Blackburnian Warbler Research Articles

General Comparative Analysis of Bird-Bat Collisions at a Wind Power Plant in the Department of Rivas, Nicaragua, between 2014 and 2022

From 2014 to 2022, eight monitoring campaigns have been carried out, documenting 119 collisions of birds belonging to 25 species corresponding to 14 families. Of the total collisions, 35 individuals could not be identified because only remains of the animal’s body (feathers) were found, due to the presence of day and night predators. Of the bird species identified, 17 are resident, three are migratory species, two are transient species, one species with transient populations that migrate south, and two species with both resident and migratory populations. During these years, no species with an important conservation category according to the IUCN were reported. Three species are on Nicaragua’s Red List, the migratory species Blackburnian Warbler (Setophaga fusca) and the resident species Mangrove Cuckoo (Coccyzus minor), both with the Near Threatened category; and the only migratory hummingbird for Nicaragua, the Ruby-throated Hummingbird (Archilochus colubris) with the Vulnerable category. The family with the highest frequency of collided bird species is the pigeons (Columbidae), these being very significant (X2 = 345.20, p < 0.01). The species with the highest frequency of collisions is the Common Ground-Dove (Columbina passerina) species, with these collisions being very significant (X2 = 72.05, p < 0.01). Collisions per month and year show very significant differences, especially for April 2016 (X2 = 41.60, p < 0.01). Tower T13 shows significant collisions in these eight monitoring campaigns (X2 = 36.48, p < 0.05). Bird collision distances show very significant collisions between 0 and 5 m away from the turbines (X2 = 268.96, p < 0.01). No differences were found regarding collisions between large and small birds (X2 = 2.09, p > 0.05). The granivore group presented a very significant frequency of collisions (X2 = 84.00, p < 0.01), as well as a very significant frequency of collisions in the non-passerines birds (X2 = 42.26, p < 0.01). Very significantly higher fatality frequencies were observed in 2016 (X2 = 60.16, p < 0.01). For the period 2014 to 2022 in bats, 134 collisions of bats belonging to 18 species corresponding to four families were observed. Of the total number of collisions, 24 individuals could not be identified because they were in poor condition. No species with important conservation criteria have been recorded according to the IUCN or the Nicaraguan Red List. The Molossidae family is the group with the highest number of very significant collisions (X2 = 53.61, p < 0.01), with the Pallas’s Mastiff Bat (Molossus molossus) being the one that presented very significant collisions (X2 = 199.69, p < 0.01). Very significant collisions occur, with a peak in November 2015 (X2 = 75.19, p < 0.01). Tower T15 presents the highest frequency of collisions, which is very significant (X2 = 39.04, p < 0.01). The frequency of collisions remains very significantly higher in the three distance categories closest to the towers, from 0 to 14.9 m (X2 = 43.64, p < 0.01). The highest frequency for very significant collisions of bats is that of insectivores (X2 = 222.10, p < 0.01). A very significant frequency of collisions was observed in 2015 (X2 = 68.75, p < 0.01). Key periods like fall and spring bird migration should be prioritized when planning collision monitoring plans. Standardized monitoring protocols and implementation of estimated mortality formulas that compensate for the search effectiveness of observers, the search area, and the removal of collisions are also important for not underestimating bird and bat collisions.

Bird communities reveal the ecological value of non-native Norway spruce plantations in Massachusetts, USA

The establishment of monoculture plantations of non-native tree species is a common practice for supplementing native timber stocks. Since native wildlife species may lack co-evolved traits needed to successfully exploit non-native tree species, non-native plantations are expected to provide inferior habitat for native biodiversity. However, some studies report that plantations may increase net biodiversity at the landscape scale by introducing novel habitats or supplementing existing natural forests. We used point counts to sample birds in 2016 and 2017 in mature Norway spruce (Picea abies) plantations in western Massachusetts, as well as representative native forest types, to evaluate bird use of these plantations relative to native forest types. Our findings showed that overall species richness for spruce plantations was similar to that of native forest habitats, and that several native conifer-dependent species (red-breasted nuthatch (Sitta canadensis), golden-crowned kinglet (Regulus satrapa), blackburnian warbler (Setophaga fusca), and brown creeper (Certhia americana) were significantly more abundant in spruce plantations relative to native deciduous, hemlock, and mixed stands. Bird species reported to associate with eastern hemlock (Tsuga canadensis), such as blue-headed vireo (Vireo solitarious) and black-throated green warbler (Setophaga virens), were observed using spruce plantations at similar levels as eastern hemlock stands. These results demonstrate that Norway spruce plantations can provide suitable habitat for native species associated with conifers, which is significant given projected continued decline of eastern hemlock in response to the hemlock wooly adelgid (Adelges tsugae). Although large-scale conversion of native forest to plantations would likely lead to a loss in biodiversity, land managers could be justified in allowing small-scale plantations to persist without suffering negative impacts to native biodiversity.

Predicting effects of selection cutting on avian diversity and abundance in shade-tolerant hardwood forests of central Ontario

Emulating natural disturbance (END) patterns to conserve biodiversity is often a goal of forest management but the impact of forest cutting is still controversial. We examined effects on avian assemblages of partially-cut forest stands of 1–10, 11–20 and > 45 years (cut classes) post-harvest differing in the % basal area retained as wildlife species’ habitat in 85 shade-tolerant hardwood stands in Algonquin Park, Ontario. Permutational multivariate analysis of variance indicated significant compositional differences among cut classes, after controlling for year and township (spatial variation in surficial geology and topography), both of which were also significant. Pairwise comparisons indicated significant compositional differences only between young and old stands. The difference in beta diversity (homogenization/differentiation) among cut classes was marginally significant (P = 0.066). Pairwise differences were significant between old versus mid-aged cut classes, marginally significant for young versus old cuts, and non-significant for young versus mid-aged cut classes. Six species and cavity users as a group were more abundant in > 45 years post-harvest stands than in the other two cut classes. Six species had higher abundances in younger cuts than > 45 years post-harvest cuts. Red-eyed vireo (Vireo olivaceus) showed a nonlinear response and was least abundant in 11–20 year cuts. Blackburnian warblers Setophaga fusca, black-throated green warblers S. virens and pileated woodpeckers Dryocopus pileatus increased with the density of supercanopy trees (≥ 60 cm diameter at breast height - dbh) and in the case of pileated woodpeckers more large snags (≥ 40 cm dbh). Brown creeper Certhia americana abundance increased with greater basal area of trees ≥ 25 cm dbh and ovenbird numbers were significantly related to overall basal area. Chestnut-sided warbler S. castanea abundance decreased with an increase in overall basal area and was higher in the 1–10 year cuts and American redstarts S. ruticilla decreased with an increase in basal area. Our modelling suggests that effects of selection cutting systems on the avian community may be reduced as tolerant hardwood stands become regulated and have higher residual basal areas. Current guidelines in Ontario for the retention of large, scattered conifer trees appear to meet the requirements for most, but not all, species; however, guidelines for supercanopy trees are too low. These results indicate that the END paradigm for single-tree selection cutting in tolerant hardwoods may be partially effective but requires modifications, such as retaining higher densities of supercanopy trees that would be beneficial for birds.

Cross-scale effects of spruce budworm outbreaks on boreal warblers in eastern Canada.

Insect outbreaks are major natural disturbance events that affect communities of forest birds, either directly by affecting the food supply or indirectly by changing the vegetation composition of forest canopies. An examination of correlations between measures of bird and insect abundance across different spatial scales and over varying time lag effects may provide insight into underlying mechanisms. We developed a hierarchical Bayesian model to assess correlations between counts of eight warbler species from the Breeding Bird Survey in eastern Canada, 1966 to 2009, with the presence of spruce budworm (Choristoneura fumiferana Clem.) at immediate local scales and time‐lagged regional scales, as measured by extent of defoliation on host tree species. Budworm‐associated species Cape May warbler (Setophaga tigrina), bay‐breasted warbler (Setophaga castanea), and Tennessee warbler (Oreothlypis peregrina) responded strongly and positively to both local and regional effects. In contrast, non‐budworm‐associated species, Blackburnian warbler (Setophaga fusca), magnolia warbler (Setophaga magnolia), Canada warbler (Cardellina canadensis), black‐throated blue warbler (Setophaga caerulescens), and black‐throated green warbler (Setophaga virens), only responded to regional effects in a manner that varied across eastern Canada. The complex responses by forest birds to insect outbreaks involve both increased numerical responses to food supply and to longer term responses to changes in forest structure and composition. These effects can vary across spatial scales and be captured in hierarchical population models, which can serve to disentangle common trends from data when examining drivers of population dynamics like forest management or climate change.

Contribution of agroecosystems to the conservation of bird diversity in the department of Caldas

En las regiones tropicales se han identificado los aportes y limitaciones de los agroecosistemas en el contexto de la conservación de la diversidad de las aves. Se ha sugerido que los agroecosistemas pueden presentar un valor diferente para la conservación, de acuerdo con la complejidad estructural de la vegetación (e.g., mayor número de estratos de la vegetación, diversidad de las especies cultivadas, entre otros). En este sentido, los agroecosistemas de una menor área (e.g., minifundios), pueden ser claves en el desarrollo de estrategias encaminadas a la conservación de la avifauna. Con el objetivo de establecer el aporte de diferentes tipos de agroecosistemas a la conservación de las aves en el departamento de Caldas (Colombia), se comparó la riqueza, abundancia y similitud de las aves asociadas a tres tipos de hábitats: (1) agroecosistemas tipo I (monocultivos con suelo limpio), (2) agroecosistemas tipo II (cultivos mixtos, potreros enmalezados con árboles dispersos y plantaciones con sotobosque) y (3) bosques secundarios. Los agroecosistemas tipo II no difirieron en la riqueza y en la similitud de las aves con respecto a los bosques secundarios, además se registraron especies con alta sensibilidad a la perturbación (Zentrygon frenata, Phaetornis guy, Phaetornis syrmatophorus, Lepidocolaptes lacrymiger y Sphenopsis frontalis). Adicionalmente en este tipo de agroecosistemas se registró una especie de interés para la conservación global (Chloropipo flavicapilla) y cuatro especies migratorias (Catharus ustulatus, Parkesia noveboracensis, Setophaga fusca y Setophaga striata). Los agroecosistemas tipo II no son hábitats completamente negativos para la avifauna y podrían desempeñar un rol importante dentro de las estrategias para la conservación en paisajes rurales.

Decade-long bird community response to the spatial pattern of variable retention harvesting in red pine (Pinus resinosa) forests

Structural complexity is widely recognized as an inherent characteristic of unmanaged forests critical to their function and resilience, but often reduced in their managed counterparts. Variable retention harvesting (VRH) has been proposed as a way to restore or enhance structural complexity in managed forests, and thereby sustain attendant biodiversity and ecosystem function. Here we examined the decade-long response of diurnal breeding birds to a VRH experiment that, for the first time, incorporated both overstory and shrub layer treatments in red pine (Pinus resinosa) dominated forests in Minnesota, USA. Overstory treatments included dispersed retention, aggregated retention achieved by cutting small (0.1ha) gaps, aggregated retention achieved by cutting large (0.3ha) gaps, and an uncut control. A shrub layer treatment of ambient or reduced shrub density was also implemented as a split-plot design in each harvest treatment. We found a consistent increase in bird species richness and abundance with all retention harvest treatments over time compared to the control; species richness was also significantly greater in the large gap-aggregated treatment compared to dispersed and small gap-aggregated retention harvests. Among guilds, foliage-gleaning and shrub- and tree-nesting birds exhibited the strongest positive response to retention harvesting. Species associated with early-successional habitat, forest edges, and shrubs responded most positively to VRH including Chestnut-sided Warbler (Setophaga pensylvanica) and American Restart (S. ruticilla), although late-successional species such as Blackburnian Warbler (S. fusca) and Black-throated Green Warbler (S. virens) also showed positive response. We found few differences due to shrub reduction, and only at the species level: Ovenbird (Seiurus aurocapilla) and American Redstart were more abundant in the ambient shrub treatment, whereas Brown Creeper (Certhia americana), Veery (Catharus fuscenscens), and Chipping Sparrow (Spizella passerina) were more abundant with a reduced density of shrubs. Results through the first 10years following harvest revealed differences in bird response to both VRH and shrub treatment, suggesting that management can result in forested landscapes with bird communities that are species rich, diverse, and abundant.

Patterns of change in body condition in wintering Neotropical-Nearctic migratory birds in shaded plantations in the Andes

Despite the widely accepted idea that shaded plantations are valuable habitats for Neotropical migrants in disturbed landscapes, little empirical evidence is available in relation to the quality of this habitat for Neotropical-Nearctic migratory birds in the Andes. We evaluated the suitability of shaded plantations for overwintering Neotropical-Nearctic migratory birds by examining diurnal and seasonal variation in body condition of migrants in these agroforests in the Andes. During October to April 2008–2009 and 2009–2010, we mist-netted eight species of Neotropical-Nearctic migrants in shaded plantations in the Colombian Andes. Body condition improved throughout the day for Cerulean Warbler (Setophaga cerulea), Blackburnian Warbler (Setophaga fusca), Tennessee Warbler (Leiothlypis peregrina), and especially Canada Warbler (Cardellina canadensis). Similarly, body condition improved across the season for Tennessee Warbler, Rose-breasted Grosbeak (Pheucticus ludovicianus), and Summer Tanager (Piranga rubra). Our results provided additional evidence that several common Neotropical migrants, including species of conservation concern such as Cerulean Warbler and Canada Warbler, may improve their body condition in shaded plantations. However, about half of the species assessed in this study did not show any significant improvement in their body condition (e.g. Red-eyed Vireo). Furthermore, on average, species were in poor condition (i.e. body condition scores were negative) in these coffee farms. Thus, the extent to which this agricultural system represents high quality habitat should be looked with caution. Overall, our data contribute novel information on daily patterns of body condition improvement for several common migratory birds in Andean shaded plantations.

Conservation value of silvopastures to Neotropical migrants in Andean forest flocks

In the face of continued loss of Andean forests, shade agroforestry is a promising approach where agricultural production and conservation can co-occur to support environmental and socioeconomic needs. Agroforestry systems provide habitat for a diverse avifauna, including several migratory species of concern. Unfortunately, shaded crops continue to be converted to sun monocultures and pastures which provide fewer ecosystem services, reduce habitat complexity, and support less biodiversity. Silvopastoral systems, which combine grazing pastures and trees, have recently been drawing worldwide attention. In an effort to evaluate the conservation value of little-studied silvopastures to Andean birds, we compared mixed-species flock communities associated with different forested habitats. In January–February of 2011–2013, species composition, flock size, and individual foraging heights were recorded for 446 flocks at 9 study areas in Antioquia, Colombia. We sampled shade-coffee, shade-cardamom, secondary forest, and silvopasture at ∼1,150–1,850m elevation and measured vegetative structure in each habitat. Less structurally-complex silvopastures supported smaller, less diverse flocks with fewer Neotropical migrants and resident forest specialists. Further, fewer male Blackburnian Warblers flocked in silvopastures compared to other habitats, which is consistent with other studies showing that overwintering male migrants tend to occupy the highest quality habitats. Although forest birds may be better served by silvopastures than conventional treeless pastures, our findings suggest that silvopastoral systems are less suitable for flocking birds than other forested habitats. However, agroforestry remains an important complementary approach to other strategies to maintain Andean forests and improve the conservation potential of degraded land.

Habitat availability for multiple avian species under modeled alternative conservation scenarios in the Two Hearted River watershed in Michigan, USA

Due to differences in the responses of species to changing landscape patterns, developing a conservation plan with an optimal outcome of supporting contrasting habitat needs can be difficult. Landscape scenario modeling can provide a means to compare alternative conservation strategies and can reveal tradeoffs of managing for one objective versus another. In order to evaluate the impacts of alternative conservation strategies in a 53,653ha landscape in Michigan's Upper Peninsula, four scenarios of alternative conservation strategies were modeled 100 years into the future using the VDDT®/TELSA® spatial model suite, and habitat availability was evaluated for five target bird species of local conservation concern under each scenario. The target species were Dendroica fusca (Blackburnian Warbler), Picoides arcticus (Black-backed Woodpecker), Dendroica kirtlandii (Kirtland's Warbler), Buteo lineatus (Red-shouldered Hawk), and Scolopax minor (American Woodcock). Scenarios were ranked based on relative performance of three habitat metric results (total primary habitat area, average size of habitat patches, and average distance to the nearest neighboring habitat patch) for each species. The final overall rank for each scenario was generally related to harvest intensity; the scenario with the smallest total area of even-aged management ranked the highest. Ranks were not consistent across all response variables. Relative species sensitivity was also evaluated, and the ranks did not match expectations, with the more habitat generalist species showing the highest sensitivity and the most specialist species showing the lowest. The approach here provides a means of projecting and comparing potential long-term impacts of alternative landscape strategies on diverse wildlife habitats. These results, when considered with budget considerations and species’ habitat area and population goals, can assist local managers and stakeholders in conservation planning by identifying tradeoffs and compromises aimed at optimizing protection for a variety of target species.

Conventional oil and gas development alters forest songbird communities

ABSTRACTEnergy extraction within forest habitat is increasing at a rapid rate throughout eastern North America from the combined presence of conventional oil and gas, shale gas, and wind energy. We examined the effects of conventional oil and gas development on forest habitat including amounts of core and edge forest, the abundance of songbird species and guilds, species diversity, and community similarity within and between mixed hardwood and oak forest types at both individual wells (local scale) and at the 25‐ha scale at differing levels of well density: reference (0 wells/site, 0 wells/km2), low (1–5 wells/site, 4–20 wells/km2), and high (10–15 wells/site, 40–60 wells/km2). Amount of cleared area, length of roads, and amount of edge increased with increasing well density, whereas amount of core forest declined. At high well densities, 85% of the study site remained forested, but the mean amount of core forest declined from 68% to 2%. Specific changes to forest structure associated with oil and gas development included decreases in basal area and canopy cover within 20 m of individual wells and with increasing well density. Of 19 species analyzed, 5 species, including ovenbird (Seiurus aurocapilla), Blackburnian warbler (Setophaga fusca), and black‐throated green warbler (Setophaga virens), had lower abundance at well sites than reference sites at either the local or 25‐ha scale. Six species including American robin (Turdus migratorius), chestnut‐sided warbler (Setophaga pensylvanica), and brown‐headed cowbird (Molothrus ater) were more abundant at well than reference sites. Eight species did not differ in abundance between well and reference sites. All 3 songbird guilds showed distinct patterns of abundance in relation to habitat differences resulting from oil and gas development that were consistent with known fragmentation effects. Forest interior species were less abundant at well sites than reference sites and showed a declining trend with increasing well density. In contrast, the guilds of early successional species and synanthropic species were more abundant at well sites than reference sites as was species richness (alpha diversity). Avian communities differed between northern hardwood and oak forest types at reference sites but became more similar when wells were present at both scales, suggesting biotic homogenization or a loss of beta diversity occurred as similar species were attracted to well sites in both forest types. The bird communities associated with northern hardwoods and oaks still retained their unique characteristics at low well densities but became similar at high well densities suggesting a threshold somewhere between the low and high well density sites. Consequently, we recommend that if well development is to occur in extensively forested landscapes, conventional oil and gas well development be limited to a maximum of 20 wells/km2 to minimize impacts to forest birds. © 2014 The Wildlife Society.

Does postharvest silviculture improve convergence of avian communities in managed and old-growth boreal forests?

Habitat change following forest management may reduce biodiversity in boreal forests, as it has done globally in many forest types. Postharvest silviculture (PHS) is implemented to improve the yield of commercial tree species and has been applied to large areas of boreal forests. PHS may also influence animal communities and so we assessed songbird responses to these treatments in stands 20–52 years old in Ontario, Canada. We expected that several old-forest species would respond positively to PHS, that avian assemblages in treated forests would be distinct from those in untreated managed forests regardless of age, and that assemblages in our oldest treated stands would begin to converge with those of mature unmanaged forests. PHS stands had higher conifer density than naturally regenerating managed stands. The avian assemblage differed between treated and untreated stands at 20–30 years but not at 31–52 years. Convergence with old-forest assemblages was incomplete at 31–52 years after harvesting, although abundances of seven of 13 old-forest species did not differ from those in unmanaged forests. Of 10 old-forest species with competitive models, only Bay-breasted Warbler (Setophaga castanea (Wilson, 1810)) responded positively to PHS at the stand level, whereas two species responded positively at the landscape scale. Brown Creeper (Certhia americana Bonaparte, 1838), Boreal Chickadee (Poecile hudsonicus Forster, 1772), and Blackburnian Warbler (Setophaga fusca (Müller, 1776)) were absent from most managed stands and so require specific attention in planning for forest management, including retention of old-forest and delaying harvest of second-growth stands to ensure their occurrence and persistence.

Taxonomic recommendations for British birds: seventh report

Taxonomic recommendations for British birds: seventh report

Negative Effects of Habitat Loss on Survival of Migrant Warblers in a Forest Mosaic

Habitat loss and fragmentation in forested landscapes often negatively affect animal abundance; however, whether these factors also affect fitness is not well known. We hypothesized that observed decreases in bird occurrence and abundance in landscapes with harvested forests are associated with reduced apparent survival of adults. We defined apparent survival as an estimate of survival that accounts for an imperfect resighting probability, but not permanent emigration (i.e., dispersal). We examined the association between spatially extensive habitat loss and apparent survival of males of 2 Neotropical migrant species, Blackburnian Warbler (Dendroica fusca) and Black-Throated Green Warbler (D. virens), over 7 years in the Greater Fundy Ecosystem, New Brunswick, Canada. We estimated apparent survival among and within breeding seasons. We quantified amount of habitat in the context of individual species. In this landscape, boundaries between land-cover types are gradual rather than clearly identifiable and abrupt. Estimated apparent within-season survival of both species decreased as a function of amount of habitat within a 2000-m radius; survival was approximately 12 times (95% CI 3.43-14) greater in landscapes with 85% habitat than in landscapes with 10% habitat. Apparent annual survival also decreased as a function of amount of habitat within a 100-m radius. Over the range of habitat amount, apparent annual survival decreased 15% (95% CI 7-29%) as the amount of habitat decreased. Our results suggest that reduced species occurrence in landscapes with low proportions of habitat is due partly to lower apparent survival at these sites. This mechanism operates both directly (i.e., via effects on mortality or dispersal during breeding) and possibly through indirect effects during the nonbreeding season. Habitat loss was associated not only with a lower number of individuals, but also with lower survival of those individuals.

17 years of integrated research, monitoring, and management of HWA and hemlock ecosystems at Delaware Water Gap National Recreation Area

AbstractDelaware Water Gap National Recreation Area (“the park”) covers 28,000 ha along the Delaware River in Pennsylvania and New Jersey. Eastern hemlock forests cover 2,200 ha (8%) of the park, and are often associated with trout streams and scenic waterfalls. Activities like trout fishing, bird watching, and hiking are concentrated in hemlock forests, and many of these areas are officially designated as “Outstanding Natural Features” having “high intrinsic or unique values.” In 1989 hemlock woolly adelgid (HWA) was detected in the park, and since 1993 the park has conducted a program to address the threats that hemlock woolly adelgid and hemlock decline poses to park resources. This program includes annual monitoring of HWA populations and hemlock tree health in permanent plots, studies of hemlock ecosystems and associated biodiversity, and efforts to suppress HWA infestations and maintain hemlock ecosystems in the park. Questions addressed include: What are the distinctive characteristics of hemlock ecosystems in the park? What effects do HWA infestations have on hemlock health? What is the rate and extent of hemlock decline and mortality? How effective are insecticides and biological controls at suppressing HWA infestations and sustaining hemlock health? What are the ecological effects of hemlock decline?Sustained monitoring and research in the park during the past 17 years have provided answers to these questions and informed management. Streams draining hemlock forests are 1oC–2oC cooler in summer, hydrologically more stable, three times more likely to support trout, and typically support 30% more species of aquatic insects than streams draining hardwood forests. Birds such as blackburnian warblers, black-throated green warblers, and blue-headed vireos are very strongly associated with hemlock forests in the park. Permanent plot trees first became infested with HWA in 1998, and by 2008 no healthy hemlocks remained, and 30% had died. A dendrochronology study in the park concluded that every 1% increase in average plot HWA infestation level resulted in an 8% increase in the likelihood of a tree being in decline. Mathematical models indicate that hemlock mortality in the park will reach 50% by 2015, and 80% between 2020 and 2030. Although we have released over 90,000 biocontrol beetles in the past ten years, they have not controlled HWA populations. Insecticides effectively suppress HWA populations and sustain tree health, and we have treated about 10,000 individual trees to date. Continued hemlock decline will have major effects on park ecosystems and biodiversity.

Cover Caption

Cover: Radar imagery can be used to map the locations from which migratory birds depart and to highlight important stopover sites. Shown are movements of long‐distance migrants, such as the Blackburnian Warbler (Dendroica fusca), detected during spring migration near Buffalo, New York. Warbler photo by Charles Eiseman. See pages 440–448.

Bird research in the ACWERN lab at the Faculty of Forestry and Environmental Management, University of New Brunswick

Research on forest bird ecology in the ACWERN (Atlantic Cooperative Wildlife Ecology Research Network) lab at the University of New Brunswick, Fredericton, since 1995 has focused on assessing the relative contributions of habitat quality at large (“landscape”) and small (“local” or “stand”) spatial scales. To do so we had to develop methods for assessing key demographic components of fitness (productivity and survival) at large spatial scales. The large extent of forest cover in the Maritimes contrasts with regions where such work has traditionally been carried out, in which forest is clearly fragmented by agriculture or residential development. Our main findings are that spatial effects in highly forested landscapes can often be detected only by using species-specific habitat models, rather than broader categories such as “mature” or “softwood”, that Blackburnian Warblers (Dendroica fusca) are effective indicators of mixedwood forest but define it differently than forest managers do, and that cavity nesters (e.g., woodpeckers) may require different habitat components for nesting and feeding and so cannot be managed for solely on the basis of providing snags for nesting. Our focus has shifted recently to intensive studies on a species at risk, Bicknell's Thrush (Catharus bicknelli), which in New Brunswick breeds in man-made regenerating softwood forest stands, and assessing its response both to precommercial thinning of the breeding habitat and to effects carrying over from the winter habitat in the Caribbean. Key words: landscape effects, thresholds, survival, productivity, fitness, carry-over, habitat, fragmentation

Thirty Years of Post-fire Succession in a Southern Boreal Forest Bird Community

Birds and vegetation were surveyed in a 9 ha plot in spring 1976 in a 73 y-old jack pine (Pinus banksiana) – black spruce (Picea mariana) forest in northeastern Minnesota. A 1368 ha wildfire burned across the area that autumn. The plot was resurveyed in 1977 and periodically through 2006. Before the fire, birds with the highest importance values were Blackburnian Warbler (Dendroica fusca), Ovenbird (Seiurus aurocapillus), Red-eyed Vireo (Vireo olivaceus) and Bay-breasted Warbler (D. castanea). Within 7 y following the fire, canopy tree cover decreased to near zero as fire-damaged trees died. Afterwards, the canopy began increasing, reaching 53% cover by 30 y. Shrub cover, 8% before the fire, peaked at over 70% two decades after fire, primarily as a result of dense jack pine and black spruce regeneration, and then decreased to 58% 30 y after fire. The total number of bird species using the area doubled the first year following the fire while the number of bird species with discernable territories decreased 40%. Thereafter, territorial species began increasing and 30 y after the fire the number exceeded the pre-fire richness by 60%. Overall, density of bird territories decreased nearly three-fold the first 3 y after the fire, but by year 30, was over 56% greater than in the pre-burn mature pine forest. Loss of canopy was related to a reduction in warbler and vireo diversity while increases in woody debris and near-ground vegetation were related to an increase in ground-brush foragers such as White-throated Sparrow (Zonotrichia albicollis) and Chipping Sparrow (Spizella passerina). Brown Creeper (Certhia americana) populations increased briefly as trees died, and for five years following fire there was an increase in woodpeckers and secondary cavity nesting species. At 7 to 10 y after fire, White-throated Sparrow, Magnolia Warbler (Dendroica magnolia), Chestnut-sided Warbler (D. pensylvanica), Nashville Warbler (Vermivora ruficapilla) and Mourning Warbler (Oporornis philadelphia) dominated. White-throated Sparrow continued to be the most important bird species through the first two decades, followed by Magnolia Warbler and Red-eyed Vireo. Thirty years after fire, the dominant birds were Nashville Warbler and Ovenbird, followed distantly by Veery (Catharus fuscescens) Swainson's Thrush (Catharus ustulatus), Least Flycatcher (Empidonax minimus) and Black-and-white Warbler (Mniotilta varia). Overall, bird species using the area after 30 y remained over 70% higher than in the mature forest before the fire.

Uneven Rates of Landscape Change as a Source of Bias in Roadside Wildlife Surveys

ABSTRACT Roadside survey data have been used frequently to assess species occurrence and population trends and to establish conservation priorities. However, most studies using such data assume that samples are representative of either the amount of habitat or its rate of change at larger spatial scales. We tested both of these assumptions for the Breeding Bird Survey (BBS) from 1974 to 2001 in New Brunswick, Canada. Our study focused on mature forest—a cover type that we predicted would be characterized by rapid change due to human activities and that is of high ecological importance. We also sought to determine whether land cover changes adjacent to BBS routes were related to bird population trends detected in BBS data. Within all 3 time periods examined (1970s, 1980s, and 1990s), the amount of mature forest adjacent to BBS routes was significantly lower than in surrounding 1° blocks of latitude and longitude. This could be problematic for studies that use roadside data to compare the relative abundance of species. On average, mature forest declined at a rate of‐1.5% per year over the 28‐year study period. We detected no significant difference in the rate of change between degree blocks and BBS routes over this time span. However, in the 1970s and 1980s, mature forest declined more rapidly in degree blocks (‐2.7%/yr) than adjacent to BBS routes (‐0.5/yr). We also found that the BBS trend for a mature forest‐associated species, blackburnian warbler (Dendroica fusca), was correlated with the trend in mature forest along BBS routes. This, combined with slower rates of mature forest change along routes in the 1970s and 1980s, suggests that BBS data may have underestimated population declines during this period. It is important that research be conducted to test for potential biases in roadside surveys caused by uneven rates of landscape change, particularly in regions characterized by rapid habitat alteration.

A test of Ontario's Habitat Suitability Matrix as a forest management planning tool for forest birds

We used point-count data collected as part of Bird Studies Canada's Boreal Forest Bird Program to validate habitat suitability models for 22 forest bird species in Ontario's Habitat Suitability Matrix. We found that many of the species'models performed relatively poorly in discriminating between occupied and unoccupied sites, primarily due to the high error of commission rates (false positive predictions). Since species presence and abundance were assessed by single, five minute point counts, insufficient sampling was at least partly responsible for some of the observed over-prediction. Results suggested that model parameters for at least nine of the species tested (hairy woodpecker [Picoides villosus], blueheaded vireo [Vireo solitarius], red-eyed vireo [Vireo olivaceus], red-breasted nuthatch [Sitta canadensis], Swainson's thrush [Catharus ustulatus], hermit thrush [Catharus guttatus], Tennessee warbler [Vermivora peregrina], Blackburnian warbler [Dendroica fusca] and dark-eyed junco [Junco hyemalis]) should be reviewed to improve the predictive capability of the models and to ensure appropriate consideration of the habitat needs of these species during forest management planning. Key words: boreal forest, forest birds, discrimination capacity, habitat models, habitat suitability matrix, model accuracy, model validation, relative operating characteristic curve, ROC

Migrant Forest Songbirds Undertake Breeding Dispersal Following Timber Harvest

We report two observations of breeding dispersal by migratory songbirds, Dendroica caerulescens (Black-throated Blue Warbler) and D. fusca (Blackburnian Warbler), from their initial territory locations following timber harvest. Forty-eight birds of each species were captured and marked as part of a long-term study on warbler survival in the Greater Fundy Ecosystem, NB. None of the birds banded in unharvested patches were re-encountered in other patches. Maximum movement distances for the displaced Blackburnian Warbler and Black-throated Blue Warbler were 1.3 km and 2.9 km, respectively. These are the longest breeding-dispersal distances reported for these species. Our paper provides the first direct evidence that birds may move once their breeding site has been altered due to timber harvesting. Potential conservation implications are discussed.