided that the best strategy
for recovering the po`ouli was continued habitat management, including predator
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control, in conjunction with translocation of a female into the home range of the
last male, in hopes that they would form a breeding pair and nest (U.S. Fish and
Wildlife Service and Hawai’i Department of Land and Natural Resources 1999).
Translocation efforts began in January 2002. If a breeding pair is created by
translocation, every effort should be made to search for nests, and any eggs
produced should be brought to the appropriate facilities for rearing and
establishment of a captive flock that eventually would produce birds for release
back into the wild.
While surveys for po`ouli have nearly exhausted the possibility of locating
new birds, additional searches may be warranted adjacent to areas already
covered. In addition, research should be conducted on the feasibility of largescale
habitat management through application of rodenticide by hand broadcast or
by aerial broadcast. Additional information on the abundance and distribution of
the bird’s prey-base would increase our understanding of whether food limits the
po`ouli population.
ecos.fws.gov/docs/recovery_plans/2003/031016.pdf
;D Hawaii contained and contains some of the most beautiful birds. Sad that it has become the "extinction capital" of the world.
