Prepared in cooperation with Hawai‘i Cooperative Studies Unit, University of Hawai‘i Hilo 

Abundance, Distribution, and Population Trends of the

Iconic Hawaiian Honeycreeper, the ‘I‘iwi (Vestiaria 

coccinea) throughout the Hawaiian Islands

Open-File Report 2013–1150

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013 

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Suggested citation:

Paxton, E.H., Gorresen, P.M., and Camp, R.J., 2013, Abundance, distribution, and 

population trends of the iconic Hawaiian Honeycreeper, the ‘I‘iwi (Vestiaria coccinea) 

throughout the Hawaiian Islands: U.S. Geological Survey Open-File Report 2013-1150, 

59 p. 

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Although this information product, for the most part, is in the public domain, it also may contain

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iii

Contents

Abstract ..........................................................................................................................................................................1

Introduction.....................................................................................................................................................................2

Methods..........................................................................................................................................................................3

Bird Surveys in Hawai‘i ...............................................................................................................................................3

Distance-Sampling ..................................................................................................................................................3

Density Estimation...................................................................................................................................................3

Abundance Estimation ............................................................................................................................................4

Assessment of Trends in Population Abundance and Species Range .......................................................................5

Trends in Density ....................................................................................................................................................6

Trends in Occurrence by Elevation .........................................................................................................................7

Probability of Detecting Small Extant Populations...................................................................................................9

Results .........................................................................................................................................................................10

Range-wide...............................................................................................................................................................10

Kaua‘i........................................................................................................................................................................13

Maui..........................................................................................................................................................................16

East Maui ..............................................................................................................................................................16

West Maui .............................................................................................................................................................18

O‘ahu and Moloka‘i ...................................................................................................................................................19

Hawai‘i ......................................................................................................................................................................21

North Windward (Hakalau)....................................................................................................................................21

Central Windward..................................................................................................................................................23

South Windward (Ka‘u) .........................................................................................................................................25

South Kona ...........................................................................................................................................................25

Central Kona .........................................................................................................................................................25

North Kona ............................................................................................................................................................26

Discussion ....................................................................................................................................................................27

Management and Research Considerations.............................................................................................................28

Acknowledgements ......................................................................................................................................................29

References Cited..........................................................................................................................................................29

Appendix ......................................................................................................................................................................33

Appendix A ...............................................................................................................................................................33

Appendix B ...............................................................................................................................................................35

Appendix C. ..............................................................................................................................................................36

Appendix D ...............................................................................................................................................................37

Appendix E ...............................................................................................................................................................44

Appendix F................................................................................................................................................................53

Appendix G...............................................................................................................................................................57
iv

Figures

Figure 1. Boundaries of the consistently sampled areas (CSA) used for assessing trends in density and range 

contraction......................................................................................................................................................................7

Figure 2. Boundaries of the consistently sampled areas (CSA) used for assessing trends in density and range 

contraction on Hawai‘i Island..........................................................................................................................................8

Figure 3. Distribution, mean population size (95% CI), and population trends by region for ‘I‘iwi across its range......11

Figure 4. Trends in ‘I‘iwi density (mean birds ha-1 and 95% CI) on Kaua‘i for the interior and exterior Constantly 

Surveyed Areas (Fig. 1)(note different survey time periods).........................................................................................13

Figure 5. Extent of species range on Kaua‘i as determined from surveys conducted in 1968-1973 (163 km2; blue 

outline), 2000 (101 km2; orange outline) and 2012 (55 km2; red outline)......................................................................14

Figure 6. Trends in occurrence of ‘I‘iwi by elevation between the years 2000 and 2012 on Kaua‘i for the combined 

interior and exterior CSAs.............................................................................................................................................15

Figure 7. Trends in ‘I‘iwi density (mean birds ha-1 and 95% CI) on Maui within the northeast and southeast 

Constantly Surveyed Areas ..........................................................................................................................................17

Figure 8. Trends in occurrence of ‘I‘iwi by elevation in the the northeast Maui CSA (left panel) and southeast Maui 

CSA (right panel)..........................................................................................................................................................18

Figure 9. ‘I‘iwi distribution on Moloka‘i (top panel) and West Maui (bottom panel) based on most recent surveys. .....20

Figure 10. Trends in ‘I‘iwi density (mean birds ha-1 and 95% CI) in the Hakalau, Keauhou, Mauna Loa, the lower and 

upper portions of the central Kona CSA, and the Pu‘u Wa‘awa‘a CSAs of Hawai‘i ......................................................22

Figure 11. Trends in occurrence of ‘I‘iwi by elevation for Hawai‘i Island CSAs ............................................................24

Tables

Table 1. Range size and mean abundance (with 95% CI) of by islands and region for ‘I‘iwi........................................10

Table 2. Trends in ‘I‘iwi density by island, consistently sampled area (CSA; see Figs. 1 and 2) and survey period.....12
1

Abundance, Distribution, and Population Trends of the 

Iconic Hawaiian Honeycreeper, the ‘I‘iwi (Vestiaria 

coccinea) throughout the Hawaiian Islands

By Eben H. Paxton1, P. Marcos Gorresen2, and Richard J. Camp2 

1 U.S. Geological Survey Pacific Island Ecosystems Research Center

2 Hawai`i Cooperative Studies Unit, University of Hawai`i at Hilo

Abstract

Naturalists in the 1800s described the ‘I‘iwi (Vestiaria coccinea) as one of the most abundant 

forest birds, detected in forested areas from sea level to tree line across all the major Hawaiian Islands. 

However, in the late 1800s, ‘I‘iwi began to disappear from low elevation forests, and by the mid-1900s, 

the species was largely absent from low- and mid-elevation areas. Today, ‘I‘iwi are restricted to highelevation forests on the islands of Hawai‘i, east Maui, and Kaua‘i, with a few birds apparently persisting

on O‘ahu, Moloka‘i, and west Maui. ‘I‘iwi are highly vulnerable to introduced disease, and the 

prevalence of avian malaria in low and mid-elevations is believed to be the cause of ‘I‘iwi being 

restricted to high elevations where temperatures are too cold for the development of the disease and its 

mosquito vector. With global warming, it is feared that the disease will move quickly into the highelevation forests where the last ‘I‘iwi reside, threatening their viability. The U.S. Fish and Wildlife 

Service was petitioned to list the ‘I‘iwi as an Endangered Species in 2010, and this report provides a 

comprehensive review of the abundance, distribution, and trends using historical survey data as well as 

the most recently available survey information (up to 2012). We estimate the total population size of 

‘I‘iwi at 550,972–659,864 (mean = 605,418) individuals. Of these, 90 percent are on the island of 

Hawai‘i, followed by east Maui (about 10 percent), with less than 1 percent on Kaua‘i. ‘I’iwi population 

trends vary across the islands. ‘I’iwi population in Kaua‘i has experienced sharp declines, with a 

projected trend of 92 percent decline over a 25 year period based on the 2000–2012 surveys. On East 

Maui, the northeastern region has experienced declines (34 percent over a 25 year period), while the 

southeastern region has been stable to moderately increasing. On the island of Hawai‘i, population 

trends are mixed. On the windward side, populations are largely declining, although the northern section 

(Hakalau Forest) has stable populations. On the leeward side, results suggest a strongly increasing 

population, with estimates of as much as a 147 percent increase over a 25 year period from the Pu’u 

Wa’awa’a region. However, it is unclear how much these results from the leeward side of Hawai‘i show 

a population trend contrary to population trends in all other areas or are an artifact of a sparsely sampled 

area. Trends by elevation suggest a large decrease in numbers of ‘I‘iwi at elevations below 1,200 meters

on Kaua‘i and northeast Maui. Low elevation ‘I‘iwi populations also appear to have decreased in other 

regions, although low-elevation areas are not surveyed as often as other areas because of their lack of 

native forest birds. An exception to this pattern was the lower portions of the Hakalau Forest National 

Wildlife Refuge Kona Unit in the central leeward part of the island of Hawai‘i, where populations 

appeared stable at the lower elevations. Based on the most recent surveys (up to 2012), approximately 

50 percent of ‘I‘iwi live in a narrow, 500-meter band at elevations of 1,200–1,700 meters, suggesting 

that ‘I‘iwi are vulnerable to future shifts in climate.
2

Introduction

The Hawaiian Islands, one of the world’s most remote archipelagos, has experienced high rates 

of extinctions since the arrival first of Polynesians between 800 and 1,200 years ago and, more recently, 

with European contact 230 years ago. Seventy-one known species and subspecies of forest birds native 

to Hawai‘i went extinct between the arrival of Polynesian and first contact with Europeans, while 

another 24 have disappeared since Europeans arrived (Banko and Banko, 2009). Today, of the 21 extant 

species, 11 are endangered or exist in only captivity. Of the species that became extinct, many vanished 

after the introduction of disease, but habitat loss, introduced predators and competitors, and invasive 

plants and animals that have degraded forests have all contributed to bring tremendous change to the 

Hawaiian Islands (Price and others, 2009).

The `I`iwi (Vestiaria coccinea) is a nectarivorous honeycreeper that currently lives on the five 

largest islands of Hawai`i, primarily above 1,200 m in elevation in closed-canopied, high-stature forests 

dominated by ‘ōhi‘a lehua (Metrosideros polymorpha) and koa (Acacia koa) trees (Fancy and Ralph, 

1998). The ‘I‘iwi is a visually spectacular bird, with bright red-orange plumage, contrasting black wings 

and tail with white edging, and a large decurved bill presumed to be adapted to curved flowers such as 

the once-common lobelioid plants (Campanulaceae) (Fancy and Ralph, 1998). Today, I’iwi primarily 

subsist on the flowers of the abundant ‘ōhi‘a tree, supplemented by flowers from other plants and 

insects. Early naturalists remarked on large flights of ‘I‘iwi up and down mountain slopes as they sought 

flowering plants and trees across the landscape. Such movements presumably exposed ‘I‘iwi to disease

when they moved to low elevations, and such large movements have not been noted in recent decades 

(Hart and others, 2011). However, research conducted in the early 2000s has shown that ‘I‘iwi do at 

least occasionally move to low-elevation forests for food (Kuntz, 2008). 

Although now restricted mostly to remote, high-elevation forests above 1,200 m, the ‘I‘iwi was 

once described by early European visitors as one of the most common species on all the Hawaiian 

Islands (Banko, 1981). Multiple accounts by early naturalists in the late 1800s described the ‘I‘iwi as 

being abundant in all wooded areas from near sea level to tree line (Banko, 1981). However, since the 

early 1900s, accounts of ‘I‘iwi have documented a steady decrease in abundance, and steady contraction 

from low-elevation forests to high-elevation forests (Banko, 1981). By the 1940s, ‘I‘iwi numbers were 

greatly reduced, with the species becoming extinct on Lānai and largely absent from Moloka’i (Munro, 

1944). In mid-elevations, I’iwi have vanished from many areas since the mid-1900s. They were 

common in the main visitor area of Hawai‘i Volcanoes National Park (elevation 1,200 m) in the 1940s, 

but had retreated to higher elevation forests (elevation 1,700 m) by the 1970s (Banko, 1981). 

The ‘I‘iwi is highly susceptible to introduced disease (Atkinson and LaPointe, 2009), with 

studies exposing ‘I‘iwi to infected mosquitoes documenting near 100 percent fatality (Atkinson and 

others, 1995). Historically, disease has been absent from high elevations where the temperatures are too 

cool for mosquitoes and the malaria parasite to develop. However, with global warming, it is feared that 

the disease will move increasingly upward in elevation and threaten the high-elevation sanctuaries 

where ‘I‘iwi are currently residing (Benning and others, 2002; Paxton and others, 2012). 

Fears of continued declines in ‘I‘iwi populations and the susceptibility of the species to alien 

diseases have driven concern for their long-term viability. In 2011 the U.S. Fish and Wildlife Service

was petitioned to list the ‘I‘iwi as an endangered species under the Endangered Species Act (Center for 

Biological Diversity, 2010). The purpose of this report is to gather all available survey data from the 

Hawaiian Islands and to provide the most thorough and up-to-date analysis of abundance, distribution, 

and population trends across the entire range of the ‘I‘iwi.
3

Methods

Bird Surveys in Hawai‘i

Between 1976 and 1983, an ambitious effort was made by the U.S. Fish and Wildlife Service to 

determine species distribution and abundance of all forest birds on the main Hawaiian islands as part of 

the Hawai‘i Forest Bird Survey (HFBS) (Scott and others, 1986). HFBS established a quantitative 

baseline from which changes in bird populations on Hawai‘i, Maui, Lāna‘i, Moloka‘i, and Kaua‘i could 

be ascertained (Scott and others, 1986), and established set protocols for subsequent bird surveys to 

ensure their comparability. Since the start of the HFBS and related efforts, more than 600 surveys using 

point-transect methods have been conducted across the main Hawaiian Islands (Camp and others, 2009). 

Although there are some issues with directly comparing all the surveys, especially when surveys are 

completed at different times of the year, these multiple decades of surveys provide a detailed record for

understanding trends. These surveys have been archived in the Hawai‘i Forest Bird Interagency 

Database to allow for analysis of distribution and trends across time and space.

Distance-Sampling

A point-transect survey is a type of distance sampling for which the probability of detecting 

birds is modeled as a function of their distance from an observer and other factors to obtain estimates of 

the effective area sampled and animal density (Buckland and others, 2001, 2004). Point-transect counts 

of Hawaiian forest birds were conducted following methods described by Scott and others, (1986). 

Observers received pre-survey training to calibrate for distance estimation and to learn bird 

vocalizations, thereby minimizing variability among observers and standardizing for local conditions. 

Trained and calibrated observers recorded the species and detection type (heard, seen, or both), and 

estimated the horizontal distance in meters from survey station center point to birds detected during 8-

minute counts (or alternatively, 6 minutes on Mauna Kea volcano, island of Hawai‘i). Time of sampling 

and weather conditions (cloud cover, rain, wind, and gust strength) also were recorded, and surveying 

was halted when conditions hindered the ability to detect birds (wind and gusts greater than 20 

kilometers per hour and heavy rain). Birds only flying over or through the survey area were excluded. 

Detections of male and female birds singing and calling were recorded, although the sex of individuals 

was not noted. Most of the birds encountered were adults because counts were timed during the 

breeding season and most juveniles had not yet fledged. 

Density Estimation

‘I‘iwi densities were calculated from point-transect distance sampling data following methods 

described by Buckland and others (2001, 2004), Camp and others (2009), and Thomas and others 

(2010). Densities (birds/ha) were calculated using the program Distance 6.0, release 2 (Thomas and 

others, 2010). Observations from all surveys conducted between December and August were pooled to 

calculate global detection functions by region or island. Stations usually were counted only once during 

an annual survey; however, when stations were counted more than once, the survey effort was adjusted 

by the number of times the station was counted. All data were treated as exact measures and modeled 

accordingly. Candidate models for the detection function were restricted to half normal and hazard-rate 

detection functions with expansion series of two orders, as recommended by Buckland and others (2001, 

p. 361 and 365). To improve model precision, the following variables were examined as potential model 

covariates: observer, time of day, cloud cover, rain, wind, gust strength, year, elevation, precipitation, 

vegetation class, and detection type. All covariates were treated as a factor, except time of day was 
4

treated as a continuous covariate, and year was treated both as a factor and a continuous covariate. 

Assessing time of day and year as a continuous covariate allowed us to determine if the detection rate 

varied across time. Data were truncated at a distance where detection probability was less than 10 

percent. This procedure facilitates modeling by deleting outliers and reducing the number of parameters 

needed to modify the detection function. The model selected was that with the lowest second-order 

Akaike’s Information Criterion corrected for small sample sizes (AICc) (Burnham and Anderson, 2002). 

Candidate model and rankings are presented in appendix A, and final models and associated effective 

detection radius (EDR) values are presented in appendix B. Survey-specific densities were estimated by 

applying the global detection function, and variances and confidence intervals (CIs) were derived by 

bootstrap methods in Distance from 999 iterations (Thomas and others, 2010). 

The distance at which birds can be detected depends partly on bird abundance. In our 

experience, counts of gregarious and highly vocal and mobile birds such as ‘I‘iwi are more challenging 

where abundance is high. This is largely attributable to the difficulty of mentally tracking numerous 

moving individuals and hearing distant birds over the vocalizations of birds nearer to the observer. An 

additional complication to modeling detectability is that most of the survey data collected after the 

HFBS for the island of Hawai‘i has been collected from a few limited areas with relatively high bird 

densities (for example, Hakalau Forest National Wildlife Refuge). The available samples are not 

spatially balanced to produce a global EDR applicable to the species range across high and low 

densities. To address this issue, we used only HFBS data to model detection functions and to calculate 

effective detection radii for surveys on the island of Hawai‘i. Unlike with most subsequent surveys, the 

HFBS data were collected across almost the entire species range and closely matched the island wide

spatial scale at which EDRs were applied in this study. Additionally, the HFBS was done primarily in 

June and July, a post-breeding period when ‘I‘iwi are dispersed across a larger area (Simon and others, 

2002). As a result of this, the low encounter rate allows birds to be detected at greater distances, and 

lessens the problem associated with estimating distances in high bird-density areas. Finally, the lower 

encounter rate of the HFBS counts better approximates the intermediate abundance observed throughout 

the species range (which includes both low- and high-density areas).

Abundance Estimation 

Population size estimates for each island or region were obtained by extrapolating mean bird 

density for surveyed areas by the area of available habitat within the species range. Species range was 

determined based on ‘I‘iwi occurrence records from the most current survey data (2012). Where current 

survey data were not available, the most recent survey results were used (most within 5 years, 2008-

2012). The species range boundary was delineated so as to include all observed occurrences, and in 

areas not surveyed, the range included areas not directly surveyed but where projected suitable habitat 

occurred near surveyed areas. Designation of suitable habitat was qualitatively determined based on 

‘I‘iwi presence at other comparable locations within the species’ range and was evaluated separately for 

each island.

Suitable habitat areas for density extrapolations were produced using elevation and vegetation 

classifications. Elevation was obtained from a 10-m resolution Digital Elevation Model produced by the 

U.S. Geological Survey for the National Elevation Dataset. For comparability, the same elevation strata 

intervals (for example, elevations 900–1,100 m, 1,100–1,300 m, and so on) used by Scott and others

(1986) were used for estimating density and abundance in this study. Vegetation classifications were

obtained from Landfire2, a GIS layer of Hawaiian land cover types (accessed April 15, 2012, at 

http://www.landfire.gov/), and vegetation classes were corroborated with high-resolution multi-spectral 

aerial photography (Emerge imagery produced by U.S. Department of Agriculture, Natural Resources 
5

Conservation Service). The vegetation types used in this study differed from those of Scott and others 

(1986) because statewide mapped data that incorporated their land cover classification system were not 

available for all areas surveyed for birds in more recent years. Limited sampling in some vegetation 

types required similar classes to be combined for purposes of modeling bird density. Vegetation class 

recombinations are listed in appendix C. 

Density and population abundance were calculated for all habitat strata for which there were bird 

survey samples. Unsampled strata did not contribute to population abundance estimates, but the areas 

constituting these strata nevertheless were presented to identify habitats for which inference was not 

available. Population abundance estimates were derived for elevation and vegetation habitat variables. 

These two estimates of abundance generally were similar to each other (appendix E). We averaged the 

two estimates to derive a single number for the overall abundance of a given island or region by taking 

the mean of the point estimates and the square root of the summed squared standard errors divided by 4, 

and multiplied by the t-distribution (1.96) for the CIs. Although this approach does not take into account 

likely covariance between the two estimates (and, therefore, likely underestimates the variance 

associated around the mean), it provides a way to include information from both stratifications and a 

single estimate of abundance per island or region. Large uncertainties associated with estimates derived

from surveys with few bird detections (generally less than 10 individuals) precluded the calculation of 

‘I‘iwi abundance for many island and island regions (specifically O‘ahu, Moloka‘i, west Maui, and 

Mauna Kea on the island of Hawai‘i); these estimates were not used in the overall abundance estimates.

Additionally, we excluded other areas where ‘I‘iwi are believed to occur but no recent surveys have 

been completed (for example, Kohala Mountains on Hawai‘i, Kula Forest Reserve on Maui).

Assessment of Trends in Population Abundance and Species Range

Detecting and interpreting trends in bird populations is an important component of evaluating 

the conservation status of species. However, such assessments can be sensitive to shifts in sampling 

effort and location over time. To address this issue, we delineated consistently sampled areas (CSAs) 

that coincided spatially across time and that were used for subsetting comparable annual survey data.

The requirement for spatial consistency was balanced against the need to include as much survey data as 

possible and to maximize the temporal resolution of the trend analyses. Nevertheless, in some cases, it 

was necessary to exclude surveys that did not fully extend across a CSA. For example, trend analyses 

for Kaua‘i required delineation of a pair of nested CSAs that spanned overlapping time periods (fig. 1).

To maintain the longest time series possible, the data for seven surveys (1989–2012) were subset based 

the extent of area first surveyed with distance-sampling methods in 1981, resulting in a smaller area but 

longer time series. In contrast, to produce a time series for the largest possible area and to better match 

the extent of the species range, a larger CSA was delineated based on the area sampled in 2000 and in 

four follow-up surveys. CSAs for the islands of Maui and Hawai‘i are shown in figures 1 and 2. 

Although the HFBS data were spatially balanced samples from which to calculate effective 

detection radii, the bias inherent in comparing abundance derived from surveys at different times of year 

meant that these samples could not be included in some analyses of density trends. On Kaua‘i, the 

HFBS and post-HFBS (“subsequent”) surveys were conducted during the same months (February–

May), and the use of HFBS data from 1981 as a baseline was appropriate for assessing population 

trends. However, on Maui and Hawai‘i, the HFBS was conducted during mid-to-late summer, whereas 

subsequent surveys were conducted during winter and spring; therefore, the two data sources were not 

directly comparable. This is especially important because ‘I‘iwi are known to disperse widely during the 

non-breeding season. As a result, the first year of the subsequent survey data periods on Maui (1992) 

and Hawai‘i (1986–1999) was used as the baseline for trend assessments with densities determined from 
6

HFBS samples included in trend graphics for reference only. However, HFBS data were used for the 

quantile regressions (see section, “Trends in Occurrence by Elevation”), where count information was 

simplified to species presence-absence for a particular elevation. The use of species presence-absence 

data, versus count data, allows us to evaluate long-term elevational shifts in distribution while 

minimizing any biases in the counts from different seasons.

Trends in Density 

For time series with more than 4 years of surveys we assessed change in ‘I‘iwi populations by 

estimating trends with a log-linear regression within a Bayesian framework. Bayesian results generally 

are more easily interpreted than frequentist tests of the null hypothesis (Camp and others, 2008). More 

importantly, this approach also permitted us to distinguish negligible or stable trends from statistically 

inconclusive outcomes. We used a log-linear regression model to calculate the distribution of the 

posterior probabilities (P) of trend parameters. The proportion of the posterior distribution that was

within or outside threshold bounds was assessed in a manner similar to the end-point comparisons; that 

is, corresponding to a 25-percent change in the population over 25 years. We categorized trends as 

increasing, decreasing, negligible (that is, stable population), or inconclusive (that is, trend uncertain). 

The evidence for a particular trend was based on how the distribution of posterior probabilities was 

apportioned by category, and was interpreted as weak (P < 0.7), strong (0.7 ≤ P < 0.9), or very strong (P 

≥ 0.9). An inconclusive result occurred when variance was high and the posterior distribution gave only 

weak evidence across the increasing, decreasing, and negligible trend categories. 

Log-linear regression was performed with WinBUGS (Lunn and others, 2000; accessed

December 1, 2006, at www.mrc-bsu.cam.ac.uk/bugs.) in program R (R version 2.15.1; 2012-06-22; R 

Development Core Team, 2011). The parameter α is the density at time t equals 0 (that is, intercept), β is 

the rate of change (that is, slope) with each unit increase in time t, and τ equals variance-1 (that is, 

precision). The parameters α and β were given uninformative normal priors, and τ was given an 

uninformative gamma prior. Year values were centered on a year corresponding to the mid-point of the 

time series. The model parameters were estimated from 50,000 iterations for each of three chains (that 

is, model runs) after discarding the first 2,000 iterations (a “burn-in” period). The three chains were 

pooled (150,000 total samples) to create a posterior distribution. The density per station data were fitted 

with a traditional least-squares model, with the “lm” command and the “blinreg” function in R used to 

sample from the joint posterior distribution of beta and sigma following model diagnostics procedures 

in Maindonald and Braun (2006). Histograms of the simulated posterior draws of the regression 

coefficients beta and error standard deviation sigma were plotted and inspected visually to detect

deviations from a normal distribution. Outliers also were identified using Bayesian residuals and 

visually inspected. Temporal autocorrelation in annual abundance was assessed with the “acf” function 

and AIC procedures were used to select the lag autocorrelation that removed serial correlation. For each 

analysis, there was no evidence that the model residuals differed from a normal distribution (no 

evidence of skewness or kertosis), and, although there were some outlier points, the trends were

conservative in that the variance was greater when they were included rather than excluded. 

Furthermore, there was no conclusive evidence that an autoregressive model was necessary to control 

for temporal correlation.
7

Figure 1. Boundaries of the consistently sampled areas (CSAs) used for assessing trends in density and range 

decreases of ‘I‘iwi (Vestiaria coccinea) in Kauai and east Maui, Hawai‘i. Top panel, Kauai: The blue outline 

depicts the area surveyed during 1981-2012. The red outline depicts the more extensive areas sampled during

2000–2012. Bottom panel, east Maui: The red outline depicts the northeast CSA and the blue line depicts the 

southeast CSA.
8

Figure 2. Boundaries of the consistently sampled areas (CSAs). Species range is shown in red, with blue 

outlines designating the Constantly Surveyed Areas used for assessing trends in density of ‘I‘iwi (Vestiaria 

coccinea) on the island of Hawai‘i, Hawai‘i.
9

Trends in Occurrence by Elevation 

Quantile regression was used to determine whether the island-specific distributions of ‘I‘iwi 

have decreased by elevation over time. Quantile regression is a method for estimating functional 

relations between variables for all parts of a probability distribution, and is useful when unequal 

variation indicates that there is more than a single slope (that is, rate of change) describing the 

relationship between a response variable and predictor variables (Cade and others, 1999). The method is 

well suited for examining range decreases as a function of elevation because such patterns are expected 

to be most pronounced at lower elevations where avian disease and invasive species are most prevalent 

(Banko and Banko, 2009). 

The seasonally dissimilar period during which the HFBS and subsequent surveys were 

conducted made problematic the use of HFBS-derived densities for trend assessments. However, the 

HFBS data were still useful for examining trends in ‘I‘iwi occurrence as a function of elevation. 

Although the HFBS surveys were conducted when ‘I‘iwi were highly dispersed, the seasonal effect was 

expected to be less pronounced for observations treated simply as binary data (that is, detected or not 

detected) than as measures of abundance.

Linear quantile regression was performed in the statistical program R version 2.15.1 (R

Development Core Team, 2011) with the package “quantreg” (Koenker, 2011). Statistical inference for 

regression coefficients (that is, standard errors, t-statistics, and p-values) were estimated, and CIs were

computed by the rank inversion method (Koenker, 2007, 2011). Trends are presented for quantiles 0.05, 

0.10, 0.25, 0.50 (median), 0.75, 0.90, and 0.95, which are associated with elevations specific to each 

region. Decreases in ‘I‘iwi occurrence with rises in elevation are indicated by positive values for slopes 

whose 95-percent CI do not bracket zero. To ensure comparability among years, occurrence data were

truncated to an elevation range common to all annual survey datasets. For example, data for surveys on 

northeast Maui were truncated to include only records above 1,000 m for the years 1980, 1992, 2001, 

2006, and 2011; a 1996 survey was excluded because all samples for this year were collected above 

1,200 m. 

Probability of Detecting Small Extant Populations 

Estimation of ‘I‘iwi density and total abundance based on distance sampling was not possible for 

parts of the species range in which birds were very rare and sparsely distributed. Because ‘I‘iwi were 

not detected in the most recent surveys on O‘ahu and Moloka‘i, we estimated the maximum population 

size on each island consistent with not being detected given the number of stations surveyed. Therefore, 

estimates of the population size were based on the extinction inference method proposed by Scott and 

others, (2008), and calculated as: 

X = log α

1−p (1) 

where X is the maximum possible population size, 

 α is the desired level of statistical confidence, and 

p is the ratio of effective area sampled (E) relative to either the range of the species or 

total survey area (A). 

We calculated E as the sum of the effective areas surveyed within A, where the effective area of 

each station was calculated from the effective detection radius (EDR) from the Kaua‘i and Maui 

distance analyses as π∙EDR2. 
10

Results

Range-wide

We estimate the overall abundance of ‘I‘iwi at 605,418 individuals (95-percent CI = 550,972–

659,864)(table 1). Most I’iwi are restricted to high-elevation forests of the island of Hawai‘i (90 

percent), followed by east Maui (about 10 percent), and Kaua‘i (less than 1 percent); only relict 

populations exist, if at all, on O‘ahu, west Maui, and Moloka‘i (fig. 3, table 1). Across the islands, an 

estimated 90 percent of ‘I‘iwi live in a narrow band at an elevation of 1,300–1,900 m, and mainly in 

montane forest, with 61 percent in montane wet forest, 35 percent in montane mesic forest, 3 percent in 

lowland wet-mesic forest, and remaining habitats constituting less than 1 percent of distribution 

(appendix E). 

Table 1. Range size and mean abundance (with 95-percent confidence interval) by islands and region for ‘I‘iwi (Vestiaria 

coccinea) throughout Hawai‘i. The abundance estimates are the mean of estimates derived separately from 

elevation and vegetation classifications (appendix E), with 95-% CIs calculated as mean abundance plus-orminus the square root of the summed squared SE divided by 4 times t-distribution (1.96). Abbreviations: ha, 

hectare; %, percent; CI, confidence interval; SE, standard error. 

Island/region Area

(ha)

Mean 

abundance

Lower 

95% CI

Upper 

95% CI

Kaua‘i 5,436 2,551 1,934 3,167

O‘ahu 2

50

Maui, east 13,201 59,859 54,569 65,148

Maui, west 1,887 1

176

Moloka’i 1,800 1

80

Hawai‘i (all regions) 174,840 543,009 516,312 569,706

Hawai‘i, north windward 24,926 277,055 258,075 296,035

Hawai‘i, central windward 40,773 71,524 62,662 80,386

Hawai‘i, Ka‘ū 33,680 28,325 23,138 33,512

Hawai‘i, south Kona 12,489 3,489 2,059 4,918

Hawai‘i, central Kona 25,441 139,829 124,649 155,009

Hawai‘i, north Kona 21,231 22,787 18,444 27,130

Kohala Mountains 5,600 1

802

Mauna Kea 4,200 1

482

3 Species total 605,418 550,972 659,864

1 Estimates from Scott and others (1986) surveys

2 Estimate from BirdLife International (2012)

3 Total estimates do not include Scott and others 1986 estimates and O‘ahu estimate 
11

Trends vary across the range of the ‘I‘iwi, with lower elevation parts of their range generally 

declining, and even most high elevation areas showing evidence of declines (fig. 1, table 2). Central 

Kona on Hawai‘i Island is one area where low elevation populations appear to be stable or increasing, 

and the entire Kona coast stands out as an area of stable to increasing populations.

Figure 3. Distribution, mean population size (95-percent confidence interval), and population trends by region for 

‘I‘iwi (Vestiaria coccinea) across its range in Hawai‘i. See table 1 for mean abundances, and table 2 for details 

on population trends.
12

Table 2. Trends in ‘I‘iwi (Vestiaria coccinea) density by island, consistently sampled area (CSA; see figs. 1 and 2), and survey period, throughout Hawai‘i. The 

ecological relevance of a trend as estimated by Bayesian log-linear regression was based on a standard metric defined as a 25% change in 

density over 25 years. The metric corresponds to an annual rate of change with significance defined by a threshold lower bound of φl = -0.0119

and an upper bound of φu = 0.0093. For log-linear regression results, statistics include the slope coefficient (β̂), standard deviation (SD), and 

95% credible interval (CI). The posterior probabilities (P) of the regression slope are assessed for each trend category (declining, negligible, and 

increasing), where 0.7 < P < 0.9 indicates strong evidence, and P > 0.9 very strong evidence of a trend. Interpretation of an observed trend is 

summarized as increasing (▲), stable (▬), decreasing (▼), stable to increasing (~∆), stable to declining (~�), and inconclusive (Inc). Given 

the observed regression slope, projected trend is a standardized measure of the percent change in population size over a 25-year period. 

Posterior Probability

Island CSA Survey 

period β� SD 95% CI Declining

β� < φl

Negligible

φl < β� < φu

Increasing

β� > φu

Observed 

trend

Projected 

trend (%) 

Kaua‘i interior 1981-2012 -0.0406 0.0027 -0.0460 to -0.0354 1.000 0 0 ▼ - 63

interior 2000-2012 -0.0794 0.0127 -0.1048 to -0.0551 1.000 0 0 ▼ - 86

exterior 2000-2012 -0.1384 0.0220 -0.1851 to -0.0989 1.000 0 0 ▼ - 97

both 2000-2012 -0.0996 0.0110 -0.0993 to -0.0786 1.000 0 0 ▼ - 92

Maui northeast 1992-2011 -0.0172 0.0047 -0.0264 to -0.0080 0.868 0.132 0 ▼ - 34

southeast 1992-2012 0.0082 0.0031 0.0021 to 0.0143 0 0.635 0.365 ~∆ + 22

Hawai‘i Hakalau 1999-2012 -0.0094 0.0034 -0.0160 to -0.0027 0.226 0.774 0 ▬ - 20

Keauhou 1995-2012 -0.0270 0.0033 -0.0334 to -0.0207 1.000 0 0 ▼ - 4

Mauna Loa 1986-2012 -0.0139 0.0104 -0.0356 to 0.0051 0.560 0.433 0.007 ~� - 29

Central Kona -

upper

1995-2012 0.0226 0.0069 0.0091 to 0.0361 0 0.027 0.973 ▲ + 71

Central Kona -

lower

1995-2012 0.0294 0.0130 0.0043 to 0.0553 0.001 0.058 0.941 ▲ + 9

Pu‘u Wa‘awa‘a 1990-2009 0.0383 0.0163 0.0075 to 0.0719 0. 001 0.031 0.967 ▲ + 147
13

Kaua‘i

The ‘I‘iwi population of Kaua‘i appears to be in rapid decline, with both the species range and 

population abundance decreasing fast (fig. 4). Early historical records (1887–1902) note the presence of 

‘I‘iwi at elevations as low as about 700 m (Banko, 1981), which suggests an expanse of available forest 

habitat of about 28,000 ha. By the late 1960s to early 1970s, the species was observed only as low as

elevations of about 900 m, and delineation of the upland area encompassing the survey sites at which 

‘I‘iwi were detected gave a species range of about 16,400 ha (fig. 5). During this time period, the core 

population in the interior of the Alaka‘i Plateau numbered about 7,800 birds (± 2,300 SE) (Scott and 

others, 1986). A 1981 survey of the same core population produced an estimate of 5,400 (± 264 SE; 

Scott and others, 1986). By 2000, the area of the species range had decreased to about 10,064 ha and the 

island-wide population numbered about 9,985 birds (± 960 SE) (Foster and others, 2004). As of 2012, 

the total population size of ‘I‘iwi on Kaua‘i was estimated at 1,934–3,167 individuals (mean = 2,551; 

table 1, appendix E.1), with a distribution limited to a 5,436-ha area and most birds observed within 

montane wet forest from 1,100 to 1,300 m in elevation (fig. 6, appendix E.1). 

Figure 4. Trends in ‘I‘iwi (Vestiaria coccinea) density (mean birds per hectare at 95-percent confidence interval) 

on Kaua‘i, Hawai‘i, for the interior and exterior constantly surveyed areas (fig. 1)(note different survey time 

periods). The shaded band represents the 95-percent confidence interval of the trend for the entire time series.
14

Figure 5. Extent of ‘I‘iwi (Vestiaria coccinea) species range on Kaua‘i, Hawai‘i, as determined from surveys 

completed during 1968–1973 (16,300 hectares; blue outline), 2000 (10,100 hectares; orange outline) and 2012 

(5,500 hectares; red outline). Sites for which ‘I‘iwi were detected (solid circles) and not detected (open circles) 

are shown for the 1968–1973 survey (source: U.S. Fish and Wildlife Service, 1983). Shading represents 

elevation from low elevation (browns) to high elevations (greens).
15

Figure 6. Trends in occurrence of ‘I‘iwi (Vestiaria coccinea) by elevation on Kaua‘i, Hawai‘i, during 2000–2012, for 

the combined interior and exterior continuously sampled areas (CSAs). Boxplot (left panel) describes the 

elevational range per year in ‘I‘iwi occurrence, and lines depict trends over time at different elevations 

corresponding to the quantiles of the entire elevational range (0.05, 0.10, 0.25, 0.50, 0.75, 0.90 and 0.95 [linear 

quantile regression coefficients and statistics are listed in appendix F.1]). Boxplot whiskers denote elevational 

range within 1.5 times the interquartile range above the 75th percentile and below the 25th percentile, 

respectively, with outliers beyond the range plotted as individual points. Numbers above boxplot whiskers 

correspond to sample size (that is, I‘iwi occurrence). Upper and lowermost trend lines (corresponding to 

quantiles 0.05 and 0.95) are shown in black, while the medium elevation (quantile 0.50) is designated as a 

dotted line. Right panel shows the mean quantile regression slope by elevation (center black line) with 95-

percent confidence intervals denoted by gray band. Decreases in ‘I‘iwi occurrence with rises in elevation are

indicated by positive values for slopes whose 95-percent confidence interval does not overlap with zero 

(vertical thin black line).

Steep declines in ‘I‘iwi densities are evident from surveys for the CSAs encompassing the 

Alaka‘i Plateau (“interior” and “exterior” CSAs combined, fig. 1). Bird density across the combined 

regions shows a significant decreasing trend from 2000 to 2012 (slope coefficient [β] = -0.0996 ± 0.0110; 

95-percent CI = -0.0993 to -0.0786), which equals a 92 percent reduction in the size of a population 

over a 25-year period (table 2, fig. 4). The trend is particularly acute for the exterior region (β̂ = -0.1384 

± 0.0220; 95-percent CI = -0.1851 to -0.0989) with a population size decline of 97 percent over 25 

years. The difference in the rates of decline between the 1981–2012 (95-percent CI = -0.0460 to -

0.0354) and 2000–2012 (95-percent CI = -0.1048 to -0.0551) survey periods for the interior region 

indicates that the trend may have accelerated since 2000. 

Analysis of ‘I‘iwi survey detections as a function of elevation (fig. 6) indicates that decreases in 

the species range on Kaua‘i primarily are occurring at the lower elevations of their distributional range. 

‘I‘iwi occurrence below about 1,232 m in elevation has decreased as indicated by significant trends in 

all quantiles between 0.05 and 0.50 (fig. 6, appendix F.1). The rate of change over the survey period is 

greatest at the lower elevations, as shown by a mean upward elevation shift of 84 m in bird distribution 
16

(1,082–1,166 m) in the 0.05 quantile. ‘I‘iwi occurrence at elevations above 1,232 m (that is, in quantiles 

greater than 0.50) has not changed significantly between 2000 and 2012. 

Maui

‘I‘iwi are distributed as two disjunct populations on Maui, with an east Maui population ranging 

across 13,201 ha separated from a 1,887-ha area on west Maui by about 30 km of highly altered lowland 

vegetation. Prior to Western contact, native Hawaiians had converted most lowland forests below 500 m 

in elevation to an “actively manipulated cultural landscape” (Kirch, 1982), and the area between the east 

and west Maui populations likely was not a viable habitat for ‘I‘iwi. Subsequent degradation from a 

variety of sources (for example, ranching, feral ungulates, and invasive plants; Pratt and Jacobi, 2009) 

made much of the remnant forest at elevations below 700 m in elevation unsuitable for ‘I‘iwi by the 

time the first quantitative bird survey was completed in 1980. 

East Maui 

Based on survey results for 2011 and 2012, the ‘I‘iwi population size on east Maui was 

estimated at 54,569–65,148 individuals (mean = 59,859; table 1, appendix E.2). About two-thirds of the 

population have been observed in montane wet forest at elevations ranging from 1,100 to 1,900 m 

(appendixes D.2 and E.2), with the remainder observed in native lowland and introduced forest and 

montane shrubland at elevations ranging from about 860 to 2,200 m. The current (2012) mean 

population estimate is about 3 times greater than the estimate of Scott and others (1986; 16,392 ± 1,006 

SE). This difference is attributable to the fact that the 1980 HFBS on Maui was done primarily in June 

and July, a post-breeding period when ‘I‘iwi are widely dispersed, especially to low elevations and, 

therefore, are present at low densities in the higher elevation areas primarily surveyed in subsequent 

years (Simon and others, 2002). Because of this, population estimates and mean density derived from 

the 1980 HFBS cannot be compared directly with estimates derived from subsequent surveys, which 

were conducted primarily from March to May. On the other hand, population estimates for east Maui 

based on 2001 surveys (Camp and others, 2009) were 80 percent higher than the estimates of this study 

(107,744 ‘I‘iwi in 2001 surveys, versus 59,859 in this study using 2011 and 2012 survey information).

This change in population size may be owing partly to declining population sizes, but is also likely an 

artifact of the variation inherent in surveys, with the 2001 surveys producing some of the highest 

densities recorded and, therefore, larger population estimates than other years. 
17

Figure 7. Trends in ‘I‘iwi (Vestiaria coccinea) density (mean birds per hectare and 95-percent confidence interval) 

on Maui, Hawai‘i, within the northeast and southeast constantly surveyed areas (fig. 1). The shaded band 

represents the 95-percent confidence interval of the trend for the entire time series. Note that the 1980 Hawai’i 

Forest Bird Survey (HFBS) densities were not included in the trend assessment because of differences in the 

time of year when the HFBS and all subsequent surveys were conducted. 

The I‘iwi population showed mixed trends in the two CSAs delineated for east Maui 

(“northeast” and “southeast”; fig. 1). Bird density in the northeast CSA showed strong evidence of a 

decline between 1980 and 2011 (β̂ = -0.0172 ± 0.0047; 95-percent CI = -0.0264 to -0.0080; table 2, fig. 

7). This trend in density averages a 34-percent decrease over 25 years. In contrast, densities observed 

for the southeast CSA from 2000 to 2012 showed a stable to increasing trend (β̂ = 0.0082 ± 0.0031; 95-

percent CI = 0.0021–0.0143)(fig. 7). This trend results in a 22-percent increase in population density 

over a 25-year period. 

The result for the northeast Maui CSA contrasts with that observed for the southeast Maui CSA, 

in which ‘I‘iwi occurrence at lower elevations of their distribution (that is, quantiles 0.05–0.50) have not 

changed significantly between 1980 and 2012 (fig. 8, appendix F.2). However, fewer I‘iwi were 

detected at higher elevations in the southeast Maui CSA over this survey period. ‘I‘iwi occurrence 

above about 1,877 m in elevation has decreased, as indicated by significant trends in the 0.75, 0.90 and 

0.95 quantiles (fig. 8, appendix F.3). The rate of change was greatest in the upper 25 percent of 

elevation distribution for southeast Maui CSA as shown by a mean downward shift of 188 m in bird 

distribution (from 1,877 to 1,689 m) over the 33-year period. The observed increase in bird density in 

the southeast Maui CSA, coupled with the declines in occurrence at the highest elevations, may indicate 

different trends in habitat quality between the drier margins of montane forest at higher elevations and 

wetter forest at mid elevations. 
18

Figure 8. Trends in occurrence of ‘I‘iwi (Vestiaria coccinea) by elevation in the northeast Maui consistently 

sampled area (CSA) (left panel) and southeast Maui CSA (right panel), Hawai‘i. Survey period includes the 

years 1980, 1992, 2001, 2003, 2005 and 2012 for the northeast Maui CSA, and 1980, 1992, 1996, 2001, 2006, 

and 2011 for the southeast Maui CSA. See figure 6 for an explanation of graphic features and appendixes F.2 

and F.3. 

West Maui

The number of ‘I‘iwi observations on west Maui were not sufficient to model detection functions 

and to accurately estimate density and population abundance. A total of 5, 2 and 11 ‘I‘iwi were detected 

in this region in 1980, 1997 and 2010, respectively (fig. 9). The west Maui population in 1980 was 

estimated at 176 birds (± 74 SE) in an area of about 1,600 ha (Scott and others, 1986). No quantitative 

inference can be made about the current (2010-2012) population size or distribution. 
19

O‘ahu and Moloka‘i

‘I‘iwi were noted to be in decline on O‘ahu by the early 1900s (Fancy and Ralph, 1998), with 

increasingly narrower distributions and smaller populations recorded up to the 1970s (Banko, 1981). 

Shallenberger and Vaughn (1978) noted during 1971–1977 surveys that ‘I‘iwi were observed at 

elevations above about 427 m. ‘I‘iwi were not detected during an island-wide survey in 1991 (Conry, 

1991), although surveys in 1995 and 1996 recorded small numbers of individuals in the north-central 

Ko‘olau Mountains (VanderWerf and Rohrer, 1996). Christmas Bird Count surveys made in the leeward 

Ko‘olau Mountains last observed ‘I‘iwi in 2001 and 2002 (a single bird in each year; National Audubon 

Society, 2002), and in 2013(John Vetter, personal commun., 2012). The sighting of a juvenile ‘I‘iwi in 

the south Wai‘anae Mountains in 2008 (E.A. VanderWerf, personal commun., 2012) indicates that 

either local breeding persists on O‘ahu or interisland movement occurs. 

Estimates of the probability of persistence of a small relict ‘I‘iwi population on O‘ahu were 

produced for a range of values representing remnant population sizes and statistical confidence. Given 

the absence of sightings on O‘ahu in 1991, the 1991 sampling effort (191 stations at elevations above 

427 m), and the average effective detection radius (35.5 m) observed for I‘iwi on the neighboring 

islands of Kaua‘i and Maui, there is a 95-percent probability that the 1991 O‘ahu population was less

than 922 individuals. That is, at least one individual would likely have been sighted given a population 

of 922 or more birds. These large values reflect the fact that, despite the 1991 survey having been the 

most extensive on O‘ahu to date, only about 0.3 percent of the available area above an elevation of 427 

m was sampled for ‘I‘iwi. Broader survey coverage might have reduced the estimates of maximum 

population size. The ‘I‘iwi population on O‘ahu was recently estimated to number less than 50 birds by 

BirdLife International (2012). 

For much of the 20th century, only a remnant population was believed to persist on Moloka‘i. 

Twelve ‘I‘iwi were detected during the 1979 HFBS of Moloka‘i, and based on these results, Scott and 

others (1986) estimated 80 + 33 birds distributed at low densities on the Kamakou Range and Oloku‘i 

Plateau (fig. 9, top panel). However, surveys between 1988 and 2010 detected very few birds (most 

recently, 3 individuals in 2004; Camp and others, 2009). Given the absence of detections on Moloka‘i in 

2010 and the 2010 sampling effort (97 stations within an 18 km2 area as the estimated extent of the 

species range by Scott and others, 1986), there is a 95-percent probability that there were less than 141 

birds. 
20

Figure 9. ‘I‘iwi (Vestiaria coccinea) distribution on Moloka‘i (top panel) and west Maui (bottom panel), Hawai‘i, 

based on most recent surveys (2004 for Moloka‘i, 2010 for west Maui). 
21

Hawai‘i

‘I‘iwi are distributed on both the windward and leeward sides of the island of Hawai‘i. With the 

possible exception of a population on Kohala Mountain, ‘I‘iwi occur as a single relatively contiguous 

population throughout the island (Scott and others, 1986; Fancy and Ralph, 1998). However, land cover 

unsuitable for territorial birds separates areas of occupied forest habitat in many parts of the species 

range and makes for a disjunct distribution. For the purposes of this study, the species range was 

delineated to encompass an area of 175,097 ha and to include only the following regions: north 

windward, central windward, Ka‘u, and Kona (fig. 2). Excluded from the range were regions of about 

5,600 ha on Kohala Mountain and 4,200 ha on Mauna Kea volcano (as estimated by Scott and others,

1986). The Kohala region was last surveyed in 1979 and only 10 ‘I‘iwi were detected there during the 

initial visit. The population at that time was estimated at 802 birds (± 286 SE) (Scott and others, 1986). 

No information is available on the occurrence or abundance of ‘I‘iwi in the Kohala region since 1979, 

although they are believed to persist there. 

‘I‘iwi abundance on Mauna Kea is related to māmane tree (Sophora chrysophylla) flower bloom 

(Hess and others, 2001), and most ‘I‘iwi on Mauna Kea may be visiting temporarily for flower 

resources. However, a small number of birds may be resident in subalpine woodland, but the delineation 

of a range boundary reflecting current (~2012) distribution is difficult given that only a few widely

dispersed ‘I‘iwi were detected during (2008-2012) surveys. For example, ‘I‘iwi decreased from 0.039 

birds per station (bps) in the 1998–2002 survey period, to 0.007 bps in the 2003–2007 survey period, 

and to 0.002 bps in the 2008–2012 survey period. ‘I‘iwi are sparsely distributed across southwest 

Mauna Kea based on recent surveys (2008-2012)(appendix D.3).

The island of Hawai‘i currently (2012) supports an estimated population of 516,312–569,706 

birds (mean = 543,009; table 1, appendix E.3). The mean estimate is about 56 percent greater than the 

340,000 birds estimated by Scott and others (1986). As with the surveys on Maui, the 1976–1979 HFBS 

was conducted primarily during June and July, a post-breeding period in which ‘I‘iwi densities typically

are lower than during the breeding season owing to dispersal to low elevations (Ralph and Fancy, 1994; 

Hart and others, 2011). Therefore, densities estimated for the HFBS are not directly comparable to those 

of subsequent surveys that were conducted in the spring during the breeding season. 

North Windward (Hakalau) 

The windward area of the island of Hawai‘i was divided into north and central regions to 

account for local differences in ‘I‘iwi densities and to improve regional population size estimates. The 

north windward region encompasses a 24,926-ha area with 258,075–296,035 birds (mean = 277,055; 

table 1, appendix E), based on the densities observed in 2012. Density in the 1,700–1,900-m elevation 

range was estimated at 13.9–18.4 birds per ha (mean = 16.1 ± 1.1 SE), constituting the highest values 

recorded for ‘I‘iwi across its range. Although sampling in the region was concentrated at upper 

elevations, with no sampling within the 4,900 ha of lowland wet-mesic forest below 1,400 m 

(appendixes D.4 and E.4), recent surveys of this habitat type in the adjacent central windward region did 

not detect ‘I‘iwi. Therefore, the unsampled strata is not expected to contribute appreciably to the 

resulting population estimate for the north windward region. 
22

Figure 10. Trends in ‘I‘iwi (Vestiaria coccinea) density (mean birds per hectare at 95-percent confidence interval) in 

the Hakalau, Keauhou, Mauna Loa, the lower and upper portions of the central Kona, and the Pu‘u Wa‘awa‘a 

consistently sampled areas (CSAs) of the island of Hawai‘i, Hawai‘i. The shaded band represents the 95-

percentconfidence interval of the trend for the entire time series. Note that the 1977 and 1978 Hawai’i Forest 

Bird Survey densities were not included in the trend assessment because of differences in the time of year 

during which it and all subsequent surveys were conducted.
23

‘I‘iwi density within the Hakalau CSA of the north windward region appears to be stable-todeclining (fig. 10). That is, the slope for the 1999–2012 survey period (β̂ = -0.0094 ± 0.0034; 95-

percent CI = -0.0160 to -0.0027; table 2) showed strong evidence of a stable trend and weak evidence of 

a negative trend. This trend would result in an average ‘I‘iwi population decrease of 20 percent over a 

25 year period. However, ‘I‘iwi showed no decreases in distribution at low elevations during 1977–2012 

within the CSA (corresponding to the area sampled within the Hakalau Forest National Wildlife Refuge) 

(fig. 2). Although the CSA is situated above 1,400 m in elevation, and lies 3–4 km above the lower edge 

of the species range, ‘I‘iwi distribution in high-elevation forest has remained unchanged despite a 

possible slight decline in bird density. 

Central Windward 

The ‘I‘iwi species range in the central windward region includes a 40,773-ha area with an

estimated 62,662–80,386 birds (mean = 71,524; table 1, appendix E.5), based on the densities observed 

in 2010 and 2012. A total of 98 percent of the estimated population occurs in montane mesic and wet 

forest, with few detections in montane dry-mesic grass-shrubland and none in other land cover types 

(appendix D.5). About 84 percent of the regional population is detected at elevations of 1,500–1,900 m, 

with the remainder observed at elevations ranging from as low as about 1,100 m to as high as 2,100 m.

‘I‘iwi densities show decreasing trends within the central windward region (table 2, fig. 10). A 

decline in ‘I‘iwi density is apparent for the Keauhou CSA, an area within the region in which the 

species is most abundant (3.7–4.8 birds per ha in 2012, mean = 4.3 ± 0.3 SE). The slope for the 1995–

2012 survey period (β̂ = -0.0270 ± 0.0033; 95-percent CI = -0.0334 to -0.0207; table 2) showed strong 

evidence of a negative trend, which would result in an average decline of 48 percent over a 25-year

period. ‘I‘iwi in the Mauna Loa CSA show highly variable densities with a stable–to-downward trend 

(β̂ = -0.0139 ± 0.0104; 95-percent CI = -0.0356–0.0051), and a projected decrease of 29 percent over 25 

years.

The sparse set of observations available for the ‘Ola‘a CSA did not allow a quantitative 

assessment of the change in the elevational distribution of ‘I‘iwi. However, a qualitative appraisal of the 

number of birds per station (bps) indicates a fairly steady decline in bird occurrence: 1.0 bps in 1977, 

0.4 bps in 1992, and 0.2 bps in 2010. The most current (2010) low-elevation record of ‘I‘iwi within the 

‘Ola‘a CSA was at an elevation of 1,210 m, and ‘I’iwi observed may have been visitors from higher 

elevations. These results may indicate that the species range in the region no longer extends into 

lowland wet forest (generally delimited by the 1,200-m elevation contour). Despite the declines in 

density apparent elsewhere in the central windward region, ‘I‘iwi occurrence did not show a pattern of 

elevation-range decreases within the Keauhou and Mauna Loa CSAs (fig. 11, appendixes F.5 and F.6).

However, both of these areas lie almost entirely above 1,500 m in elevation, and consequently appear to 

be situated above the zone in which changes in distribution are evident. 
24

Figure 11. Trends in occurrence of ‘I‘iwi (Vestiaria coccinea) by elevation for island of Hawai‘i consistently sampled 

areas (CSAs), Hawai‘i. A) Hakalau CSA, with surveys from 1977, and 1999 to 2012; B) Keauhou CSA, with 

surveys from 1977, 1995, 1996, 1997, 1998, 2002, 2003, 2005, 2006, 2007, 2008, 2009, 2010, 2011, and 

2012; C) Mauna Loa CSA, with surveys from 1978, 1986, 1987, 1990, 1991, 1992, 1993, and 1994; D) Pu‘u 

Wa‘awa‘a CSA, with surveys from 1978, 1990, 1991, 1996, 2003, and 2009; E) lower portion (elevations of 

1,000–1,500 meters) central Kona CSA, with surveys from 1978, 1995, 1999, 2000, 2005, 2009, and 2012; and 

F) upper portion (elevations greater than 1,500 meters) central Kona CSA, with surveys from 1978, 1995, 

1999, 2000, 2001, 2005, 2006, 2009, and 2012. 

E F

C D

A B
25

South Windward (Ka‘u) 

The part of the ‘I‘iwi range that includes the Ka‘u region covers a 33,680-ha area with 23,138–

33,512 birds (mean = 28,325; table 1, appendix E.6), based on the densities observed in 2004, 2008, and 

2010. Most ‘I‘iwi are distributed in the northern half of the Ka‘u Forest Reserve (appendix D.6). About 

94 percent of the population occurs in montane mesic and wet forest, with few recent (2004-2010) 

detections in lowland wet-mesic forest and none in other land cover types. Eighty-six percent of the 

regional population is about equally distributed from 1,300 to 1,900 m in elevation, with another 10 

percent occurring as low as about 1,100 m, and the remaining few percent occurring as low as about 900 

m and as high as 2,100 m (appendix E.6). 

Despite the expected bias of underestimated densities associated with HFBS surveys, given they 

were surveyed in the summer when birds are widely distributed, the densities from recent (2004-2010) 

surveys are significantly lower for all three areas (north, central, and south) of Ka‘u (appendix G) 

compared to the HFBS surveys. At the forested north end of Ka‘u, the 1976 HFBS within the Kapapala 

Forest Reserve showed ‘I‘iwi to be about twice as abundant as they were in 2004 (2.7 [± 1.1 SE] versus 

1.4 [± 1.1 SE] birds per ha)(Gorresen and others 2007). The 1976 HFBS within the central and main 

portion of the CSA also showed a three-fold decrease in density relative to that observed in 2008 (1.8 [± 

0.1 SE] versus 0.6 [± 0.1 SE] birds per ha). Already uncommon during the 1978 HFBS (0.6 [± 0.2 SE] 

birds per ha), ‘I‘iwi were wholly absent from the south Ka‘u CSA in 2005 and 2010. Gorresen and 

others (2007) reported a total population of 78,154 birds at Ka‘u, based on 2002 surveys—a population 

estimate almost three times larger than the estimate in this report. Although ‘I‘iwi may have declined, 

more likely the discrepancies are owing to different count estimates from each survey creating large 

variations in density estimates, and, thus, in abundance estimates. 

South Kona

The ‘I‘iwi range on the leeward side of the island of Hawai‘i was divided into three regions to 

better reflect local differences in density and to improve population estimates: south Kona (12,489 ha), 

central Kona (25,441 ha), and north Kona (21,231 ha). The south Kona region has an estimated 2,059–

4,918 birds (mean = 3,489; table 1), based on surveys conducted in 2003, 2009 and 2010. A total of 74

percent of the population occurs in montane mesic forest and 26 percent in montane wet forest, with no 

detections in other habitat types (appendix D.7 and E.7). About 21 percent of the regional population 

occurs within the 1,100–1,300-m elevation range, albeit at relatively low densities (0.3 [± 0.3 SE] birds 

per ha), with the remainder of ‘I‘iwi occurring as high as a little more than 1,700 m in elevation. 

Assessments of density changes for the south Kona region only can be made in comparison to

HFBS data. The south Kona area, with an elevation gradient of 960–1,640 m, showed a decrease in 

‘I‘iwi density from 1978 (HFBS) to 2009 (2.6 [± 0.4 SE] versus 0.1 [± 0.1 SE] birds per ha; appendix 

G). The HFBS values are likely biased toward higher densities at low to mid elevations because of postbreeding dispersal, which suggests that the resulting decrease is likely greater than indicated. However, 

comparisons from the Honomalino area (appendix G) focus on the elevation gradient of 1,360–1,810 m, 

and indicates that density may have diminished from 2005 to 2010 (0.7 [± 0.2 SE] versus 0.4 [± 0.2 SE] 

birds per ha).

Central Kona

The central Kona region has an estimated ‘I‘iwi population of 124,649–155,009 birds (mean = 

139,829; table 1) based on the densities observed in 2009 and 2010. About 96 percent of the population 

occurs in montane mesic and wet forest, with a small number of detections in lowland wet-mesic forest 
26

and montane dry forest and woodland (appendix D.7). Ninety-two percent of the regional population 

occurs at elevations of 1,300–1,900 m. The 1,900–2,100m elevation range above the CSA has not been 

sampled since the 1978 HFBS, and ‘I‘iwi were not detected at that range during those surveys. 

However, this area may support about 420 birds (given the 4,300-ha area is composed mostly of 

montane dry forest and woodland, which has a mean density of 0.1 birds per ha elsewhere; appendix 

E.8).

‘I‘iwi density within the lower and upper portions of the CSA in the central Kona region appears 

to be increasing during the 1995–2012 survey period (fig. 10). The CSA spans an elevation gradient of 

1,000–1,500 m (lower) and 1,500–1,900 m (upper). Slopes observed for both areas show strong 

evidence of positive trends (lower part: β̂ = 0.0226 ± 0.0069; 95-percent CI = 0.0091–0.0361; upper 

part: β̂ = 0.0294 ± 0.0130; 95-percent CI = 0.0043–0.0553; table 2). The average of these trends over a 

25 year period would result in a 71 and a 97 percent increase in population size for lower and upper 

elevations, respectively. 

The distribution of ‘I‘iwi (presence-absence) from 1978 to 2012 shows no decreases in ‘I‘iwi 

distribution at low elevations in the central Kona CSA (corresponding to most of the Kona Forest Unit 

of the Hakalau Forest National Wildlife Refuge; fig. 11). Bird distribution is annually variable in the 

lower portion of this area but shows no trend indicative of diminished occurrence in the 1,000–1,500 m 

or 1,500–1,900 m elevation ranges. However, habitat at elevations below the lower portion of the CSA 

(that is, less than 1,000 m) has not been surveyed since the 1978 HFBS, and a comparison to current 

survey results is not possible. Although relatively uncommon, ‘I‘iwi were detected at elevations as low 

as 400 m during the 1978 survey (that is, 47 detections at 65 stations, or about 0.7 birds per station, 

along HFBS transects 63, 64, and 65); however, this may indicate a post-breeding dispersal to low 

elevations. As elsewhere in leeward Hawai‘i, it is unlikely that the current species range still includes 

habitat below elevations of 1,000 m in the central Kona region. 

North Kona

The ‘I‘iwi population in north Kona seems restricted entirely to the northern and possibly the 

western slopes of Hualalai Volcano, and is estimated at 18,444–27,130 birds (mean = 22,787; table 1), 

based on survey results from 2003 and 2009. An extensive tract of degraded forest habitat lies between 

the populations in north Hualalai and central Kona, and much of this land cover likely is unsuitable 

habitat for resident ‘I‘iwi. ‘I‘iwi in the region were detected only in mesic forest, and at relatively 

moderate densities (3.7 [± 0.5 SE] birds per ha). About 1,135 ha of montane wet forest on west Hualalai 

was not sampled for birds, and may support ‘I‘iwi at a low density. Assuming a density one-half that of 

montane mesic forest (as observed in central Kona), montane wet forest in north Kona may contain 

about 2,043 additional birds. Lowland wet-mesic forest in the region lies entirely below elevations of 

1,200 m, and given the infrequency of ‘I‘iwi detections at such elevations elsewhere in leeward Hawai‘i, 

this habitat does not likely contribute substantially to the population estimate. 

‘I‘iwi density within the Pu‘u Wa‘awa‘a CSA in the north Kona region appears to have 

increased during the 1990–2009 survey period (fig. 10). The area spans an elevation range of 1,300–

1,900 m (upper)(appendix D.7 and E.9). The regression slope shows strong evidence of a positive trend 

(β̂ = 0.0383 ± 0.0163; 95-percent CI = 0.0075 to 0.0719; table 2), which is a 147-percent increase over 

25 years. However, the time series for the CSA only is composed of 5 surveys over a 19-year period, 

and the 95-percent CI for the trend is relatively broad. Survey results from 1978 to 2009 demonstrate no 

decreases in ‘I‘iwi distribution at the lower elevations in the Pu‘u Wa‘awa‘a CSA in the north Kona 

region (fig. 11).
27

Discussion

The status and trends of the ‘I‘iwi across the Hawaiian Islands for much of the last century have 

been characterized largely by low-elevation populations declining and higher-elevation populations 

remaining stable. ‘I‘iwi were described by early European visitors as one of the most common birds in 

all forests. If we use an estimate of 866,930 ha of potential forest habitat in pre-historical time (wet, 

mesic, and montane dry forests combined across all island; John Price, unpublished data) and the 

average density of ‘I‘iwi from high-elevation areas of Hakalau Forest National Wildlife Refuge (a place 

where ‘I‘iwi are one of the most common birds in the forest with 16.1 birds per ha), then there may have 

been as many as 13,870,896 ‘I‘iwi just a few centuries ago. However, early descriptions of abundance 

were replaced by comments on ‘I‘iwi disappearing from low-elevation forests as early as the late 1800s 

(Banko, 1981). By the mid-1900s, ‘I‘iwi had virtually ceased to occur in low and mid-elevation forests, 

but high-elevation forests were still strongholds for the birds. In recent years, we see a continuation of 

that pattern. Populations on the lowest-elevation islands (specifically O‘ahu, Lānai, and Moloka‘i) have 

all but disappeared over the last hundred years, with possible remnant populations or rare visitors from 

neighboring high islands. Kaua‘i, a mid-elevation island, has seen dramatic decreases in ‘I‘iwi 

populations over the last decade (2000-2012), with an estimated 96-percent decline over a 25-year 

period. However, even many of the high-elevation sites are showing signs of decline based on the most 

current surveys. 

Estimating abundance and trends over a large and diverse area such as the entire Hawaiian

archipelago was a difficult task. Although certain areas (continuously sampled areas [CSAs]) were 

surveyed multiple times over several decades, providing good information to evaluate trends, these 

CSAs represent a small part of the entire range of ‘I‘iwi, and typically at the higher elevations of the 

species’ range. Similarly, abundance for the entire range, including many areas never surveyed, had to 

be extrapolated from a small part of the species’ range in which surveys had been conducted. By 

stratifying density estimates into habitat types and elevational ranges, and extrapolating those densities 

by strata to unsurveyed areas, we were able to reasonably estimate ‘I‘iwi populations in unsurveyed 

areas. However, these are projections across areas with little or no information. Another difficulty, 

inherent in all time series of count data, is that each set of surveys is a random sample from the 

population across time, and these estimates will overcount or undercount the “true” population size by 

some unknown amount. Although distance analysis attempts to remove some of this variation, this 

variation results in density estimates that can fluctuate greatly from one survey to the next. Therefore,

population estimates based on different surveys can result in large differences that may be owing in part 

to population trends, but also could be owing to simple sampling error.

‘I‘iwi are highly sensitive to disease, particularly avian malaria (Atkinson and others, 1995), and 

the prevalence of disease at low and middle elevations is believed to have largely determined the 

modern-day distribution of ‘I‘iwi. Avian malaria, transmitted by mosquitoes, is limited to low- and midelevation areas where the temperatures are sufficiently warm for the mosquitoes and the disease to 

develop (LaPointe and others, 2009). With global warming, rising temperatures are expected to facilitate 

the spread of mosquitoes and disease into high-elevation sanctuaries of the ‘I‘iwi (Benning and others,

2002), and unless the ‘I‘iwi develops resistance, such areas are not likely to support viable populations 

in the future. The trade wind cloud inversion layer (about 1,800–2,400 m elevation) caps precipitation at 

upper elevations and sets the effective tree line for the forest; the inversion zone is expected to persist 

into the future, potentially inhibiting forests from developing in higher-elevation areas (Cao and others, 

2007). Therefore, the narrow elevation band in which ‘I‘iwi currently reside is expected to narrow

further. ‘I‘iwi also are known to be highly mobile, flying across large areas to access flowering plants 

(Fancy and Ralph, 1998), and such movements can take them into areas where disease potentially is 
28

present (Kuntz, 2008). Therefore, the gradual retreat of ‘I‘iwi populations into increasingly higher 

elevation sanctuaries is likely owing to increasing temperatures, which increase the risk of disease,

continued degradation of forest habitats, that also promote disease occurrence (LaPointe and others, 

2009), amplified by high mobility of the ‘I‘iwi’ and its sensitivity to disease. 

Although disease is believed to be the main driver of the absence of ‘I’iwi at low-to-mid 

elevations, other factors besides elevation interact with diseases and their vectors to influence the 

distribution of disease. For example, in the east region of Maui, ‘I‘iwi densities have increased, with 

detections as low as 860 m in elevation. This is well below typical elevations on the island of Hawai‘i, 

where ‘I‘iwi rarely occur below 1,500 m, and even on Kaua‘i, where ‘I‘iwi occur only above 1,000 m. 

The east region of Maui receives much annual precipitation (2–6 m), but surveys of the prevalence of 

mosquitoes and avian malaria detected very low prevalence rates in the Kīpahulu region of east Maui 

(Aruch and others, 2007). The study attributed low malaria rates in Kīpahulu to high rainfall events that 

flush larval mosquito habitats in stream drainages, and relatively cool temperatures even at low 

elevations that limit mosquito and malaria development. Additionally, the National Park Service has 

actively managed this area to control weeds and has eradicated feral pigs, removing the role that feral 

pigs have in creating standing water sources suitable for mosquito breeding (Atkinson and others, 

1995). The forest habitats in the northeast and east regions of Maui also are large tracts of 

predominately native vegetation, without the ranching and urban-suburban development that degrade 

and fragment habitats introducing artificial water sources and corridors that allow mosquitoes to 

penetrate forests. Therefore, not only elevation, but quality of forest and sources of larval habitat seem

critical in determining the distribution and abundance of ‘I‘iwi.

One interesting trend was the decrease in ‘I‘iwi at higher elevations in their range in some 

regions. This trend may be because of the degradation of upper-range habitat owing to continued 

persistent grazing by feral ungulates and drought conditions. Both forces have been shown to negatively 

affect bird populations (Banko and others, 2013). Another possibility is that as ‘I‘iwi populations 

decline, their distribution contracts inward to core habitat and away from marginal habitat. Most ‘I‘iwi 

occur in a narrow elevational band across the islands (Appendix E), with most trends suggesting this 

narrow band will get smaller. This highlights the importance of a relatively small area in which the 

‘I‘iwi live—an area that is continuing to shrink. 

Management and Research Considerations

1) Rapidly assess distributional shifts: Given concern about the status of ‘I‘iwi and evidence of 

population declines and distributional contractions across their range, we suggest establishing several 

transects that span the full elevational breadth of ‘I‘iwi occurrence on multiple islands as a long-term 

monitoring and early warning system for ‘I‘iwi (as well as for other birds of conservation concern). 

Ideally, such surveys would be conducted yearly, and would consist of a number of transects that strike 

a balance between a sufficient numbers to adequately describe general distributional trends, and yet not 

so many that the cost is prohibitive. Candidate locations for transects should use existing survey areas, 

and should be chosen for large elevational ranges, which may require establishing new stations at lower

elevations to extend existing transects. 

2) Survey Kohala Mountains, Hawai‘i: The Kohala Mountains have not been surveyed since the late 

1970s, at which time they supported an estimated 802 ‘I‘iwi—a population much larger than any other 

remnant population at the time. Whether or not ‘I‘iwi exist there today is unknown, but if they persist in 

the Kohalas, they may represent an important disease-resistant population (see item 3). We suggest that 

a one-time survey of the Kohalas be undertaken to search for ‘I‘iwi, as well as other rare species.
29

3) Answer the question of whether isolated low-elevation ‘I’iwi populations are important: West 

Maui, Moloka‘i, Oahu, and possibly the Kohala Mountains represent low-elevation populations where 

disease is presumably present. These populations may be susceptible to disease and barely persisting, 

perhaps subsidized by high-elevation immigrants, or they may represent populations persisting in the 

presence of disease, and developing disease resistance. If these populations are persisting and are 

developing disease resistance, then they are very important populations for the long-term persistence of 

‘I‘iwi. We suggest targeted research at one or more of these populations to 1) determine whether 

individuals present are resident and breeding, or are immigrants from neighboring high-elevation 

mountains; and 2) determine the prevalence of disease in the birds. If these populations are developing 

disease resistance, then efforts to protect the populations may be warranted to ensure that the evolution 

of disease resistance continues both to maintain the current low-elevation populations, and possibly to 

translocate to other areas where disease resistance has not evolved.

4) Understand drivers of Population declines: Populations decline when productivity or survival rates 

are insufficient to support stable populations, or emigration is high and immigration is low. Establishing 

demographic studies at several locations across the range of ‘I‘iwi would provide managers with the 

information on the actual drivers of population change (for example, reduced survival, reduced 

productivity). Although disease may be an important depressor of survival rates, productivity may be 

low, indicating problems beyond disease that may need to be managed. Ideally, several sites would be 

chosen to capture low-elevation dynamics (for example, at Kaua‘i), as well as higher-elevation sites on 

Hawai‘i and Maui.

5) Protect and expand high-elevation habitats: With evidence of ‘I‘iwi declining at low to medium

elevations across much of its range, efforts to stabilize the species would best be directed at the core 

areas where populations are stable or increasing. Many of these core areas are protected or plans are 

underway to increase protection (such as fencing and ungulate exclusion), but efforts to increase habitat 

at higher elevations above these sites could help buffer populations to the effects of warming 

temperatures in the future.

Acknowledgments

This work is an analysis of over 30 years of intensive bird sampling by scores of people across 

some of the most difficult terrain and weather conditions observed anywhere in the world. We thank 

those dedicated surveyors for their hard work and dedication to the ecology and conservation of Hawai‘i 

forest birds. Kevin Brinck made several important contributions to the analysis. Jack Jeffrey graciously 

provided the cover photo for this report. Funding was provided by the U.S. Fish and Wildlife Service 

Pacific Islands Office and the U.S. Geological Survey Pacific Island Ecosystems Research Center.

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33

Appendixes

Appendix A

Selection of ‘I‘iwi (Vestiaria coccinea) detection function models. Models were ranked by differences between each 

candidate model and the model with the lowest second-order Akaike’s Information Criterion value (∆AICc) after correcting 

for small sample size. Base models included half normal (H-norm) and hazard-rate (H-rate) key detection functions with 

cosine (Cos), hermite polynomial (H-poly) and simple polynomial (S-poly) adjustment terms. Covariates were incorporated 

with the highest AIC ranked base model. Covariates included survey region (Region; for the island of Hawai‘i only), year of 

survey (Year), observer (Obs), detection type (Det; auditory [A], visual [V], both auditory and visual [B]), vegetation type 

(Veg), wind speed (Wind), gust speed (Gust), rain (Rain), and cloud cover (Cloud). For each model, the number of estimated 

parameters (Par), estimate of the log-likelihood (LogL) and AIC model weight (wi) are provided. The top-ranked model for 

each island was used for estimation of bird density. 

Island Model Adjustment

terms

Covariates Par -LogL AICc ∆AICc wi

Kaua‘i H-rate Key Det 4 8,489.74 16,987.50 0.00 0.57

H-rate Key 1DetVB 3 8,491.04 16,988.09 0.59 0.43

H-rate Key 2DetAB 3 8,569.09 17,144.18 156.68 0.00

H-rate Key Obs 32 8,546.19 17,157.45 169.95 0.00

H-rate Key 3Year 9 8,603.54 17,225.18 237.68 0.00

H-rate Key Wind 5 8,625.00 17,260.04 272.54 0.00

H-rate Key Cloud 5 8,632.18 17,274.39 286.89 0.00

H-rate 4Key 2 8,636.20 17,276.42 288.92 0.00

H-rate 4S-poly 3 8,635.86 17,277.74 290.24 0.00

H-rate 4Cos 3 8,635.98 17,277.96 290.46 0.00

H-rate Key Rain 4 8,635.71 17,279.45 291.95 0.00

H-rate Key Veg 5 8,635.86 17,281.76 294.26 0.00

H-rate Key Gust 5 8,638.92 17,287.86 300.36 0.00

H-norm 4Cos 3 8,641.94 17,289.89 302.39 0.00

H-rate Key 5Year 3 8,642.15 17,290.30 302.80 0.00

H-norm 4Key 1 8,661.68 17,325.37 337.87 0.00

H-norm 4H-poly 2 8,661.30 17,326.61 339.11 0.00

Maui H-rate Key Det 4 28,757.78 57,523.57 0.00 1.00

H-rate Key 1DetVB 3 28,777.46 57,560.91 37.34 0.00

H-rate Key 2DetAB 3 29,089.47 58,184.94 661.37 0.00

H-rate Key Obs 29 29,244.67 58,547.58 1,024.01 0.00

H-rate Key 3Year 20 29,336.45 58,713.01 1,189.44 0.00

H-rate Key Gust 7 29,435.78 58,885.57 1,362.00 0.00

H-rate Key Veg 6 29,440.00 58,892.01 1,368.44 0.00

H-rate Key 5Year 3 29,447.45 58,900.89 1,377.32 0.00

H-rate Key Wind 6 29,455.96 58,923.93 1,400.36 0.00

H-rate Key Cloud 13 29,449.19 58,924.42 1,400.85 0.00

H-rate 4Key 2 29,469.54 58,943.08 1,419.51 0.00

H-rate Key Rain 6 29,465.55 58,943.12 1,419.55 0.00

H-rate 4Cos 2 29,469.53 58,945.06 1,421.49 0.00
34

Island Model Adjustment

terms

Covariates Par -LogL AICc ∆AICc wi

H-norm 4H-poly 3 29,478.51 58,963.02 1,439.45 0.00

H-norm 4Key 1 29,489.31 58,980.62 1,457.05 0.00

6

H-norm 4Cos 3 - - - -

6

H-rate 4S-poly 3 - - - -

Hawai‘i H-rate Key 1DetVB 3 19,965.76 39,937.52 0.00 1.00

H-rate Key Obs 14 20,165.88 40,359.85 422.33 0.00

H-rate Key 2DetAB 3 20,181.01 40,368.02 430.50 0.00

H-rate Key 3Year 6 20,296.70 40,605.41 667.89 0.00

H-rate Key Veg 10 20,294.17 40,608.38 670.86 0.00

H-rate Key Gust 4 20,314.78 40,637.56 700.04 0.00

H-rate Key Cloud 13 20,307.37 40,640.82 703.30 0.00

H-rate Key Wind 6 20,316.03 40,644.08 706.56 0.00

H-rate Cos 4 20,325.16 40,658.34 720.82 0.00

H-norm H-poly 3 20,326.20 40,658.34 720.88 0.00

H-rate 4S-poly 2 20,327.92 40,659.84 722.32 0.00

H-rate Key 2 20,327.92 40,659.84 722.32 0.00

H-rate Key 5Year 3 20,327.50 40,661.00 723.48 0.00

H-rate Key Rain 4 20,327.30 40,662.61 725.09 0.00

H-rate Key Elev 3 20,328.86 40,663.72 726.20 0.00

H-norm 4Cos 1 20,337.86 40,677.71 740.19 0.00

H-norm Key 1 20,337.86 40,677.71 740.19 0.00

6

H-rate Key Det 4 - - - -

1 Detection types V and B pooled

2 Detection types A and B pooled

3 Year treated as a categorical variable (that is, factor)

4 Base model

5 Year treated as a continuous variable

6 Model failed to converge
35

Appendix B

Effective detection radius (EDR) from top-ranked ‘I‘iwi (Vestiaria coccinea) detection function model by island. EDR mean, 

standard error (SE), and 95-percent (95%) confidence interval (CI) are presented separately for each model covariate.

Island Model Covariate Covariate EDR (mean ± SE) Covariate EDR (95% CI)

Kaua‘i H-rate Key auditory 49.918 ± 1.017 47.962-51.953

auditory and visual 22.315 ± 1.060 20.326-24.499

Maui H-rate Key auditory 40.739 ± 0.327 40.103-41.385

visual 16.239 ± 0.503 15.282-17.256

auditory and visual 22.725 ± 0.489 21.785-23.706

Hawai‘i H-rate Key auditory 45.151 ± 0.515 44.153-46.172

auditory and visual 24.327 ± 0.505 23.355-25.338
36

Appendix C

Landfire2 land cover types reclassified to consolidate categories and to derive a sufficient number of survey observations for 

developing ‘I‘iwi (Vestiaria coccinea) detection models.

Original land cover class Revised class

Hawai'i lowland dry forest Lowland dry forest

Hawai'i lowland dry grassland Lowland dry-mesic grassland-shrubland

Hawai'i lowland dry shrubland Lowland dry-mesic grassland-shrubland

Hawai'i lowland mesic forest Lowland wet-mesic forest

Hawai'i lowland mesic grassland Lowland dry-mesic grassland-shrubland

Hawai'i lowland mesic shrubland Lowland dry-mesic grassland-shrubland

Hawai'i lowland rainforest Lowland wet-mesic forest

Hawai'i montane rainforest Montane wet forest

Hawai'i montane-subalpine dry forest and woodland Montane dry forest and woodland

Hawai'i montane-subalpine dry grassland Montane dry-mesic grass-shrubland

Hawai'i montane-subalpine dry shrubland Montane dry-mesic grass-shrubland

Hawai'i montane-subalpine mesic forest Montane mesic forest

Hawai'i montane-subalpine mesic grassland Montane dry-mesic grass-shrubland

Hawaiian introduced deciduous shrubland Introduced grass-shrubland

Hawaiian introduced dry forest Introduced forest

Hawaiian introduced evergreen shrubland Introduced grass-shrubland

Hawaiian introduced perennial grassland Introduced grass-shrubland

Hawaiian introduced wet-mesic forest Introduced forest

Hawaiian managed tree plantation Introduced forest

Barren Barren

Agriculture-cultivated crops and irrigated agriculture Other

Developed-low intensity Other

Developed-medium intensity Other

Developed-high intensity Other

Developed-open space Other
37

Appendix D 

Location and abundance of ‘I‘iwi based on the most recent surveys (see figure captions for year). 

D.1: ‘I‘iwi (Vestiaria coccinea) distribution and abundance on Kaua‘i, Hawai‘i. The vegetation types and elevation contours 

shown correspond to strata for which density and abundance were estimated for the area within the species range (red 

outline; appendix E.1). Density per station values (points) are derived from survey counts conducted in 2012.
38

D.2: ‘I‘iwi (Vestiaria coccinea) distribution and abundance on east Maui, Hawai‘i. The vegetation types and elevation 

contours shown correspond to strata for which density and abundance were estimated for the area within the species range 

(red outline; appendix E.2). Density per station values (points) are derived from survey counts made in 2011 and 2012.
39

D.3: ‘I‘iwi (Vestiaria coccinea) distribution in the Mauna Kea region of the island of Hawai‘i, Hawai‘i. Occurrence records 

(points) are grouped by a 5-year interval for surveys made between 1998 and 2012.
40

D.4: ‘I‘iwi (Vestiaria coccinea) distribution and abundance in the north windward region of the island of Hawai‘i, Hawai‘i. 

The vegetation types and elevation contours shown correspond to strata for which density and abundance were estimated for 

the area within the species range (red outline; appendix E.4). Density per station values (points) are derived from survey 

counts made in 2012.
41

D.5: ‘I‘iwi (Vestiaria coccinea) distribution and abundance in the central windward region of the island of Hawai‘i, Hawai‘i. 

The vegetation types and elevation contours shown correspond to strata for which density and abundance were estimated for

the area within the species range (red outline; appendix E.5). Density per station values (points) are derived from survey 

counts made in 2010 and 2012.
42

D.6: ‘I‘iwi (Vestiaria coccinea) distribution and abundance in the Ka‘u region of the island of Hawai‘i. The vegetation types 

and elevation contours shown correspond to strata for which density and abundance were estimated for the area within the 

species range (red outline; appendix E.6). Density per station values (points) are derived from survey counts made in 2004, 

2008, and 2010. 
43

D.7: ‘I‘iwi distribution and abundance in the Kona region of the island of Hawai‘i, Hawai‘i (depicted separately for the north 

Kona region [left panel] and the central and south Kona regions [right panel]). The vegetation types and elevation contours 

shown correspond to strata for which density and abundance were estimated for the area within the species range (red 

outline; appendixes E.7, E.8., and E.9). Density per station values (points) are derived from survey counts made in 2003 and 

2009 (north Kona), 2009 and 2010 (central Kona), and 2003, 2009, and 2010 (south Kona).
44

Appendix E

Density and population abundance estimates by elevation and vegetation type for the area encompassed by the species range. Year of survey from which 

estimates are derived is specified following each island- or region-specific name. Sample size (number of stations sampled) and detections (number of birds 

observed) are indicated with K and n, respectively. Total population density (birds per hectare) and abundance by habitat variable for all strata are summarized in 

shaded rows. Unsampled strata do not contribute to population abundance estimates, but are included to provide areas used in the species range size values 

specific to islands or island-regions.

E.1: Kaua‘i – survey year 2012 

Habitat 

variable Stratum Area (ha) K n 

Mean

density SE CV (%)

Lower 

95% CI

Upper

95% CI

Mean

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 900-1,100 m 266 19 1 0.093 0.102 110 0.000 0.333 25 27 110 0 89

1,100-1,300 m 3,808 172 54 0.563 0.110 20 0.370 0.789 2,143 419 20 1,411 3,004

1,300-1,500 m 1,385 76 15 0.314 0.089 28 0.160 0.499 435 124 28 222 691

all sampled strata 5,459 267 70 0.477 0.083 17 0.328 0.645 2,603 453 17 1,789 3,520

Vegetation Montane wet forest 4,587 216 61 0.486 0.090 18 0.324 0.675 2,227 412 18 1,482 3,091

Lowland wet-mesic 

forest 825 51 9 0.340 0.133 39 0.105 0.611 271 106 39 84 487

Introduced forest 47 0 - - - - - - - - - - -

all sampled strata 15,412 267 70 0.464 0.081 18 0.319 0.640 2,498 437 18 1,718 3,442
45

E.2: East Maui – survey years 2011 and 2012 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 500-700 m 83 0 - - - - - - - - - - -

700-900 m 824 22 4 0.557 0.321 58 0.000 1.254 459 264 58 0 1,033

900-1,100 m 1,979 30 50 3.465 0.937 27 1.955 5.568 6,859 1,855 27 3,870 11,021

1,100-1,300 m 2,817 52 128 4.613 0.676 15 3.361 6.035 12,996 1,904 15 9,470 17,001

1,300-1,500 m 2,555 68 188 3.990 0.466 12 3.115 4.969 10,193 1,191 12 7,958 12,696

1,500-1,700 m 2,249 87 344 5.865 0.453 8 5.039 6.737 13,189 1,020 8 11,331 15,149

1,700-1,900 m 1,576 53 364 6.873 0.572 8 5.798 8.117 10,829 901 8 9,136 12,614

1,900-2,100 m 1,035 28 183 4.597 0.644 14 3.345 5.970 4,760 667 14 3,463 6,181

2,100-2,300 m 358 2 2 0.345 0.241 70 0.000 0.734 123 86 70 0 262

2,300-2,500 m 8 0 - - - - - - - - - - -

all sampled strata 113,393 342 1,263 4.436 0.292 7 3.873 5.019 59,407 3,915 7 51,874 67,218

Vegetation Montane dry-mesic 

grass-shrubland 907 24 128 3.517 0.719 20 2.117 4.919 3,189 652 20 1,919 4,461

Montane wet forest 7,812 237 1,015 5.648 0.345 6 4.986 6.314 44,124 2,696 6 28,949 49,320

Lowland wet-mesic 

forest 3,495 77 117 3.174 0.502 16 2.286 4.347 11,092 1,756 16 7,989 15,194

Introduced forest 794 4 3 2.399 1.300 54 0.000 4.983 1,906 1,033 54 0 3,959

all sampled strata 13,008 342 1,263 4.636 0.286 6 4.102 5.179 60,310 3,715 6 53,356 67,363
46

E.3: Hawai‘i (all regions)

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation all sampled strata 1174,579 1,852 2,798 3.465 0.119 3 3.242 3.699 531,868 18,198 3 497,655 567,911

Vegetation all sampled strata 1175,100 3.417 0.125 4 3.174 3.654 554,150 20,272 4 514,708 592,558

E.4: Hawai‘i, north windward – survey year 2012 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 700-900 m 474 0 - - - - - - - - - - -

900-1,100 m 2,046 0 - - - - - - - - - - -

1,100-1,300 m 6,807 0 - - - - - - - - - - -

1,300-1,500 m 8,599 19 86 7.807 0.659 8 6.556 9.031 67,135 5,670 8 56,373 77,660

1,500-1,700 m 7,608 125 684 13.279 1.034 8 11.390 15.289 101,025 7,870 8 86,652 116,322

1,700-1,900 m 4,887 105 634 16.113 1.149 7 13.932 18.377 78,744 5,616 7 68,087 89,807

1,900-2,100 m 1,784 16 27 5.021 2.337 47 1.158 9.934 8,957 4,169 47 2,066 17,722

2,100-2,300 m 350 0 - - - - - - - - - - -

all sampled strata 122,878 265 1,431 11.184 0.533 5 10.142 12.213 255,861 12,205 5 232,023 279,406

Vegetation Montane dry-mesic 

grass-shrubland 255 0 - - - - - - - - - - -

Montane dry forest & 

woodland 1 0 - - - - - - - - - - -

Montane mesic forest 4,701 103 509 11.579 1.155 10 9.318 13.894 54,432 5,428 10 43,804 65,314

Montane wet forest 18,198 162 922 13.398 0.779 6 11.909 14.985 243,816 14,183 6 216,723 272,705

Lowland wet-mesic 

forest 4,904 0 - - - - - - - - - - -

Lowland dry-mesic 

grass-shrubland 45 0 - - - - - - - - - - -

Introduced grassshrubland 4,075 5 0 0 0 0 0 0 0 0 0 0 0

Introduced forest 324 0 - - - - - - - - - - -

Barren and other 161 0 - - - - - - - - - - -

all sampled strata 126,974 270 1,431 11.057 0.558 5 10.024 12.172 298,249 15,038 5 270,393 328,335
47

E.5: Hawai‘i, central windward – survey years 2010 and 2012 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 900-1,100 m 78 0 - - - - - - - - - - -

1,100-1,300 m 10,030 76 10 0.205 0.098 48 0.041 0.411 2,061 979 48 412 4,121

1,300-1,500 m 9,946 153 34 0.316 0.077 24 0.183 0.480 3,141 763 24 1,819 4,773

1,500-1,700 m 9,117 140 187 2.854 0.305 11 2.274 3.441 26,020 2,781 11 20,732 31,371

1,700-1,900 m 7,668 153 303 4.207 0.372 9 3.547 4.997 32,259 2,852 9 27,197 38,317

1,900-2,100 m 3,739 19 18 1.680 0.676 40 0.493 3.142 6,282 2,527 40 1,844 11,747

2,100-2,300 m 358 0 - - - - - - - - - - -

all sampled strata 140,500 541 552 1.723 0.121 7 1.502 1.970 69,763 4,912 7 60,838 79,772

Vegetation Montane dry-mesic 

grass-shrubland 6,089 41 2 0.245 0.170 69 0 0.622 1,494 1,037 69 0 3,788

Montane dry forest & 

woodland 491 2 0 0 0 0 0 0 0 0 0 0 0

Montane mesic forest 8,009 304 380 2.376 0.193 8 2.009 2.761 19,026 1,546 8 16,088 22,116

Montane wet forest 16,643 106 170 3.170 0.441 14 2.365 4.074 52,765 7,335 14 39,362 67,802

Lowland wet-mesic 

forest 4,295 38 0 0 0 0 0 0 0 0 0 0 0

Lowland dry-mesic 

grass-shrubland 32 0 - - - - - - - - - - -

Introduced grassshrubland 1,402 32 0 0 0 0 0 0 0 0 0 0 0

Introduced forest 150 3 0 0 0 0 0 0 0 0 0 0 0

Barren and other 3,966 15 0 0 0 0 0 0 0 0 0 0 0

all sampled strata 141,045 541 552 1.785 0.185 10 1.447 2.180 73,285 7,592 10 59,393 89,483
48

E.6: Hawai‘i, Ka‘ū – survey years 2004, 2008, and 2010 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 700-900 m 682 5 0 0 0 0 0 0 0 0 0 0 0

900-1,100 m 3,883 31 2 0.101 0.069 69 0 0.252 391 268 69 0 978

1,100-1,300 m 6,461 130 44 0.528 0.115 22 0.312 0.769 3,414 742 22 2,018 4,970

1,300-1,500 m 6,302 116 87 1.270 0.189 15 0.920 1.660 8,002 1,189 15 5,797 10,462

1,500-1,700 m 7,184 67 55 1.738 0.374 22 1.113 2.523 12,482 2,690 22 7,999 18,124

1,700-1,900 m 5,932 22 13 1.443 0.607 42 0.426 2.808 8,561 3,602 42 2,526 16,654

1,900-2,100 m 3,299 7 1 0.223 0.198 89 0 0.669 736 652 89 0 2,208

2,100-2,300 m 151 0 - - - - - - - - - - -

all sampled strata 133,743 378 202 0.995 0.137 14 0.748 1.290 33,587 4,624 14 25,242 43,531

Vegetation Montane dry-mesic 

grass-shrubland 5,070 3 0 0 0 0 0 0 0 0 0 0 0

Montane dry forest & 

woodland 353 0 - - - - - - - - - - -

Montane mesic forest 7,513 163 130 1.422 0.203 14 1.047 1.846 10,684 1,527 14 7,868 13,866

Montane wet forest 13,127 131 64 0.838 0.149 18 0.564 1.158 11,005 1,957 18 7,403 15,195

Lowland wet-mesic 

forest 7,045 64 8 0.195 0.091 47 0.024 0.390 1,375 642 47 172 2,750

Lowland dry-mesic 

grass-shrubland 45 0 - - - - - - - - - - -

Introduced grassshrubland 338 13 0 0 0 0 0 0 0 0 0 0 0

Introduced forest 37 1 0 0 0 0 0 0 0 0 0 0 0

Barren and other 487 3 0 0 0 0 0 0 0 0 0 0 0

all sampled strata 133,617 378 202 0.686 0.077 11 0.540 0.835 23,063 2,576 11 18,149 28,055
49

E.7: Hawai‘i, south Kona – survey years 2003, 2009, and 2010 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 500-700 m 100 5 0 0 0 0 0 0 0 0 0 0 0

700-900 m 1,998 17 0 0 0 0 0 0 0 0 0 0 0

900-1,100 m 2,343 22 0 0 0 0 0 0 0 0 0 0 0

1,100-1,300 m 2,309 27 2 0.269 0.269 100 0 0.807 621 621 100 0 1,863

1,300-1,500 m 2,241 42 9 0.506 0.257 51 0.081 1.077 1,133 576 51 181 2,413

1,500-1,700 m 1,966 65 16 0.499 0.165 33 0.214 0.849 981 324 33 421 1,669

1,700-1,900 m 944 13 2 0.240 0.224 93 0 0.721 227 211 93 0 680

1,900-2,100 m 19 0 - - - - - - - - - - -

all sampled strata 111,901 191 29 0.249 0.079 32 0.118 0.422 2,962 945 32 1,407 5,016

Vegetation Montane dry-mesic 

grass-shrubland 238 1 0 0 0 0 0 0 0 0 0 0 0

Montane mesic forest 4,645 110 27 0.636 0.156 25 0.365 0.963 2,953 725 25 1,695 4,475

Montane wet forest 1,035 8 2 1.027 0.839 82 0 2.826 1,062 868 82 0 2,925

Lowland wet-mesic 

forest 4,368 53 0 0 0 0 0 0 0 0 0 0 0

Lowland dry-mesic 

grass-shrubland 93 0 - - - - - - - - - - -

Introduced grassshrubland 163 0 - - - - - - - - - - -

Barren and other 1,412 14 0 0 0 0 0 0 0 0 0 0 0

all sampled strata 113,077 191 29 0.307 0.085 28 0.154 0.491 4,015 1,111 28 2,019 6,417
50

E.8: Hawai‘i, central Kona – survey years 2009 and 2010 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 500-700 m 11 0 - - - - - - - - - - -

700-900 m 1,303 6 0 0 0 0 0 0 0 0 0 0 0

900-1,100 m 2,947 16 7 0.683 0.309 45 0.190 1.366 2,013 911 45 561 4,026

1,100-1,300 m 3,473 30 38 2.487 0.498 20 1.585 3.540 8,636 1,729 20 5,503 12,293

1,300-1,500 m 3,928 37 126 8.825 1.233 14 6.497 11.334 34,664 4,842 14 25,520 44,521

1,500-1,700 m 3,910 36 157 13.041 1.897 15 9.590 16.700 50,992 7,419 15 37,496 65,296

1,700-1,900 m 4,369 34 119 11.752 1.446 12 9.015 14.653 51,345 6,316 12 39,388 64,020

1,900-2,100 m 4,300 0 - - - - - - - - - - -

2,100-2,300 m 3,289 30 1 0.052 0.052 101 0 0.156 171 172 101 0 514

2,300-2,500 m 57 1 0 0 0 0 0 0 0 0 0 0 0

2,500-2,700 m 0 0 - - - - - - - - - - -

all sampled strata 123,276 190 448 6.351 0.486 8 5.438 7.365 147,822 11,304 8 126,582 171,422

Vegetation Montane dry-mesic 

grass-shrubland 1,160 9 0 0 0 0 0 0 0 0 0 0 0

Montane dry forest & 

woodland 3,956 16 1 0.098 0.097 99 0 0.293 386 383 99 0 1,158

Montane mesic forest 9,423 82 323 11.235 1.042 9 9.364 13.284 105,869 9,817 9 88,233 125,174

Montane wet forest 3,510 41 107 6.081 1.039 17 4.261 8.401 21,344 3,645 17 14,956 29,487

Lowland wet-mesic 

forest 5,747 36 17 0.737 0.198 27 0.347 1.130 4,237 1,137 27 1,994 6,493

Lowland dry-mesic 

grass-shrubland 20 0 - - - - - - - - - - -

Introduced grassshrubland 1,489 2 0 0 0 0 0 0 0 0 0 0 0

Introduced forest 14 0 - - - - - - - - - - -

Barren and other 2,320 4 0 0 0 0 0 0 0 0 0 0 0

all sampled strata 127,605 190 448 4.776 0.384 8 4.057 5.563 131,836 10,590 8 111,998 153,561
51

E.9: Hawai‘i, north Kona – survey years 2003, 2009, and 2010 

Habitat 

variable Stratum Area (ha) K n 

Mean 

density SE CV (%)

Lower 

95% CI

Upper 

95% CI

Mean 

abundance SE CV (%)

Lower 

95% CI

Upper 

95% CI

Elevation 700-900 m 398 0 - - - - - - - - - - -

900-1,100 m 4,017 0 - - - - - - - - - - -

1,100-1,300 m 4,969 14 3 0.335 0.238 71 0 0.892 1,663 1,184 71 0 4,433

1,300-1,500 m 3,696 48 20 1.128 0.471 42 0.405 2.188 4,168 1,742 42 1,496 8,085

1,500-1,700 m 4,650 87 53 1.829 0.423 23 1.082 2.707 8,504 1,968 23 5,033 12,587

1,700-1,900 m 4,770 110 60 1.580 0.320 20 1.027 2.254 7,539 1,527 20 4,898 10,754

1,900-2,100 m 3,136 28 0 0 0 0 0 0 0 0 0 0 0

2,100-2,300 m 1,588 0 - - - - - - - - - - -

2,300-2,500 m 460 0 - - - - - - - - - - -

2,500-2,700 m 3 0 - - - - - - - - - - -

all sampled strata 121,221 287 136 1.031 0.156 15 0.740 1.366 21,873 3,303 15 15,704 28,986

Vegetation Montane dry-mesic 

grass-shrubland 1,274 7 0 0 0 0 0 0 0 0 0 0 0

Montane dry forest & 

woodland 7,068 121 0 0 0 0 0 0 0 0 0 0 0

Montane mesic forest 6,467 105 136 3.665 0.457 12 2.807 4.577 23,701 2,955 12 18,154 29,601

Montane wet forest 1,135 0 - - - - - - - - - - -

Lowland wet-mesic 

forest 5,354 0 - - - - - - - - - - -

Lowland dry-mesic 

grass-shrubland 1,248 39 0 0 0 0 0 0 0 0 0 0 0

Introduced grassshrubland 3,998 10 0 0 0 0 0 0 0 0 0 0 0

Introduced forest 22 0 - - - - - - - - - - -

Barren and other 1,085 5 0 0 0 0 0 0 0 0 0 0 0

all sampled strata 121,240 287 136 1.116 0.139 12 0.855 1.394 23,701 2,955 12 18,154 29,601

1 Total excludes unsampled strata areas.

53

Appendix F

Trends in occurrence of ‘I‘iwi (Vestiaria coccinea) by island- or region-specific consistently sampled area (CSA). The 

quantiles represent subsets of locations (that is, survey stations) at which ‘I‘iwi were detected, and range in elevation from 

0.05 (lowest), 0.50 (median) and 0.95 (highest). The parameter coefficient “intercept” specifies the initial mean elevation 

(that is, at first year of survey). The coefficient “slope” and associated statistics describe the magnitude and direction of the 

per-year trend in ‘I‘iwi occurrence by elevation.

F.1: Kaua‘i, interior and exterior

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1082 7.00 1.856 5.11 9.83 3.771 0.000

0.10 1136 4.08 1.868 1.37 6.96 2.186 0.029

0.25 1186 3.00 1.039 0.76 4.82 2.886 0.004

0.50 1232 2.60 1.098 0.01 4.58 2.368 0.018

0.75 1305 -0.08 1.659 -2.42 2.58 -0.050 0.960

0.90 1360 -0.75 1.415 -3.64 1.24 -0.530 0.596

0.95 1389 -1.50 0.973 -3.19 0.19 -1.542 0.124

F.2: Maui, northeast 

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1093 2.50 1.412 0.12 4.06 1.771 0.077

0.10 1162 2.71 1.543 0.42 4.95 1.759 0.079

0.25 1348 1.03 1.515 -0.99 3.61 0.681 0.496

0.50 1587 0.00 1.614 -2.48 2.61 0.000 1.000

0.75 1794 -0.55 1.284 -2.95 1.75 -0.427 0.669

0.90 1974 -1.53 1.717 -4.12 1.60 -0.889 0.374

0.95 2032 0.00 1.124 -2.20 0.41 0.000 1.000
54

F.3: Maui, southeast

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1159 -0.90 1.095 -2.86 0.03 -0.822 0.412

0.10 1188 -0.44 1.004 -1.86 0.35 -0.438 0.661

0.25 1361 -1.68 2.304 -4.28 2.28 -0.731 0.465

0.50 1623 -2.38 1.576 -5.90 0.15 -1.507 0.132

0.75 1877 -5.71 2.066 -9.32 -2.21 -2.766 0.006

0.90 2025 -4.53 1.600 -7.68 -2.33 -2.833 0.005

0.95 2087 -3.58 1.630 -7.72 -0.39 -2.198 0.028

F.4: Hawai‘i, Hakalau

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1487 -0.15 0.458 -0.64 1.62 -0.321 0.748

0.10 1514 -0.13 0.379 -0.63 0.66 -0.345 0.730

0.25 1582 -0.29 0.454 -1.23 0.80 -0.629 0.529

0.50 1671 -0.29 0.473 -1.50 0.58 -0.604 0.546

0.75 1788 -0.71 0.547 -1.89 0.25 -1.291 0.197

0.90 1871 -0.71 0.481 -1.46 0.09 -1.472 0.141

0.95 1891 -0.35 0.260 -0.63 0.27 -1.366 0.172

F.5: Hawai‘i, Keauhou

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1592 -0.54 0.399 -1.30 0.08 -1.361 0.174

0.10 1621 -0.62 0.462 -1.36 0.20 -1.338 0.181

0.25 1699 -0.75 0.505 -2.15 0.03 -1.486 0.137

0.50 1750 0.77 0.390 -0.60 1.84 1.973 0.050

0.75 1819 0.00 0.274 -0.81 0.14 0.000 1.000

0.90 1886 -0.69 0.380 -1.13 0.06 -1.823 0.068

0.95 1906 -0.67 0.367 -1.43 0.20 -1.814 0.070
55

F.6: Hawai‘i, Mauna Loa

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1544 -1.29 0.727 -1.60 0.08 -1.769 0.078

0.10 1545 0.00 0.764 -0.64 1.28 0.000 1.000

0.25 1560 3.69 2.146 -1.18 5.35 1.720 0.086

0.50 1709 1.67 2.466 -1.76 5.68 0.676 0.499

0.75 1825 -0.75 2.564 -4.31 4.53 -0.293 0.770

0.90 1916 1.64 2.481 -4.30 4.84 0.662 0.508

0.95 1977 0.50 1.673 -1.11 4.06 0.299 0.765

F.7: Hawai‘i, central Kona, mid-elevation (1,000–1,500 meters) 

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1094 0.62 1.458 -0.64 2.82 0.424 0.672

0.10 1159 0.31 1.409 -1.29 1.63 0.218 0.827

0.25 1251 0.50 1.381 -1.52 2.17 0.362 0.718

0.50 1359 -0.23 0.981 -1.95 1.54 -0.232 0.817

0.75 1424 -0.45 0.800 -2.10 1.81 -0.564 0.573

0.90 1464 -0.08 0.742 -1.38 1.42 -0.112 0.911

0.95 1479 0.00 0.537 -0.70 0.46 0.000 1.000

F.8: Hawai‘i, central Kona, upper-elevation (greater than or equal to 1,500 meters)

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1522 0.00 0.651 -1.23 1.00 0.000 1.000

0.10 1532 0.00 0.763 -1.21 1.34 0.000 1.000

0.25 1596 0.00 0.803 -1.02 1.48 0.000 1.000

0.50 1674 0.29 1.230 -2.58 2.45 0.232 0.816

0.75 1757 0.14 0.886 -1.28 2.25 0.161 0.872

0.90 1809 0.00 0.966 -1.06 1.69 0.000 1.000

0.95 1835 -0.39 0.673 -1.09 0.27 -0.581 0.561
56

F.9: Hawai‘i, Pu‘u Wa‘awa‘a

Quantile 

Intercept 

(initial 

elevation)

Slope SE Lower 

95% CI

Upper 

95% CI t-value Pr(>|t|)

0.05 1388 0.03 1.892 -2.17 2.38 0.017 0.986

0.10 1452 -0.68 2.188 -2.55 3.14 -0.310 0.757

0.25 1525 0.92 2.161 -1.75 4.26 0.427 0.670

0.50 1626 2.24 2.201 -2.19 4.60 1.018 0.311

0.75 1754 1.24 1.585 -2.62 3.63 0.782 0.436

0.90 1837 0.45 1.308 -1.31 1.78 0.345 0.730

0.95 1870 0.00 0.827 -0.32 0.93 0.000 1.000
57

Appendix G

Estimates of ‘I‘iwi density used in trend analyses by island- or region-specific consistently sampled area (CSA) (results 

presented in table 2). Year of survey from which estimates are derived is specified following each island- or region-specific 

name. Sample size (number of stations sampled) and detections (number of birds observed) are indicated with K and n, 

respectively. Mean annual density (birds per hectare) are reported with associated standard error (SE), percent coefficient of 

variation (%CV), and lower and upper 95-percent (95%) confidence intervals (CIs). Locations consisting of just two years 

of consistently sampled areas, especially using the HFBS data, are included here but not in the mani body of the report.

Island CSA Year K n Density SE %CV Lower 

95% CI

Upper 

95% CI

Kaua‘i interior 1981 140 546 2.798 0.146 5 2.512 3.083

1989 118 267 3.041 0.190 6 2.668 3.414

1994 111 110 1.722 0.179 10 1.371 2.072

2000 193 323 1.702 0.128 8 1.451 1.954

2005 173 84 0.967 0.111 11 0.750 1.185

2007 103 68 1.003 0.169 17 0.671 1.335

2008 173 96 1.093 0.133 12 0.832 1.354

2012 162 60 0.568 0.090 16 0.391 0.744

exterior 2000 261 326 1.401 0.123 9 1.160 1.642

2005 142 72 0.946 0.188 20 0.577 1.315

2007 104 19 0.298 0.115 39 0.073 0.523

2008 148 59 0.572 0.114 20 0.349 0.796

2012 153 30 0.169 0.056 33 0.058 0.279

both 2000 454 649 1.529 0.004 0 1.521 1.537

2005 315 156 0.958 0.006 1 0.946 0.969

2007 207 87 0.649 0.007 1 0.635 0.663

2008 321 155 0.853 0.005 1 0.843 0.863

2012 315 90 0.374 0.003 1 0.368 0.380

Maui northeast 1980 146 175 2.886 0.276 10 2.345 3.425

1992 146 335 6.401 0.364 6 5.688 7.110

1993 164 528 8.161 0.365 4 7.446 8.873

1998 94 251 6.842 0.591 9 5.684 7.993

1999 96 305 8.283 0.458 6 7.385 9.176

2000 112 400 9.815 0.498 5 8.840 10.785

2001 139 460 9.413 0.491 5 8.450 10.371

2005 111 371 8.348 0.400 5 7.565 9.127

2012 125 355 8.351 0.627 8 7.122 9.574

southeast 1980 273 268 2.356 0.198 8 1.968 2.741

1992 200 421 5.673 0.412 7 4.866 6.476

1996 56 278 5.091 0.660 13 3.798 6.379

2001 169 495 5.889 0.434 7 5.039 6.735

2006 178 401 4.322 0.276 6 3.781 4.860

2011 184 909 4.056 0.249 6 3.568 4.542
58

Island CSA Year K n Density SE %CV Lower 

95% CI

Upper 

95% CI

Hawai‘i Hakalau 1977 122 705 10.963 0.777 7 9.440 12.486

1999 233 1267 13.096 0.624 5 11.873 14.319

2000 339 2013 14.569 0.526 4 13.537 15.600

2001 323 1582 11.886 0.460 4 10.984 12.789

2002 324 1455 10.295 0.425 4 9.461 11.128

2003 329 1652 11.805 0.540 5 10.748 12.863

2004 326 1712 12.565 0.524 4 11.537 13.592

2005 288 1513 12.768 0.601 5 11.589 13.947

2006 277 1442 12.116 0.568 5 11.004 13.228

2007 274 1315 9.387 0.450 5 8.504 10.270

2008 292 1412 11.242 0.528 5 10.208 12.277

2010 248 1256 12.097 0.749 6 10.629 13.565

2011 255 1378 11.600 0.636 5 10.354 12.845

2012 271 1497 12.181 0.664 5 10.880 13.482

Waiakea 1977 120 263 2.971 0.221 7 2.537 3.405

2002 118 230 3.627 0.323 9 2.994 4.261

‘Ola‘a 1977 70 73 2.044 0.423 21 1.215 2.873

2010 68 12 0.272 0.112 41 0.051 0.492

Keauhou 1977 112 315 5.411 0.472 9 4.486 6.336

1995 244 2272 8.096 0.415 5 7.282 8.911

1996 117 554 6.879 0.771 11 5.368 8.390

1997 281 2603 7.045 0.308 4 6.441 7.649

1998 227 790 6.349 0.434 7 5.498 7.199

2002 196 701 6.253 0.373 6 5.523 6.984

2003 204 541 5.124 0.346 7 4.446 5.802

2005 188 516 4.968 0.350 7 4.281 5.655

2006 200 488 4.465 0.302 7 3.872 5.058

2007 199 650 4.688 0.416 9 3.873 5.503

2008 134 501 6.144 0.527 9 5.111 7.176

2009 201 557 4.889 0.351 7 4.200 5.577

2010 213 562 5.458 0.390 7 4.694 6.222

2011 212 660 6.175 0.436 7 5.320 7.029

2012 213 481 4.267 0.293 7 3.692 4.841

Mauna Loa 1978 98 62 1.099 0.246 22 0.617 1.580

1986 87 46 1.189 0.322 27 0.558 1.819

1987 85 152 0.838 0.239 28 0.370 1.306

1990 109 275 1.694 0.403 24 0.903 2.484

1991 112 219 2.544 0.347 14 1.863 3.224

1992 125 441 3.130 0.386 12 2.374 3.886

1993 138 175 1.790 0.253 14 1.294 2.286

1994 128 230 1.835 0.320 17 1.209 2.462
59

Island CSA Year K n Density SE %CV Lower 

95% CI

Upper 

95% CI

2010 77 29 0.635 0.194 31 0.255 1.016

north Ka‘ū 1976 40 69 2.724 0.592 22 1.563 3.885

2004 75 76 1.436 0.194 13 1.057 1.816

central Ka‘ū 1976 484 433 1.840 0.140 8 1.565 2.114

2008 238 69 0.586 0.127 22 0.337 0.835

south Ka‘ū 1978 72 20 0.581 0.174 30 0.240 0.922

2005 51 0 0 0 0 0 0

south Kona 1978 89 126 2.562 0.423 17 1.732 3.391

2009 43 5 0.145 0.087 60 -0.026 0.316

Honomalino 2005 46 21 0.694 0.199 29 0.303 1.085

2010 43 9 0.416 0.179 43 0.065 0.766

Central Kona -

upper

1978 22 71 3.852 0.720 19 2.441 5.264

1995 73 133 3.068 0.397 13 2.290 3.847

1999 71 219 8.536 0.862 10 6.846 10.225

2000 72 218 9.106 0.984 11 7.177 11.036

2001 70 237 7.693 0.780 10 6.165 9.222

2005 73 259 7.555 0.637 8 6.307 8.804

2006 64 243 10.464 1.296 12 7.923 13.005

2009 71 339 11.537 1.196 10 9.193 13.880

2012 72 233 6.488 0.655 10 5.205 7.771

Central Kona -

lower 1978 23 72 5.212 1.217 23 2.828 7.597

1995 58 117 4.523 0.993 22 2.577 6.469

1999 79 73 2.433 0.518 21 1.418 3.449

2000 79 93 2.947 0.607 21 1.757 4.137

2005 49 88 4.288 0.969 23 2.389 6.187

2009 73 178 5.179 0.723 14 3.762 6.596

2012 73 175 4.744 0.558 12 3.650 5.837

Pu‘u Wa‘awa‘a 1978 32 93 3.958 0.546 14 2.888 5.027

1990 34 38 2.189 0.578 26 1.056 3.322

1991 34 46 2.592 0.660 25 1.300 3.885

1996 33 24 1.320 0.439 33 0.459 2.180

2003 33 50 4.306 0.967 22 2.411 6.201

2009 34 52 3.888 0.879 23 2.166 5.611