Incorporating weather in counts and trends of migrating Common Nighthawks.

Effective conservation planning for species of concern requires long-term monitoring data that can accurately estimate population trends. Supplemental or alternative methods for estimating population trends are necessary for species that are poorly sampled by traditional breeding bird survey methods. Counts of migrating birds are commonly used to assess raptor population trends and could be useful for additional taxa that migrate diurnally and are difficult to monitor during the breeding season. In North America, the Common Nighthawk (Chordeiles minor) is challenging to detect during comprehensive dawn surveys like the North American Breeding Bird Survey and is considered a species of conservation concern because of steep population declines across its range. We conducted standardized evening counts of migrating Common Nighthawks at a fixed survey location along western Lake Superior each autumn from 2008 to 2022. To document peak migration activity, counts spanned ~3 hours each evening from mid-August to early September for a mean of 19.4 ± 2.4 days. These count data were then used to assess the effects of weather on daily counts and high-count days and to calculate population trends over this 15-year period. We used generalized linear mixed effects models to determine the relationship between daily counts and high-count days (i.e., ≥1000 migrating nighthawks) and weather variables. Additionally, using our 15-year dataset, we calculated a geometric mean passage rate that accounted for annual differences in weather to estimate count trends. Annual counts averaged ~18,000 (min = 2514, max = 32,837) individuals and high-count days occurred 56 times throughout the course of the study. Model results indicated lighter, westerly winds and warmer temperatures were associated with higher daily counts and greater probability of a large migratory flight. Results from the trend analyses suggest stable or non-significantly increasing trends for Common Nighthawks during this monitoring period; however, the trend models explained a relatively low percentage of the variation in the counts. Results from a power analysis suggest that continued monitoring efforts and adjustments with weather covariates will be necessary to effectively use visible migration count data to estimate Common Nighthawk trends. Establishing annual monitoring programs that use standardized visual counts to document Common Nighthawk migration at key sites across North America may provide supplemental information useful for population trend estimates of this species. Therefore, we advocate for the use of visible migration counts to monitor Common Nighthawks in North America and emphasize the value of long-term monitoring efforts.

Des données de suivi à long terme permettant de calculer avec précision les tendances démographiques sont garantes d'une planification réussie de la conservation d'espèces préoccupantes. Des méthodes complémentaires ou alternatives d'estimation des tendances démographiques sont nécessaires dans le cas d'espèces mal échantillonnées par les méthodes traditionnelles de relevé d'oiseaux nicheurs. Le dénombrement d'oiseaux migrateurs est couramment utilisé pour évaluer la tendance des populations de rapaces et pourrait servir pour d'autres taxons qui migrent de jour et sont difficiles à suivre pendant la saison de nidification. En Amérique du Nord, l'Engoulevent d'Amérique (Chordeiles minor) est difficile à détecter au cours de relevés généraux réalisés à l'aube, tel le Relevé des oiseaux nicheurs d'Amérique du Nord (BBS), et est considéré comme une espèce dont la conservation est préoccupante en raison de la baisse marquée de ses effectifs dans toute son aire de répartition. Nous avons effectué des comptages en soirée standardisés d'engoulevents en migration à un site fixe localisé du côté ouest du lac Supérieur, chaque automne de 2008 à 2022. Afin de caractériser le pic d'activité migratoire, les comptages ont duré ~3 heures chaque soir de la mi-août au début de septembre, durant 19,4 ± 2,4 jours en moyenne. Ces données ont ensuite servi pour évaluer l'effet des conditions météorologiques sur les comptages quotidiens et les jours d'activité migratoire élevée et calculer la tendance démographique au cours de ces 15 ans. Nous avons utilisé des modèles linéaires généralisés à effets mixtes pour déterminer la relation entre les comptages quotidiens et les jours d'activité migratoire élevée (c.-à-d. ≥1000 engoulevents) et les variables météorologiques. En outre, en utilisant notre jeu de données sur 15 ans, nous avons calculé la moyenne géométrique du taux de passage tenant compte des différences météorologiques annuelles afin d'estimer la tendance des comptages. La moyenne des comptages annuels était de ~18 000 (min = 2514, max = 32 837) individus et nous avons observé 56 cas d'activité migratoire élevée au cours de l'étude. Les résultats du modèle ont indiqué que des vents plus légers et de l'ouest, et des températures plus chaudes étaient associés à des comptages quotidiens plus élevés et à une plus grande probabilité d'une activité migratoire importante. Les résultats de l'analyse des tendances indiquent que les engoulevents ont montré une tendance stable ou en augmentation non significative au cours de cette période de suivi; cependant, les modèles de tendances n'ont expliqué qu'un pourcentage relativement faible de la variation des comptages. Les résultats d'une analyse de puissance révèlent que des suivis réguliers et des ajustements avec des covariables météorologiques seront nécessaires pour utiliser efficacement les données de comptages visuels réalisés en migration afin d'estimer la tendance de l'Engoulevent d'Amérique. La mise en place d'un programme de suivis annuels fondés sur des comptages visuels standardisés destiné à caractériser la migration de l'Engoulevent d'Amérique sur des sites clés en Amérique du Nord pourrait fournir des informations supplémentaires utiles pour estimer les tendances démographiques de cette espèce. Par conséquent, nous préconisons l'utilisation de comptages visuels en migration pour suivre l'Engoulevent d'Amérique en Amérique du Nord et soulignons la valeur de suivis à long terme.

Increasing human environmental footprint does not lead to biotic homogenization of forest bird communities in northern USA.

Studies have shown negative impacts of increased human pressures on biodiversity at local (alpha-diversity) and regional (gamma-diversity) scales. However, the diversity between local sites (beta-diversity) has received less attention. This is an important shortcoming since beta-diversity acts as a linkage between the local and regional scales. Decreased beta-diversity means that local sites lose their distinctiveness, becoming more similar to each other. This process is known as biotic homogenization. However, the mechanisms causing biotic homogenization have not been fully studied nor its impacts on different facets of biodiversity. We examined if land-use change due to human actions causes biotic homogenization of taxonomic, functional, and phylogenetic diversity in bird communities of forested habitats in the state of Minnesota, USA. We address if forest loss and increased human domination in a region were associated with decreased beta-diversity. Our results showed that elevated human pressure was not related to increased biotic homogenization in this study region. Effects of landscape change were incongruent among taxonomic, functional, and phylogenetic diversity. At all spatial scales, taxonomic diversity was unrelated to forest loss or human domination. Interestingly, increased human domination appeared to increase the functional beta-diversity of bird communities. This association was driven by a decrease in local diversity. Forest habitat loss was associated with decreasing functional and phylogenetic diversity in local communities (alpha-diversity) and in regional species pool (gamma-diversity), but not in beta-diversity. We highlight the importance of considering multiple facets of biodiversity as their responses to human land-use is varied. Conservation significance of beta-diversity hinges on local and regional diversity responses to human land-use intensification, and organization of biodiversity should therefore be analyzed at multiple spatial scales.

Foraging Ecology Differentiates Life Stages and Mercury Exposure in Common Terns (Sterna hirundo).

Some populations of common terns (Sterna hirundo) breeding at inland lakes in North America are declining, including the Laurentian Great Lakes. Terns nesting at inland colonies forage in freshwater during the breeding season and primarily in coastal marine environments during the nonbreeding season. As piscivores, they are susceptible to dietary Hg exposure. To characterize patterns of Hg exposure in this population, we 1) quantified within and among season differences in total mercury (THg) concentrations (µg/g) in blood and feathers at 2 Lake Superior breeding colonies, and 2) documented spatial and temporal variation in exposure by studying adult foraging ecology using geospatial tracking devices and stable isotopes. We used general linear models to assess the relationship between isotopic composition and THg concentrations in bird tissues relative to sex, age, colony location, and season. The THg concentrations were lowest in winter-grown feathers (geometric mean [95% confidence limits]): 1.32 (1.09-1.59) µg/g dw (n = 60), higher at the more industrially influenced colony (chick feathers: 4.95 [4.62-5.37] µg/g dw [n = 20]), and increased with a riverine-based diet. During the breeding season, Hg exposure varied along a gradient from lake to river, with adult females having lower blood THg concentrations than males (females: 0.83 [0.67-1.03]) µg/g ww (n = 7); males: 1.15 (0.92-1.45) µg/g ww (n = 5). Stable isotope values suggested adults obtained 42 ± 12% (n = 12) of their diet from the river during incubation, which was validated with tracking data. During chick-rearing, chicks obtained 68 ± 19% (n = 44) of their diet from the river. Our results indicate colony location, foraging behavior, and season influenced Hg exposure for these Lake Superior colonies and underscores the importance of local contamination with respect to exposure. Integr Environ Assess Manag 2021;17:398-410. © 2020 SETAC.

Feather mercury increases with feeding at higher trophic levels in two species of migrant raptors, Merlin (Falco columbarius) and Sharp-shinned Hawk (Accipiter striatus).

Mercury (Hg) is a toxic heavy metal that, when methylated to form methylmercury (MeHg), bioaccumulates in exposed animals and biomagnifies through food webs. The purpose of this study was to assess Hg concentrations in raptors migrating through the upper midwestern USA. From 2009 to 2012, 966 raptors of 11 species were captured at Hawk Ridge, Duluth, Minnesota, USA. Breast feathers were sampled to determine the concentration of total Hg. Mean Hg concentrations ranged from 0.11 to 3.46 µg g-1 fresh weight across species and were generally higher in raptors that feed on birds in comparison with those that feed on mammals. To evaluate the effect of dietary sources on Hg biomagnification, carbon and nitrogen stable isotope ratios were measured in feathers of the 2 species with the highest Hg concentrations, Merlin (Falco columbarius) and Sharp-shinned Hawk (Accipiter striatus). Measured δ 13C values were similar in both species and indicated a primarily terrestrial-derived diet, whereas δ 15N values suggested that individual Merlin and Sharp-shinned Hawk feeding at higher trophic levels accumulated higher concentrations of Hg. The risk to birds associated with measured levels of feather Hg was evaluated by calculating blood-equivalent values using an established algorithm. Predicted blood values were then compared to heuristic risk categories synthesized across avian orders. This analysis suggested that while some Merlin and Sharp-shinned Hawk were at moderate risk to adverse effects of MeHg, most of the sampled birds were at negligible or low risk.

El mercurio (Hg) es un metal pesado tóxico que, cuando se metila para formar metilmercurio (MeHg), se acumula en los tejidos de los animales expuestos y se bio-magnifica a través de las redes tróficas. El propósito de este estudio fue evaluar las concentraciones de Hg en rapaces que migran a través de la parte alta del medio oeste de Estados Unidos. De 2009 a 2012, capturamos 966 rapaces de 11 especies en Hawk Ridge, Duluth, Minnesota, EEUU. Tomamos muestras de plumas del pecho para determinar la concentración de Hg total. Las concentraciones medias de Hg fluctuaron entre 0.11 y 3.46 µg g−1 de peso fresco para las distintas especies y fueron generalmente más altas en las rapaces que se alimentan de aves en comparación con aquellas que se alimentan de mamíferos. Para evaluar el efecto de las fuentes de alimento sobre la bio-magnificación de Hg, se midieron los cocientes de isótopos estables de carbón y nitrógeno en las plumas de las dos especies con las concentraciones más altas de Hg, Falco columbarius y Accipiter striatus. Los valores medidos de δ 13C fueron similares en ambas especies e indicaron una dieta derivada principalmente del medio terrestre, mientras que los valores de δ 15N sugirieron que los individuos de F. columbarius y A. striatus que se alimentan a niveles tróficos más altos acumularon concentraciones más altas de Hg. El riesgo para las aves asociado con los niveles medidos de Hg en las plumas fue evaluado mediante el cálculo de valores equivalentes en sangre usando un algoritmo establecido. Los valores predichos en sangre fueron luego comparados con categorías de riesgo heurístico sintetizadas a través de los órdenes de aves. Este análisis sugirió que mientras algunos individuos de F. columbarius y A. striatus tuvieron un riesgo moderado a los efectos adversos de MeHg, la mayoría de las aves muestreadas tuvieron un riesgo insignificante o bajo.

Leveraging a Landscape-Level Monitoring and Assessment Program for Developing Resilient Shorelines throughout the Laurentian Great Lakes.

Traditionally, ecosystem monitoring, conservation, and restoration have been conducted in a piecemeal manner at the local scale without regional landscape context. However, scientifically driven conservation and restoration decisions benefit greatly when they are based on regionally determined benchmarks and goals. Unfortunately, required data sets rarely exist for regionally important ecosystems. Because of early recognition of the extreme ecological importance of Laurentian Great Lakes coastal wetlands, and the extensive degradation that had already occurred, significant investments in coastal wetland research, protection, and restoration have been made in recent decades and continue today. Continued and refined assessment of wetland condition and trends, and the evaluation of restoration practices are all essential to ensuring the success of these investments. To provide wetland managers and decision makers throughout the Laurentian Great Lakes basin with the optimal tools and data needed to make scientifically-based decisions, our regional team of Great Lakes wetland scientists developed standardized methods and indicators used for assessing wetland condition. From a landscape perspective, at the Laurentian Great Lakes ecosystem scale, we established a stratified random-site-selection process to monitor birds, anurans, fish, macroinvertebrates, vegetation, and physicochemical conditions of coastal wetlands in the US and Canada. Monitoring of approximately 200 wetlands per year began in 2011 as the Great Lakes Coastal Wetland Monitoring Program. In this paper, we describe the development, delivery, and expected results of this ongoing international, multi-disciplinary, multi-stakeholder, landscape-scale monitoring program as a case example of successful application of landscape conservation design.

Patterns in diurnal airspace use by migratory landbirds along an ecological barrier.

Migratory bird populations and survival are affected by conditions experienced during migration. While many studies and conservation and management efforts focus on terrestrial stoppage and staging areas, the aerial environment through which migrants move also is subjected to anthropogenic impacts with potential consequences to migratory movement and survival. During autumn migration, the northern coastline of Lake Superior acts as an ecological barrier for many landbirds migrating out of the boreal forests of North America. From 24 observation points, we assessed the diurnal movements of birds throughout autumn migration, 2008-2010, within a 210 × 10 km coastal region along the northern coast of Lake Superior. Several raptor species showed patterns in airspace associated with topographic features such as proximity to the coastline and presence of ridgelines. Funneling movement, commonly used to describe the concentration of raptors along a migratory diversion line that either prevents or enhances migration progress, occurred only for Bald and Golden Eagles. This suggests a "leaky" migration funnel for most migratory raptors (e.g., migrating birds exiting the purported migration corridor). Passerines migrating during the late season showed more spatial and temporal structure in airspace distribution than raptors did, including funneling and an association with airspace near the coast. We conclude that (1) the diurnal use of airspace by many migratory landbirds is patterned in space and time, (2) autumn count sites situated along ecological barriers substantially underestimate the number of raptors due to "leakage" out of these concentration areas, and (3) the magnitude and structure of diurnal passerine movements in airspace have been overlooked. The heavy and structured use of airspace by migratory landbirds, especially the airspace associated with anthropogenic development (e.g., buildings, towers, turbines) necessitates a shift in focus to airspace management and conservation attention for these animals.

Estimating the effects of detection heterogeneity and overdispersion on trends estimated from avian point counts.

Point counts are a common method for sampling avian distribution and abundance. Although methods for estimating detection probabilities are available, many analyses use raw counts and do not correct for detectability. We use a removal model of detection within an N-mixture approach to estimate abundance trends corrected for imperfect detection. We compare the corrected trend estimates to those estimated from raw counts for 16 species using 15 years of monitoring data on three national forests in the western Great Lakes, USA. We also tested the effects of overdispersion by modeling both counts and removal mixtures under three statistical distributions: Poisson, zero-inflated Poisson, and negative binomial. For most species, the removal model produced estimates of detection probability that conformed to expectations. For many species, but not all, estimates of trends were similar regardless of statistical distribution or method of analysis. Within a given combination of likelihood (counts vs. mixtures) and statistical distribution, trends usually differed by both stand type and national forest, with species showing declines in some stand types and increases in others. For three species, Brown Creeper, Yellow-rumped Warbler, and Black-throated Green Warbler, temporal patterns in detectability resulted in substantial differences in estimated trends under the removal mixtures compared to the analysis of raw counts. Overall, we found that the zero-inflated Poisson was the best distribution for our data, although the Poisson or negative binomial performed better for a few species. The similarity in estimated trends that we observed among counts and removal mixtures was probably a result of both experimental design and sampling effort. First, the study was originally designed to avoid confounding observer effects with habitats or time. Second, our time series is relatively long and our sample sizes within years are large.

Human influences on water quality in Great Lakes coastal wetlands.

A better understanding of relationships between human activities and water chemistry is needed to identify and manage sources of anthropogenic stress in Great Lakes coastal wetlands. The objective of the study described in this article was to characterize relationships between water chemistry and multiple classes of human activity (agriculture, population and development, point source pollution, and atmospheric deposition). We also evaluated the influence of geomorphology and biogeographic factors on stressor-water quality relationships. We collected water chemistry data from 98 coastal wetlands distributed along the United States shoreline of the Laurentian Great Lakes and GIS-based stressor data from the associated drainage basin to examine stressor-water quality relationships. The sampling captured broad ranges (1.5-2 orders of magnitude) in total phosphorus (TP), total nitrogen (TN), dissolved inorganic nitrogen (DIN), total suspended solids (TSS), chlorophyll a (Chl a), and chloride; concentrations were strongly correlated with stressor metrics. Hierarchical partitioning and all-subsets regression analyses were used to evaluate the independent influence of different stressor classes on water quality and to identify best predictive models. Results showed that all categories of stress influenced water quality and that the relative influence of different classes of disturbance varied among water quality parameters. Chloride exhibited the strongest relationships with stressors followed in order by TN, Chl a, TP, TSS, and DIN. In general, coarse scale classification of wetlands by morphology (three wetland classes: riverine, protected, open coastal) and biogeography (two ecoprovinces: Eastern Broadleaf Forest [EBF] and Laurentian Mixed Forest [LMF]) did not improve predictive models. This study provides strong evidence of the link between water chemistry and human stress in Great Lakes coastal wetlands and can be used to inform management efforts to improve water quality in Great Lakes coastal ecosystems.

Integrated measures of anthropogenic stress in the U.S. Great lakes basin.

Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales.

Environmentally stratified sampling design for the development of Great Lakes environmental indicators.

Understanding the relationship between human disturbance and ecological response is essential to the process of indicator development. For large-scale observational studies, sites should be selected across gradients of anthropogenic stress, but such gradients are often unknown for apopulation of sites prior to site selection. Stress data available from public sources can be used in a geographic information system (GIS) to partially characterize environmental conditions for large geographic areas without visiting the sites. We divided the U.S. Great Lakes coastal region into 762 units consisting of a shoreline reach and drainage-shed and then summarized over 200 environmental variables in seven categories for the units using a GIS. Redundancy within the categories of environmental variables was reduced using principal components analysis. Environmental strata were generated from cluster analysis using principal component scores as input. To protect against site selection bias, sites were selected in random order from clusters. The site selection process allowed us to exclude sites that were inaccessible and was shown to successfully distribute sites across the range of environmental variation in our GIS data. This design has broad applicability when the goal is to develop ecological indicators using observational data from large-scale surveys.

Rationale for a new generation of indicators for coastal waters.

More than half the world's human population lives within 100 km of the coast, and that number is expected to increase by 25% over the next two decades. Consequently, coastal ecosystems are at serious risk. Larger coastal populations and increasing development have led to increased loading of toxic substances, nutrients and pathogens with subsequent algal blooms, hypoxia, beach closures, and damage to coastal fisheries. Recent climate change has led to the rise in sea level with loss of coastal wetlands and saltwater intrusion into coastal aquifers. Coastal resources have traditionally been monitored on a stressor-by-stressor basis such as for nutrient loading or dissolved oxygen. To fully measure the complexities of coastal systems, we must develop a new set of ecologic indicators that span the realm of biological organization from genetic markers to entire ecosystems and are broadly applicable across geographic regions while integrating stressor types. We briefly review recent developments in ecologic indicators and emphasize the need for improvements in understanding of stress-response relationships, contributions of multiple stressors, assessments over different spatial and temporal scales, and reference conditions. We provide two examples of ecologic indicators that can improve our understanding of these inherent problems: a) the use of photopigments as indicators of the interactive effects of nutrients and hydrology, and b) biological community approaches that use multiple taxa to detect effects on ecosystem structure and function. These indicators are essential to measure the condition of coastal resources, to diagnose stressors, to communicate change to the public, and ultimately to protect human health and the quality of the coastal environment.