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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 4. December 2012 
and Fancy 1994, Wakelee 1996). Information on 
the distance of dispersal of either immature* or 
adults is lacking; however, Wakelee (1996) 
claimed 'Oma‘o have unexceptional dispersal 
ability. Forty-one 'Oma'o were translocated to 
the Pu'u Wa'awa'a Forest Bird Sanctuary in 1996 
in an el foil to re-establish a leeward population 
(Fancy et al. 2001). Most birds remained close to 
release sites but the population did not persist. 
Only four birds were detected in 1999 and no 
‘Oma'o have been detected since (Camp et al. 
2009. Pratt et al. 2010). ‘Oma'o demonstrated a 
recent expansion into windward wet forests on 
Hawai'i Island where it was considered rare or 
absent in the mid-twentieth century (Reynolds et 
al. 2003). ‘Oma'o in this region occur down to 
470 m and their densities are comparable with 
populations at higher elevations (Reynolds et al. 
2003, Gorresen et al. 2009). 
Scott et al. G986) estimated the island-wide 
population of ‘Oma'o in forest habitat at 170,452 
± 3,499 (SE) individuals. The last detections 
recorded in leeward regions were in 1978 at two 
locations in woodland and scrub alpine habitats on 
Mauna Loa (van Riper and Scott 1979). Scott et 
al. (1986:100) speculated these birds were “not 
remnants of the original Kona forest population" 
but were instead individuals from either a 
windward forest or alpine population. 
We document the reoccurrence of ‘Oma’o to 
leeward woodland habitats, estimate their abun¬ 
dance. and speculate on the source population and 
likely causes of ‘Oma'o dispersion. We also 
identify the potential range of 'Oma'o in the scrub 
alpine habitat and discuss how our Findings are 
beneficial for the species and conservation of 
leeward woodlands. 
METHODS 
Bird surveys were conducted using poin 
transect sampling, which uses distance samplin 
to estimate abundance for individuals that ar 
undetected as a function of the distance betwee 
the observer and birds (Buckland et al. 2001 
Surveys were conducted in three leeward Hawai’ 
Volcanoes National Park (HAVO) tracts; Horn, 
mal.no. Northwest Kahuku, and Papa from T 
April through 13 May 2010. an area of 2,901 h; 
TVKl™' areas were established usini 
AicMap 9.J.1 (Environmental Systems Researcl 
Institute. Redlands. CA, USAl. A minimun 
convex pnlygc,, was creatcd „ sjng Edi|0] . Tqo 
m ArcMap for each tract and was adjustec 
according to habitat coverage, terrain, adjacent 
boundaries, trails, and roads. A 150-m buffer was 
added to the adjusted polygon to create an 
inference area for each tract. The final inference 
areas (ha) were calculated using Xtools Pro. 
Sampling was conducted along 18 transects 
from 195 stations spaced 150 m apart. Previously 
surveyed legacy transects, following a split panel 
design, w'ere assigned to the fixed panel and the 
random panel consisted of newly established 
transects (Camp et al. 2011). Land cover types 
surveyed included woodland, shrubland. and 
pioneer vegetation ranging from 1,371 to 
2,560 m in elevation. Each tract was dominated 
by ‘ohi a (Metrosideros polymorpha), maniane 
(Sophora chrysopliylln), and naio (Myoporum 
sanchvicemis) trees. 
Three primary and three secondary counters 
were trained, prior to the start of the survey, to 
calibrate lor distance estimation and native and 
exotic bird vocalizations, minimizing variability 
among observers and standardizing for local 
conditions. Each station was sampled once. 
Detection type (heard, seen, or both) and hori¬ 
zontal distance from the station center point to 
individual birds detected were recorded during an 
8-min count. Birds flying over or through the 
survey area were excluded. Detections of both 
males and females singing and calling were 
recorded. Most birds encountered were adults 
because counts were timed during the breeding 
season when most juveniles had not yet fledged 
Observers also recorded cloud cover, rain. wind, 
gusts, time of day. and the habitat characteristics 
of dominant vegetation, canopy cover, and height 
at each station. Sampling w>as conducted between 
dawn and 1100 hrs, and halted w'hen rain. wind, or 
gusts exceeded prescribed levels (light rain and 
wind level 3 on the Beaufort scale). 
‘Oma'o density estimates (birds/ha ± SE) were 
calculated using Program DISTANCE. Version 
5.0, Release 2 (Thomas et al. 2005). The 
candidate detection function models were limited 
to halt normal and hazard-rate detection functions 
with expansion series of order two ( Buckland et al. 
-001). Hall normal was paired with cosine and 
I lei mite polynomial adjustments following Buck- 
land et al. (2001). and hazard-rate was paired with 
cosine and simple polynomial adjustments. Model 
precision was improved by incorporating sam- 
p mg covariates in the multiple covariate distance 
sampling (MCDS) engine of DISTANCE 
(Marques and Buckland 2004, Thomas et al. 
