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Building collisions, and particularly collisions with windows, are a major anthropogenic threat to birds, with rough estimates of between 100 million and 1 billion birds killed annually in the United States. However, no current U.S. estimates are based on systematic analysis of multiple data sources. We reviewed the published literature and acquired unpublished datasets to systematically quantify bird–building collision mortality and species-specific vulnerability. Based on 23 studies, we estimate that between 365 and 988 million birds (median = 599 million) are killed annually by building collisions in the U.S., with roughly 56% of mortality at low-rises, 44% at residences, and <1% at high-rises. Based on >92,000 fatality records, and after controlling for population abundance and range overlap with study sites, we identified several species that are disproportionately vulnerable to collisions at all building types. In addition, several species listed as national Birds of Conservation Concern due to their declining populations were identified to be highly vulnerable to building collisions, including Golden-winged Warbler (Vermivora chrysoptera), Painted Bunting (Passerina ciris), Canada Warbler (Cardellina canadensis), Wood Thrush (Hylocichla mustelina), Kentucky Warbler (Geothlypis formosa), and Worm-eating Warbler (Helmitheros vermivorum). The identification of these five migratory species with geographic ranges limited to eastern and central North America reflects seasonal and regional biases in the currently available building-collision data. Most sampling has occurred during migration and in the eastern U.S. Further research across seasons and in underrepresented regions is needed to reduce this bias. Nonetheless, we provide quantitative evidence to support the conclusion that building collisions are second only to feral and free-ranging pet cats, which are estimated to kill roughly four times as many birds each year, as the largest source of direct human-caused mortality for U.S. birds.

To recover species at risk, it is necessary to identify habitat critical to their recovery. Challenges for species with large ranges (thousands of square kilometres) include delineating management unit boundaries within which habitat use differs from other units, along with assessing any differences among units in amounts of and threats to habitat over time. We developed a reproducible framework to support identification of critical habitat for wide-ranging species at risk. The framework (i) reviews species distribution and life history; (ii) delineates management units across the range; (iii) evaluates and compares current and (iv) potential future habitat and population size and (v) prioritizes areas within management units based on current and future conditions under various scenarios of climate change and land-use. We used Canada Warbler (Cardellina canadensis) and Wood Thrush (Hylocichla mustelina) in Canada as case studies. Using geographically weighted regression models and cluster analysis to measure spatial variation in model coefficients, we found geographic differences in habitat association only for Canada Warbler. Using other models to predict current habitat amount for each species in different management units, then future habitat amount under land use and climate change, we projected that: (1) Canada Warbler populations would decrease in Alberta but increase in Nova Scotia and (2) Wood Thrush populations would increase under most scenarios run in Quebec, New Brunswick and Nova Scotia, but not in Ontario. By comparing results from future scenarios and spatial prioritization exercises, our framework supports identification of critical habitat in ways that incorporate climate and land-use projections.

Context Spatial variation in abundance is influenced by local- and landscape-level environmental variables, but modeling landscape effects is challenging because the spatial scales of the relationships are unknown. Current approaches involve buffering survey locations with polygons of various sizes and using model selection to identify the best scale. The buffering approach does not acknowledge that the influence of surrounding landscape features should diminish with distance, and it does not yield an estimate of the unknown scale parameters. Objectives The purpose of this paper is to present an approach that allows for statistical inference about the scales at which landscape variables affect abundance. Methods Our method uses smoothing kernels to average landscape variables around focal sites and uses maximum likelihood to estimate the scale parameters of the kernels and the effects of the smoothed variables on abundance. We assessed model performance using a simulation study and an avian point count dataset. Results The simulation study demonstrated that estimators are unbiased and produce correct confidence interval coverage except in the rare case in which there is little spatial autocorrelation in the landscape variable. Canada warbler abundance was more highly correlated with site-level measures of NDVI than landscape-level NDVI, but the reverse was true for elevation. Canada warbler abundance was highest when elevation in the surrounding landscape, defined by an estimated Gaussian kernel, was between 1300 and 1400 m. Conclusions Our method provides a rigorous way of formally estimating the scales at which landscape variables affect abundance, and it can be embedded within most classes of statistical models.

Understanding population dynamics of migratory birds requires baseline knowledge of nonbreeding distributions, migratory routes, and population-specific migratory connectivity. The Canada Warbler (Cardellina canadensis) is a declining Nearctic–Neotropical migratory songbird, but limited information exists describing its population-specific migration ecology. We aimed to understand how individuals from a central Appalachian breeding population were spatially distributed during the stationary nonbreeding period, infer the strength and pattern of migratory connectivity, and understand migratory route patterns. We deployed 32 geolocator tags on adult male birds in 2020 and 10 tags retrieved in 2021 provided usable data. Stationary nonbreeding season locations suggest moderate population connectivity, with birds clustered on the Andean slopes on each side of the Magdalena Valley in northern Colombia. Post-breeding (boreal fall) migration was largely overland through Mexico and Central America, and pre-breeding (boreal spring) migration routes were significantly farther east based on the westernmost longitude recorded during migration (mean difference = 232 km), consistent with a pattern of counterclockwise loop migration. The evidence of counterclockwise loop migration is a novel finding in Canada Warblers and suggests the shorter duration of pre-breeding migration may be due to a time-minimizing strategy involving trans-Gulf flights. Our data additionally provide the first insight into the migratory ecology of a population of Canada Warblers breeding near the southern extent of their range and serve as a foundation for full annual cycle demographic modeling. Entender las dinámicas de población de las aves migratorias requiere conocimiento de línea base de sus distribuciones no reproductivas, rutas de migración y conectividad migratoria específica de la población. La reinita Cardellina canadensis es un ave canora migratoria Neártica-Neotropical, pero existe información limitada que describa la ecología migratoria específica de sus poblaciones. Nuestro objetivo era entender cómo los individuos de la población reproductiva de los Appalachian centrales estaba distribuida espacialmente durante el periodo estacionario no reproductivo, inferir la fuerza y el patrón de conectividad migratoria y entender los patrones de rutas migratorias. Colocamos 32 marcas de geolocalización en aves masculinas adultas en el 2020 y recuperamos 10 marcas en el 2021 con datos utilizables. Las localizaciones estacionarias de la estación no reproductiva sugieren una moderada conectividad de poblaciones, con aves agrupadas en las pendientes de los Andes en cada lado del Valle de Magdalena en el norte de Colombia. La migración post reproductiva (otoño boreal) fue mayormente sobre el continente a través de Mexico y Centroamérica y las rutas pre reproductivas (primavera boreal) fueron significativamente más hacia el este basadas en la longitud más al oeste registrada durante la migración (diferencia promedio = 232 km), lo que es consistente con un patrón de migración circular en dirección contra reloj. La evidencia de la migración circular a contra reloj es un descubrimiento nuevo para las reinitas Cardellina canadensis y sugiere que la duración menor de migración pre reproductiva puede deberse a una estrategia de minimizar el tiempo que involucran los vuelos trans-Golfo. Nuestros datos adicionales dan un primer acercamiento a la ecología migratoria de una población de reinitas Cardellina canadensis que se reproducen cerca de la parte más sureño de su rango y sirve como base para modelar de un ciclo anual demográfico completo. Palabras clave: ciclo anual, Andes colombianos, migración circular, conectividad migratoria, West Virginia.

The Canada Warbler (Cardellina canadensis) is a threatened species in Canada due to an annual decline of ∼3% over the last 50 yr. Some studies suggest that Canada Warblers prefer old-growth forest and that forestry practices may reduce suitable habitat, while other research indicates that the species will also use harvested areas. Differences in scale between habitat use studies and behavioral phenomena such as conspecific attraction may explain this discrepancy. We examined how Canada Warblers responded to forestry and conspecifics in Alberta, Canada. We used point counts, burst sampling, and behavioral observations to determine how the density, home range placement (second-order habitat use), within-home-range space use (third-order habitat use), and probability of pairing and fledging young of male Canada Warblers were influenced by postharvest conditions (i.e. amount, age [≤ 30 yr postharvest], and retention of unharvested fragments) and conspecifics. Male density was 86% lower in postharvest than in unharvested stands. However, males were 16.6 times more likely to place their home ranges in postharvest stands within 100 m of unharvested stands than 300 m into harvested areas, and 3 times more likely to place their home ranges 100 m from conspecifics than 300 m away. Within-home-range space use was 1.1 times higher 50 m from conspecifics than 350 m away, and 2.6 times higher 300 m from an edge than 100 m away. Use of harvested areas did not affect reproductive activity, but the probability of pairing was 1.8 times higher for males in low-density (2 males per 17.3 ha) than in high-density areas (7 males per 17.3 ha). Our results suggest that Canada Warbler use of postharvest stands on the boreal breeding grounds is more heavily influenced by conspecifics than by postharvest conditions. Because Canada Warbler territories are clustered, conservation efforts should prioritize the retention of large tracts of unharvested forest near occupied breeding sites.

Efforts to understand population dynamics and identify high-quality habitat require information about spatial variation in demographic parameters. However, estimating demographic parameters typically requires labor-intensive capture–recapture methods that are difficult to implement over large spatial extents. Spatially explicit integrated population models (IPMs) provide a solution by accommodating spatial capture–recapture (SCR) data collected at a small number of sites with survey data that may be collected over a much larger extent. We extended the spatial IPM framework to include a spatio-temporal point process model for recruitment, and we applied the model to 4 yr of SCR and distance-sampling data on Canada Warblers (Cardellina canadensis) near the southern extent of the species' breeding range in North Carolina, USA, where climate change is predicted to cause population declines and distributional shifts toward higher elevations. To characterize spatial variation in demographic parameters over the climate gradient in our study area, we modeled density, survival, and per capita recruitment as functions of elevation. We used a male-only model because males comprised >90% of our point-count detections. Apparent survival was low but increased with elevation, from 0.040 (95% credible interval [CI]: 0.0032–0.12) at 900 m to 0.29 (95% CI: 0.16–0.42) at 1,500 m. Recruitment was not strongly associated with elevation, yet density varied greatly, from <0.03 males ha–1 below 1,000 m to >0.2 males ha–1 above 1,400 m. Point estimates of population growth rate were <1 at all elevations, but 95% CIs included 1. Additional research is needed to assess the possibility of a long-term decline and to examine the effects of abiotic variables and biotic interactions on the demographic parameters influencing the species' distribution. The modeling framework developed here provides a platform for addressing these issues and advancing knowledge about spatial demography and population dynamics.

Aim: In birds, patterns of migratory connectivity are influenced by landscape structure experienced throughout the annual cycle. Assessing how landscape patterns drive the movements and distributions of migratory species is important for understanding the evolution of migration and determining conservation priorities. We determined migratory connectivity in the Canada Warbler {Cardellina canadensis), a declining Neotropical migratory bird, and evaluated the degree to which the Andean mountains influence winter population distribution in this montane forest specialist. Location: Seven study regions across the Western, Central, and Eastern Andes of Colombia. Methods: We inferred breeding and natal origins of Canada Warblers overwintering in Colombia by analysing stable hydrogen isotope values (δ²H) in feathers and assigning wintering populations to breeding origins using an established feather δ²H isoscape for North America. Results: We found strong evidence for parallel migration between breeding and wintering sites, giving rise to moderately strong migratory connectivity between breeding and wintering regions. The model best explaining population distribution in the Colombian Andes implied that populations were most similar within basins or valleys. Such segregation is notable, given that basins are separated by less than 300 km on the wintering grounds, while breeding populations may be separated by more than 3000 km from east to west. Main conclusions: Our results suggest that the high spine of each Andean cordillera acts to shape the winter distribution of individuals from different breeding populations. To our knowledge, this is the first demonstration that the topography of the Andean mountains can act to shape the winter distribution of populations of a migratory bird. The strength of migratory connectivity found in Canada Warblers may inhibit evolutionary responses to environmental change, and the more rapid population declines recorded in some eastern breeding populations may be related to habitat loss and local environmental conditions in the Eastern Andes, where individuals from these populations were more likely to overwinter.

1. Atlas data provide biodiversity information at a relatively fine spatial grain over a broad spatial extent and, increasingly, at multiple points in time, which make them invaluable for understanding processes that affect species distributions over time. The effect of survey effort on species detection has long been appreciated and Atlases typically include survey standards and records of effort, but challenges remain in analysing Atlas data that have not been collected using a repeated sampling protocol designed to correct for imperfect detection. 2. We developed a single-visit dynamic occupancy model to quantify the effects of climatic and land-use drivers on local species extinction and colonization while accounting for imperfect detection using repeat Atlas data. We evaluated model stability using data simulated under alternative scenarios and, ultimately, applied the model to empirical data for Canada warbler Cardellina canadensis, a wide-spread species exhibiting a long-term population decline 3. At sample sizes that are realistic for many Atlases (n = 1000-10 000 independent survey blocks), our models produced unbiased estimates of detection, occupancy, colonization and extinction parameters. Slope estimates for explanatory covariates were somewhat less stable than overall occupancy, colonization and extinction rates, with covariate effects being sensitive to the total number of, and relationships among, explanatory variables. 4. In comparison to other analyses of Canada warbler distributions that indicated minor changes over time, our approach identified a widespread decline in occupancy probability across New York, consistent with the broader population trend, particularly in the areas where it was initially more likely to occur. 5. Synthesis and applications. A single-visit dynamic occupancy model is a novel method for analysing common, ecologically valuable datasets, such as Atlases, that lack repeated sampling necessary to correct for imperfect detection using alternative multi-season occupancy modelling approaches. As a result, using this method can improve understanding of species distributions and factors that shape them over time, thereby providing more accurate information to guide conservation and management.

The Canada Warbler Cardellina canadensis is a steeply declining Neotropical migratory bird and > 50% of its non-breeding range is within the Colombian Andes. Despite being an abundant migrant in Andean forests, the species’ elevational distribution and non-breeding ecology have yet to be studied, thereby precluding the design of effective conservation actions. During four non-breeding periods (2012–2016), we surveyed Colombia’s three Andean ranges, carrying out passive 5-minute point counts between 700 and 3,150 m asl in five habitats (mature forest, secondary growth, forest edges/riparian forest, shade coffee, sun coffee), recording the perpendicular distance, sex, foraging height, and association with mixed species flocks of Canada Warbler. Habitat variables were recorded at each point. Based on 819 passive point counts, Canada Warblers occupied elevations between 750 and 2,300 m, being more abundant between 1,000 and 2,200 m. Relative densities were higher in mature forest compared to shade coffee and secondary forest, and accordingly abundance increased with canopy height. There was no evidence for a difference in elevation or habitat use by males and females. Within forests, birds foraged at mid-levels, 5–15 m above the ground, and the probability of Canada Warblers occurring in mixed species flocks increased with elevation. Models of variation in relative density throughout the Eastern Andes showed a positive relation with cloud cover and above-ground forest biomass, implying a preference for humid, forested regions. Of the areas in the Eastern Andes with high predicted relative density, ∼ 14% overlapped with protected areas and we identify priority areas where protective measures could benefit the conservation status of the species. For maximum effectiveness, conservation actions should focus on protecting forest fragments and initiating reforestation projects at mid-elevations (1,000–2,200 m), as well as supporting agroforestry practices in humid regions of the Colombian Andes.

Canada Warblers (Cardellina canadensis) are long-distance Neotropical migrants, but little is known about their migratory behavior and ecology. We examined the fall migration of Canada Warblers at two sites, Darién and the Sierra Nevada de Santa Marta, in northern Colombia from 2011 to 2015 using constant-effort mist-netting. Our objectives were to determine: 1) breeding origins and connectivity patterns, 2) migratory pathways, 3) the phenology of migration, 4) possible differences in movements between ages and sexes, 5) their body condition when arriving in Colombia, and 6) evidence of stopover and refueling. Stable hydrogen isotopes (δ²Hf) in flight feathers were analyzed to estimate breeding origins of captured Canada Warblers in North America. The δ²Hf values revealed that most Canada Warblers captured in the Darién likely originated from the central and northeastern regions of their breeding range. The capture of all but one of 162 Canada Warblers in the Darién also indicates a migration route through Central American rather than across the Caribbean Sea. Most captured birds were hatch-year birds (91% vs. 9% after hatch-year birds), and we captured more females (67%) than males (33%). Canada Warblers migrated through the Darién from 20 September to early November, with most arriving in mid-October. Most (89%) individuals arrived with low fuel reserves. These results combined with estimated flight ranges revealed that 46% of the individuals captured in the Darién likely needed to refuel to continue migrating, whereas 31% could continue 50 to 200 km beyond our capture site. However, no individuals were recaptured so stopover duration could not be determined. Canada Warblers may adopt a strategy of 1-d stopovers and short flights or, alternatively, the Darién may represent low-quality habitat and birds quickly left our study site in search of suitable habitat. Further study is needed to determine the possible importance of other (montane) habitats for Canada Warblers in the Darién region to prioritize conservation actions. Las Reinitas del Canadá (Cardellina canadensis) son migrantes Neotropicales de larga distancia, pero poco se sabe de su comportamiento migratorio y ecología. Examinamos la migración de otoño de las Reinitas del Canadá en dos sitios, Darién y la Sierra Nevada de Santa Marta, en el norte de Colombia de 2011 a 2015 utilizando el método de esfuerzo constante de captura con redes de niebla. Nuestro objetivo fueron determinar: 1) orígenes de cría y patrones de conectividad, 2) caminos migratorios, 3) la fenología de la migración, 4) posibles diferencias en los movimientos entre edades y sexos, 5) su conditión física cuando llegan a Colombia, y 6) evidencias de paradas intermedias y reabastecimiento. Isótopos estables de hidrógeno (δ²Hf) en plumas de vuelo fueron analizadas para estimar los orígenes de cría de las Reinitas del Canadá capturadas en Norte América. Los valores δ²Hf revelan que la mayoría de las Reinitas del Canadá capturadas en Darién muy probablemente tuvieron su origen en las regiones central y noreste de su rango reproductivo. La captura de todas menos una de las 162 las Reinitas del Canadá de Darién también indicaron una ruta migratoria a través de América Central en vez de atravesando el Mar Caribe. La mayoría de las aves capturadas eran adultos nacidos en ese mismo año (91% vs. 9% adultos nacidos en años previos), y capturamos más hembras (67%) que machos (33%). Las Reinitas del Canadá migran a través de Darién del 20 de Septiembre a principios de Noviembre, llgando la mayoría en la mitad de Octubre. Muchos (89%) indivduos llegaron con bajas reservas de energía. Estos resultados combinados con los rangos de vuelo estimados rebelaron que el 46% de los individuos capturados en Darién probablemente necesitaron reabastecerse para continuar migrando, mientras que el 31% pudo continuar por 50 a 200 km más lejos de nuestro sitio de captura. Aún así, ningún individuo pudo ser capturado por lo cual la duratión de la parada intermedia no pudo ser determinada. Las Reinitas del Canadá podrían adoptar la estrategia de paradas intermedias por un día y vuelos cortos o, alternativamente, Darién podría representar un hábitat de baja calidad y las aves rápidamente dejan nuestro sitio de estudio en busca de un hábitat más adecuado. Futuros estudios son necesarios para determinar la posible importancia de otros hábitats (montanos) para las Reinitas del Canadá en la región de Darién a fin de priorizar acciones de conservación.