Application of habitat thresholds in conservation: Considerations, limitations, and future directions

AbstractHabitat thresholds are often interpreted as the minimum required area of habitat, and subsequently promoted as conservation targets in natural resource policies and planning. Unfortunately, several recent reviews and messages of caution on the application of habitat thresholds in conservation have largely fallen on deaf ears, leading to a dangerous oversimplification and generalization of the concept. We highlight the prevalence of oversimplification/over-generalization of results from habitat threshold studies in policy documentation, the consequences of such over-generalization, and directions for habitat threshold studies that have conservation applications without risking overgeneralization. We argue that in order to steer away from misapplication of habitat thresholds in conservation, we should not focus on generalized nominal habitat values (i.e., amounts or percentages of habitat), but on the use of habitat threshold modeling for comparative exercises of area-sensitivity or the identification of environmental dangers. In addition, we should remain focused on understanding the processes and mechanisms underlying species responses to habitat change. Finally, studies could that focus on deriving nominal value threshold amounts should do so only if the thresholds are detailed, species-specific, and translated to conservation targets particular to the study area only

Opportunities and challenges for big data ornithology

Recent advancements in information technology and data acquisition have created both new research opportunities and new challenges for using big data in ornithology. We provide an overview of the past, present, and future of big data in ornithology, and explore the rewards and risks associated with their application. Structured data resources (e.g., North American Breeding Bird Survey) continue to play an important role in advancing our understanding of bird population ecology, and the recent advent of semistructured (e.g., eBird) and unstructured (e.g., weather surveillance radar) big data resources has promoted the development of new empirical perspectives that are generating novel insights. For example, big data have been used to study and model bird diversity and distributions across space and time, explore the patterns and determinants of broad-scale migration strategies, and examine the dynamics and mechanisms associated with geographic and phenological responses to global change. The application of big data also holds a number of challenges wherein high data volume and dimensionality can result in noise accumulation, spurious correlations, and incidental endogeneity. In total, big data resources continue to add empirical breadth and detail to ornithology, often at very broad spatial extents, but how the challenges underlying this approach can best be mitigated to maximize inferential quality and rigor needs to be carefully considered. Los avances recientes en la tecnolog´ıa de la informaci ´on y la adquisici ´on de datos han creado tanto nuevas oportunidades de investigaci ´on como desaf´ıos para el uso de datos masivos (big data) en ornitolog´ıa. Brindamos una visi ´on general del pasado, presente y futuro de los datos masivos en ornitolog´ıa y exploramos las recompensas y desaf´ıos asociados a su aplicaci ´ on. Los recursos de datos estructurados (e.g., Muestreo de Aves Reproductivas de Am´erica del Norte) siguen jugando un rol importante en el avance de nuestro entendimiento de la ecolog´ıa de poblaciones de las aves, y el advenimiento reciente de datos masivos semi-estructurados (e.g., eBird) y desestructurados (e.g., radar de vigilancia clima´tica) han promovido el desarrollo de nuevas perspectivas emp´ıricas que esta´n generando miradas novedosas. Por ejemplo, los datos masivos han sido usados para estudiar y modelar la diversidad y distribuci ´on de las aves a trav´es del tiempo y del espacio, explorar los patrones y los determinantes de las estrategias de migraci ´on a gran escala, y examinar las dina´micas y los mecanismos asociados con las respuestas geogra´ficas y fenol ´ ogicas al cambio global. La aplicaci ´on de datos masivos tambi´en contiene una serie de desaf´ıos donde el gran volumen de datos y la dimensionalidad pueden generar una acumulaci ´on de ruido, correlaciones espurias y endogeneidad incidental. En total, los recursos de datos masivos contin ´uan agregando amplitud y detalle emp´ırico a la ornitolog´ıa, usualmente a escalas espaciales muy amplias, pero necesita considerarse cuidadosamente c ´omo los desaf´ıos que subyacen este enfoque pueden ser mitigados del mejor modo para maximizar su calidad inferencial y rigor

Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in southern New England?

Early successional birds have declined in the northeastern United States due to the regeneration of forest on abandoned farm fields and the suppression of natural disturbances that once provided appropriate habitat. These species have become increasingly dependent on early successional habitats generated by such activities as timber harvesting. Recent approaches of timber harvesting, which range from single-tree harvesting to clearcutting, create forest openings of different sizes and configurations embedded in landscapes with different land use patterns. To assess the importance of forest openings created by timber harvesting for shrubland birds, we surveyed birds on 50m radius plots in 34 harvest sites (0.5–21ha). We collected data on multi-scaled habitat variables ranging from plot-level vegetation characteristics to land use patterns within 1km of each study site. We also monitored mating and nesting success of Blue-winged Warblers (Vermivora pinus) in 10 forest openings. The abundance of most shrubland species was influenced by plot-level habitat variables, such as tree density and vegetation height, rather than shrubland area or the composition of land uses in the surrounding landscape. Only Eastern Towhees (Pipilo erythrophthalmus) were more frequent in survey plots in larger forest openings. In contrast, neither abundance nor reproductive activity of Blue-winged Warblers was correlated with the size of the forest opening. Their abundance was negatively related to vegetation height, however. Only 54% of the territorial male Blue-winged Warblers in forest openings were mated. We documented relatively low nest success rates of 21.1% during the egg laying and incubation nest stages, but increased success rates during the later stages of nesting. Our results indicate that even small forest openings with low vegetation provide habitat for Blue-winged Warblers and other shrubland birds. The overall reproductive rate of territorial male Blue-winged Warblers in forests openings was low during the 2 years of the study, however. Further studies are needed to assess the long-term value of this type of habitat for sustaining shrubland bird populations

BCCH_cap_hist_1415

Capture history and site covariates, including winter microclimate variables. Variable abbreviations are as follows: ch = capture history; yr = year; spp = species; Ag = Age (0 = HY; 1 = AHY); treeden = density of trees/ha; disttourb = distance to urban center (km); Area = focal patch area (ha); hdd = cumulative degree-days (C); MeanT = Average winter temperature (C); MinT = Average minimum temperature (C); CVT = Coefficient of variation in minimum temperature; Snow = total accumulated snowfall (cm); Ncoldwet = Number of cold (below -18C) and wet (> 1cm snowfall) days; Mi = Body condition index; ISI = Impervious surface (%); Pfor = Percent forest (%); For_ED = Forest Edge Density (m^2); For_ENN = Area-weighted mean Euclidean Nearest Neighbor distance between forest patches in the landscape (m^2); PA = Perimeter:Area ratio of focal forest patch

Data from: Forest fragmentation alters winter microclimates and microrefugia in human-modified landscapes

With over half of earth’s terrestrial biota living beneath forest canopies, our ability to accurately capture organism-climate relationships in forested ecosystems is imperative for predicting species’ vulnerability to future climate change. Assessing the vulnerability of forest dependent species, however, hinges on quantifying microclimates that exist below the forest canopy and might be influenced by varying levels of disturbance in human-modified landscapes. The goal of our study was to examine the multi-scaled predictors of subcanopy microclimate variability across a heterogeneous landscape in Midwestern USA during winter, and to further evaluate whether a widely available interpolated climate model accurately captures this variability. By deploying a network of temperature sensors along a fragmentation gradient, we found that forests in more fragmented landscapes experienced colder minimum and average daily temperatures throughout the winter than forests in less fragmented landscapes. We found that greater tree densities and higher elevations led to warmer microclimates while increasing distances from urban centers led to colder microclimates. The negative effect of forest edge on minimum temperatures was lessened by the effect of increasing basal area, highlighting the importance of local- and landscape-scale features on microclimate heterogeneity. Temperature discrepancies between subcanopy microclimates and climate interpolations were influenced by many of the same features, and could be of a similar magnitude as those predicted by future climate change scenarios. Using a biological threshold based on metabolic and demographic constraints for winter birds, we found that the variability in microclimates along our forest fragmentation gradient (50 km) was comparable to the magnitude captured by weather stations across a latitudinal gradient spanning more than 650 km. Our results suggest that biophysical properties of landscapes can alter spatial gradients of microclimates and should be considered when assessing species’ vulnerabilities to future climate change

EFFECTS OF MOWING AND BURNING ON SHRUBLAND AND GRASSLAND BIRDS ON NANTUCKET ISLAND, MASSACHUSETTS

Volume: 118Start Page: 353End Page: 36