Empidonax Difficilis Research Articles

Utilizing artificial nesting platforms as a management tool: enhancing breeding productivity of Western Flycatchers ( Empidonax difficilis occidentalis ) in southwestern Colorado and southern Arizona, USA

Utilizing artificial nesting platforms as a management tool: enhancing breeding productivity of Western Flycatchers ( Empidonax difficilis occidentalis ) in southwestern Colorado and southern Arizona, USA

Comparative genomics of two Empidonax flycatchers reveal candidate genes for bird song production.

Whole-genome level comparisons of sister taxa that vary in phenotype against a background of high genomic similarity can be used to identify the genomic regions that might underlie their phenotypic differences. In wild birds, this exploratory approach has detected markers associated with plumage coloration, beak and wing morphology, and complex behavioral traits like migration. Here, we use genomic comparisons of two closely related suboscine flycatchers (Empidonax difficilis and E. occidentalis) and their hybrids to search for candidate genes underlying their variation in innate vocal signals. We sequenced the genomes of 20 flycatchers that sang one of two species-specific parental song types and 14 putative hybrid individuals with intermediate song types. In the resulting genomic comparisons, we found six areas of high differentiation that may be associated with variation in non-learned songs. These narrow regions of genomic differentiation contain a total of 67 described genes, three of which have been previously associated with forms of language impairment and dyslexia in humans, and 18 of which are known to be differentially expressed in the song nuclei regions of the avian brain compared to adjacent parts of the avian brain. This 'natural experiment' therefore may help identify loci associated with song differences that merit further study across bird lineages with both learned and innate vocalizations.

Visualizing Connectivity for Wildlife in a World Without Roads

Roads are not the only determining factor for wildlife movement across the landscape, but due to the extensive distribution of the road network their impact can be dramatic. Although it has been well documented that roads decrease habitat connectivity for wildlife due to animal-vehicle collisions, habitat fragmentation, and avoidance behavior, approaches for identifying connectivity across the landscape often do not fully examine the barrier effect of roads. Here, we explored the extent of the impact of roadways on wildlife connectivity by using Omniscape to model connectivity including and without the barrier effect of roads, then evaluating the difference between these two models. We created these connectivity models for three organisms that represent different taxa, movement types, and habitat requirements: northern red-legged frog, Pacific-slope flycatcher, and Columbian black-tailed deer. We found that roads had a strong impact on connectivity for all three species. Change in flow was most pronounced on the roads, especially where they ran through permeable habitat for a species. Roads also influenced connectivity well beyond the footprint of the roadway, affecting flows intersecting the roads and diffusely around them. The extent and nature of this impact depended on the species, road density, and surrounding habitat. The different effects across species highlight the importance of considering different taxa simultaneously while planning. Moreover, the ability to assess modeled wildlife habitat connectivity in the absence of existing widespread linear infrastructure allows for critical evaluation of where mitigation activities, such as wildlife crossing structures and fencing, may be most beneficial. Hence, this novel approach has practical application for increasing connectivity for wildlife across roads.

Evaluating the role of active management in mature Douglas-fir (Pseudotsuga menziesii) stands for songbird conservation

Forest birds, particularly those associated with late-successional forests, are of widespread conservation interest. Although birds are among the more widely studied taxa of forest wildlife, relatively few studies have examined the long-term effects of active management (i.e., intentional stand density reduction) on the forest bird assemblage. This is an important omission, as changes in stand structure and composition over the decades following harvesting may influence wildlife utilization of forest stands. We developed an observational study to evaluate forest bird response to stand structural development multiple decades following harvesting with differing levels of overstory density reduction, and in unmanaged stands. We focused, in particular, on songbirds and cavity excavating species associated with old-growth Douglas-fir forests, and the active management strategies that we examined – thinning and structural retention harvesting – were selected based on their potential to accelerate stand structural development. Our 18 mature stands (age range: 107–187 years) were located in the western hemlock zone of western Oregon, and bird surveys were conducted an average of 41 years and 22 years post-harvest in thinned and retention harvest stands, respectively. Poisson generalized linear models were formulated to evaluate the effects of management condition on forest birds. Although five species were associated with specific management conditions, relative abundance was not statistically different between unmanaged, thinned and retention harvest stands for a majority of the species in our analysis. Species richness was also relatively invariant across management conditions. Our results do suggest that retention harvesting adversely affects some songbird species associated with old-growth forests – Pacific-slope flycatcher (Empidonax difficilis) and Pacific wren (Troglodytes pacificus) for example - but our findings also indicate that retention harvesting has long-term benefits for birds associated with early-successional forests. This includes migrant species that have experienced significant population declines in Western North America over recent decades, such as Wilson’s and MacGillivray’s warblers (Cardellina pusilla and Geothlypis tolmiei, respectively). Overall, our results imply that for many species of forest birds, including those associated with old-growth forests, managers have some flexibility in overstory density management where long-term species persistence is an objective. Equally significant, our results provide strong support for the application of variable retention harvesting as a tool for the conservation of bird species associated with early-successional forests, while also reinforcing the value of mature structural legacies for bird species associated with late-successional forests. While also reinforcing the value of mature structural legacies for birds associated with late-successional forests.

Long-term response of forest bird communities to retention forestry in northern temperate coniferous forests

Retention forestry aims to maintain structural and functional continuity in managed stands. While short-term benefits to forest dwellers are well documented, few studies have followed patterns over decades to assess whether benefits continue. Initiated in 1992, the Date Creek Research Forest in northwest BC includes four replicates of four retention levels: 0% (clearcut), 40%, 70% and 100% (unharvested control). These ~20-hectare stands, with retention designed to mimic typical insect and wind disturbance, are now entering the canopy closure seral stage. We followed breeding bird community dynamics over 25 years (pre-harvest and 24 years post-harvest). Given relatively consistent landscape conditions over time, we focused on stand-level changes in bird community composition and species abundance. Community similarity to controls decreased as retention decreased; communities changed over time, with those in clearcuts changing most. Patterns in species abundance varied with habitat preference. Conifer-forest species declined immediately after harvest, with some responding linearly to retention level while others responded similarly to 40%, 70% and 100% treatments; Pacific Slope Flycatcher, Pacific Wren and Brown Creeper remained significantly less abundant in some treatments by year 24. Open-habitat and generalist species increased most in clearcut and somewhat in 40% retention stands, with generalists taking advantage of the increased heterogeneity immediately and open-habitat species colonizing by year 10; some of these species, particularly shrub specialists, remained at high abundance in harvested stands in year 24. Mixed-forest species reached their highest abundance at 40% retention in year 2 and 10, and dropped to control levels by year 24. Although conifer-forest, open-habitat and generalist species treated retention stands as intermediate between clearcuts and controls, mixed-forest species perceived them as a different, preferred habitat for the first decade. We conclude first that most forest birds do not discriminate between 70% retention stands and unharvested forest, confirming strategies in the region to maintain biodiversity in landscape corridors, second that aggregated 40% patch retention partially or fully mitigates impacts for conifer-forest birds, and provides new habitat for mixed-forest and open-habitat species, and third that bird communities are still changing after 24 years as these stands enter canopy closure.

Long-term changes in the seasonal timing of landbird migration on the Pacific Flyway

ABSTRACT The seasonal phenology of latitudinal movements is one of the key life-history traits of migratory birds. We used quantile regression to examine long-term changes in the timing of spring and autumn migration in 5 species of migratory passerine birds captured at a banding station in northern California, USA, over a 22 yr period from 1987 to 2008. Our 5 study species included 3 short-distance migrants, Pacific-slope Flycatcher (Empidonax difficilis), Orange-crowned Warbler (Oreothlypis celata), and Wilson's Warbler (Cardellina pusilla); and 2 long-distance migrants, Swainson's Thrush (Catharus ustulatus) and Yellow Warbler (Setophaga petechia). Median timing of migration advanced in spring for 2 of the 5 species (−2.5 days decade−1) but was delayed during autumn migration for 3 of the species (+2.9 days decade−1). The duration of the migration period also became compressed in some species but more protracted in others. We tested whether annual variation in migration timing was related to 3 indices ...

Species Identification of Vagrant Empidonax Flycatchers in Northeastern North America Via Non-Invasive DNA Sequencing

Vagrant individuals from cryptic species complexes pose a persistent challenge for accurate species identification, hindering our understanding of vagrancy in these taxa. Here, we used non-invasive sampling of fecal matter to sequence the ND2 mitochondrial gene of 2 vagrant western flycatchers observed in northeastern North America. The DNAsequence data we recovered from these vagrants fell within a clade of known Empidonax difficillis (Pacific-slope Flycatcher) haplotypes. Our work provides robust records of 2 vagrant Pacific-slope Flycatchers in the northeastern US. These findings illustrate the power of non-invasive sampling for species identification of vagrants from cryptic species complexes.

Simple technique for distinguishing Yellow-bellied Flycatchers from Cordilleran and Pacific-slope flycatchers

Flycatchers of the genus Empidonax are readily misidentified in the field, in the hand, and even in museum collections. We describe a novel plumage feature that can be used to distinguish Yellow-bellied Flycatchers (E. flaviventris) from the two species that comprise the Western Flycatcher complex, Cordilleran Flycatchers (E. occidentalis) and Pacific-slope Flycatchers (E. difficilis). The length of the buffy fringing on the anterior edge of each secondary feather, visible on the folded wing, is significantly shorter in Yellow-bellied Flycatchers than in Western flycatchers, with minimal overlap. A definitive identification can be made using a simple formula that includes measurements of wing chord and the length of the buffy fringing along the outer edge of the first secondary (S1). This method provides definitive in-hand identification, and the difference in length of the buffy fringing on the secondaries is also a useful field mark for visual identification. Testing our method with 113 museum specimens that had been identified a priori based on locality, we correctly identified 112 specimens. The exception was a specimen from Illinois that had been assumed to be a Yellow-bellied Flycatcher. However, based on our formula, it was a Western flycatcher and analysis of its mtDNA sequence confirmed this result, proving the utility of our method. Técnica simple para distinguir al Mosquetero vientre amarillo de los mosqueteros cordillerano y californiano Los tiránidos del genero Empidonax son constantemente mal identificados en el campo, en mano, y aún en colecciones de museo. Describimos un novedoso carácter de plumaje que puede ser usados para distinguir al Mosquetero vientre amarillo (E. flaviventris) de las otras dos especies que comprenden el complejo Mosqueteros del oeste, el Mosquetero cordillerano (E. occidentalis) y el Mosquetero californiano (E. difficilis). El largo de la franja difusa en el borde anterior de cada pluma secundaria, visible cuando el ala está plegada, es significativamente más corta en el Mosquetero vientre amarillo que en los Mosqueteros del oeste, con un solapamiento mínimo. Una identificación definitiva puede hacerse usando una simple fórmula que incluye medidas del largo del ala y del largo de la franja difusa a lo largo del borde externo de la primera secundaria (S1). Este método provee identificación definitiva en mano, y la diferencia en el largo de la banda difusa en las secundarias es también una marca útil en el campo para la identificación visual. Al poner a prueba nuestro método con 113 especímenes de museo que han sido identificados a priori basándose en la localidad, hemos identificado correctamente a 112 especímenes. La excepción fue un espécimen de Illinois que se ha asumido que es un Mosquetero vientre amarillo. Aún así, basándonos en nuestra fórmula, se trataba de un Mosquetero cordillerano, y análisis de secuencias de mtDNA confirmaron este resultado, probando la utilidad del método. Disclaimer: Supplementary materials have been peer-reviewed but not copyedited. Supplementary Appendix S1 Table S1. Specimens used in the study, with measurement data, age, URL links to online specimen records, where applicable, and Genbank accession numbers. Specimens are held in the collections of the Museum of Vertebrate Zoology (MVZ), Field Museum of Natural History (FMNH), and Museum of Southwestern Biology (MSB). Specimens that did not have age data were aged by coloration of coverts, shape and wear of primary coverts, and shape of tail feathers following Pyle (1997a). Table S2. Morphological measurements, in millimeters (mm), of FMNH:Bird:472922 compared to reported ranges for Yellow-bellied, Pacific-slope, and Cordilleran flycatchers from Pyle (1997a, b), and Heindel and Pyle (1999). Table S3. Pairwise mean uncorrected p-distance among Empidonax species and FMNH:Bird:472922 based on 1041 bp of the mitochondrial gene ND2. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The Birds of the Ciénega de Santa Clara, a wetland of international importance within the Colorado River Delta

The Ciénega de Santa Clara is the largest marsh in the Sonoran Desert and the most important wetland in the Colorado River delta. We present the information on the state of the birds in the Ciénega and a checklist of the species that have been detected at the site. We also summarize the ornithological work that has been conducted and compiled recommendations for bird conservation. A total of 261 species of birds have been detected in the Ciénega de Santa Clara, representing 71% of the species known to the Colorado River delta. The birds of the Ciénega include 189 migratory species (70.4%), 49 year-round residents (18.7%), and 28 breeding visitors (10.7%). Twenty-seven species are federally protected in Mexico, four of them as Endangered, eight as Threatened, and 15 under Special Protection. The Ciénega provides critical habitat for migratory waterbirds, with maximum counts of 280,000 shorebirds in the southern mudflats, as well as for breeding marsh birds, including Yuma Clapper Rails, Virginia Rails and California Black Rails, with maximum estimates of 8600, 7150 and 400 individuals respectively. Other species of concern that occur regularly in the Ciénega include Least Bittern, Snowy Plover, Least Tern, and Large-billed Savannah Sparrow. This wetland also provides important stopover habitat for 81 species of Neotropical migratory landbirds during their northbound spring migration, particularly for Wilson's Warbler, Swainson's Thrush, Yellow Warbler, Pacific-slope Flycatcher, and Willow Flycatcher. Binational cooperation is essential to protect the Ciénega in the long-term, especially in terms of dedicating the necessary water for its maintenance. Active management actions are also becoming an important part of habitat conservation, including land protection mechanisms, sediment removal, and fire management.

Short‐term responses of birds to prescribed fire in fire‐suppressed forests of California

AbstractPrescribed fire is one tool for restoring fire‐suppressed forests, but application of fire during spring coincides with breeding and arrival of migrant birds. We examined effects of low‐severity prescribed fires on counts of birds in a managed forest in the Sierra Nevada of California immediately, 1 year, and 3–6 years after fire was applied in spring. Of 26 species analyzed, counts of 3 species increased after fire (Pacific‐slope flycatcher [Empidonax difficilis], brown creeper [Certhia americana], and American robin [Turdus migratorius]), and 6 species decreased after fire (Anna's hummingbird [Calypte anna], Hutton's vireo [Vireo huttoni], warbling vireo [Vireo gilvus], golden‐crowned kinglet [Regulus satrapa], Nashville warbler [Vermivora ruficapilla], hermit warbler [Dendroica occidentalis]). Black‐throated gray warbler (Dendroica nigrescens) increased in the first year following fire but decreased 3–6 years after fire. When grouped into guilds, habitat association and foraging guild best explained responses to fire, with the greatest changes occurring for oak‐associated species (negative), riparian‐associated species (positive), aerial foragers (positive), and bark foragers (positive). Lastly, when we compared our counts to those collected during the 1910s, changes were consistent with those predicted from fire suppression and species' affinity for burned forests, suggesting that results from contemporary fire studies should be interpreted within an ecological context that includes effects of fire suppression. We found that low‐severity prescribed fires applied in spring served to drive the bird community towards pre‐suppression conditions. © 2011 The Wildlife Society.

Effects of fuel reduction on bird density and reproductive success in riparian areas of mixed-conifer forest in southwest Oregon

Studies in southwest Oregon suggest that riparian areas within mixed-conifer forests historically burned with frequencies and intensities similar to upland areas and that fire played an important role in maintaining both of these ecosystems. Currently, most fuel reduction projects do not include riparian, due to the perception that these riparian areas are negatively affected by anthropogenic disturbance. However, there is very little information on the ecological consequences of including riparian areas in fuel reduction projects. We compared the effects of non-commercial thin and handpile treatments followed by prescribed burns in riparian areas of intermittent and perennial streams that were treated to the streamside (unbuffered), to the typical prescription in which sites were treated only in the adjacent upland (buffered). Unbuffered fuel reduction treatments have the potential to affect bird density and reproductive success differently than buffered treatments by altering (1) available nest habitat, (2) predator and nest parasite abundance, and (3) food availability in riparian areas. This study assessed whether unbuffered fuel reduction treatments yielded similar bird response as buffered treatments by quantifying differences in density and reproductive success of five bird species, vegetation structure, the frequency of occurrence of predators and a nest parasite, and arthropod biomass. Density was greater for the shrub and tree-nesting Pacific-slope Flycatcher in buffered streams post treatment. Reproductive success showed a minimal, near-term effect for the shrub-nesting Black-headed Grosbeak. For potential causal factors, we found differences between buffered and unbuffered streams only for available nest habitat in the upper-ground strata and frequency of occurrence of raptors. Overall, results suggest that fuel reduction in riparian areas as compared with typical upland treatments with buffers had a small effect on bird density and a near-term effect on reproductive success. Additional study of fuel reduction in riparian areas is warranted because of its effectiveness in reducing the risk of unnaturally severe wildfire and, correspondingly, the potential benefit to bird communities over the long-term.

AVIAN NEST SURVIVAL IN COASTAL FORESTED BUFFER STRIPS ON PRINCE OF WALES ISLAND, ALASKA

Abstract In an effort to provide wildlife habitat and link blocks of forested habitat, coastal forested buffer strips in the Pacific Northwest are managed to mitigate effects of fragmentation that result from timber harvesting adjacent to a coastline. We examined the effect of coastal forest buffer strip width on avian nest survival on Prince of Wales Island, Alaska, in 2003 and 2004. We established nest monitoring plots in two buffer width treatments, narrow ( 350 m, n = 3), and monitored a total of 142 nests of six species: the Pacific-slope Flycatcher (Empidonax difficilis), Chestnut-backed Chickadee (Poecile rufescens), Winter Wren (Troglodytes troglodytes), Swainson's Thrush (Catharus ustulatus), Hermit Thrush (Catharus guttatus), and Varied Thrush (Ixoreus naevius). We modeled and compared the daily survival rate (DSR) of each species in both buffer width treatments. Point estimates for DSRs were slightly higher within wide buffers, but confidence intervals overlapped for al...

Forested Buffer Strips and Breeding Bird Communities in Southeast Alaska

Abstract: Forested buffer strips are used to mitigate fragmentation and habitat loss and are a common feature in management of riparian landscapes. Low‐elevation, old‐growth coastal forests are a rare riparian habitat that can benefit from similar conservation measures. We evaluated the effectiveness of postlogging, forested buffer strips for forest‐dwelling birds in the coastal temperate rainforest of southeast Alaska, USA. Our objective was to compare bird composition and density among forested buffer strips of differing widths and controls at the stand and landscape scales. We applied a 2‐stage sampling design stratified by forested buffer width and randomly selected 24 managed and 18 control sites to sample over 2 breeding seasons. We estimated abundance of birds using the paired‐observer, variable‐circular plot method. We modeled combined effects of buffer width and vegetation and landscape characteristics on bird density at 2 spatial scales. Species richness and diversity were greatest in the narrowest buffers, but species composition in the largest buffers (≥400 m) was most similar to that in control blocks. Abundance of 3 of 10 common species differed across forested buffer treatments and controls. Densities of red‐breasted sapsucker (Sphyrapicus ruber) and Pacific‐slope flycatcher (Empidonax difficilis) were positively related to buffer width, whereas density of ruby‐crowned kinglet (Regulus calendula) was negatively associated with buffer width. Parameter estimates for buffer width effects at both spatial scales were similar within species. We found few habitat and landscape variables that clearly affected density of our focal species, and among species no predictor variables affected density in a similar fashion. We recommend retaining forested buffers ≥400 m to support composition and abundance of forest‐dwelling birds, particularly those species that rely on interior forest conditions. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):674‐681; 2008)

PRESENCE OF SALMON INCREASES PASSERINE DENSITY ON PACIFIC NORTHWEST STREAMS

Abstract The annual migration of Pacific salmon (Oncorhynchus spp.) to freshwater streams and lakes provides an important nutrient subsidy to terrestrial systems in North America. We investigated the effects of salmon and other habitat variables on abundance of Winter Wren (Troglodytes troglodytes), Swainson's Thrush (Catharus ustulatus), Varied Thrush (Ixoreus naevius), Pacific-slope Flycatcher (Empidonax difficilis), Golden-crowned Kinglet (Regulus satrapa), and Chestnut-backed Chickadee (Poecile rufescens) on the central coast of British Columbia. In our comparisons of salmon-bearing and non-salmon-bearing reaches of two rivers that had waterfall barriers to salmon partway upstream, we found that position above or below the falls and proximity to the stream were the major predictors of songbird abundance. Each species, except for Chestnut-backed Chickadee, had higher densities below the falls at both rivers. Our results suggest that salmon-derived nutrients influence songbird density, and thus benefit ...

Estimating Detection Probability and Density from Point-Count Surveys: A Combination of Distance and Double-Observer Sampling

AbstractPoint counts are the method most commonly used to estimate abundance of birds, but they often fail to account properly for incomplete and variable detection probabilities. We developed a technique that combines distance and double-observer sampling to estimate detection probabilities and effective area surveyed. We applied this paired-observer, variable circular-plot (POVCP) technique to point-count surveys (n = 753) conducted in closed-canopy forests of southeast Alaska. Distance data were analyzed for each species to model a detection probability for each observer and calculate an estimate of density. We then multiplied each observer's density estimates by a correction factor to adjust for detection probabilities <1 at plot center. We compared analytical results from four survey methods: single-observer fixed-radius (50-m) plot; single-observer, variable circular-plot (SOVCP); double-observer fixed-radius (50-m) plot; and POVCP. We examined differences in detection probabilities at plot center, effective area surveyed, and densities for five bird species: Pacific-slope Flycatcher (Empidonax difficilis), Winter Wren (Troglodytes troglodytes), Golden-crowned Kinglet (Regulus satrapa), Hermit Thrush (Catharus guttatus), and Townsend's Warbler (Dendroica townsendi). Average detection probabilities for paired observers increased ≈8% (SE = 2.9) for all species once estimates were corrected for birds missed at plot center. Density estimators of fixed-radius survey methods were likely negatively biased, because the key assumption of perfect detection was not met. Density estimates generated using SOVCP and POVCP were similar, but standard errors were much lower for the POVCP survey method. We recommend using POVCP when study objectives require precise estimates of density. Failure to account for differences in detection probabilities and effective area surveyed results in biased population estimators and, therefore, faulty inferences about the population in question.Estimaciones de la Densidad y de las Probabilidades de Detección a Partir de Muestreos Utilizando Conteos en Puntos: Una Combinación de Muestreos de Distancia y de Doble Observador

HABITAT USE BY RIPARIAN AND UPLAND BIRDS IN OLD-GROWTH COASTAL BRITISH COLUMBIA RAINFOREST

The value of riparian habitats to birds differs among ecosystems. I tested whether riparian habitat near large streams and rivers in the Pacific Northwest supported a higher abundance and diversity of birds than adjacent upland forest. From 1996 to 1998, I surveyed breeding birds at four 9-ha sites in coastal western hemlock forest on western Vancouver Island, British Columbia. Five species of forest generalists dominated both riparian and upland bird communities: Winter Wren (Troglodytes troglodytes), Chestnut-backed Chickadee (Poecile rufescens), American Robin (Turdus migratorius), Swainson's Thrush (Catharus ustulatus), and Pacific-slope Flycatcher (Empidonax difficilis). Species richness and total abundance were similar over the riparian-to-upland gradient, whereas abundances of riparian specialists and aerial foragers declined with distance from the river. To explore whether vegetation composition and structure explained bird distribution patterns, I sampled three locations along both riparian and upland transects at each site. Riparian areas had higher densities of deciduous trees; conifer and snag densities were higher in upland areas. Salmonberry (Rubus spectabilis) cover was marginally higher in riparian areas and blueberry (Vaccinium spp.) cover was higher in upland areas. There was little effect of distance from the river on most bird species, but there were stronger associations of birds with specific vegetation attributes. Tree and snag densities explained the most variation in abundance of aerial foragers, and eight of nine individual species, whereas distance from the river and shrub cover were important predictors of Hammond's Flycatcher (Empidonax hammondii) abundance. Apart from riparian specialists and a few species with strong vegetation associations, bird assemblages in riparian and upland habitats of this moist forest type were dominated by similar sets of generalist species.

BREEDING BIRDS OF RESEARCH NATURAL AREAS IN SOUTHEASTERN ALASKA

Abstract The Tongass National Forest encompasses a large expanse of temperate rainforest in southeastern Alaska and contains 12 designated Research Natural Areas (RNAs). Existing in as near a natural condition as possible, RNAs receive minimal commercial and recreational use. Because few bird studies have been conducted on RNAs, we used point counts and area searches to determine the occurrence and abundance of breeding landbirds present in vegetation communities of RNAs. Of 49 species of small landbirds detected during area searches, the most widely distributed birds among RNAs were rufous hummingbird (Selasphorus rufa), chestnut-backed chickadee (Poecile rufescens), winter wren (Troglodytes troglodytes), golden-crowned kinglet (Regulus satrapa), Swainson's thrush (Catharus ustulatus), hermit thrush (C. guttatus), varied thrush (Ixoreus naevius), and Townsend's warbler (Dendroica townsendi). The 8 most abundant species recorded on 187 point counts (>0.5 birds/point) were Pacific-slope flycatcher (Empidon...

RESPONSE OF BIRDS TO THINNING YOUNG DOUGLAS‐FIR FORESTS

Silvicultural practices, such as thinning, are increasingly performed both for commodity production and to help achieve biodiversity goals and promote ecological restoration. However, relatively little research has examined effects of thinning conifer forests on vertebrates. We experimentally manipulated stands using a randomized block design to evaluate influences of two thinning intensities on populations of diurnal breeding birds in western Oregon. We conducted point counts of birds seven times each year in 1994 (prior to treatment) and from 1995 through 2000 (subsequent to treatment). We analyzed data using multiple linear regression and information‐theoretic approaches to model selection. Of the 22 species for which we had sufficient data for analysis, detections of nine species decreased and eight species increased in thinned stands relative to controls, and there was no strong evidence that thinning influenced numbers of five species. Of the 17 species that responded to thinning, the magnitude of response of eight species varied with thinning intensity; for each of these species, response was greatest in the more heavily thinned stands. Although no species was extirpated from stands following thinning, detections of Hutton's Vireos (Vireo huttoni), Golden‐crowned Kinglets (Regulus satrapa), Brown Creepers (Certhia americana), Black‐throated Gray Warblers (Dendroica nigrescens), and Varied Thrushes (Ixoreus naevius) decreased to less than half of the detections in controls in one or more treatment types, suggesting thinning significantly reduces their numbers. In contrast, American Robins (Turdus migratorius), Townsend's Solitaires (Myadestes townsendi), and Hammond's Flycatchers (Empidonax hammondii) were rare or absent in controls but regularly present in thinned stands, and detections of Western Tanagers (Piranga ludoviciana), Evening Grosbeaks (Coccothraustes vespertinus), and Hairy Woodpeckers (Picoides villosus) increased by threefold or more in thinned stands relative to controls. Only Pacific‐slope Flycatchers (Empidonax difficilis), Warbling Vireos (Vireo gilvus), and Western Tanagers showed strong evidence of temporal trends in response. For these species, differences between numbers in controls and treated stands became more extreme through time. Our findings suggest that thinning densely stocked conifer stands in landscapes dominated by younger stands enhances habitat suitability for several species of birds, but that some unthinned patches and stands should be retained to provide refugia for species that are impacted by thinning.

Response of Passerine Birds to Forest Edge in Coast Redwood Forest Fragments

Abstract The response of passerine birds to forest edge was examined in old-growth and mature second-growth coast redwood (Sequoia sempivirens) forest in northern California. The study objectives were to determine which common passerine species are sensitive to edges during the breeding season and to estimate edge width for forest interior species. Response to edge was measured along twelve 100 × 400 m plots extending from the edge into the forest interior to obtain relative density of birds. Plots were surveyed 4 to 5 times in 1996 and 8 to10 times in 1997. We found that 14 common passerines showed a gradient of edge sensitivity. Steller's Jay (Cyanocitta stelleri) and Swainson's Thrush (Catharus ustulatus) had higher relative densities near edges than in the forest interior (P < 0.05) and were categorized as edge species. Brown Creeper (Certhia americana), Winter Wren (Troglodytes troglodytes), Pacific-slope Flycatcher (Empidonax difficilis), and Varied Thrush (Ixoreus naevius) had lower relative densities near edges (P < 0.05) and were categorized as interior birds. Based on exponential regression models, estimated edge widths were 140 m for Varied Thrushes, 85 m for Brown Creepers, 120 m for Winter Wrens, and 125 m for Pacific-slope Flycatchers. Creation of edges would probably benefit Steller's Jays (which may be a nest predator), may not benefit Swainson's Thrushes, and may be detrimental to species that avoid edges. We recommend that edge effects be taken into consideration when planning for the conservation of bird species in the region.

Breeding Bird Response to Riparian Buffer Width in Managed Pacific Northwest Douglas-Fir Forests

We examined the relative importance of riparian vs. upland habitats to breeding birds by comparing species abundance, richness, and similarity of bird communities in managed Douglas-fir forests in western Washington State, USA. We also examined whether forested buffer strips along second- and third-order streams effectively maintain the pre-logging riparian breeding bird community by comparing species abundance, richness, and turnover among three treatments: (1) unharvested controls; (2) sites that were clear-cut, leaving a narrow (∼14 m) forested buffer on both sides of the stream; and (3) sites that were clear-cut, leaving a wide (∼31 m) forested buffer along both sides of the stream. Deciduous trees, berry-producing shrubs, and other deciduous shrubs less common in adjacent upland forest characterized streamside zones. Despite different vegetation features, riparian and upland habitats did not differ in any measures of bird species richness and composition. No species or species group was more abundant in the upland. Neotropical migrants, resident species, and species associated with deciduous trees and shrubs in forested habitats were more abundant in riparian habitats than in adjacent uplands. Total bird abundance and abundance of four species (American Robin [Turdus migratorius], Pacific-slope Flycatcher [Empidonax difficilis], Black-throated Gray Warbler [Dendroica nigrescens], and Winter Wren [Troglodytes troglodytes]) were higher in riparian habitats. Abundance of these riparian associates was correlated with percent cover of berry-producing shrubs and the number of deciduous trees in the canopy. We found that the number of breeding bird species on sites with narrow buffers increased from slightly fewer than controls before harvest to an average of 10 more species than controls after harvest, a change reflected in an average 20% increase in species turnover on narrow-buffer sites relative to controls. Total bird abundance did not differ between treatments and controls. Resident species, those species associated with shrubs in forested habitats and conifer trees, declined on both buffer treatments. Species associated with upland and riparian forests (Black-throated Gray Warbler, Golden-crowned Kinglet [Regulus satrapa], and Brown Creeper [Certhia americana]) decreased in abundance on riparian buffer treatments relative to controls, whereas species associated with open, shrubby habitats (Dark-eyed Junco [Junco hyemalis], Cedar Waxwing [Bombycilla cedrorum], and Song Sparrow [Melospiza melodia]) increased in abundance on one or both riparian buffer treatments. High species turnover on narrow-buffer treatments indicated that buffers <14 m on each side of the stream did not maintain the pre-logging bird community. There was little difference in species turnover or species richness between the wide-buffer treatment and the control, indicating that a 30-m buffer on both sides of second-order and third-order streams maintains most of the pre-logging bird community in the first two years postharvest. The Black-throated Gray Warbler was the only riparian associate to decline on both the narrow- and wide-buffer treatments; its abundance was positively correlated with buffer width, and a buffer ≥45 m wide on each side of second- and third-order streams was needed to support populations at densities found on unharvested controls. To maintain the entire breeding bird community associated with forested riparian habitats in the coastal Northwest, we recommend a minimum buffer of 45 m along both sides of second- and third-order streams. Habitat features such as deciduous trees (Alnus rubra and Acer macrophyllum) and berry-producing shrubs (especially Rubus spectabilis) appear to be important and should be maintained within forested riparian buffer strips. This study documents short-term effects of riparian treatments on the breeding bird community, which may take several years to respond to habitat manipulations. Thus, we recommend continued monitoring to assess long-term effects of buffer width reduction.