White-headed Woodpecker Research Articles

Forest management, forest vegetation, and climate influence nesting ecology of a focal bird species in the western USA

Landscape-scale forest restoration aims to restore ecological structure and function and provide habitat for wildlife. However, forest management likely has varying impacts across wildlife life stages, with consequences for population persistence. Using 10 years of nest (n = 294) survey data for a focal bird species, white-headed woodpecker (Dryobates albolarvatus), we assessed how forest management (tree removal and prescribed burning) at two spatial scales (stand [2.25 ha] and landscape [314 ha]), forest vegetation variables at three spatial scales (nest tree, local [0.4 ha], and landscape [314 ha]), and climate influenced nest initiation date, egg production, egg survival, and nestling survival. We applied Bayesian hierarchical mixed effects models to these data to identify and compare drivers at each life stage. None of the variables we considered influenced egg production; white-headed woodpeckers laid an average of four eggs. As the extent of the landscape with tree removal increased, nests initiated later. Egg survival was higher in nests with prescribed burning at the stand scale. Nestling survival was higher in sites that had been managed with burning and tree removal at the stand scale, but the relationship with burning switched to negative at the landscape scale. Only nestling survival was shaped by attributes of the nest cavity itself. Egg survival increased with increased variation in forest patch sizes at the landscape scale. Woodpeckers initiated nests earlier under warmer conditions, with previous August and September temperatures being particularly influential. Both egg and nestling survival increased with cumulative precipitation. While increased temperatures decreased egg survival, nestling survival peaked at an optimal maximum temperature (∼32 °C). This study illustrates how forest management, forest vegetation, and climate factors affecting nesting ecology vary throughout the nesting season. Additionally, effects that switch directions (positive versus negative) across spatial scales indicate spatially dependent ecological processes (e.g., nest suitability versus adult foraging). This study provides a model for assessing the effects of forest management on bird population persistence by considering the nesting season as stages with distinct ecological limitations linked to spatially-dependent factors.

Passive acoustic recorders increase White-headed Woodpecker detectability in the Blue Mountains

Passive acoustic recorders increase White-headed Woodpecker detectability in the Blue Mountains

Annual survival of adult White-headed Woodpeckers (Dryobates albolarvatus) in ponderosa pine forest with a history of forest management

Las tasas vitales pueden proveer una visión de los efectos del manejo en poblaciones de fauna silvestre. Sin embargo, para muchas aves de Norteamérica, especialmente para carpinteros (Picidae), dichas tasas vitales no están bien documentadas. Aquí estimamos la sobrevivencia anual del carpintero Dryobates albolarvatus a lo largo de un periodo de 10 años (2011–2021) en bosques manejados de pino ponderosa (Pinus ponderosa) en la vertiente este de la cordillera Cascade en Washington, EUA. Anillamos machos y hembras de carpintero con combinaciones únicas de anillos de colores y los re-observamos en sus territorios reproductivos de marzo–julio de cada año. Anillamos 116 carpinteros, la mayoría de los cuales determinamos como del primer año (n = 49) o del segundo año (n = 32) al momento de ser anillados y todos habían pasado el periodo de dependencia crítica cuando la mortandad es más alta. Estimamos probabilidades de recaptura y sobrevivencia anual de 33 machos y 24 hembras reproductivos usando modelos Cormack-Jolly-Seber para poblaciones abiertas que incluyeron 2 covariables: edad de primera captura (AGE) y sexo (SEX). Combinamos estas aves en 3 clases de AGE: clase 1 (del primer año), clase 2 (del segundo año y después del segundo año) y clase 3 (≥ después del segundo año). Las probabilidades de recaptura de hembras fueron más altas que las de los machos, aunque ambas fueron >0.85. Las aves de la clase 1 de AGE tuvieron la más baja probabilidad de recaptura, aunque estas estimaciones fueron imprecisas. Las probabilidades de sobrevivencia fueron >0.80 para todas las aves, independientemente del modelo evaluado. Estas estimaciones de sobrevivencia podrían estar infladas porque algunos adultos que son no-reproductivos y se dispersaron del área de estudio podrían tener tasas de sobrevivencia más bajas. No encontramos evidencia de diferencias en la probabilidad de sobrevivencia por SEX o AGE. Nuestros resultados sugieren que, si bien las parcelas con plantaciones de pino ponderosa bajo manejo tienen árboles de diámetros menores y mayores densidades que las parcelas históricas, estos carpinteros tienen una alta probabilidad de sobrevivencia año con año en este tipo de bosque. Palabras clave: anillos de colores, captura-recaptura, estimaciones de sobrevivencia, parcelas de pino, Washington.

Cellobiase Activity as an Indicator of Fungal Decay in the Wood of Woodpecker Nest Cavities in the Pacific Northwest.

Woodpeckers require trees and snags with decayed wood in order to excavate nest and roost cavities, and interior wood hardness is considered an important factor determining where a woodpecker can create a cavity. In most ecosystems, saprophytic fungi are responsible for the decay and softening of wood, and are thought to be important in providing soft wood for woodpecker cavity excavation. We conducted a study of cellulose-degrading enzymes in the wood surrounding woodpecker nest cavities. We measured wood hardness, percent wood density loss (PWDL), and activity of cellobiase (an extracellular fungal cellulase that degrades cellulose) within wood surrounding the nest cavities of the northern flicker (Colaptes auratus), black-backed woodpecker (Picoides arcticus), white-headed woodpecker (Dryobates albolarvatus), and hairy woodpecker (D. villosus) in Oregon and Washington. We found that mean wood hardness was significantly lower, and cellobiase and PWDL were significantly higher, at nest cavities than controls for each woodpecker species. Wood hardness was higher and cellobiase lower at nests of black-backed woodpecker than northern flicker, but did not differ among the other woodpecker species. Our results suggest that increased amounts of cellobiase result in softer wood due to the increased decay caused by higher fungal enzyme activity and that measuring cellobiase can be used to estimate wood decay without directly measuring wood hardness. All four woodpecker species selected nest substrates with softer wood and higher fungal enzyme activity than controls. This supports findings from previous studies of the importance of saprophytic fungi for woodpecker cavity excavation.

DNA metabarcoding reveals broad woodpecker diets in fire-maintained forests

Abstract Ecological disturbance is a key agent shaping the spatial and temporal landscape of food availability. In forests of western North America, disturbance from fire can lead to resource pulses of deadwood-associated arthropods that provide important prey for woodpeckers. Although the foraging strategies among woodpecker species often demonstrate pronounced differences, little is known about the ways in which woodpeckers exploit and partition prey in disturbed areas. In this study, we employed DNA metabarcoding to characterize and compare the arthropod diets of 4 woodpecker species in Washington and California, USA—Black-backed Woodpecker (Picoides arcticus), Hairy Woodpecker (Dryobates villosus), Northern Flicker (Colaptes auratus), and White-headed Woodpecker (Dryobates albolarvatus)—primarily using nestling fecal samples from burned forests 1–13 years postfire. Successful sequencing from 78 samples revealed the presence of over 600 operational taxonomic units (OTUs) spanning 32 arthropod orders. The nestling diets of two species in particular—Northern Flicker and Black-backed Woodpecker—proved to be much broader than previous observational studies suggest. Northern Flicker nestlings demonstrated significantly higher diet diversity compared to other focal species, all of which displayed considerable overlap in diversity. Wood-boring beetles, which colonize dead and dying trees after fire, were particularly important diet items for Black-backed, Hairy, and White-headed woodpeckers. Diet composition differed among species, and diets showed limited differences between newer (≤5 yr) and older (>5 yr) postfire forests. Our results show mixed evidence for dietary resource partitioning, with three of the four focal species exhibiting relatively high diet overlap, perhaps due to the pulsed subsidy of deadwood-associated arthropods in burned forests. Woodpeckers are frequently used as management indicator species for forest health, and our study provides one of the first applications of DNA metabarcoding to build a more complete picture of woodpecker diets.

Description and molecular characterization of novel Leucocytozoon parasite (Apicomplexa: Haemosporida: Leucocytozoidae), Leucocytozoon polynuclearis n. sp. found in North American woodpeckers.

We describe Leucocytozoon polynuclearis n. sp. (Haemosporida: Leucocytozoidae) from two North American woodpeckers, the northern flicker (Colaptes auratus Linnaeus) and white-headed woodpecker (Dryobates albolarvatus Boie, 1826), based on the morphology of its blood stages and portions of the mitochondrial cytochrome b gene. The most distinctive features of Leucocytozoon polynuclearis n. sp. development are the triangular-shaped host cell nuclei and position of host cell nuclei above gametocytes. This parasite inhabits thrombocytes. Leucocytozoon squamatus Nandi, 1986, the only other Leucocytozoon species detected from Picidae birds, lacks features that are commonly found with L. polynuclearis n. sp. infections. Phylogenetic analysis identified DNA lineages associated with L. polynuclearis n. sp. and showed that this parasite is more closely related to other North American Leucocytozoon species than to L. squamatus, whose initial description was from infected Old World Picidae species. Although there are reports of L. squamatus in North American Picidae species, these detections were based only on microscopic examinations, remain genetically non-characterized, and might be misidentifications with regards to L. polynuclearis n. sp. Available parasite distribution data indicate that L. polynuclearis n. sp. infects Picidae species throughout North America and L. squamatus distribution probably is restricted to Old World Piciformes birds.

White-headed woodpecker nesting habitat at multiple spatial scales: Are habitat preferences adaptive?

Ecological theory predicts that animals will select habitats for breeding that confer an adaptive advantage through increased reproductive success. We therefore expect to see congruence between habitat preferences and measures of fitness. We studied abundance, nest site selection, and nest survival in white-headed woodpeckers (Picoides albolarvatus) in four forest types along an elevational gradient in the southern Sierra Nevada, California. Our primary objective was to ascertain what habitat features white-headed woodpeckers were selecting for nesting and at what scale, and whether those choices translated into increased reproductive success. We examined sets of models that included abiotic factors and habitat at three spatial scales: nest site (0.04 ha), local (~1 ha), and home range (~125 ha). White-headed woodpeckers were more abundant at higher elevations, with low abundance in low-elevation ponderosa pine forest, moderate abundance in mid-elevation mixed conifer forest, and reached their highest abundance in true fir habitat before becoming rare in high-elevation lodgepole pine forest. They both selected for and nested more successfully at higher elevations in true fir forest. White-headed woodpecker nesting ecology in the Sierra Nevada demonstrated a mixed pattern of congruence between characteristics important to nest habitat selection and nest survival. We found congruence for abiotic and home range scale models (agreement between preferences and nest survival), indicating adaptive selection. At the landscape scale, White-headed woodpeckers selected closed-canopy conifer forests with abundant edges. Habitat preferences at the nest site scale were negatively related to nest survival, suggesting maladaptive habitat selection at this scale. White-headed woodpeckers selected open forest with higher basal area of snags compared to available sites, but nest survival was higher in forest with higher canopy closure and lower basal area of snags. Local scale models were weak and did not help clarify habitat relationships. Our results highlight the importance of considering multiple spatial scales when examining habitat preferences. The primary management considerations for white-headed woodpecker habitat include retention of large, suitable snags and the need to consider forest heterogeneity. The close association with ponderosa pine forests and large-seeded pines found over most of their range did not hold in the Sierra Nevada, where white-headed woodpeckers were most abundant in true fir forests and selected and nested more successfully in true fir forests. Habitat models developed outside the area for which they were developed should be validated before they are applied to other locations.

The influence of climate and habitat on stable isotope signatures and the isotopic niche of nestling White-headed Woodpeckers (Dryobates albolarvatus).

The majority of landbird species feed their nestlings arthropods and variation in arthropod populations can impact reproductive outcomes in these species. Arthropod populations in turn are influenced by climate because temperature affects survival and reproduction, and larval development. Thus, climate factors have the potential to influence many bird species during their reproductive phases. In this study, we assessed climate factors that impact the diet of nestling White‐headed Woodpecker (Dryobates albolarvatus), an at‐risk keystone species in much of its range in western North America. To do this, we measured stable isotope signatures (δ13C and δ15N) in 152 nestlings across six years and linked variation in isotopic values to winter (December–February) and spring (June) precipitation and temperature using mixed effects models. We also explored habitat factors that may impact δ13C and δ15N and the relationship between δ15N and nest productivity. Last, we estimated isotopic niche width for nestlings in different watersheds and years using Bayesian standard ellipses, which allowed us to compare dietary niche width and overlap. We found that colder winter temperatures were associated with an increase in δ15N and δ15N levels had a weak positive relationship with nest productivity. We also found that sites with a more diverse tree community were associated with a broader isotopic niche width in nestlings. Our findings suggest that nestling diet is affected by climate, and under future warming climate scenarios, White‐headed Woodpecker nestling diet may shift in favor of lower trophic level prey (prey with lower δ15N levels). The impact of such changes on woodpecker populations merits further study.

Development and evaluation of habitat suitability models for nesting white-headed woodpecker (Dryobates albolarvatus) in burned forest.

Salvage logging in burned forests can negatively affect habitat for white-headed woodpeckers (Dryobates albolarvatus), a species of conservation concern, but also meets socioeconomic demands for timber and human safety. Habitat suitability index (HSI) models can inform forest management activities to help meet habitat conservation objectives. Informing post-fire forest management, however, involves model application at new locations as wildfires occur, requiring evaluation of predictive performance across locations. We developed HSI models for white-headed woodpeckers using nest sites from two burned-forest locations in Oregon, the Toolbox (2002) and Canyon Creek (2015) fires. We measured predictive performance by developing one model at each of the two locations and quantifying discrimination of nest from reference sites at two other wildfire locations where the model had not been developed (either Toolbox or Canyon Creek, and the Barry Point Fire [2011]). We developed and evaluated Maxent models based on remotely sensed environmental metrics to support habitat mapping, and weighted logistic regression (WLR) models that combined remotely sensed and field-collected metrics to inform management prescriptions. Both Maxent and WLR models developed either at Canyon Creek or Toolbox performed adequately to inform management when applied at the alternate Toolbox or Canyon Creek location, respectively (area under the receiver-operating-characteristic curve [AUC] range = 0.61-0.72) but poorly when applied at Barry Point (AUC = 0.53-0.57). The final HSI models fitted to Toolbox and Canyon Creek data quantified suitable nesting habitat as severely burned or open sites adjacent to lower severity and closed canopy sites, where foraging presumably occurs. We suggest these models are applicable at locations similar to development locations but not at locations resembling Barry Point, which were characterized by more (pre-fire) canopy openings, larger diameter trees, less ponderosa pine (Pinus ponderosa), and more juniper (Juniperus occidentalis). Considering our results, we recommend caution when applying HSI models developed at individual wildfire locations to inform post-fire management at new locations without first evaluating predictive performance.

Predictive habitat suitability models for nesting woodpeckers following wildfire in the Sierra Nevada and Southern Cascades of California

AbstractWoodpeckers are often focal species for informing management of recently burned forests. Snags generated by wildfire provide key nesting and foraging resources for woodpeckers, and nest cavities excavated by woodpeckers are subsequently used by many other species. Habitat suitability models applicable in newly burned forest are important management tools for identifying areas likely to be used by nesting woodpeckers. Here we present and test predictive models for mapping woodpecker nest-site habitat across wildfire locations that can be used to inform post-fire planning and salvage logging decisions. From 2009 to 2016, we monitored 313 nest sites of 4 species—Black-backed Woodpecker (Picoides arcticus), Hairy Woodpecker (Dryobates villosus), White-headed Woodpecker (D. albolarvatus), and Northern Flicker (Colaptes auratus)—from 3 wildfires in the Northern Sierra Nevada and Southern Cascades 1–5 yr after fire. Using these data, we developed habitat suitability index models that compared nest vs. non-nest sites for each species using (1) exclusively remotely sensed covariates, and (2) combinations of remotely sensed and field-collected covariates. We emphasized predictive performance across wildfire locations when selecting models to retain generalizable habitat relationships useful for informing management in newly burned locations. We identified models for all 4 species with strong predictive performance across wildfire locations despite notable variation in conditions among locations, suggesting broad applicability to guide post-fire management in the Sierra Nevada region. Top models for nest-site selection underscored the importance of high burn severity at the local scale, lower burn severity at the 1-km scale, mid-sized nest-tree diameters, and nest trees with broken tops. Models restricted to remotely sensed covariates exhibited similar predictive performance as combination models and are valuable for mapping habitat across entire wildfire locations to help delineate project areas or habitat reserves. Combination models are especially relevant for design of silvicultural prescriptions.

Haemoproteosis lethality in a woodpecker, with molecular and morphological characterization of Haemoproteus velans (Haemosporida, Haemoproteidae).

A juvenile White-headed woodpecker (Dryobates albolarvatus) fitted with a radio tag was located dead at approximately 22-days post-fledging in Yakima county in central Washington in July 2015. Postmortem examination revealed an enlarged liver and spleen plus evidence of iron sequestration. Microscopic examination observed young gametocytes within the cytoplasm of erythrocytes, and exo-erythrocytic meronts within the cytoplasm of capillary endothelial cells, hepatocytes, and myocytes, and free in the tissues. These attributes implicated a haemosporidian infection that likely resulted in mortality. Subsequent sampling results of local woodpecker species in the same area during the breeding season in June–July 2016 and May–July 2017 showed other individuals infected with Haemoproteus parasites. Nested Polymerase Chain Reaction (PCR), sequencing, and microscopic analyses for avian haemosporidians revealed infections with Haemoproteus velans (Haemosporida, Haemoproteidae). This parasite was characterized molecularly and morphologically. This is the first report of a haemosporidian infection in a White-headed woodpecker anywhere in its range, and the first reported suspected mortality from haemoproteosis for a woodpecker (Piciformes, Picidae). The use of radio-tagged birds is an asset in wildlife haemosporidian studies because the effect of the pathogen can be monitored in real time. Additionally, this methodology provides opportunities to collect fresh material for microscopic and histological examination from wild birds that have died from natural causes.

Veiled Polypore (Cryptoporus volvatus) as a Foraging Substrate for the White-Headed Woodpecker (Picoides albolarvatus)

In the northwest, White-headed Woodpeckers (Picoides albolarvatus) are an uncommon species restricted to interior, dry coniferous forests. This species forages primarily by probing in bark crevices, surface gleaning, and excavating below the bark. Here we report on an observation from Mt. Ashland in southern Oregon of a White-headed Woodpecker feeding on insects in and around the sporophores of Veiled Polypore (Cryptoporus volvatus). Inspection of other sporophores with signs of woodpecker feeding revealed abundant fly larvae and beetles (adults and larvae). This widespread decay fungus colonizes the sapwood of recently dead trees where it is frequently associated with bark beetles. A suite of other insects is attracted to the sporophore, many using the enclosed pouch as a pupation chamber. In addition to exploring the significance of C. volvatus as a foraging substrate for White-headed Woodpeckers, we discuss the potential role of White-headed Woodpeckers as dispersal agents for C. volvatus and the possible interplay between C. volvatus-induced decay, insect availability, and habitat selection by White-headed Woodpeckers.

Simulations inform design of regional occupancy-based monitoring for a sparsely distributed, territorial species.

Sparsely distributed species attract conservation concern, but insufficient information on population trends challenges conservation and funding prioritization. Occupancy‐based monitoring is attractive for these species, but appropriate sampling design and inference depend on particulars of the study system. We employed spatially explicit simulations to identify minimum levels of sampling effort for a regional occupancy monitoring study design, using white‐headed woodpeckers (Picoides albolvartus), a sparsely distributed, territorial species threatened by habitat decline and degradation, as a case study. We compared the original design with commonly proposed alternatives with varying targets of inference (i.e., species range, space use, or abundance) and spatial extent of sampling. Sampling effort needed to achieve adequate power to observe a long‐term population trend (≥80% chance to observe a 2% yearly decline over 20 years) with the previously used study design consisted of annually monitoring ≥120 transects using a single‐survey approach or ≥90 transects surveyed twice per year using a repeat‐survey approach. Designs that shifted inference toward finer‐resolution trends in abundance and extended the spatial extent of sampling by shortening transects, employing a single‐survey approach to monitoring, and incorporating a panel design (33% of units surveyed per year) improved power and reduced error in estimating abundance trends. In contrast, efforts to monitor coarse‐scale trends in species range or space use with repeat surveys provided extremely limited statistical power. Synthesis and applications. Sampling resolutions that approximate home range size, spatially extensive sampling, and designs that target inference of abundance trends rather than range dynamics are probably best suited and most feasible for broad‐scale occupancy‐based monitoring of sparsely distributed territorial animal species.

Cameras Show Sciurids Visiting White-Headed Woodpecker Nests Without Depredating Contents

Abstract In western North America, rodents in the family Sciuridae are considered woodpecker nest predators and management to reduce sciurid habitat has been suggested. However, there have been few actual observations of woodpecker nest predation. In 2014, we used passive infrared cameras in an attempt to identify nest predators for white-headed woodpeckers Picoides albolarvatus in Washington. We monitored 17 nests for 4,296 observer-hours and were surprised to document 33 cases in which two putative nest predators—chipmunks Tamias spp. and Douglas squirrels Tamiasciurus douglasii—visited but did not depredate nests. Most nests visited by these rodents were successful (71.4%) and no eggs or nestlings were lost to predation (no partial depredations). Future studies using continuous video surveillance at nests would help identify nest predators of white-headed woodpecker and quantify proportions of nests depredated by different species.

Using an agent-based model to examine forest management outcomes in a fire-prone landscape in Oregon, USA

Fire-prone landscapes present many challenges for both managers and policy makers in developing adaptive behaviors and institutions. We used a coupled human and natural systems framework and an agent-based landscape model to examine how alternative management scenarios affect fire and ecosystem services metrics in a fire-prone multiownership landscape in the eastern Cascades of Oregon. Our model incorporated existing models of vegetation succession and fire spread and information from original empirical studies of landowner decision making. Our findings indicate that alternative management strategies can have variable effects on landscape outcomes over 50 years for fire, socioeconomic, and ecosystem services metrics. For example, scenarios with federal restoration treatments had slightly less high-severity fire than a scenario without treatment; exposure of homes in the wildland-urban interface to fire was also slightly less with restoration treatments compared to no management. Treatments appeared to be more effective at reducing high-severity fire in years with more fire than in years with less fire. Under the current management scenario, timber production could be maintained for at least 50 years on federal lands. Under an accelerated restoration scenario, timber production fell because of a shortage of areas meeting current stand structure treatment targets. Trade-offs between restoration outcomes (e.g., open forests with large fire-resistant trees) and habitat for species that require dense older forests were evident. For example, the proportional area of nesting habitat for northern spotted owl (Strix occidentalis) was somewhat less after 50 years under the restoration scenarios than under no management. However, the amount of resilient older forest structure and habitat for white-headed woodpecker (Leuconotopicus albolarvatus) was higher after 50 years under active management. More carbon was stored on this landscape without management than with management, despite the occurrence of high-severity wildfire. Our results and further applications of the model could be used in collaborative settings to facilitate discussion and development of policies and practices for fire-prone landscapes.

Between-Year Breeding Dispersal by White-Headed Woodpeckers: A Caution About Using Color Bands to Estimate Survival

Abstract Between-year breeding dispersal has not been previously documented in White-headed Woodpeckers (Picoides albolarvatus). Therefore, resightings of color-banded adults on previous years' breeding territories have been considered a means of estimating annual adult survival. From 2013 to 2015, I observed 2 cases of between-year breeding dispersal by adult color-banded White-headed Woodpeckers in central Washington. Mean dispersal distance was 6.9 km, and both adults were successful in fledging young in their new territories. Without extensive searches outside of previous years' territories, such dispersal events could have been classified as mortalities leading to annual survival estimates that were biased low.

Foraging plasticity by a keystone excavator, the white-headed woodpecker, in managed forests: Are there consequences for productivity?

Information on the foraging ecology of animals is important for conservation and management, particularly for keystone species whose presence affects ecosystem health. We examined foraging by an at-risk cavity excavator, the white-headed woodpecker (Picoides albolarvatus). The foraging needs of this species are used to inform management of ponderosa pine (Pinus ponderosa) forests in some areas of western North America. Past observational studies indicated that white-headed woodpeckers forage predominately on cones and trunks of large-diameter (>68cm) pines in old-growth stands, although habitat selection while foraging has not been formally examined. We used radio telemetry to track forage substrate use among 37 adult, breeding woodpeckers for 176h (10,576min) in forest stands that had been recently thinned and/or burned with prescribed fire. We used discrete choice models to examine forage site selection and multinomial regression to examine consequences of foraging on nest productivity. Woodpeckers foraged on more than ten individual substrates and switched substrates seasonally, presumably to take advantage of prey availability. Dead wood and fir foliage were used commonly in the nesting period (86% and 68% of foraging, respectively), whereas pine foliage and trunk foraging dominated in the fledgling (66% of foraging) and post-fledgling periods (73% of foraging). Average size of used trees was 49cm (±20cm) and pine cones were rarely used (4% of foraging). During the nesting period, substrate use (χ2=1.49, df=4, P=0.83) and distances traveled from nests for foraging did not affect productivity (F(3,16)=0.61, P=0.62), which was high even for birds with the longest (2.1km) and shortest (0.39km) maximum forage distances. Habitats selected for foraging matched substrate use, and woodpeckers selected areas with low basal areas of live trees in the nesting period, but high basal areas in the post-nesting period. The variable foraging that we observed suggests that white-headed woodpeckers are plastic in their foraging in managed forests, and this plasticity has no negative consequences for productivity.

Space use by white‐headed woodpeckers and selection for recent forest disturbances

ABSTRACTWhite‐headed woodpeckers (Picoides albolarvatus) are important cavity excavators that recently have become the focus of much research because of concerns over population declines. Past studies have focused on nest site selection and survival but information is needed on factors influencing their space use when away from the nest. We examined space use by white‐headed woodpeckers during the nesting (May–Jul) and post‐nesting (Jul–Oct) periods and compared the role of environmental factors (e.g., landcover) and socio‐demographic factors (e.g., age, breeding success) in home range size and selection of location. Average size of 99% kernel home ranges was 125 ha (SD ± 59 ha; n = 19) in the nesting period and 137 ha (SD ± 70 ha; n = 30) in the post‐nesting period. Minimum convex polygons were generally comparable to or smaller than ranges reported from previous radio‐telemetry studies with this species. Although bird weight and age best explained variation in home range size compared to other factors, neither parameter estimate was significant in our models. Thus, even though weight and age were the most‐supported factors in our analysis, home range size was largely influenced by factors that we did not measure. We found that most woodpeckers selected home ranges within forest patches that had undergone a recent disturbance; these areas included forests that had recently been burned with prescribed fire by the United States Forest Service (82%) or subject to disease (16%). Most burned patches in our study were small (approx. 4.8 ha) and occurred within otherwise live forest but had nearly complete mortality of adult trees. We suggest that recent forest disturbances, especially mixed‐severity prescribed burns, may have been selected by white‐headed woodpeckers because they created snags for nesting and future studies should explore this hypothesis. Because home range size was variable and not linked with productivity, it should not be used as an indication of habitat quality without more detailed studies on causal factors that affect space use in this species. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Improving inferences from short-term ecological studies with Bayesian hierarchical modeling: white-headed woodpeckers in managed forests.

Pilot studies are often used to design short-term research projects and long-term ecological monitoring programs, but data are sometimes discarded when they do not match the eventual survey design. Bayesian hierarchical modeling provides a convenient framework for integrating multiple data sources while explicitly separating sample variation into observation and ecological state processes. Such an approach can better estimate state uncertainty and improve inferences from short-term studies in dynamic systems. We used a dynamic multistate occupancy model to estimate the probabilities of occurrence and nesting for white-headed woodpeckers Picoides albolarvatus in recent harvest units within managed forests of northern California, USA. Our objectives were to examine how occupancy states and state transitions were related to forest management practices, and how the probabilities changed over time. Using Gibbs variable selection, we made inferences using multiple model structures and generated model-averaged estimates. Probabilities of white-headed woodpecker occurrence and nesting were high in 2009 and 2010, and the probability that nesting persisted at a site was positively related to the snag density in harvest units. Prior-year nesting resulted in higher probabilities of subsequent occurrence and nesting. We demonstrate the benefit of forest management practices that increase the density of retained snags in harvest units for providing white-headed woodpecker nesting habitat. While including an additional year of data from our pilot study did not drastically alter management recommendations, it changed the interpretation of the mechanism behind the observed dynamics. Bayesian hierarchical modeling has the potential to maximize the utility of studies based on small sample sizes while fully accounting for measurement error and both estimation and model uncertainty, thereby improving the ability of observational data to inform conservation and management strategies.

Evaluating habitat suitability models for nesting white‐headed woodpeckers in unburned forest

ABSTRACTHabitat suitability models can provide guidelines for species conservation by predicting where species of interest are likely to occur. Presence‐only models are widely used but typically provide only relative indices of habitat suitability (HSIs), necessitating rigorous evaluation often using independently collected presence‐absence data. We refined and evaluated presence‐only habitat suitability models for nesting white‐headed woodpeckers (Picoides albolarvatus), a narrowly distributed species of conservation concern that occupies dry conifer forests of the Inland Pacific Northwest, USA. We developed 2 models using Mahalanobis D2 and Maxent techniques from nest location datasets collected on the eastside of the Cascade Mountain Range, Oregon (1 dataset in 1997–2004 and another, sampling a broader spatial extent, in 2010–2011). Consistent with known ecology of white‐headed woodpeckers, both HSI models related positively with percent ponderosa pine, moderate levels of canopy cover (approx. 40%), and moderate‐to‐high levels of heterogeneity in forest structure. Unlike Mahalanobis HSIs, however, Maxent HSIs were consistently and positively related with nest prevalence and positively related with habitat use estimated with independent point count data. Locations with high Maxent HSIs were characterized by canopy openings adjacent to closed canopy forests. The fact that this habitat feature was described by Maxent HSIs but not by Mahalanobis HSIs possibly explains why Maxent HSIs better predicted white‐headed woodpecker occurrence. Additionally, we used presence‐absence data for model evaluation that sampled a broader spatial extent than nest surveys and therefore allowed us to demonstrate the generality of Maxent HSIs. Additional nest location data collected across a broader portion of the species range would be valuable for further model improvement and evaluation, but until such data are available, we recommend use of Maxent HSIs to guide habitat conservation and restoration efforts in unburned dry forests of Oregon. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.