ArticlePDF Available

Abstract and Figures

Limited resources for biodiversity conservation demand strategic science-based recovery efforts, particularly on islands, which are global hotspots of both endemism and extinction. The Akikiki (Oreomystis bairdi) and the Akekee (Loxops caeruleirostris) are critically endangered honeycreepers endemic to the Hawaiian island of Kauai. Recent declines and range contraction spurred investigation of the habitat characteristics influencing range-wide occupancyof these species. We surveyed Akikiki and Akekee and habitat covariates within 5 study areas on the Alakai Plateau of Kauai along a gradient of forest conditions. Occupancy rates for both species increased from west to east along theplateau (Akikiki: ψ=0.02 6 0.07 to 0.55 6 0.21; Akekee: ψ=0.03 6 0.10 to 0.53 6 0.33), but were low throughout the ranges of both species. Canopy height was positively correlated with occupancy for both species, which suggests thedamage done by hurricanes in 1982 and 1992 may be one factor restricting these birds to the most intact forest remaining. Vegetation surveys revealed several key differences in forest composition and structure between areas, indicative of broader changes occurring across the plateau. Invasive plants such as Himalayan ginger (Hedychium gardnerianum) were dominant in the western portion of the plateau, where there was a corresponding decline innative plant cover. Conversely, ground disturbance by feral ungulates was higher in more eastern native-dominated areas. These results highlight the need to protect habitat in the regions where Akikiki and Akekee occupancy ishighest, and restore habitat in other parts of their range. These actions should occur in concert with the mitigation of other known threats to Hawaiian honeycreepers such as avian disease. Without significant investment to address thesethreats and protect suitable habitat for these species, it is unclear how long these birds will persist.
Content may be subject to copyright.
Volume 118, 2016, pp. 148–158
DOI: 10.1650/CONDOR-15-80.1
RESEARCH ARTICLE
Occupancy and habitat use of the endangered Akikiki and Akekee
on Kauai Island, Hawaii
Lucas A. H. Behnke,
1,2,a
* Liba Pejchar,
1
and Lisa H. Crampton
2
1
Department of Fish, Wildlife and Conservation Biology, Colorado State University, Fort Collins, Colorado, USA
2
Department of Land and Natural Resources, Kauai Forest Bird Recovery Project, State of Hawaii, Hanapepe, Hawaii, USA
a
Current address: The Nature Conservancy, Hawaii Program, Lihue, Hawaii, USA
* Corresponding author: lbehnke@tnc.org
Submitted May 11, 2015; Accepted October 1, 2015; Published December 10, 2015
ABSTRACT
Limited resources for biodiversity conservation demand strategic science-based recovery efforts, particularly on
islands, which are global hotspots of both endemism and extinction. The Akikiki (Oreomystis bairdi) and the Akekee
(Loxops caeruleirostris) are critically endangered honeycreepers endemic to the Hawaiian island of Kauai. Recent
declines and range contraction spurred investigation of the habitat characteristics influencing range-wide occupancy
of these species. We surveyed Akikiki and Akekee and habitat covariates within 5 study areas on the Alakai Plateau of
Kauai along a gradient of forest conditions. Occupancy rates for both species increased from west to east along the
plateau (Akikiki: w¼0.02 60.07 to 0.55 60.21; Akekee: w¼0.03 60.10 to 0.53 60.33), but were low throughout the
ranges of both species. Canopy height was positively correlated with occupancy for both species, which suggests the
damage done by hurricanes in 1982 and 1992 may be one factor restricting these birds to the most intact forest
remaining. Vegetation surveys revealed several key differences in forest composition and structure between areas,
indicative of broader changes occurring across the plateau. Invasive plants such as Himalayan ginger (Hedychium
gardnerianum) were dominant in the western portion of the plateau, where there was a corresponding decline in
native plant cover. Conversely, ground disturbance by feral ungulates was higher in more eastern native-dominated
areas. These results highlight the need to protect habitat in the regions where Akikiki and Akekee occupancy is
highest, and restore habitat in other parts of their range. These actions should occur in concert with the mitigation of
other known threats to Hawaiian honeycreepers such as avian disease. Without significant investment to address these
threats and protect suitable habitat for these species, it is unclear how long these birds will persist.
Keywords: Hawaiian forest birds, invasive species, Loxops caeruleirostris,Oreomystis bairdi, range contraction,
habitat degradation, endangered species, feral ungulates
Ocupaci ´
on y uso de ha
´bitat de las especies amenazadas Oreomystis bairdi yLoxops caeruleirostris en la
isla Kauai, Hawaii
RESUMEN
Los limitados recursos para la conservaci ´
on de la biodiversidad demandan esfuerzos estrat´
egicos basados en ciencia,
particularmente en islas que son puntos calientes de endemismo y extinci ´
on. Oreomystis bairdi yLoxops caeruleirostris
son especies cr´
ıticamente amenazadas de la isla hawaiana de Kauai. Los declives poblacionales recientes y la
contracci ´
on de su distribuci ´
on geogra
´fica estimul ´
o la investigaci ´
on sobre las caracter´
ısticas del ha
´bitat que influyen en
la ocupaci ´
on del a
´rea de distribuci ´
on de estas especies. Estudiamos a O. bairdi yL. caeruleirostris y las covariables de su
ha
´bitat en cinco a
´reas de estudio en la meseta Alakai de Kauiai a lo largo de un gradiente de condiciones de bosque.
Las tasas de ocupaci ´
on para ambas especies se incrementaron de occidente a oriente a lo largo de la meseta (O. bairdi
w¼0.02 60.07 to 0.55 60.21; L. caeruleirostris:w¼0.03 60.10 to 0.53 60.33), pero fueron bajas a trav´
es de sus
distribuciones. La altura del dosel se correlacion ´
o positivamente con la ocupaci ´
on en ambas especies, lo que sugiere
que el da ˜
no causado por huracanes en 1982 y 1992 podr´
ıa ser un factor que restringe a estas aves a los remanentes de
bosque ma
´s intactos. Los censos de vegetaci ´
on revelaron varias diferencias clave en la composici´
on de los bosques y la
estructura entre a
´reas, lo que indica que ocurren cambios ma
´s amplios en la meseta. Las plantas invasoras como
Hedychium gardnerianium fueron dominantes en la porci ´
on occidental de la isla, mientras que hubo un declive
correspondiente en la cobertura de plantas nativas. Por el contrario, el disturbio en el suelo causado por ungulados
asilvestrados fue mayor en a
´reas dominadas por plantas nativas hacia el oriente. Estos resultados resaltan la necesidad
de proteger el ha
´bitat en las regiones donde la ocupaci ´
on de O. bairdi yL. caeruleirostris es ma
´s alta, y de restaurar el
ha
´bitat en otras partes de su distribuci ´
on. Estas acciones deben ocurrir en concierto con la mitigaci ´
on de otras
amenazas conocidas contra los mieleros hawaianos, como las enfermedades. Sin una inversi ´
on significativa para
Q2016 Cooper Ornithological Society. ISSN 0010-5422, electronic ISSN 1938-5129
Direct all requests to reproduce journal content to the Central Ornithology Publication Office at aoucospubs@gmail.com
enfrentar estas amenazas y proteger el ha
´bitat id ´
oneo para estas especies, no es claro por cua
´nto tiempo puedan
persistir.
Palabras clave: aves de bosque hawaianas, contracci ´
on de la distribuci ´
on, degradaci ´
on de ha
´bitat, especies
amenazadas, especies invasoras, Loxops caeruleirostris,Oreomystis bairdi, ungulados asilvestrados
INTRODUCTION
The loss of Hawaii’s endemic birds is well documented
(Perkins 1903, Olson and James 1982, Gorresen et al.
2009); since the arrival of humans, 68% of Hawaii’s 109
endemic bird species have gone extinct (Scott et al. 2001,
Reed et al. 2012). Of the remaining species, 33 are listed as
federally endangered, and several of these are likely already
extinct (Elphick et al. 2010, USFWS 2015). Thus, Hawaii
hosts over 30% of all listed bird species in the United
States, despite representing only 0.25% of its land mass.
The primary drivers of past extinctions and threats to
Hawaii’s extant forest birds are habitat loss and degradation,
predation by nonnative mammals, and introduced diseases
such as avian malaria (Scott et al. 1986, 2001, Pratt et al.
2009, VanderWerf 2009). These well-known causes of
decline, combined with climate change and stochastic events
such as hurricanes, threaten the persistence of Hawaiis
endemic forest birds (Benning et al. 2002). These threats are
particularly acute on relatively low-elevation islands such as
Kauai where all native forest is exposed to at least seasonal
transmission of avian disease (Atkinson et al. 2014).
Six extant forest bird species are endemic to Kauai,
including 2 honeycreepers recently listed as federally
endangered under the U.S. Endangered Species Act. The
2010 listing of the Akekee or Kauai Akepa (Loxops
caeruleirostris; Figure 1A) and Akikiki or Kauai Creeper
(Oreomystis bairdi;Figure1B),previouslyacandidate
species for over a decade, was prompted by declines in
abundance and apparent range contraction (Foster et al.
2004, VanderWerf and American Bird Conservancy 2007,
Camp and Gorresen 2010). Both species are restricted to
the Alakai Plateau, a remote area with relatively intact
native montane forest that comprises the summit of the
island (Foster et al. 2004; Figure 1C). Akikiki feed
primarily on arthropods by gleaning and flaking bark
along the boles and branches of live and dead canopy and
understory trees (Foster et al. 2000), and Akekee forage
primarily in the canopy of ohia (Metrosideros polymor-
pha)byusingtheirslightlycrossedbilltopryopen
terminal leaf nodes to extract invertebrates including
spiders, psyllids, and caterpillars (Lepson and Pratt 1997).
These 2 distinct foraging strategies may lead to different
patterns of habitat use across their current range.
Understanding these patterns in light of current and past
disturbance events (e.g., hurricane damage and invasive
species; Figure 1D) is important, particularly because
management interventions to improve habitat quality
maybemorefeasiblethanmitigatingdiseaseinthis
system in the near term.
Given the lack of protected status prior to 2010, the
remoteness of their current range, and low population
densities, neither species has been the subject of rigorous
scientific study. Although there are no quantitative data on
the habitat requirements, key threats, or potential conser-
vation measures for these 2 species, research on other
Hawaiian endemic birds has illuminated many of the causal
mechanisms of decline (Pratt et al. 2009). Understanding
the factors influencing habitat use (e.g., proportion of native
and introduced vegetation, predation, and disease) is
urgently needed to implement meaningful conservation
action. Acquiring this information before these birds
become too scarce for recovery is critical, as illustrated by
the recent extinction of the Poouli (Melamprosops phaeso-
ma) on another Hawaiian Island (VanderWerf et al. 2006).
The primary objective of this study was to determine
spatial patterns of occupancy and predictors of habitat use
of Akikiki and Akekee across their known range on the
Alakai Plateau, as defined by Foster et al. (2004) and Camp
and Gorresen (2010). Due to their flexibility, cost-
effectiveness, and relative ease of interpretation, occupancy
metrics have increasingly been used for assessing the status
and distribution of species of conservation concern (Noon
et al. 2012). This approach allows biologists to assess
population dynamics across a large spatial scale with
multiple species of concern (Bailey et al. 2007). We
estimated and compared probability of occupancy at 5
sites across the range of Akikiki and Akekee to assess
spatial trends, which could be correlated with changes in
habitat and/or disease prevalence. At the sites where
occupancy was high enough to do so, we coupled these
data with vegetation surveys and measures of habitat
disturbance by nonnative ungulates to provide insight into
predictors of current habitat use. Our second objective was
to examine potential differences in structure and compo-
sition across the Alakai Plateau to provide additional
insight into avian species distribution patterns in this last
remaining contiguous native forest on Kauai (USGS 2011).
Finally, we build on our results to recommend research
and management priorities for these species.
METHODS
Study Area
This study was conducted in the Alakai Wilderness
Preserve, Kokee State Park, and Na Pali Kona Forest
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
L. A. H. Behnke, L. Pejchar, and L. H. Crampton Occupancy and habitat use of Akikiki and Akekee 149
Reserve on the Alakai Plateau of Kauai Island, Hawaii
(228050N1598300W; Figure 2). The plateau is bounded to
the east by the highest point on the island, Mt. Kawaikini
(~1600 m), and by Kokee State Park to the west where the
elevation reaches just over 1000 m. The forest on the
plateau transitions from wet montane forest dominated by
ohia in the east, receiving ~900 cm of rain per year, to the
relatively mesic mixed ohia–koa (Acacia koa) in the west
with rainfall of 190 cm per year (Giambelluca et al. 2013).
Sampling Design
We measured occupancy of Akikiki and Akekee from
March to July 2012, and described habitat characteristics at
5 sites in 3 study regions (Figure 2). We chose study
regions based on recent estimates of the density and range
of Akikiki and Akekee (Foster et al. 2004, Camp and
Gorresen 2010), and took logistics (i.e. accessibility and
existing research infrastructure) into consideration. Two
study regions, East Alakai (EAK) and Mohihi (MOH), had
medium to high densities of both Akikiki and Akekee
according to recent quantitative data (Foster et al. 2004,
Camp and Gorresen 2010). The third study region,
Kawaikoi (KWK), previously supported medium densities
of Akikiki and Akekee (Foster et al. 2004), but few birds
were observed during subsequent surveys in 2005 and
2008 (Camp and Gorresen 2010). Although KWK is more
mesic than EAK or MOH, all 3 regions are dominated by
native ohia canopy and a diverse understory of native
shrubs and ferns, with varying cover of nonnative plants
(Figure 1).
Within each study region, we randomly located 2 non-
overlapping 100-ha polygons for our study sites using ESRI
ArcGIS (Version 10.1; ESRI, Redlands, California, USA)
and generated a random point within each polygon as a
starting point for area searches. Two study sites were
established at KWK (K1 and K2) and EAK (E1 and E2).
FIGURE 1. Photographs of the study species and contrasting habitat conditions, Kauai, Hawaii. (A) Akekee (Loxops caeruleirostris),
photo by Lucas Behnke. (B) Akikiki (Oreomystis bairdi), photo by Robby Kohley. (C) Relatively intact native forest with high mean
canopy cover typical of EAK. Photo by Maria Costantini. (D) Degraded forest with invasive ginger and blackberry typical of KWK.
Photo by Ruby Hammond.
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
150 Occupancy and habitat use of Akikiki and Akekee L. A. H. Behnke, L. Pejchar, and L. H. Crampton
Due to logistical and topographic constraints, the original
2 study sites at MOH were merged into one (M1),
resulting in a total of 5 study sites across the 3 study
regions (Figure 2). During a pilot study in 2011, we
searched and mapped territories (Bibby et al. 2000)
outward in all directions from the random starting point
within each study site, as permitted by topography, until
we found .10 territories or covered 75–100 ha; the
amount of area covered in 2011 determined the size of the
occupancy study sites in 2012. Within each of the 5 study
sites we established a systematic grid of sampling points
based on a new random starting location (Figure 2). At
each point we conducted occupancy surveys and measured
habitat variables.
Occupancy Surveys
Following the sampling guidelines in MacKenzie et al.
(2002) and Bailey et al. (2007), we quantified occupancy of
Akikiki and Akekee in each study site by conducting
repeated surveys at sampling points in each of the 5 study
sites (n¼70–96). Points were spaced 100 m apart, which
slightly exceeded the farthest known distance traveled by a
color-banded Akikiki during regular resighting efforts
from 2007 to 2010 (Hawaii Division of Forestry and
Wildlife personal communication). The placement of our
sampling grids intercepted several point–line transects
used for long-term population monitoring across the
Alakai Plateau, which facilitated comparison of our results
to previously collected data (Foster et al. 2004; Camp and
Gorresen 2010).
Following MacKenzie and Royle (2005), we surveyed
occupancy at each point at least 3 times during the
breeding season. At each point, we separated the survey
into 2 periods. In the first, we passively surveyed and
recorded presence/absence of all bird species for 4 min. In
the second period, we recorded only presence or absence
of Akikiki and Akekee for an additional 4 min, during
which we intermittently broadcasted short (5–10 sec) call
or song segments of each species, alternating between
species, for a total of ~1 min per species. Detections were
so sparse that we pooled both time periods in our analyses.
To model detection probability (p), we also recorded
sampling covariates including observer, sustained wind
speed, highest gust speed, precipitation, and cloud cover.
Two primary assumptions of standard single-season
occupancy modeling are that occupancy at a particular
survey point, w
i
, is constant for the entire season and that
sampling points are independent (MacKenzie et al. 2002).
FIGURE 2. Location and distribution of sampling points across 3 study regions (KWK, MOH, EAK) containing the 5 study sites
Kawaikoi West (K1), Kawaikoi East (K2), Mohihi (M1), Halehaha (H1), and Halepaakai (H2) on the Alakai plateau on Island of Kauai
(Hawaii, USA) where occupancy and habitat surveys were conducted for Akikiki and Akekee.
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
L. A. H. Behnke, L. Pejchar, and L. H. Crampton Occupancy and habitat use of Akikiki and Akekee 151
The assumption of constant occupancy is likely to have
been met based on personal observation and long-term
bird survey data (Camp and Gorresen 2010). If, as in the
case of a species with a particularly large home range,
survey points cannot be assumed to be independent or
occupancy during the season is not constant (i.e. an
individual is away from a survey location when it is
sampled), then the interpretation of wand pmust be
adapted (MacKenzie et al. 2006). Although the sampling
design used in this study was based on previously observed
movement of the focal species, during the study both
Akikiki and Akekee were observed moving longer
distances than the 100 m between sampling points, leading
to our interpretation of was ‘‘use’’ of a particular point
within the study site, and pas ‘‘detection’’ given that the
sampling point was ‘‘used.’ Thus our use of the term
‘‘occupancy’’ is not specifically intended as a metric of
abundance, but rather as a measure of relative habitat use
across the landscape.
Vegetation Surveys
We collected data on habitat characteristics at every other
bird survey point at the 3 low-occupancy sites and at every
point at the 2 high-occupancy sites (n¼223; Figure 2).
This sampling design was selected to evaluate the
influence of vegetation structure and composition on
habitat use by the focal species at the sites where the
species were most abundant. Circular vegetation plots
measuring 100 m
2
were centered on the sampling points
(Camp 2011). At each plot, we measured vegetation
variables within 25 m
2
quadrants systematically placed at
4 locations at the edge of the plot in each cardinal
direction.
We collected data on ground, shrub, and canopy
structure and composition, and feral pig (Sus scrofa)
disturbance within each vegetation plot. We measured
forest profile, an index of understory density, as the
proportion of a modified Robel pole obscured by
vegetation at heights of 0–1 m (fp1) and 1–2 m (fp2)
when viewed from each cardinal direction while placed at
the center of the plot (Robel et al. 1970). We estimated
total % shrub cover (sct) within each quadrant as cover of
vegetation greater than 1 m tall, and the proportion of
native shrub cover (scn) was also estimated for each
quadrant. We estimated total % ground cover (gct) and
proportion of native ground cover (gcn) inside a 1 m
2
quadrat on the counterclockwise side of the edge of the
plot in each cardinal point. We estimated canopy density
(den) at each cardinal point using a spherical densiometer.
We estimated canopy height (ht) using an electronic range
finder and clinometer. To summarize variables for each
plot, we used the mean of measurements taken from each
cardinal point (fp1, fp2, ht, den), the mean percent cover
from the 4 quadrants (sct, scn), and the mean percent
ground cover within the 4 quadrats (gct, gcn). We
measured moss cover (moss) on all trees greater than 10
cm diameter at breast height by taking an estimate of the
tree surface area covered by moss from breast height to 1
m above breast height. The mean of all moss measure-
ments recorded in the plot was calculated and used in
analyses. Maximum diameter at breast height (mdbh) from
each plot was also used in analyses. We also measured the
total area (m
2
) of relatively recent pig sign (pig) in each
plot by summing the area covered by scat, digging, or trails
that appeared to be less than 3 months old.
Statistical Analysis
We used Program PRESENCE (Hines 2006) to (1) estimate
and compare occupancy (w) of the 2 focal species among
study regions and sites based on the most parsimonious
model for each species (Anderson 2008), and (2)
investigate relationships between habitat and occupancy
in the EAK region while accounting for detection
probability (p). For each focal species, we used Akaike’s
Information Criterion adjusted for small sample size
(AIC
c
), a likelihood-based information theoretic approach
to model selection (Anderson 2008). First we assessed
detection probability by constructing models of all
combinations of sampling covariates. We then used the
resulting best model (DAIC
c
¼0) to construct sets of
covariates using region, site, and habitat to predict
occupancy, while holding detection probability constant
for each species. To investigate occupancy probability
across the range of Akikiki and Akekee, we compared
region and site as covariates to determine the best model
for each species. The specific predictions tested were that
(1) occupancy is lower in the west (KWK), higher in the
east (EAK), and intermediate at MOH for both species
(models with region as the covariate); and (2) that regional
trends in occupancy are more detectable than differences
between study sites.
For the EAK study region where detections were most
frequent, we examined habitat use of each species by
constructing models with normalized covariate data from
habitat surveys as predictor variables and occupancy as the
dependent variable. The normalized value was the differ-
ence between a given value and the mean of the sample,
divided by the standard deviation. Given the small sample
size, these models were restricted to 3 covariates to limit the
number of parameters, with the exception of one global (all
covariates) model for comparison. Because we were most
interested in the relative importance of habitat covariates,
we model-averaged parameter estimates (Burnham and
Anderson 2002) to reduce bias and account for model
selection uncertainty (Doherty et al. 2012). The predictions
we examined, based on each species’ biology, were that (1)
for Akikiki, a subcanopy trunk-and-bole gleaner, occupancy
is best predicted by an open understory, tall canopy stature,
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
152 Occupancy and habitat use of Akikiki and Akekee L. A. H. Behnke, L. Pejchar, and L. H. Crampton
and large tree diameter; and (2) Akekee occupancy is best
predicted by high canopy cover.
To gain insights into bird distribution where occupancy
was too sparse to model against habitat predictors, we also
analyzed differences in habitat characteristics (dependent
variables) among the study sites across the Alakai plateau
(independent variable) in a multivariate analysis of
variance (MANOVA). Based on prior observation, we
predicted that habitat structure (e.g., canopy height and
canopy density) would vary across the plateau, with forest
stature generally increasing from west to east in our study
area. We also predicted that disturbance metrics (e.g.,
invasive plant cover and feral pig disturbance) would
decrease from west to east, and be undetectable in the EAK
study region. We used an arcsine transformation of habitat
variables involving count or percentage data to meet the
assumption of normality. Data based on continuous
measurements (canopy height and diameter at breast
height) were not transformed. We used Pillai’s Trace
statistic to assess significance, followed by post-hoc one-
way analysis of variance (ANOVA) using least significant
differences (LSD) and t-tests (a¼0.05) in SPSS (PASW
Statistics 18; IBM, Armonk, New York, USA). Figures and
results are presented as untransformed or back-trans-
formed means 6SE.
RESULTS
Detection Probability and Occupancy across the Study
Area
Detection probability was low for both species (Akikiki p¼
0.63 60.40; Akekee p¼0.30 60.19). It was negatively
affected by highest gust speed during the survey period for
both species, and by survey month for Akekee. For Akekee,
pwas highest in May, slightly lower in March–April, and
lowest in June. As predicted, we found an increasing trend
in estimates of occupancy (w) for each species from west to
east (Figure 3). For Akikiki, the region covariate was
included in the best model of w, and the best model for
Akekee included the site covariate (Table 1). Akikiki
occupancy was substantially greater in the eastern EAK
region (w: 0.55 60.21) compared with the other 2 regions
(KWK w: 0.02 60.07 and MOH w: 0.04 60.10; Figure
3A). Akekee occupancy increased gradually from west to
east across study sites, and only differed substantially
between K1 and H2 sites (w¼0.03 60.10 and w¼0.53 6
0.33, respectively; Figure 3B).
Occupancy as a Function of Habitat Variables in the
East Alakai Region
Occupancy of both species varied as a function of tree size
within EAK. Akekee and Akikiki occupancy were positively
correlated with mean canopy height (Figure 4A,B; Akikiki:
b¼479.6 60.71, Akekee b¼0.142 60.074). Akikiki were
FIGURE 3. Occupancy estimates for Akikiki by study region (A) and for Akekee by study site (B). Figures report means 695% CI.
TABLE 1. Model results for occupancy (w) across the range of
Akikiki and Akekee. Results are by species and include model
sets comparing survey data grouped by region (n¼3) and by
site (n¼5) with the number of estimated parameters (K), the
maximized log-likelihood (2*LogL), the simple difference of
second-order Akaike’s Information Criterion adjusted for small
sample size (DAIC
c
) and the Akaike weight (w
i
) for each model.
Species Model K2*LogLDAIC
c
w
i
Akikiki w(region), p(g) 6 253.8 0 0.83
w(site), p(g) 8 252.81 3.16 0.17
Akekee w(site), p(gþmonth) 11 531.2 0 0.99
w(region), p(gþmonth) 9 545.09 9.68 0.01
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
L. A. H. Behnke, L. Pejchar, and L. H. Crampton Occupancy and habitat use of Akikiki and Akekee 153
absent from survey points where mean canopy height was
10 m or less (Figure 4A). Mean canopy height was present
in 9 of the top 10 models for Akikiki and 3 of the top 4
models for Akekee (Table 2). Maximum diameter at breast
height of ohia also was positively correlated with
occupancy and was present in 8 of the top 10 candidate
models for Akekee (b¼0.019 60.012), while canopy
density was positively associated with Akikiki occupancy
(b¼32.7 67.9) and was present in several top models
(Table 2).
Comparing Habitat Characteristics among Study Sites
In the MANOVA, habitat characteristics differed signifi-
cantly across the 5 study sites (Pillai’s Trace 1.18, F¼
3188.72, df ¼9, a¼0.05). Tests of the between-subjects
effects showed significant differences (a¼0.05) between 7
of the 9 variables sampled (Table 3). Forest profile, total
shrub cover (Figure 5A), native shrub cover (Figure 5B),
mean canopy height (Figure 5C), and moss cover all
showed significant differences between at least 2 of the
sites (p¼,0.001); total ground cover, and pig sign (Figure
5D) also differed significantly among sites (p¼0.001 and
p¼0.002, respectively). Maximum ohia diameter and
canopy density did not differ significantly among sites. The
westernmost study site (K1) differed from the other study
sites for most structural variables, and contributed to the
overall difference between regions.
FIGURE 4. Relationship between occupancy (w) and model-
averaged mean canopy height (ht) for Akikiki (A) and Akekee (B)
in the East Alakai (EAK) study region.
TABLE 2. Model results for Akikiki and Akekee occupancy (w)as
predicted by habitat characteristics in the East Alakai (EAK) study
region. Models with DAIC
c
.4 have been excluded, with the
exception of the global model for Akekee, which contains all
covariates. See Table 1 for column header definitions. See Table
3 for definition of model parameters.
Species Model K2*LogLDAIC
c
w
i
Akikiki w(fp2þht), p(g) 5 208.04 0.00 0.22
w(global), p(g) 11 194.79 0.24 0.19
w(sctþdenþht), p(g) 6 206.49 0.62 0.16
w(denþht), p(g) 5 209.46 1.42 0.11
w(denþhtþpig), p(g) 6 208.55 2.68 0.06
w(gctþsctþden), p(g) 6 208.60 2.73 0.06
w(ht), p(g) 4 213.54 3.36 0.04
w(gctþht), p(g) 5 211.44 3.40 0.04
w(htþpig), p(g) 5 211.63 3.59 0.04
Akekee w(htþmdbh), p(gþmonth) 9 278.60 0.00 0.26
w(htþpigþmdbh), p(gþmonth) 10 277.80 1.49 0.12
w(mdbh), p(gþmonth) 8 283.41 2.54 0.07
w(htþmoss), p(gþmonth) 9 281.24 2.64 0.07
w(pigþmdbh), p(gþmonth) 9 281.89 3.29 0.05
w(mdbhþgct), p(gþmonth) 9 282.13 3.53 0.04
w(gctþmdbh), p(gþmonth) 9 282.13 3.53 0.04
w(ht), p(gþmonth) 8 284.79 3.92 0.04
...
w(global), p(gþmonth) 15 274.29 9.98 0.00
TABLE 3. MANOVA results showing multivariate effects of study site on habitat variables measured at bird survey stations on the
Alakai plateau (a¼0.05).
Dependent variable Abbreviation Df FSig. Partial eta squared
Forest profile 1–2 m (%) fp2 4 5.977 ,0.001 0.101
Shrub cover: total (%) sct 4 7.292 ,0.001 0.121
Shrub cover: native (%) scn 4 88.18 ,0.001 0.625
Canopy height: mean (m) ht 4 11.9 ,0.001 0.183
Moss cover: average (%) moss 4 16.28 ,0.001 0.235
Ground cover: total (%) gct 4 5.014 0.001 0.086
Pig sign (m
2
) pig 4 4.507 0.002 0.078
Canopy density (%) den 4 1.491 0.206 0.027
Ohia diameter: maximum (cm) mdbh 4 0.951 0.436 0.018
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
154 Occupancy and habitat use of Akikiki and Akekee L. A. H. Behnke, L. Pejchar, and L. H. Crampton
DISCUSSION
Akikiki and Akekee, both single-island endemics, have
nearly disappeared from their last remaining habitat. Our
results demonstrate that occupancy rates within this
narrow range are extremely low for both species, even
when compared to another endangered Kauai passerine,
the Puaiohi (Myadestes palmeri), across a similar range (L.
H. Crampton personal observation), and other federally
listed species in the U.S. (e.g., Golden-cheeked Warbler,
Setophaga chrysoparia; Reidy et al. 2015). As predicted and
corroborated by spatial patterns of bird density, there is a
slight increase toward the eastern end of the Alakai Plateau
(Foster et al. 2004, Camp and Gorresen 2010). Even
compared to surveys published only 11 (Foster et al. 2004)
and 5 (Camp and Gorresen 2010) years ago, our results
indicate that the range of these species continues to
contract. Where Akikiki and Akekee were still present, we
documented a correlation between occupancy and forest
characteristics, such as canopy height. Across the range of
these species, native shrub cover was associated with
higher occupancy, and feral pig sign appeared to be
associated with intermediate occupancy. These range-wide
patterns suggest that controlling invasive plants and
restoring native plant cover, fencing remaining habitat,
and eradicating or reducing the density of feral pigs in this
region is critical to the survival of these Hawaiian
honeycreepers. Even with significant protection from
other threats, avian disease is likely to increasingly limit
forest bird range and populations on Kauai (Atkinson et al.
2014); thus other conservation measures, such as mosquito
control, captive breeding, and translocation outside of
their historical range, should be considered.
The difference between Akikiki occupancy in the central
and western regions (KWK, MOH) and the eastern region
(EAK) was large and abrupt (Figure 3A). In contrast, Akekee
occupancy declined gradually from east to west (Figure 3B).
Although these trends are based on only one year of data,
FIGURE 5. The habitat characteristics ‘‘shrub cover’’ (A, B), ‘‘canopy height’’ (C), and ‘‘pig sign’(D) vary across study sites from west
to east on the Alakai plateau. Figures report means 695% CI.
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
L. A. H. Behnke, L. Pejchar, and L. H. Crampton Occupancy and habitat use of Akikiki and Akekee 155
which limits our inference, these findings are consistent
with the results of long-term bird surveys (Foster et al.
2004). The dissimilar pattern of occupancy among Akikiki
and Akekee could be a result of different resource
requirements and foraging behavior. For example, as canopy
foragers, Akekee can cover large distances more readily than
Akikiki in order to access available canopy resources. The
cumulative effect of changes in forest structure, spread of
nonnative vegetation, disturbance by feral pigs, and the slow
recovery of the native forest following Hurricanes Iwa
(1982) and Iniki (1992), are other factors that may shape the
distribution of both species across the plateau. Additional
research on potentially important drivers of survival and
reproductive success—such as nest predation by introduced
rats, which caused some Akikiki nest failure (Hammond et
al. 2015), and avian malaria, which is increasing across this
east–west gradient (Atkinson et al. 2014)—is critical to
developing a comprehensive strategy for the conservation
and recovery of these species.
The relationship between occupancy and habitat
characteristics at EAK may provide insights into habitat
use of these species across the plateau, which could not be
measured directly because occupancy was too low outside
of this study region. Habitat data from EAK indicated that
canopy height and density were strongly associated with
occupancy for Akikiki. This species is primarily an
understory, branch- and bole-foraging ‘‘creeper’’ (Foster
et al. 2000), so it is not surprising that canopy density may
be an important predictor of occupancy; closed-canopy
ohia forest provides a high degree of foraging structure.
Contrary to our predictions, however, canopy height
appears to be a better indicator of occupancy than
understory density. This result may indicate that Akikiki
prefer mature forest, possibly because of greater availabil-
ity of food resources, and may explain the near absence of
these species from KWK and MOH, where mean canopy
height is well below the threshold 10-m canopy height that
predicts occupancy at EAK (Figure 4A). The lack of a
significant difference between EAK and KWK in other
factors apparently important to Akikiki occupancy, such as
maximum ohia diameter (mdbh) and canopy cover (den),
may indicate that disease transmission also may limit
Akikiki occupancy in KWK; malaria prevalence is greater
at KWK than EAK (Atkinson et al. 2014). The positive
relationship between Akekee occupancy and canopy height
and maximum ohia diameter (mdbh) indicates that this
species, a canopy-foraging ‘‘crossbill’’ (Lepson and Pratt
1997), may preferentially use habitat with large trees. This
observation is consistent with our prediction that Akekee
occupancy would be related to canopy density, and further
indicates that large, mature trees are particularly important
resources for this species.
The weak relationship between weed cover, disturbance,
and occupancy in the EAK region may be attributable to
the low variation in these predictor variables among
vegetation plots in the EAK study area. While there was no
detectable effect on occupancy within regions, these
factors may be important determinants of occupancy
among regions, but could not be examined directly
because so few birds were detected at regions other than
EAK. Vegetation characteristics and ungulate disturbance
did vary across the range of these species, with the lowest
proportions of native plant cover found in the western-
most region (KWK), and the highest incidence of pig sign
in the more central region (MOH), i.e. in the regions where
occupancy of these 2 species, especially Akikiki, was
lowest. We also found moderate levels of pig sign in the
easternmost region (EAK), which we had predicted to
contain the most intact native forest, and where we
documented the highest occupancy of Akikiki and Akekee.
Management in the MOH and EAK regions, including
weed control but not ungulate removal, has likely slowed
the invasion of habitat-modifying plants such as Hima-
layan ginger (Hedychium gardnerianum) and strawberry
guava (Psidium cattleianum). The evidence of damage by
pigs, which are vectors for the spread of nonnative plant
species in Hawaii (Simberloff and Van Holle 1999) and
which may create habitat for larval mosquitoes, is of
immediate concern. Lack of active ungulate management
in this region may facilitate the spread of invasive species
and continued degradation of an area that currently
supports the highest occupancy of Kauai’s rarest forest
birds.
Recommendations for Research and Management
To build on these findings, we recommend consistent
population-level monitoring to detect trends over time,
and research to investigate other factors that may
synergistically contribute to the decline of these species.
Our results suggest that occupancy may provide a useful
conservation metric for these and other rare species.
Traditional line–transect point counts provide important
baseline data on range and population size of Kauai’s forest
bird community (Foster et al. 2004, Gorresen et al. 2009).
However, as these and other species become increasingly
rare and more difficult to detect, the amount of effort and
funding necessary to provide good estimates of population
size and habitat use with this method becomes untenable
(Camp and Gorresen 2010). By estimating detection
probability, we also provided a quantitative measure of
the difficulty of detecting these species that could help
guide future survey efforts (MacKenzie et al. 2002).
In addition to monitoring Akikiki and Akekee to assess
trends over time and the effectiveness of future manage-
ment actions, research to address knowledge gaps on other
threats to these species is of high priority. Specifically, we
recommend continued investigation of management
techniques such as ungulate fencing, invasive plant and
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
156 Occupancy and habitat use of Akikiki and Akekee L. A. H. Behnke, L. Pejchar, and L. H. Crampton
rat removal, and attempting mosquito control to limit
disease transmission, to evaluate the relative importance of
these factors for population dynamics and habitat use.
Both the continued control of invasive plants and the
removal of feral ungulates from these areas are likely to
increase the resiliency of the Alakai Plateau’s forests,
possibly providing time for the birds themselves to adapt
to avian disease (Kilpatrick 2006). For example, the
implementation of current plans to fence and remove
ungulates from ~3,000 acres surrounding the study region
with the highest bird densities (Hawaii Department of
Land and Natural Resources 2011) will be critical for
halting the degradation of the last strongholds of the
Akikiki and Akekee.
Given the low occupancy and increasingly narrow range
of these 2 species, we emphasize that immediate conser-
vation action based on the best available science is
essential. There is, however, a significant lag time in the
recovery of the habitats that support these species.
Additionally, climate change is predicted to exacerbate
existing stressors to Kauai’s forest birds through increased
disease transmission (Benning et al. 2002, LaPointe et al.
2009, Atkinson et al. 2014) and by further limiting
availability of food and suitable foraging and nesting
habitat. If disease or nonnative predators are the most
important threats to these species, habitat management
alone will not be sufficient to prevent their extinction on
Kauai. In response to this threat, eggs of both species were
collected and a captive breeding program was initiated in
2015 (L. H. Crampton personal observation). If the
synergistic effects of climate change, disease, and other
factors make Kauai uninhabitable, the only option for
sustaining Akikiki and Akekee in the wild will be to
establish new populations in suitable habitat outside their
known historic range where disease and predators are
minimal or absent.
ACKNOWLEDGMENTS
P. K. Roberts was instrumental in initially guiding and grant
writing for this work. The research would not have been
possible without the dedicated full-time and seasonal field
staff of the Kauai Forest Bird Recovery Project, including B.
Heindl, R. Hammond, L. Solomon, A. Wang, B. Williams, M.
Walters, and Americorps interns C. Hagen, J. Liebrecht, and
N. Ozaki, as well as volunteer data entry assistance by K.
Maling. We are especially grateful for statistical advice from L.
Bailey, and for comments that improved earlier drafts of this
manuscript from J. Vetter, D. Leonard, R. Camp, and 2
anonymous reviewers.
Funding statement: We thank the U.S. Fish and Wildlife
Service Pacific Islands Fish and Wildlife Office, the State of
Hawaii Division of Forestry and Wildlife, and the Warner
College of Natural Resources at Colorado State University for
generously funding this research. None of our funders had any
influence on the content of the submitted or published
manuscript nor did they require approval of the final
manuscript to be published.
Ethics statement: All research was conducted following an
IACUC protocol submitted through Colorado State Univer-
sity (Protocol ID: 10-2395A) and followed applicable federal
and state regulations and permitting procedures.
Author contributions: L.A.H.B., L.P., and L.H.C. conceived
the idea and design. L.A.H.B. collected the data. L.A.H.B., L.P.,
and L.H.C. wrote the paper. L.A.H.B. analyzed the data. L.P.
and L.H.C. contributed substantial materials, resources, and
funding.
LITERATURE CITED
Anderson, D. R. (2008). Model Based Inference in the Life
Sciences: A Primer on Evidence. Springer, New York, NY, USA.
Atkinson, C. T., R. B. Utzurrum, D. A. Lapointe, R. J. Camp, L. H.
Crampton, J. T. Foster, and T. W. Giambelluca (2014).
Changing climate and the altitudinal range of avian malaria
in the Hawaiian Islands—an ongoing conservation crisis on
the island of Kauai. Global Change Biology. doi:10.1111/gcb.
12535.
Bailey, L. L., J. E. Hines, J. D. Nichols, and D. I. MacKenzie (2007).
Sampling design trade-offs in occupancy studies with
imperfect detection: Examples and software. Ecological
Applications 17:281–290.
Benning, T. L., D. LaPointe, C. T. Atkinson, and P. M. Vitousek
(2002). Interactions of climate change with biological
invasions and land use in the Hawaiian Islands: Modeling
the fate of endemic birds using a geographic information
system. Proceedings of the National Academy of Sciences
USA 99:14246–14249.
Bibby, C. J., N. D. Burges, D. A. Hill, and S. H. Mustoe (2000). Bird
Census Techniques, 2nd ed. Academic Press, London, United
Kingdom.
Burnham, K. P., and D. R. Anderson (2002). Model Selection and
Multimodel Inference: A Practical Information-Theoretic
Approach, 2nd ed. Springer-Verlag, New York, NY, USA.
Camp, R. J. (2011). Standard operating procedure (SOP) #8,
documenting landbird habitat, Version 1.00. In Landbirds
Vital Sign Monitoring Protocol–Pacific Island Network (R. J.
Camp, T. K. Pratt, C. Bailey, and D. Hu). Natural resources
report NPS/PWR/PACN/NRR. National Park Service, Oakland,
CA, USA.
Camp, R. J., and P. M. Gorresen (2010). Design of forest bird
monitoring for strategic habitat conservation on Kauai Island,
HI. U.S. Fish and Wildlife Service, Portland, OR, USA.
Department of Land and Natural Resources, State of Hawaii
(2011). The rain follows the forest: A plan to replenish
Hawaii’s source of water. http://dlnr.hawaii.gov/rain/files/
2014/02/The-Rain-Follows-the-Forest.pdf
Doherty, P. F., G. C. White, and K. P. Burnham (2012). Comparison
of model building and selection strategies. Journal of
Ornithology 152:317–323.
Elphick, C. S., D. L. Roberts, and J. M. Reed (2010). Estimated
dates of recent extinctions for North American and Hawaiian
birds. Biological Conservation 143:617–624.
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
L. A. H. Behnke, L. Pejchar, and L. H. Crampton Occupancy and habitat use of Akikiki and Akekee 157
Foster, J. T., J. M. Scott, and P. W. Sykes Jr. (2000). Akikiki
(Oreomystis bairdi). In The Birds of North America Online (A.
Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA.
doi:10.2173/bna.552.
Foster, J. T., E. J. Tweed, R. J. Camp, B. L. Woodworth, C. D. Adler,
and T. Telfer (2004). Long-term population changes of native
and introduced birds in the Alakai Swamp, Kaua’i. Conserva-
tion Biology 18:716–725.
Giambelluca, T. W., Q. Chen, A. G. Frazier, J. P. Price, Y. L. Chen,
P.-S. Chu, J. K. Eischeid, and D. M. Delparte (2013). Online
rainfall atlas of Hawaii. Bulletin of The American Meteoro-
logical Society 94:313–316. doi:10.1175/BAMS-D-11-00228.1.
Gorresen, P. M., R. J. Camp, M. H. Reynolds, B. L. Woodworth, and
T. K. Pratt (2009). Status and trends of native Hawaiian
songbirds. In Conservation Biology of Hawaiian Forest Birds:
Implications for Island Avifauna (T. K. Pratt, C. T. Atkinson, P.
C. Banko, J. D. Jacobi, B. L. Woodworth, Editors). Yale
University Press, New Haven, CT, USA. pp. 108–193.
Hammond, R. H., L. H. Crampton, and J. T. Foster (2015).
Breeding biology of two endangered forest birds on the
island of Kauai, Hawaii. The Condor: Ornithological Applica-
tions 117:31–40.
Hines, J. E. (2006). PRESENCE2 – Software to estimate patch
occupancy and related parameters. USGS-PWRC, Laurel, MD,
USA. http://www.mbr-pwrc.usgs.gov/software/presence.html
Kilpatrick, A. M. (2006). Facilitating the evolution of resistance to
avian malaria (Plasmodium relictum) in Hawaiian birds.
Biological Conservation 128:475–485.
LaPointe, D. A., C. T. Atkinson, and S. I. Jarvi (2009). Managing
disease. In Conservation Biology of Hawaiian Forest Birds:
Implications for Island Avifauna (T. K. Pratt, C. T. Atkinson,
P. C. Banko, J. D. Jacobi, and B. L. Woodworth, Editors). Yale
University Press, New Haven, CT, USA. pp. 405–424.
Lepson, J. K., and H. D. Pratt (1997). Akekee (Loxops caeruleir-
ostris). In The Birds of North America Online (A. Poole, Editor).
Cornell Lab of Ornithology, Ithaca, NY, USA. doi:10.2173/bna.
295.
MacKenzie, D. I., J. D. Nichols, G. B. Lachman, S. Droege, J. A.
Royle, and C. A. Langtimm (2002). Estimating site occupancy
rates when detection probabilities are less than one. Ecology
83:2248–2255.
MacKenzie, D. I., and J. A. Royle (2005) Designing occupancy
studies: General advice and allocating survey effort. Journal
of Applied Ecology 42:1105–1114.
MacKenzie, D. I., J. D. Nichols, J. A. Royle, K. P. Pollock, L. L. Bailey,
and J. E. Hines (2006). Occupancy Estimation and Modeling:
Inferring Patterns and Dynamics of Species Occurrence.
Academic Press, San Diego, CA, USA.
Noon, B. R., L. L. Bailey, T. D. Sisk, and K. S. McKelvey (2012).
Efficient species-level monitoring at the landscape scale.
Conservation Biology 26:432–441.
Olson, S. L., and H. F. James (1982). Fossil birds from the
Hawaiian Islands: Evidence for wholesale extinction by man
before Western contact. Science 217:633–635.
Perkins, R. C. L. (1903). Vertebrata. In Fauna Hawaiiensis, Vol. I, pt.
IV (D. Sharp, Editor). University Press, Cambridge, England.
pp. 365–466.
Pratt, T. K., C. T. Atkinson, P. C. Banko, J. D. Jacobi, and B. L.
Woodworth (Editors) (2009). Conservation Biology of Hawai-
ian Forest Birds: Implications for Island Avifauna. Yale
University Press, New Haven, CT, USA.
Reed, J. M., D. W. Desrochers, E. A. VanderWerf, and J. M. Scott
(2012). Long-term persistence of Hawaii’s endangered
avifauna through conservation-reliant management. BioSci-
ence 62:881–892.
Reidy, J. L., F. R. Thompson, C. Amundson, and L. O’Donnell
(2015). Landscape and local effects on occupancy and
densities of an endangered wood-warbler in an urbanizing
landscape. Landscape Ecology doi:10.1007/s10980-015-0250-0.
Robel, R. J., J. N. Briggs, A. D. Dayton, and L. C. Hulbert (1970).
Relationships between visual obstruction measurements and
weight of grassland vegetation. Journal of Range Manage-
ment 23:295–297.
Scott, J. M., S. Mountainspring, F. L. Ramsey, and C. B. Kepler
(1986). Forest Bird Communities of the Hawaiian Islands:
Their Dynamics, Ecology, and Conservation. Studies in Avian
Biology 9.
Scott J. M, S. Conant, and C. Van Riper III (Editors) (2001).
Evolution, Ecology, and Management of Hawaiian Birds: A
Vanishing Avifauna. Studies in Avian Biology 22.
Simberloff, D., and B. Von Holle (1999). Positive interactions of
nonindigenous species: Invasional meltdown? Biological
Invasions 1:21–32.
U.S. Fish and Wildlife Service (2015). Environmental Conservation
Online System (ECOS): Listed Species Believed or Known to
Occur in Hawaii. http://ecos.fws.gov/tess_public/reports/
species-listed-by-state-report?state¼HI&status¼listed.
U.S. Geological Survey (2011). Gap Analysis Program (GAP):
National Land Cover, Version 2.0.
VanderWerf, E. A., J. J. Groombridge, J. S. Fretz, and K. J.
Swinnerton (2006). Decision analysis to guide recovery of the
Poouli, a critically endangered Hawaiian honeycreeper.
Biological Conservation 129:383–392.
VanderWerf, E. A., and American Bird Conservancy (2007).
Petition to list the Akikiki or Kauai Creeper (Oreomystis bairdi)
and the Akekee or Kauai Akepa (Loxops caeruleirostris)as
endangered or threatened under the U.S. Endangered
Species Act. Submitted to the U.S. Fish and Wildlife Service,
October 2007.
VanderWerf, E. A. (2009). Importance of nest predation by alien
rodents and avian poxvirus in conservation of Oahu Elepaio.
Journal of Wildlife Management 73:737–746.
The Condor: Ornithological Applications 118:148–158, Q2016 Cooper Ornithological Society
158 Occupancy and habitat use of Akikiki and Akekee L. A. H. Behnke, L. Pejchar, and L. H. Crampton
... Diet strongly affects microbiome composition across taxa (Pascoe et al., 2017;Youngblut et al., 2019;Teyssier et al., 2020) ʻAkikiki and ʻakekeʻe are both insectivorous species with almost entirely overlapping ranges (Behnke, Pejchar & Crampton, 2016). Nonetheless, the two species forage in different canopy levels and use different foraging techniques (Foster, Scott & Sykes, 2000;Lepson & Pratt, 1997), which may indicate niche partitioning. ...
... Samples were collected from across the Alakaʻi Plateau on the island of Kauaʻi, Hawaiʻi, representing the remaining range of both species in the wild (Fig. 1). The main field site of the study, Halepaʻakai, is located on the eastern side of the plateau and contains the highest occupancy of both species (Behnke, Pejchar & Crampton, 2016). They are also observed with less frequency, at the Upper Kawaikōi field site. ...
... Halepaʻakai is considered the last stronghold for the species, where most of the population exists. Furthermore, it is a relatively pristine, undisturbed forest with minor inundation by non-native vegetation (Behnke, Pejchar & Crampton, 2016). In contrast, the sub-population at Upper Kawaikōi was recently discovered in 2018 and represented a small fraction of the total population. ...
Article
Full-text available
Background The gut microbiome of animals is an important component that has strong influence on the health, fitness, and behavior of its host. Most research in the microbiome field has focused on human populations and commercially important species. However, researchers are now considering the link between endangered species conservation and the microbiome. In Hawaiʻi, several threats ( e.g ., avian malaria and habitat loss) have caused widespread population declines of Hawaiian honeycreepers (subfamily: Carduelinae). These threats can have a significant effect on the avian gut microbiome and may even lead to disruption of microbial function. However, the gut microbiome of honeycreeper in the wild has yet to be explored. Methods We collected 13 and 42 fecal samples, respectively, from two critically endangered honeycreeper species, the ʻakikiki ( Oreomystis bairdi ) and the ʻakekeʻe ( Loxops caeruleirostris ). The 16S rRNA gene was sequenced and processed though a MOTHUR-based bioinformatics pipeline. Bacterial ASVs were identified using the DADA2 program and bacterial community analyses, including alpha and beta diversity measures, were conducted using R packages Phyloseq and vegan . Results A total of 8,958 bacterial ASVs were identified from the fecal samples. Intraspecific differences in the gut microbiome among individual birds explained most of the variation present in the dataset, however differences between species did exist. Both species had distinct microbiomes with minimal overlap in beta diversity. ‘Akikiki had a more diverse microbiome compared to ‘akekeʻe. Additionally, small but stastically significant differences in beta diversity also exist between sampling location and sexes in ʻakikiki. Conclusion ʻAkikiki and ʻakekeʻe are currently the focus of captive breeding efforts and plans to translocate the two species to other islands are underway. This baseline knowledge will help inform management decisions for these honeycreeper species in their native habitats, on other islands, and in captivity.
... Adequate canopy structure is therefore critical to Akikiki survival and influences their current distribution. Previous work has shown that Akikiki occur in greater numbers in areas with tall and dense tree canopies (Behnke et al. 2016) and that their occupancy and density varied across their range: northwestern portions exhibited the lowest occupancy and densities while southeastern areas had higher occupancy and densities (Behnke et al. 2016, Paxton et al. 2016. This gradient corresponds positively with changes in elevation, precipitation, and vegetation metrics, including native shrub cover and canopy height (Behnke et al. 2016). ...
... Adequate canopy structure is therefore critical to Akikiki survival and influences their current distribution. Previous work has shown that Akikiki occur in greater numbers in areas with tall and dense tree canopies (Behnke et al. 2016) and that their occupancy and density varied across their range: northwestern portions exhibited the lowest occupancy and densities while southeastern areas had higher occupancy and densities (Behnke et al. 2016, Paxton et al. 2016. This gradient corresponds positively with changes in elevation, precipitation, and vegetation metrics, including native shrub cover and canopy height (Behnke et al. 2016). ...
... Previous work has shown that Akikiki occur in greater numbers in areas with tall and dense tree canopies (Behnke et al. 2016) and that their occupancy and density varied across their range: northwestern portions exhibited the lowest occupancy and densities while southeastern areas had higher occupancy and densities (Behnke et al. 2016, Paxton et al. 2016. This gradient corresponds positively with changes in elevation, precipitation, and vegetation metrics, including native shrub cover and canopy height (Behnke et al. 2016). ...
Article
Full-text available
Abstract The Akikiki (Oreomystis bairdi) and Akekee (Loxops caeruleirostris) are two honeycreepers endemic to Kauai, Hawaii, that were listed as federally endangered in 2010. Both species are rare, little‐studied, and occur in a remote, roadless area. We analyzed high‐resolution airborne lidar data to identify forest structure and topography metrics associated with Akikiki and Akekee nest locations (88 for Akikiki and 22 for Akekee) and occurrences (3706 for Akikiki and 1581 for Akekee) from 2012 to 2017 on the Alakai Plateau to predict their distribution in unsurveyed areas. Akikiki and Akekee nested in areas with similar forest structure at 10 m resolution, but different maximum tree heights. Akikiki and Akekee foraged in areas with significantly different forest structure (maximum tree height, mean canopy height, relative heights) and topography (slope) based on occurrences. Elevation was consistently one of the most important metrics for predicting both species nest locations and occurrences across scales (10, 100, 250 m) and it appears that both species are at the upper limits of their elevational range. We estimate that the area of suitable nesting habitat for Akikiki is 17.59 km2 while the area of suitable nesting habitat for Akekee is 11.10 km2 at 10 m resolution. The Akikiki has a potential range of 38 km2 while the Akekee has a range of 58 km2 at 100 m resolution. We produce predictive nest and occurrence maps at 10 m and 100 m resolutions to spatially target conservation actions. Results suggest that if avian malaria cannot be controlled and both species populations do not stabilize over the coming years, translocation may be needed to insure their viability.
... Average annual rainfall is 2800 mm at Kawaikoi and 3600 mm at Mohihi [49]. Both sites are characterized by wet montane forest dominated by the canopy tree ohia lehua (Metrosideros polymorpha), with no differences in ohia lehua canopy cover or tree diameter [50] Other common canopy and sub-canopy trees include ohia ha (Syzygium sandwicensis), lapalapa (Cheirodendron platyphyllum), olapa (Cheirodendron trigynum), alani (Melicope spp.), and manono (Kadua terminalis). The understory is dominated by woody plants such as ohelo (Vaccinium calycinum), kanawao (Broussaisia arguta), haha aiakamanu (Clermontia fauriei), pilo (Coprosoma sp.), pukiawe (Styphelia tameiameiae), uki uki (Dianella sandwicensis) and ohenaupaka (Scaevola glabra). ...
... The understory is dominated by woody plants such as ohelo (Vaccinium calycinum), kanawao (Broussaisia arguta), haha aiakamanu (Clermontia fauriei), pilo (Coprosoma sp.), pukiawe (Styphelia tameiameiae), uki uki (Dianella sandwicensis) and ohenaupaka (Scaevola glabra). Himalayan ginger (Hedychium gardnerianum), thimbleberry (Rubus parviflorus) and blackberry (Rubus argutus) are introduced invasive plants present at both sites but particularly abundant at Kawaikoi [50]. A third introduced invasive species, strawberry guava (Psidium cattleianum), occurs only along a few streams in Kawaikoi. ...
... All sampling points were located in or adjacent to current or previously occupied Puaiohi territories in Kawaikoi and Mohihi. These points were selected from occupancy survey locations previously established by the Kauai Forest Bird Recovery Project (KFBRP) at both study sites [50] (Fig 1). Because Puaiohi are so rare, the best index of Puaiohi relative abundance is occupancy, which was surveyed on both Kawaikoi and Mohihi in 2011. ...
Article
Full-text available
Hawaii has experienced a catastrophic decline in frugivorous native birds coupled with the introduction of non-native species. Puaiohi (Myadestes palmeri), a critically endangered thrush, is the sole extant native songbird capable of dispersing fleshy fruited plants in the rainforest of Kauai island, Hawaii. As this species has declined to occupy a small proportion of its original range, a suite of largely omnivorous non-native birds have been introduced to this region, including the common and widespread Japanese White-eye (Zosterops japonicus). This reshuffling of the bird community could have long-term implications for plant community composition if introduced birds incompletely replace the ecological role of native species. The objective of this study was to evaluate the potential consequences of the local extirpation of Puaiohi for seed dispersal. Specifically, we compared the diet of Puaiohi and Japanese White-eye, vegetation characteristics, and seed rain at sites with and without Puaiohi in the Na Pali-Kona Forest Reserve on the island of Kauai. We found high overlap in the composition of seeds consumed by the two bird species, but differences in the characteristics of seeds consumed; Japanese White-eye appeared more likely to consume smaller seeded species compared with Puaiohi. Sites with Puaiohi received substantially higher seed rain during the study period, despite no significant differences in overall fruit abundance. Our results suggest that non-native birds are unlikely to completely replace the seed dispersal services provided by Puaiohi. If Puaohi continue to be rare and range restricted, we predict a shift in plant community composition through an increase in non-native and small-seeded plants, and possible dispersal failure of other native species. Our findings lend further support to efforts to conserve Puaiohi across its current and former range, and to consider introductions to other suitable areas to ensure the persistence not only of the species and but also its functional role in Hawaii’s montane ecosystems.
... However, breeding Rusty Blackbirds in New England have been found to nest up to 400 m away from wetlands, and fledglings can move over 1 km away from their nests within a few weeks of fledging [37], so we were not able to assume that site occupancy was constant throughout the study period. Thus, we considered sites with at least one positive Rusty Blackbird detection to be "used" rather than "occupied" [38]. ...
Article
Full-text available
The Rusty Blackbird (Euphagus carolinus) is an imperiled migratory songbird that breeds in and near the boreal wetlands of North America. Our objective was to investigate factors associated with Rusty Blackbird wetland use, including aquatic invertebrate prey and landscape features, to better understand the birds’ habitat use. Using single-season occupancy modeling, we assessed breeding Rusty Blackbird use of both active and inactive beaver-influenced wetlands in New Hampshire and Maine, USA. We conducted timed, unlimited-radius point counts of Rusty Blackbirds at 60 sites from May to July 2014. Following each point count, we sampled aquatic invertebrates and surveyed habitat characteristics including percent mud cover, puddle presence/absence, and current beaver activity. We calculated wetland size using aerial imagery and calculated percent conifer cover within a 500 m buffer of each site using the National Land Cover Database 2011. Percent mud cover and invertebrate abundance best predicted Rusty Blackbird use of wetlands. Rusty Blackbirds were more likely to be found in sites with lower percent mud cover and higher aquatic invertebrate abundance. Sites with Rusty Blackbird detections had significantly higher abundances of known or likely prey items in the orders Amphipoda, Coleoptera, Diptera, Odonata, and Trichoptera. The probability of Rusty Blackbird detection was 0.589 ± 0.06 SE. This study provides new information that will inform habitat conservation for this imperiled species in a beaver-influenced landscape.
... Hawaiian native forest birds have been a major focus of conservation efforts in Hawai'i Pratt, 1994). This species group has experienced multiple extinctions (Gorresen, Camp, Reynolds, Woodworth, & Pratt, 2009;Ohlemuller et al., 2008) and today is mostly absent from lower elevations primarily due to habitat loss and the introduction of avian malaria and its mosquito vector (Atkinson et al., 2014;Behnke, Pejchar, & Crampton, 2015;Benning, LaPointe, Atkinson, & Vitousek, 2002;van Riper & Scott, 2001). Hawai'i's sharp climatic gradients have allowed the native bird species to persist in higher elevation areas where avian malaria cannot develop and mosquito densities are low (Benning et al., 2002;van Riper, van Riper, Goff, & Laird, 1986). ...
Article
Full-text available
Hawaiian forest birds are imperiled, with fewer than half the original >40 species remaining extant. Recent studies document ongoing rapid population decline and project complete climate-based range losses for the critically endangered Kaua'i endemics ‘akeke’e (Loxops caeruleirostris) and ‘akikiki (Oreomystis bairdi) by end-of-century due to projected warming. Climate change facilitates the upward expansion of avian malaria into native high elevation forests where disease was historically absent. While intensified conservation efforts attempt to safeguard these species and their habitats, the magnitude of potential loss and the urgency of this situation require all conservation options to be seriously considered. One option for Kaua’i endemics is translocation to islands with higher elevation habitats. We explored the feasibility of interisland translocation by projecting baseline and future climate-based ranges of ‘akeke’e and ‘akikiki across the Hawaiian archipelago. For islands where compatible climates for these species were projected to endure through end-of-century, an additional climatic niche overlap analysis compares the spatial overlap between Kaua’i endemics and current native species on prospective destination islands. Suitable climate-based ranges exist on Maui and Hawai'i for these Kaua'i endemics that offer climatically distinct areas compared to niche distributions of destination island endemics. While we recognize that any decision to translocate birds will include assessing numerous additional social, political, and biological factors, our focus on locations of enduring and ecologically compatible climate-based ranges represents the first step to evaluate this potential conservation option. Our approach considering baseline and future distributions of species with climatic niche overlap metrics to identify undesirable range overlap provides a method that can be utilized for other climate-vulnerable species with disjointed compatible environments beyond their native range.
... The dominant canopy tree is 'ōhi'a (Metrosideros polymorpha), with koa (Acacia koa) codominant in drier areas in the west. The higher elevations contain some of the most intact native ecosystems left in Hawai'i, but invasive alien plants occur throughout the native forest and are dominant in some parts of the plateau, especially in lower elevation areas (28). All eight native forest bird species on Kaua'i are restricted to the Alaka'i Plateau. ...
Article
Full-text available
The viability of many species has been jeopardized by numerous negative factors over the centuries, but climate change is predicted to accelerate and increase the pressure of many of these threats, leading to extinctions. The Hawaiian honeycreepers, famous for their spectacular adaptive radiation, are predicted to experience negative responses to climate change, given their susceptibility to introduced disease, the strong linkage of disease distribution to climatic conditions, and their current distribution. We document the rapid collapse of the native avifauna on the island of Kaua‘i that corresponds to changes in climate and disease prevalence. Although multiple factors may be pressuring the community, we suggest that a tipping point has been crossed in which temperatures in forest habitats at high elevations have reached a threshold that facilitates the development of avian malaria and its vector throughout these species’ ranges. Continued incursion of invasive weeds and non-native avian competitors may be facilitated by climate change and could also contribute to declines. If current rates of decline continue, we predict multiple extinctions in the coming decades. Kaua‘i represents an early warning for the forest bird communities on the Maui and Hawai‘i islands, as well as other species around the world that are trapped within a climatic space that is rapidly disappearing.
Article
Many species around the world are declining precipitously as a result of multiple threats and changing climate. Managers tasked with protecting species often face difficult decisions in regard to identifying which threats should be addressed, given limited resources and uncertainty in the success of any identified management action. On Kaua‘i Island, Hawai‘i, USA, forest bird species have experienced accelerated declines over the last 20 years, and 2 species, the ‘akikiki (Oreomystis bairdi) and ‘akeke‘e (Loxops caeruleirostris), are now at the brink of extinction. Both species face multiple threats, and managers face difficult decisions on whether to mitigate threats in the wild, establish a captive population as insurance against extinction, translocate birds to novel locations, or some combination of these actions. Each set of actions (alternatives) would require substantial resources with considerable uncertainty in success. In 2014, we brought together 14 experts representing biologists and managers familiar with the species and island to develop a conservation strategy under a structured decision making (SDM) framework, an approach for making complex decisions under uncertainty. The group's challenge was to identify a set of alternatives that reduces the risk of extinction, set the foundation for one or more genetically viable, reproducing, stable to increasing populations in 10 years, and promote conditions for long‐term persistence in the wild. Multiple alternatives were evaluated, via expert judgement, in terms of the probability they would achieve the objectives concerning immediate extinction risk, near‐term viability, and adequacy of habitat. Factors that might impede the success of each action were also evaluated. The process identified the establishment of a captive population and efforts to stabilize the existing wild population as the approach most likely to meet the objectives of preventing imminent extinction and ensuring long‐term viability. On Kaua‘i Island, Hawai‘i, two forest bird species, the ‘akikiki (Oreomystis bairdi) and ‘akeke‘e (Loxops caeruleirostris), are at the brink of extinction. Both species face multiple threats, and managers face difficult decisions on whether to mitigate threats in the wild, establish a captive population as insurance against extinction, translocate birds to novel locations, or some combination of these actions. This paper summarizes the results of a structured decision making (SDM) process to identify a set of conservation actions to reduce the risk of extinction and set the foundation for stable to increasing populations in 10 years.
Article
Full-text available
Population sizes of endemic songbirds on Kaua‘i have decreased by an order of magnitude over the past 10–15 years to dangerously low numbers. The primary cause appears to be the ascent of invasive mosquitoes and Plasmodium relictum, the agent of avian malaria, into elevations formerly free of introduced malarial parasites and their vectors. Given that these declines in native bird populations appear to be continuing, last resort measures to save these species from extinction, such as conservation breeding, are being implemented. Using 200–1439 SNPs from across the genome, we assessed kinship among individuals, levels of genetic variation, and extent of population decline in wild birds of the two most critically endangered Kaua‘i endemic species, the ‘akikiki (Oreomystis bairdi) and ‘akeke‘e (Loxops caeruleirostris). We found relatively high genomic diversity within individuals and little evidence of spatial population genetic structure. Populations displayed genomic signatures of declining population size, but individual inbreeding coefficients were universally negative, likely indicating inbreeding avoidance. Diversity within the founding conservation breeding population largely mirrored that in the wild, indicating that genetic variation in the conservation breeding population is representative of the wild population and suggesting that the current breeding program captures existing variation. Thus, although existing genetic diversity is likely lower than in historical populations, contemporary variation has been retained through high gene flow and inbreeding avoidance. Nonetheless, current effective population size for both species was estimated at fewer than 20 individuals, highlighting the urgency of management actions to protect these species.
Article
‘Ōhi‘a lehua is a species of tree endemic to the islands of Hawai‘i. Its existence is vital to the survival of many pollinator insects and endangered bird species and to the integrity of multiple islands’ watersheds. Rapid ‘Ōhi‘a Death (ROD) is an emerging fungal disease that poses a significant health risk for these trees and is spread by human traffic, ambrosia beetles, and wind dispersal. Loss of ‘ōhi’a forests will negatively affect Hawai‘i’s economy and ecology and will have detrimental impacts on Hawaiian culture, particularly because of the role of lehua flowers in hula. While transmission of ROD Death is not yet fully understood, human activity is currently considered the main proponent of its spread. Hawai‘i’s economy is largely built on the tourism industry; however, tourists are often unaware of the disease and the practices implemented to contain the current outbreak while visiting the Hawaiian Islands. ROD is a conservation issue that connects humans with the environment and must be addressed using a one-health perspective. This article aims to elucidate the anthropogenic factors contributing to the depletion of ‘ōhi‘a lehua through the spread of ROD and to propose prevention measures that can be adopted by citizens and visitors. At the end of this case study, readers will understand the cultural, ecological, and economic significance of ‘ōhi’a lehua. Readers will also be able to identify important stakeholders and examine the complexity of behavior change in conservation issues.
Article
Full-text available
Accurate estimates of the distribution and abundance of endangered species are crucial to determine their status and plan recovery options, but such estimates are often difficult to obtain for species with low detection probabilities or that occur in inaccessible habitats. The Puaiohi (Myadestes palmeri) is a cryptic species endemic to Kauaʻi, Hawai‘i, and restricted to high elevation ravines that are largely inaccessible. To improve current population estimates, we developed an approach to model distribution and abundance of Puaiohi across their range by linking occupancy surveys to habitat characteristics, territory density, and landscape attributes. Occupancy per station ranged from 0.17 to 0.82, and was best predicted by the number and vertical extent of cliffs, cliff slope, stream width, and elevation. To link occupancy estimates with abundance, we used territory mapping data to estimate the average number of territories per survey station (0.44 and 0.66 territories per station in low and high occupancy streams, respectively), and the average number of individuals per territory (1.9). We then modeled Puaiohi occupancy as a function of two remote-sensed measures of habitat (stream sinuosity and elevation) to predict occupancy across its entire range. We combined predicted occupancy with estimates of birds per station to produce a global population estimate of 494 (95% CI 414–580) individuals. Our approach is a model for using multiple independent sources of information to accurately track population trends, and we discuss future directions for modeling abundance of this, and other, rare species.
Article
Full-text available
Context Golden-cheeked warblers (Setophaga chrysoparia), an endangered wood-warbler, breed exclusively in woodlands co-dominated by Ashe juniper (Juniperus ashei) in central Texas. Their breeding range is becoming increasingly urbanized and habitat loss and fragmentation are a main threat to the species’ viability. Objectives We investigated the effects of remotely sensed local habitat and landscape attributes on point occupancy and density of warblers in an urban preserve and produced a spatially explicit density map for the preserve using model-supported relationships. Methods We conducted 1507 point-count surveys during spring 2011–2014 across Balcones Canyonlands Preserve (BCP) to evaluate warbler habitat associations and predict density of males. We used hierarchical Bayesian models to estimate multiple components of detection probability and evaluate covariate effects on detection probability, point occupancy, and density. Results Point occupancy was positively related to landscape forest cover and local canopy cover; mean occupancy was 0.83. Density was influenced more by local than landscape factors. Density increased with greater amounts of juniper and mixed forest and decreased with more open edge. There was a weak negative relationship between density and landscape urban land cover. Conclusions Landscape composition and habitat structure were important determinants of warbler occupancy and density, and the large intact patches of juniper and mixed forest on BCP (>2100 ha) supported a high density of warblers. Increasing urbanization and fragmentation in the surrounding landscape will likely result in lower breeding density due to loss of juniper and mixed forest and increasing urban land cover and edge.
Article
Full-text available
Transmission of avian malaria in the Hawaiian Islands varies across altitudinal gradients and is greatest at elevations below 1,500 m where both temperature and moisture are favorable for the sole mosquito vector, Culex quinquefasciatus, and extrinsic sporogonic development of the parasite, Plasmodium relictum. Potential consequences of global warming on this system have been recognized for over a decade with concerns that increases in mean temperatures could lead to expansion of malaria into habitats where cool temperatures currently limit transmission to highly susceptible endemic forest birds. Recent declines in two endangered species on the island of Kaua'i, the 'Akikiki (Oreomystis bairdi) and 'Akeke'e (Loxops caeruleirostris), and retreat of more common native honeycreepers to the last remaining high elevation habitat on the Alaka'i Plateau suggest that predicted changes in disease transmission may be occurring. We compared prevalence of malarial infections in forest birds that were sampled at three locations on the Plateau between 1994-1997 and again between 2007-2013, and also evaluated changes in the occurrence of mosquito larvae in available aquatic habitats during the same time periods. Prevalence of infection increased significantly at the lower (1,100 m, 10.3% to 28.2%), middle (1,250 m, 8.4% to 12.2%) and upper ends of the Plateau (1,350 m, 2.0% to 19.3%). A concurrent increase in detections of Culex larvae in aquatic habitats associated with stream margins indicates that populations of the vector are also increasing. These increases are at least in part due to local transmission because overall prevalence in Kaua'i 'Elepaio (Chasiempis sclateri), a sedentary native species, has increased from 17.2% to 27.0%. Increasing mean air temperatures, declining precipitation, and changes in streamflow that have taken place over the past 20 years are creating environmental conditions throughout major portions of the Alaka'i Plateau that support increased transmission of avian malaria. This article is protected by copyright. All rights reserved.
Article
Two forest bird species endemic to the island of Kauai in the Hawaiian Archipelago were listed under the U.S. Endangered Species Act in 2010 due to recent population declines. This research represents the first comprehensive breeding biology study of both species, the 'Akikiki or Kauai Creeper (Oreomystis bairdi) and 'Akeke'e or Akekee (Loxops caeruleirostris). The 2-year study was initiated in 2012 to determine if low nesting success may be a cause of their population declines. We monitored 20 'Akikiki and 8 'Akeke'e nests to assess basic nesting biology parameters (e.g., brood size; nest height; length of construction, incubation, and nestling periods) and to derive estimates of nesting success and investigate causes of failure. In general, 'Akikiki and 'Akeke'e breeding biology was similar to other insectivorous Hawaiian honeycreepers. Mean nest height for 'Akikiki and 'Akeke'e was high (9.2 +/- 2.3 m SD and 11.1 +/- 2.3 m SD, respectively) compared to most Kauai forest birds. Nesting success, calculated using program MARK, was 0.77 +/- 0.12 SE for 'Akikiki and 0.71 +/- 0.17 SE for 'Akeke'e. Three 'Akikiki and 2 'Akeke'e nests failed. One 'Akikiki nest failed due to nest predation and the other 2 to unknown causes. One 'Akeke'e nest failed due to poor nest attendance and the other to hatching failure. Nest sample sizes were small and should be considered with caution; however, these results suggest that low nesting success may not be a primary cause of decline in these species. Future research on both species should assess post-fledging, juvenile, and adult survival as potential causes of their populations' declines. Determining which demographic parameters currently have the largest negative impact on these populations is imperative for guiding effective management actions to conserve these species.
Article
Visual obstruction measurements were used to determine height and density of vegetation in a Kansas grassland. These visual obstruction measurements were compared with the weight of vegetation collected from each site. The weight of vegetation collected was significantly correlated with the visual obstruction measurements.
Book
Science is about discovering new things, about better understanding processes and systems, and generally furthering our knowledge. Deep in science philosophy is the notion of hypotheses and mathematical models to represent these hypotheses. It is partially the quantification of hypotheses that provides the illusive concept of rigor in science. Science is partially an adversarial process; hypotheses battle for primacy aided by observations, data, and models. Science is one of the few human endeavors that is truly progressive. Progress in science is defined as approaching an increased understanding of truth – science evolves in a sense.