U.S. Department of the Interior USGS FS 2006-3104

U.S. Geological Survey July 2006

Background

The palila (Loxioides bailleui) is a member of the Hawaiian honeycreeper family of birds (Drepanidinae), which is 

renowned for the profusion of species—many with bizarre bills 

and specialized feeding habits—that radiated from a single 

ancestral type. Most of the 57 or so honeycreeper species are 

extinct, and the palila is endangered because of its high degree 

of dependence on the maˉmane tree (Sophora chrysophylla) 

(Figure 1) and its restricted distribution on the upper slopes of 

Mauna Kea (Figure 2). Three decades of research have revealed 

many important facts about palila, providing the foundation 

and impetus for conservation programs in the wild and captivity. Additionally, an ambitious public conservation campaign 

arose due to the land-use conflicts on Mauna Kea. Here we 

summarize progress in palila conservation biology and outline 

steps that might overcome the remaining major challenges to its 

recovery. We also highlight lessons learned from palila research 

that may help the recovery of other Hawaiian forest birds.

Palila and two closely-related species on the tiny islands of 

Nihoa and Laysan are the last of the seed-eating honeycreeper 

species in the Hawaiian Islands. About a quarter of the honeycreeper species known from living and fossil specimens 

had finch-like bills suited mainly for eating seeds and fruits. 

Because of their dietary specialization, palila are vulnerable to 

changes in forest size and quality, as was also likely the case 

for extinct species of seed specialists. Palila and many other 

forest bird species were once distributed in dry, lowland forests. 

Fossil records indicate that palila also occurred in the lowlands 

of O‘ahu and Kaua‘i until human settlement of those islands. 

However, because lowland habitats have been highly modified 

by humans and because maˉmane occurs today primarily at high 

elevation, palila are the only native bird species found 

exclusively in dry, subalpine habitat (2000–2850 m).

Similar to other feeding specialists, palila lay few

eggs, raise few young each year, and take a relatively long time to complete the nesting cycle. 

Low rates of reproduction result in low rates 

of population growth and low potential for 

recovery from disturbances.

Long-term studies of palila offer important 

insights into the conservation biology of all 

Hawaiian forest bird species, particularly feeding specialists like the palila. Palila face many 

challenges common to both generalist and specialist 

Hawaiian honeycreeper species. Habitat loss and degradation, as well as introduced avian diseases, have reduced their 

numbers and limited their distribution to a very small portion of 

their historic range. Introduced mammals prey on palila, while 

alien insects reduce caterpillars that are particularly important in 

Palila Restoration: Lessons from Long-term Research

the diet of nestlings. Securing legal protection and funding for 

palila restoration has been challenging. Understanding how the 

palila has avoided extinction can help managers plan its recovery, and better design recovery plans for species with different 

feeding strategies in other habitats.

Challenges to Palila Recovery

Suitable Habitat Limited

Habitat loss and degradation are problems facing all Hawaiian species, but habitat degradation has been more severe in 

low-elevation areas, where agriculture and other human 

activity have been concentrated. Palila are currently 

restricted to subalpine maˉmane forest on the 

western slope of Mauna Kea (Figure 2). This is 

a small remnant of their historic range; as recently as 900 years ago palila inhabited coastal 

sites on multiple islands. Sites where maˉmane 

occur across a broad elevation represent better 

potential palila habitat than do forest fragments 

with a restricted elevational gradient. Because 

maˉmane flower and set seed at different times at 

high and low elevations, food resources are available throughout the year at sites where maˉmane is 

broadly distributed. The western slope of Mauna Kea supports the largest remaining expanse of maˉmane forest across an 

extensive elevation gradient. There are few potential reintroduction sites with appropriate forested habitat, a problem hampering recovery efforts for all endangered Hawaiian bird species. 

Figure 1. The stout beak of the palila is well adapted for extracting and 

consuming seeds from ma ̄ mane pods. (Photo © Jack Jeffrey.)
At this point in time, only high elevation habitat is suitable 

because palila are highly susceptible to introduced diseases, and 

the species survived primarily because it had a high elevation 

component to its historic range. The mosquito vectors necessary 

for disease transmission are absent or rare at high elevations, 

therefore exotic avian diseases (e.g., malaria and pox) currently 

pose little threat to palila. Although disease is not impacting 

palila in their current distribution, it is important to understand 

disease threats before trying to establish new populations at 

lower elevations.

Browsing Animals Damage Ma ̄mane Forests

Introduced ungulates (hoofed animals) are established in 

many Hawaiian ecosystems where they cause significant habitat 

degradation. These animals forage on native plants that evolved 

in the absence of mammalian herbivory. Sheep, goats, and 

cattle destroy palila habitat by damaging mature maˉmane trees 

and inhibiting their regeneration (Figure 3). In 1979 and 1986, 

federal courts ordered the removal of these animals from palila 

habitat on Mauna Kea to promote the recovery of the maˉmane 

forest. Forest regeneration in many areas where these animals 

were removed has been encouraging. However, there are still 

noticeable impacts of ungulates in palila habitat, indicating that 

current efforts to reduce sheep may not be sufficient to enable 

maˉmane forests to recover completely.

Alien Grasses and Fire

Invasive plants are recognized as another significant threat 

to Hawaiian ecosystems. Particularly in dry habitats, alien 

plants alter fire regimes. Alien grasses, in particular, increase 

the frequency and severity of fire in Hawai‘i, where most native 

plants are not adapted to frequent fires. Alien grass cover is high 

in much of the palila’s range, raising the risk that fires could 

render large areas of habitat temporarily unsuitable to palila.

Introduced Predators Threaten Palila and Their Food Resources

Having evolved in the absence of mammalian predators, 

native birds suffer from predation by introduced mammals, such 

as cats, mongooses and rats, particularly during the breeding 

season, when eggs and nestlings are depredated. Removing 

alien predators may be one of the most effective management 

options for protecting small populations of birds that have low 

reproductive capacity. 

Despite specialization on maˉmane seeds, palila also prey 

on native caterpillars found inside maˉmane pods. The protein 

provided by these caterpillars is particularly important to developing chicks and possibly to adult females during the nesting 

season. Unfortunately, alien insects threaten this important 

food resource, particularly at lower elevations. Yellowjackets 

(Vespula pensylvanica) and several ant species, particularly 

Argentine ants (Linepithema humile), are voracious predators 

and consume many species of native caterpillars. Additionally, 

parasitoid wasps kill native caterpillars by laying their eggs 

on, or inside of, them. By limiting caterpillar abundance, these 

exotic insects may indirectly influence palila populations.

Legal Challenges to Palila Protection

The palila was federally recognized as endangered in 1966 

and included in the original Endangered Species Act of 1973. 

Figure 3. A. Territorial foresters removed nearly 47,000 sheep and many 

pigs and cattle from palila habitat on Mauna Kea during the 1930s and 

1940s. The sharp reduction in browsing pressure resulted in regeneration of ma ̄ mane trees and may have been the most important factor 

in the survival of palila. However, because not all the animals were 

removed, populations built up rapidly and it became necessary to again 

reduce their numbers. Ongoing removal efforts have resulted in increased ma ̄ mane populations in many areas. 

However, current removal rates are unlikely to result 

in eradication of sheep and mouflon sheep (a non-domesticated species) from palila habitat. (Photo by L. W. 

Bryan, December 1936, courtesy of Jon G. Giffin.) 

B. Heavy browsing by sheep and mouflon sheep denudes the lower branches of ma ̄ mane trees, creating a 

distinct “browse line.” (Photo by Jon G. Giffin, 1975.) 

C. Despite reductions in their numbers, sheep and mouflon sheep continue to damage ma ̄ mane trees, in this case by gnawing the bark.

Figure 2. On Hawai‘i Island, palila historically occurred throughout 

ma ̄ mane forests on Mauna Kea, Huala ̄ lai, and western Mauna Loa. 

The present population is concentrated on western Mauna Kea, where 

the forest is most extensive. As mitigation for realigning Saddle Road 

through critical habitat, palila were recently reintroduced to Pu‘u Mali. 

Palila from the main population on the western slope are expected to 

naturally reoccupy the lands of Ka‘ohe as pastures are converted to 

forest (see p. 3, Establishing Additional Populations).

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Palila were unusual among endangered species in that “critical habitat” was designated for 

them. Critical habitat of a listed species is an 

area with physical or biological features essential 

to its conservation, whether occupied and unoccupied by that species. Within critical habitat, protection of the species and its habitat is the primary land use 

objective, however, other compatible land uses may be allowed. 

Since 1979, the protection of palila critical habitat from ungulates has been legally challenged six different times. Palila have 

prevailed in each case, yielding important nationwide applications of the ESA. The designation of critical habitat has played a 

pivotal role in justifying and funding palila restoration research. 

A significant portion of recent palila research was funded 

to mitigate the construction of a highway through an unoccupied area of critical habitat. In December 1999, the U.S. Fish 

and Wildlife Service (USFWS) approved a proposal to realign 

Saddle Road (Highway 200), the interior connection between 

eastern and western Hawai‘i, through palila critical habitat on 

condition that the loss of habitat be mitigated (see Biological 

Opinion of the U.S. Fish and Wildlife Service for the Saddle 

Road realignment and improvement project, 27 July 1998, 

Honolulu, HI.). A key component of the mitigation plan was to 

temporarily suspend cattle grazing in pastures adjacent to palila 

range (Figure 2) to allow habitat recovery in these areas. Funding 

from the mitigation also enabled the expansion or continuation 

of studies of palila ecology and limiting factors, maˉmane ecology and food availability, predator ecology and management, 

and fire ecology. Further, mitigation funding provided for the reintroduction of palila near Pu‘u Mali, on Mauna Kea’s northern 

slope. Additional funds were secured to initiate research into 

forest restoration ecology. However, these actions by themselves 

do not fulfill all the requirements to recover the palila, as designated in the USFWS Draft Hawai‘i Forest Bird Recovery Plan.

Establishing Additional Populations

Because palila are concentrated on the western slope of 

Mauna Kea, the entire species is highly vulnerable to extinction 

Palila Tolerate Toxic Chemicals 

in Ma ̄mane Trees

USGS research suggests that although ma ̄mane seeds are generally 

toxic to vertebrate species, palila have 

evolved tolerance to the chemicals 

contained within the seeds. While palila 

depend on ma ̄mane seeds for their 

survival, they do not eat the entire seed. 

Rather, they consume only the seed’s embryo, removing or eating around the seed coat. 

Chemical analysis has shown that ma ̄mane embryos are 

well-balanced nutritionally and contain protein, lipids, and carbohydrates that enable the birds to survive in a relatively harsh 

environment. In contrast, seed coats contain high levels of 

nondigestible fiber and are presumably harder to digest 

than embryos. Interestingly, all trees may not be 

equally toxic; some are more heavily exploited and 

are nicknamed “restaurant” trees.

from events such as drought, fire, storms, disease, and predation. Palila have not independently resettled recovering maˉmane 

forest, so interdisciplinary teams developed techniques for 

bolstering wild palila populations through translocation of wild 

birds and release of birds bred in captivity. Creating additional 

populations on Mauna Kea and elsewhere in their historic range 

will reduce the species’ vulnerability to local catastrophe.

Site Selection

The northern slope of Mauna Kea was chosen for palila reintroduction for several reasons: ungulate populations have been 

reduced; maˉmane recruitment is robust in some areas; highly 

invasive alien weeds are not currently threatening the forest; 

and it is relatively inaccessible to people. The original palila 

population on the northern slope was eliminated, apparently 

as a result of habitat degradation caused by ungulates. 

Hopefully, after ungulates have been removed and 

fenced out from the mitigation parcels, forest 

restoration research will reveal ways to accelerate the rehabilitation of maˉmane trees capable 

of sustaining a viable population of palila.

The southern slope of Mauna Kea also was 

considered for reintroduction because it supports a large expanse of high-density maˉmane 

forest along substantial elevation and rainfall 

gradients that could provide food to birds throughout the year. However, there were concerns regarding 

possible disturbance from military training and more active 

human use at the south site. 

Estimating Their Numbers

Palila have been monitored longer than any other Hawaiian forest bird; annual surveys started just as ungulate removal 

began on Mauna Kea in 1980. Population estimates varied 

greatly until the mid-1990s, when surveys began to reflect a 

trend towards stability around a population of about 3,000 

birds. Stabilization of the population suggests that the many 

young maˉmane trees that sprouted after sheep reduction may be 

slowly beginning to benefit palila during periods of drought and 

food scarcity, when populations formerly dipped. Palila tend to 

forage in larger trees, and many saplings have matured since 

1980. Maˉmane trees grow slowly in the subalpine environment, 

therefore the response of palila to forest restoration efforts will 

also occur slowly. However, with continued and increased forest improvement, population stabilization could eventually be 

followed by population growth, which would signify a major 

milestone in the recovery of the species. 

Translocation

By the end of 2005, 160 wild palila had been translocated 

from western Mauna Kea to the northern slope, a distance of approximately 16 km (Figure 4). Although many of the translocated birds (~ 65%) returned to the area where they were captured, 

a small colony of about 25 birds remains on the northern slope 

and at least five translocated birds moved repeatedly between 

the western and northern slopes. An additional 28 birds were 

translocated in 2006, although their rate of persistence at the site 

is still unknown. 
B

For additional information please contact:

Paul C. Banko, Ph.D.

USGS Pacific Island Ecosystems Research Center

Phone: 808/967-7396

Email: paul_banko@usgs.gov

For More Information

• USGS Pacific Island Ecosystems Research Center

biology.usgs.gov/pierc/

• US Fish & Wildlife Service, Environmental Conservation

ecos.fws.gov

• Hawai‘i Dept. of Forestry and Wildlife

www.state.hi.us/dlnr/dofaw/cwcs/index.html

• Zoological Society of San Diego

www.conservationandscience.org/projects/sp_hawaii_birds.html

• Birds of North America species account

bna.birds.cornell.edu/BNA/account/Palila

• Feral cats: Too long a threat to Hawaiian wildlife.

USGS Fact Sheet #2006-3006 

Several birds from the western slope have immigrated naturally, if perhaps temporarily, to the northern slope since the 

establishment of the satellite colony, suggesting that these populations could become linked by normal movements. Two pairs 

of translocated birds are known to have nested on the northern 

slope: in 2004, a pair produced two chicks that were not seen 

after they apparently fledged from the nest; and in 2005, a pair 

fledged a chick that survived past independence from parental 

care. This milestone indicates that translocation could become 

an important tool for developing additional, wild populations of 

palila and possibly other endangered species. Increased nesting 

activity by translocated pairs in 2006 validates this conclusion.

Captive Breeding

Another approach to bolstering wild bird populations is 

releasing captive-bred birds into the wild. In 1996, staff of the 

San Diego Zoo began building a captive breeding flock at the 

Keauhou Bird Conservation Center by hatching eggs that were 

harvested from wild palila nests. Of 15 captive-reared palila 

released to the wild during 2003–2004, at least seven persisted 

in the reintroduction area for at least one year and some of these 

birds nested on the northern slope. One pair produced only an 

infertile egg in 2004; but a captive-reared male nested with a 

translocated female in 2005, and together they produced two 

chicks that survived approximately to independence. One juvenile was last observed 108 days after fledging and the other died 

after 126 days. Breeding activity since 2005 has demonstrated 

promise in releasing captive-reared birds to increase wild 

populations.

Conclusion

Extensive research into the basic ecology of the palila 

has provided the scientific foundation and a major impetus 

for recovery. The collaboration of research and management 

agencies continues to address the effects of ungulate browsing, 

exotic mammals and insects. There are two pressing areas of 

research, the first being to develop the most effective techniques 

of dry forest restoration. This complicated subject includes 

studies of germination rates, weed removal techniques, and fire 

fuels management. The second area is continued research on 

establishing additional palila populations, both on the northern slope of Mauna Kea and other sites within former range. 

Although mitigation funding for research is coming to an end, 

science-based approaches to restoration have produced practical 

results. The recent successes are encouraging for the future of 

the species and suggest that continued management may lead to 

species recovery.

Figure 4. A. Palila captured on the western slope of Mauna Kea are 

banded and fitted with radio transmitters (inset) before transport to the 

northern slope. B. The ma ̄ mane forest most frequently used by palila at 

the release site. C (inset, page 1). A palila is prepared for release. 

D. Following release, palila are relocated via radio receivers.

D

A

Cooperators

• Federal Highway Administration

• U.S. Army Garrison, Hawai‘i

• U.S. Fish & Wildlife Service

• Zoological Society of San Diego

• Hawai‘i Division of Forestry and Wildlife (Photo © 

Jack Jeffrey.)