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Offspring quality is an important issue in avian life-history theory, particularly with regard to birds that have low reproductive rates and extended parental care. Offspring mass has been identified as an indicator of quality in several bird species. These studies have shown that nestling mass is predictive of offspring survival outside the nest, but few studies have considered the role of fledgling mass. Mass during the fledgling period may change and influence juvenile survival. Fledgling mass may be especially relevant for tropical birds that have very long fledgling periods during which food conditions randomly or seasonally change. Here, we show that fledgling mass predicts juvenile survival in the Hawaii Akepa (Loxops coccineus coccineus), an endangered Hawaiian Honeycreeper with high annual adult survival and a two-egg clutch. Juvenile survival of Hawaii Akepa approximated a trimodal pattern of no survival, low survival, and high survival that corresponded to ascending mass classes. Fledglings in the highest mass class had an apparent juvenile survival probability that was more than double that of fledglings of the lower mass classes and that was statistically indistinguishable from survival rates of adults. This mass-dependent juvenile survival has important implications for understanding the life-history evolution and population biology of the Hawaii Akepa and perhaps of other tropical birds. La calidad de las crías es un aspecto importante de la teoría sobre las historias de vida de las aves, particularmente para las que presentan tasas reproductivas bajas y cuidado parental extendido. La masa de las crías ha sido identificada como un indicador de la calidad en varias especies de aves. Esos estudios han mostrado que la masa de los pichones predice la supervivencia de las crías fuera del nido, pero pocos estudios han considerado el papel de la masa de los volantones al momento de abandonar el nido. La masa durante el período de emplumamiento puede cambiar e influenciar la supervivencia de las aves jóvenes. La masa de los volantones podría ser especialmente relevante para las aves tropicales que tienen períodos de emplumamiento muy largos, durante los cuales las condiciones cambian aleatoria o estacionalmente. En este estudio demostramos que la masa de emplumamiento predice la supervivencia de las aves jóvenes en Loxops coccineus coccineus, una especie de mielero hawaiano amenazada que presenta una supervivencia anual de los adultos alta y una nidada de dos huevos. La supervivencia de los jóvenes se aproximó a un patrón trimodal de no supervivencia, supervivencia baja y supervivencia alta, que correspondió a una escala creciente de clases de masa. Los volantones en la clase de masa más alta presentaron una probabilidad de supervivencia aparente de más del doble en comparación con la de los volantones de las clases de masa menores, y su tasa de supervivencia fue estadisticamente indistinguible de la de las aves adultas. Esta supervivencia dependiente de la masa en las aves jóvenes tiene implicaciones importantes para entender la evolución de la historia de vida y la biología poblacional de L. c. coccineus y quizás de otras aves tropicales.

Many wildlife monitoring programmes collect annual data on population abundance. The resulting abundance estimates fluctuate over time partly because of true population change and partly because of observation error. These two components of variation can be separated by fitting the estimates to a population dynamics model within a Bayesian state-space modelling framework. By constraining the population trajectory to be biologically realistic, more precise estimates can be obtained. Independent biological knowledge can be incorporated through choice of model structure and by specifying informative prior distributions on demographic parameters. We illustrate the approach using a 31-year point transect study of the Hawai’i ’ākepa (Loxops coccineus). We fitted five models, each making different assumptions about how population change, recruitment and/or adult survival varied over time. Overall, the ’ākepa geometric mean growth rate was 1.02, indicating an increasing population over the 31-year time series, although there were periods of slow decline potentially associated with low recruitment and more rapid recovery associated with pulses of high recruitment. Abundance estimates derived from the population models were substantially more precise than the ‘raw’ point transect estimates: 95% credible interval (CrI) was on average 51.7% (s.d. = 14.1%) narrower.

Birds are often obligate to specific habitats which can result in study areas with complex boundaries due to sudden changes in vegetation or other features. This can result in study areas with concave arcs or that include holes of unsuitable habitat such as lakes or agricultural fields. Spatial models used to produce species’ distribution and density estimates need to respect such boundaries to make informed decisions for species conservation and management. The soap film smoother is one model for complex study regions which controls the boundary behaviour, ensuring realistic values at the edges of the region. We apply the soap film smoother to account for boundary effects and compare it with thin plate regression spline (TPRS) smooth and design-based conventional distance sampling methods to produce abundance estimates from point-transect distance sampling collected data on Hawai‘i ‘Ākepa Loxops coccineus in the Hakalau Forest Unit of the Big Island National Wildlife Refuge Complex, Hawai‘i Island, USA. The soap film smoother predicted zero or near zero densities in the northern part of the domain and two hotspots (in the southern and central parts of the domain). Along the boundary the soap film model predicted relatively high densities where ‘Ākepa occur in the adjacent forest and near zero elsewhere. The design-based and soap film abundance estimates were nearly identical. The width of the soap film confidence interval was 16.5% and 0.8% wider than the width of the TPRS smooth and design-based confidence intervals, respectively. The peaks in predicted densities along the boundary indicates leakage by the TPRS smooth. We provide a discussion of the statistical methods, biological findings and management implications of applying soap film smoothers to estimate forest bird population status.

Endangered Hawai'i 'Ākepas (Loxops coccineus) are endemic to Hawai'i island, where they occur in five spatially distinct populations. Data concerning the status and population trends of these unique Hawaiian honeycreepers are crucial for assessing the effectiveness of recovery and management actions. In 2016, we used point-transect distance sampling to estimate the abundance of Hawai'i 'Akepas in portions of Hawai'i Volcanoes National Park (HAVO) and the Ka'ū Forest Reserve (KFR) on Mauna Loa volcano. We then compiled the survey data from four other populations to provide a global population estimate. In our HAVO and KFR study area, we mapped habitat classes to determine the population densities in each habitat. Densities were highest (1.03 birds/ha) in open-canopy montane 'ōhi'a (Metrosideros polymorpha) woodland. I contrast, densities of the largest 'Ākepa population on Mauna Kea volcano were highest in closed-canopy 'ōhi'a and koa (Acacia koa) forest where the species is dependent on nest cavities in tall (> 15 m), large (> 50-cm diameter at breast height) trees. We surveyed potential nesting habitat in HAVO and KFR and found only one cavity in the short-stature montane 'ōhi'a woodland and five cavities in the tall-stature forest. Differences in densities between the Mauna Kea and Mauna Loa populations suggest that Hawai'i 'Ākepas may exhibit different foraging and nesting behaviors in the two habitats. The estimated overall population density in the HAVO and KFR study area was 0.52 birds/ha, which equates to 3663 (95% CI 1725-6961) birds in their 11,377-ha. population range. We calculated a global population of 16,428 (95% CI 10,06525,198) birds, which is similar to an estimate of 13,892 (95% CI 10,315-17,469) birds made in 1986. Our results suggest that populations are stable to increasing in the two largest populations, but the three other populations are smaller (range = 77-1443 birds) and trends for those populations are unknown. Las Akepas Hawianas (Loxops coccineus) son aves en peligro de extinción endémicas de las Islas de Hawái, donde se distribuyen en cinco poblaciones distintas espacialmente separadas. Datos sobre el estatus y las tendencias poblacionales de estos mieleros hawaianos únicos son cruciales para evaluar la efectividad de acciones de recuperación y manejo. En 2016, usamos muéstreos por distancia a transecta de puntos para estimar la abundancia de las Akepas Hawaianas en porciones del Parque Nacional de los Volcanes (HAVO) y la Reserva Forestal (KFR) en el volcán Mauna Loa. Compilamos también datos de muestreo de las otras cuatro poblaciones para proporcionar un estimado poblacional global. En nuestras áreas de estudio de HAVO y KFR, mapeamos clases de habitat para determinar las densidades poblacionales en cada hábitat. Las densidades fueron más alta (1.03 birds/ha) en el bosque montanos de dosel abierto de 'ōhi'a (Metrosideros polymorpha). En contraste, las densidades de la mayor población de Akepas en el volcán Mauna Kea fueron más altas en bosques de dosel cerrado de 'ōhi'a y koa (Acacia koa) donde la especie depende de cavidades de nido en árboles altos (> 15 m) y grandes (> 50-cm de diámetro medido a la altura del pecho). Muestreamos el hábitat potencial de nidada en HAVO y KFR y encontramos sólo una cavidad en el estrato bajo del bosque montano de 'ōhi'a, y cinco cavidades en el estrato alto del bosque. Diferencias en densidad en las poblaciones de Mauna Kea y Mauna Loa sugieren que las Akepas Hawaianas pueden exhibir comportamientos de forrajeo y nidada diferentes es estos dos hábitats. La densidad poblacional global en las áreas de estudio de HAVO y KFR fue de 0.52 aves/ha, lo cual equivale a 3663 (95% IC 1725-6961) aves en su rango poblacional de 11,377-ha. Calculamos la población global en 16,428 (95% IC 10,065-25,198) aves, lo cual es similar al estimado de 13,892 (95% IC 10,315-17,469) aves que se hizo en 1986. Nuestros resultados sugieren que las poblaciones son estables y tienden al crecimiento en las dos poblaciones más grandes, pero que las otras tres poblaciones son menores (rango = 77-1443 aves) y las tendencias para estas poblaciones son desconocidas.

For most species the timing of extinction events is uncertain, occurring sometime after the last sighting. However, the sightings themselves may also be uncertain. Recently a number of methods have been developed that incorporate sighting uncertainty in the inference of extinction based on a series of sightings. Here we estimate the timing of extinction for 41 of 52 North American and Hawaiian bird taxa and populations, the results of which suggest all became extinct before 2009. By acknowledging sighting uncertainty it results in two opposite effects, one pushing the timing of extinction away from the last sighting and the other drawing the timing of extinction nearer to it. However, for 14 assessed taxa and populations the upper 95% bounds lie beyond the end of the observation period and therefore suggest the possibility of continued persistence. This has important implications for conservation decision-makers and potentially reduces the likelihood of Romeo’s Error.

Accurate analysis of trends in densities estimated from survey data depends on selection of a model that fits the data. When such analysis uses data recorded at different times in the same area but from different transects, then the target species’ density and spatial heterogeneity become an issue. It is possible, even in the absence of environmental change, that one set of transects may underestimate or overestimate the density entirely on the basis of location. The resulting risk is that the density estimated earlier may falsely indicate a decline or an increase when compared to the densities estimated later. We investigate this problem for trend analysis of two species of endangered Hawaiian birds at Hakalau Forest National Wildlife Refuge, island of Hawaii. Assertions based on Bayesian regression, and accepted by the U.S. Fish and Wildlife Service, purportedly indicate increases in the density of the endangered Hawaii Akepa (Loxops coccineus coccineus) from 1977 to 2007 and of the endangered Hawaii Creeper (Oreomystis mana) from 1987 to 2007. Here we show, at four study sites spanning the south–north axis of the refuge, that capture rates per mist-net hour of both species declined significantly and the 1977 transects used underestimated density because of location. We submit that the main reason for the differences between our piecewise regression and Bayesian regression is the inappropriate use of Bayesian regression. Analysis by the appropriate model indicates that since 2000 all Hawaiian birds at Hakalau Forest National Wildlife Refuge have been declining.

Accurate analysis of trends in densities estimated from survey data depends on selection of a model that fits the data. When such analysis uses data recorded at different times in the same area but from different transects, then the target species' density and spatial heterogeneity become an issue. It is possible, even in the absence of environmental change, that one set of transects may underestimate or overestimate the density entirely on the basis of location. The resulting risk is that the density estimated earlier may falsely indicate a decline or an increase when compared to the densities estimated later. We investigate this problem for trend analysis of two species of endangered Hawaiian birds at Hakalau Forest National Wildlife Refuge, island of Hawaii. Assertions based on Bayesian regression, and accepted by the U.S. Fish and Wildlife Service, purportedly indicate increases in the density of the endangered Hawaii Akepa (Loxops coccineus coccineus) from 1977 to 2007 and of the endangered Hawaii Creeper (Oreomystis mana) from 1987 to 2007. Here we show, at four study sites spanning the south—north axis of the refuge, that capture rates per mist-net hour of both species declined significantly and the 1977 transects used underestimated density because of location. We submit that the main reason for the differences between our piecewise regression and Bayesian regression is the inappropriate use of Bayesian regression. Analysis by the appropriate model indicates that since 2000 all Hawaiian birds at Hakalau Forest National Wildlife Refuge have been declining.

The Hawaii Akepa (Loxops coccineus coccineus) is an endangered bird that has declined dramatically in the last 100 years, and is now rare or absent from many areas that appear to support suitable habitat. Food availability may play a role in these distribution patterns, but differences in food between sites may arise from different sources. I compared prey availability between a site supporting a large, stable Hawaii Akepa population, and a site from which Hawaii Akepa have declined in the last 100 years for unknown reasons. I used three spatial scales to compare food between sites to explore the basis of differences in food between sites. At a scale appropriate for comparing prey population dynamics (scale 1), I found that prey population densities are similar between sites, suggesting that introduced (or native) predators or parasitoids have not affected prey populations differently between sites. At two larger scales incorporating habitat structure, I found that food availability is much lower at the site of Hawaii Akepa declines. Differences in canopy density per square meter (scale 2), and in canopy cover per square kilometer (scale 3), result in lower food availability that may have effects on individual foraging birds as well as on potential Hawaii Akepa population density. These findings illustrate the importance of explicitly incorporating spatial scale into inquiries about food for Hawaii Akepa, and suggest that the site of population declines may not be suitable habitat with respect to food for this species.Original Abstract: Loxops coccineus coccineus es un ave amenazada de Hawai que ha declinado dramaticamente en los ultimos 100 anos y que es ahora rara o esta ausente de muchass areas que parecen poseer habitat adecuado. La disponibidad de alimento puede jugar un rol en estos patrones de distribucion, pero diferencias entre sitios en los alimentos pueden deberse a causas diferentes. Compare la disponibilidad de presas entre un sitio con una poblacion grande y estaable de L. c. coccineus y un sitio en el cual esta especie ha declinado por causas desconocidas en los ultimos 100 anos. Utilice tres escalas espaciales oara comparar los alimentos entre sitios y para explorar el origen de las diferencias. A una escala apropiada para comparar la dinamica de las poblaciones de presas (escala 1), encontre que las densidades de lss poblaciones de presas son similares entre sitios, sugiriendo que los depredadores o parasitoides introducidos (o nativos) no han afectado de modo diferente entre sitios a las poblaciones de presas. A dos escalas mayores que incorporan la estructura del habitat, encontre que la disponibilidad de alimento es mucho mas baja en el sitio donde L. c. coccineus esta declinando. Las diferencias en la densidad del dosel por metro cuadrado (escala 2) y en la cobertura del dosel por kilometro cuadrado (escala 3) resultaron en unaa menor disponibilidad de alimento que puedede tener efectos sobre el forrajeco se aves individuales asi como en lass densidades poblaciones potenciales de L. c. coccines. Estos resultados senalan la importancia de incorporar explicitamente la escala espacial en estudios de los alimentos para L. c. coccines, y sugieren que el sitio donde la poblacion esta declinando puede no representar habitat adecuado para la alimentacion de esta especie.

Surveys are essential for conservation of populations, because they provide estimates of density that may reveal a change in status. Managers therefore depend on analysis of density estimates to evaluate effectiveness of their actions. However, statistical problems associated with trend analysis make declines caused by environmental change difficult to detect. Here we apply piecewise regression to analysis of trends in eight species of Hawaiian passerines to determine if slopes following a year of documented change differ from slopes estimated before the change. Using estimates of densities of forest birds at Hakalau Forest National Wildlife Refuge, we show that estimates of trends based on 21 years of survey data and expressed as a single slope missed an environmental change in year 14. Analysis of residuals indicates that analysis of trends as a single slope violated the model's assumptions, giving a false impression that populations were either stable or increasing and at variance with independent indicators of population decline based on banded birds. In contrast, piecewise regression shows that the slopes of all eight species were positive before the change and negative after it and meets the model's assumptions. The Hawai'i ‘Ākepa (Loxops coccineus coccineus) and the ‘I’iwi (Vestiaria coccinea) are declining significantly, with several other species likely declining. On the basis of the structure of the data, the positive slopes were anomalous. We suggest that piecewise regression may be the more appropriate technique for dealing with environmental changes toward the end of long-term data sets.

The sexually dichromatic and endangered Island of Hawaii subspecies of Akepa (Loxops coccineus coccineus) is a 10- to 12-g Hawaiian honeycreeper that shows remarkable variation in male plumage coloration, ranging from dull gray to bright orange. We found that this variation is primarily due to a two-year delay in plumage maturation by young males. Second-year males possess a mainly grayish-green plumage that is similar to that of females, and rarely try to breed. Third-year males have a partially orange plumage that is intermediate between that of females and adult males, and competently breed in small numbers. In addition, there are variations within age classes that reflect alternative life histories and perhaps diet. The existence of both femalelike and malelike subadult plumage in a population is unlike North American passerines with delayed plumage maturation, especially cardueline finches, which are considered to be the closest relatives of the Hawaiian honeycreepers. The extreme delay is associated with high survivorship, strong philopatry, and a varied prebreeding competition among males that includes group displays and which lasts for six months or more each year. These characteristics are common in lekking or cooperatively breeding species, but are unusual for a small, monogamous passerine with biparental care.