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The nature of the common loon, from biology to behavior, from one of the world's foremost observers of the revered waterbird Even those who know the loon's call might not recognize it as a tremolo, yodel, or wail, and may not understand what each call means, how it's made, and why. And those who marvel at the loon's diving prowess might wonder why this bird has such skill, or where loons go when they must leave northern lakes in winter. For these and so many other mysteries, Loon Lessons provides evolutionary and ecological explanations that are curious and compelling. Written by one of the world's foremost experts on the subject, the book is a compendium of knowledge about the common loon and an engaging record of scientific sleuthing, documenting more than twenty-five years of research into the great northern diver. James D. Paruk has observed and compared loons from Washington and Saskatchewan to the coasts of California and Louisiana, from high elevation deserts in Nevada to mountain lakes in Maine. Drawing on his extensive experience, a wealth of data, and well-established scientific principles, he considers every aspect of the loon, from its plumage and anatomy to its breeding, migration, and wintering strategies. Here, in the first detailed scientific account of the common loon in more than thirty years, Paruk describes its biology in an accessible and entertaining style that affords a deeper understanding of this beautiful and mysterious bird's natural history and annual life cycle.

Biological mercury (Hg) hotspots were identified in the northeastern United States and southeastern Canada using a data set of biotic Hg concentrations. Eight layers representing three major taxa and more than 7300 observations were used to locate five biological Hg hotspots and nine areas of concern. The yellow perch and common loon were chosen as indicator species for the human and ecological effects of Hg, respectively. Biological Hg hotspots receive elevated atmospheric Hg deposition, have high landscape sensitivity, and/or experience large reservoir fluctuations. In the Merrimack River watershed, local Hg emissions are linked to elevated local deposition and high Hg concentrations in biota. Time series data for this region suggest that reductions in Hg emissions from local sources can lead to rapid reductions of Hg in biota. An enhanced Hg monitoring network is needed to further document areas of high deposition, biological hotspots, and the response to emissions reductions and other mitigation strategies.

Poisoning from lead fishing tackle has been identified as the leading cause of mortality in adult common loons (Gavia immer). As a K-selected species, adult survival is a critical component in the population demography of loons, but the population-level effects of mortality from ingested lead tackle on loons have not been quantified. We used a long-term dataset (1989–2012) on common loon mortality in New Hampshire, USA, to describe the types of lead tackle ingested by loons, investigate methods of ingestion of lead tackle, document the number and rate of adult mortalities resulting from lead tackle, and test for a population-level effect of lead tackle on the loon population in New Hampshire. Nearly half (48.6%) of collected adult mortalities resulted from lead toxicosis from ingested lead fishing tackle, representing an adjusted annual mortality rate of 1.7 ± 0.6% (SD) of the statewide population. Jigs accounted for 52.6% and sinkers for 38.8% of the archived lead tackle objects removed from loons, a higher proportion of jigs than has been reported in previous studies. The timing of lead tackle mortalities and a high incidence of accompanying non-lead associated fishing gear (hooks, fishing line, leaders, swivels, wire), which peaked in July and August, suggest that loons obtain the majority of lead tackle from current fishing activity rather than from a reservoir of lead tackle on lake bottoms. To project the statewide loon population in the absence of lead fishing tackle as a stressor, we constructed a retrospective population model, which re-inserted loons that died from lead tackle into the population, and used linear regression to test for a population-level effect. We defined a population-level effect as a difference in the population growth rate (λ). We estimated that lead tackle mortality reduced the population growth rate (λ) by 1.4% and the statewide population by 43% during the years of the study. This study suggests that replacing lead fishing sinkers and jigs weighing ≤28.4 g with non-toxic alternatives would result in an immediate benefit to the loon population in New Hampshire.

Bald Eagles (Haliaeetus leucocephalus) and Common Loons (Gavia immer) have been the subject of intensive recovery efforts over 4 decades in New Hampshire. In the last 2 decades, eagles have increased from 1 to 40 territorial pairs, and loons have increased from 208 to 284 territorial pairs. Eagle predation of loons and loon eggs has been documented in a limited but increasing number of cases. We looked for evidence that this predation has begun to limit loon productivity or provoke territorial shifts to avoid predation during the initial period of Bald Eagle population recovery (1998-2013). Using 16 yr of breeding census data, we found support for the prediction that eagle nest proximity may be contributing to >3% of observed loon nest failures. Our findings indicate that eagles may already be exerting a measurable predation pressure. However, at current eagle densities, this pressure does not explain observed local declines in loon abundance. Our counterfactual analysis identified subsets of the data (e.g., loon nest sites on islands) where eagle nest density had the strongest negative association with loon productivity; it may be a useful tool for similar ecological models. Received 28 February 2018. Accepted 18 November 2018. Key words: Bald Eagle, Common Loon, counterfactual analysis, population density, predation, spatial avoidance (Spanish)--Las aguilas Haliaeetus leucocephalus y los colimbos Gavia immer han sido sujetos a esfuerzos intensivos de recuperacion por mas de cuatro decadas en New Hampshire. En las ultimas dos decadas, las aguilas se han incrementado de 1 a 40 parejas territoriales y los colimbos se han inerementado de 208 a 284 parejas territoriales. La depredacion de colimbos y sus huevos por aguilas se ha documentado un pequeno pero creciente numero de casos. Revisamos evidencia de que dicha depredacion ha comenzado a limitar la poblacion de colimbos durante el periodo inicial de recuperacion de la poblacion del aguila (1998-2013). Utilizando 16 anos de datos del censo de reproduccion, encontramos soporte para la prediccion de que la proximidad de los nidos de aguila podria eontribuir con >3% de los fallos observados en la anidacion de colimbos. Nuestros hallazgos indican que las aguilas ya podrian representar una presion de depredacion cuantificable. Sin embargo, las densidades actuales de las aguilas no explican los declines locales en la abundancia de colimbos. Nuestro analisis contrafactico identifica varios subconjuntos de datos (e.g., sitios de anidacion de colimbos en islas) donde la densidad de nidos de aguilas tuvo la asociacion negativa mas fuerte con la productividad de colimbos. Este metodo podria ser una herramienta util para modelos ecologicos similares. Palabras clave: analisis contrafactico, densidad dc poblacion, depredacion, evasion espacial

Populations of scoter and loon species that winter in the Atlantic are understudied in North America, but coastal observatories may provide the data required to fill some of the knowledge gaps. The migration of scoters and loons has been monitored at the Point Lepreau Bird Observatory (PLBO) in the Bay of Fundy every spring since 1996, but little peer-reviewed research based on the resultant database has been published. Using data collected over 18 years at the Bay of Fundy (2000–2017), our objectives were to (1) determine the most accurate method of modeling hourly migration rates for Surf (Melanitta perspicillata), White-winged (M. deglandi), and Black (M. americana) scoters, and Red-throated (Gavia stellata) and Common (G. immer) loons, and (2) assess trends in hourly migration rates for our five focal species to determine if the numbers of migrants passing PLBO have changed over time. We calculated hourly migration rates for each of our five focal species and evaluated drivers (i. e., timing and environmental conditions) of migration and annual trends using zero-inflated generalized linear mixed models (GLMMs). We found that drivers of migration differed among species. Specifically, hourly migration rates decreased with increasing tide height for all species except Red-throated Loons. In addition, hourly migration rates increased with increasing wind vector (i. e., a tailwind) for the three scoter species, but decreased with increasing wind vector for the two loon species. Scoter migration rates peaked daily between 11:00 and 13:00 UTC, but we found no daily peak for either loon species. Peak hourly migration rates of Black and Surf scoters occurred from 12 to 26 April, but migration rates of White-winged Scoters and both loon species continued to increase throughout our migration-monitoring window. Finally, we found no changes in hourly migration rates over time for any of our focal species, suggesting no changes in abundance over the 18 years of data collection. Our study reveals the importance and utility of long-term, coastal observation stations, and we recommend their continued funding and use as valuable sources of monitoring data. Las poblaciones de especies de negrones y colimbos que pasan el invierno en el Atlántico están poco estudiadas en América del Norte, pero los observatorios costeros pueden proporcionar los datos necesarios para llenar algunos de los vacíos de conocimiento. La migración de negrones y colimbos ha sido monitoreada en el Observatorio de Aves Point Lepreau (PLBO) en la Bahía de Fundy cada primavera desde 1996, pero se han publicado pocos estudias arbitrados por pares basados en la base de datos resultante. Utilizando los datos recopilados durante 18 años en la Bahía de Fundy (2000–2017), nuestros objetivos fueron (1) determinar el método más preciso para modelar las tasas de migración por hora para el Negrón costero (Melanitta perspicillata), el aliblanco (M. deglandi), y el americano (M. americana), y el Colimbo chico (Gavia stellata) y grande (G. immer), y (2) evalúan las tendencias en las tasas de migración por hora para nuestras cinco especies focales para determinar si el número de migrantes que pasan PLBO han cambiado con el tiempo. Calculamos las tasas de migración por hora para cada una de nuestras cinco especies focales y evaluamos los factores impulsores (es decir, el tiempo y las condiciones ambientales) de la migración y las tendencias anuales utilizando modelos mixtos lineales generalizados inflados a cero (GLMM). Encontramos que los impulsores de la migración diferen entre las especies. Específicamente, las tasas de migración por hora disminuyeron con el aumento de la altura de la marea para todas las especies, excepto para el Colimbo chico. Además, las tasas de migración por hora aumentaron al aumentar el vector de viento (es decir, un viento de cola) para las tres especies de negrones, pero disminuyeron al aumentar el vector de viento para las dos especies de colimbos. Las tasas de migración de negrones alcanzaron su punto máximo diariamente entre las 11:00 y las 13:00 UTC, pero no encontramos un pico diario para ninguna de las especies de colimbos. Las tasas pico de migración por hora del Negrón americano y costero ocurrieron del 12 al 26 de abril, pero las tasas de migración del Negrón aliblanco y ambas especies de colimbos continuaron aumentando a lo largo de nuestra ventana de monitoreo de la migración. Finalmente, no encontramos cambios en las tasas de migración por hora a lo largo del tiempo para ninguna de nuestras especies focales, lo que sugiere que no hubo cambios en la abundancia durante los 18 años de recopilación de datos. Nuestro estudio revela la importancia y utilidad de las estaciones de observación costera a largo plazo, y recomendamos su financiamiento continuo y su uso como valiosas fuentes de datos de monitoreo.

Anthropogenic inputs of mercury (Hg) into the environment have significantly increased in the past century. Concurrently, the availability of methylmercury (MeHg) in aquatic systems has increased to levels posing risks to ecological and human health. We use the common loon (Gavia immer) as an upper trophic level bioindicator of aquatic Hg toxicity in freshwater lakes. Multiple endpoints were selected to measure potential negative impacts from MeHg body burdens on behavior, physiology, survival and reproductive success. A robust spatio-temporal dataset was used that included nearly 5,500 loon Hg measurements over an 18-year period. We measured significant changes related to elevated MeHg body burdens, including aberrant incubation behavior, lethargy, and wing area asymmetry. Mercury body burdens in adult loons increased an average of 8.4% per year. Increasing Hg body burdens reduced the number of fledged chicks per territorial pair, with highest risk loons producing 41% fewer fledged young than our reference group. Our multiple endpoints establish adverse effect thresholds for adult loons at 3.0 ug/g (wet weight) in blood and 40.0 ug/g (fresh weight) in feathers. Mercury contamination in parts of Maine and New Hampshire is a driving stressor for creating breeding population sinks. Standardized monitoring programs are needed to determine if population sinks occur elsewhere and to track aquatic ecosystem responses to changes in Hg emissions and deposition.

1. Understanding and conserving migratory species requires a method for characterizing the seasonal flow of animals among habitats. Source-sink theory describes the metapopulation dynamics of species by classifying habitats as population sources (i.e. net contributors) or sinks (i.e. net substractors). Migratory species may have non-breeding habitats important to the species (e.g. overwintering or stopover habitats) that traditional source-sink theory would classify as sinks because these habitats produce no individuals. Conversely, existing migratory network models can evaluate the relative contribution of non-breeding nodes, but these models make an equilibrium assumption that is difficult to meet when examining real migratory populations. 2. We extend a pathway-based metric allowing breeding habitats, non-breeding habitats and migratory pathways connecting these habitats to be classified as sources or sinks. Rather than being based on whether place- or season-specific births exceed deaths, our approach quantifies the total demographic contribution from a node or migratory pathway over a flexibly defined yet limited time period across an organism's life cycle. As such, it provides a snapshot of a migratory system and therefore does not require assumptions associated with equilibrium dynamics. 3. We first develop a generalizable mathematical notation and then demonstrate how the metric may be used with two case studies: the common loon (Gavia immer) and Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri). These examples highlight how Stressors can impact stopover and wintering habitats (loons) and habitat management targeting migratory pathways can improve population status (trout). 4. Synthesis and applications. Each of the two case studies presented describes how effects at one location are felt by populations in another through the seasonal flow of individuals. The contribution metric we present should be helpful in allocating regulatory and management attention to times and locations most critical to migratory species persistence.

Understanding how risk factors affect populations across their annual cycle is a major challenge for conserving migratory birds. For example, disease outbreaks may happen on the breeding grounds, the wintering grounds, or during migration and are expected to accelerate under climate change. The ability to identify the geographic origins of impacted individuals, especially outside of breeding areas, might make it possible to predict demographic trends and inform conservation decision‐making. However, such an effort is made more challenging by the degraded state of carcasses and resulting low quality of DNA available. Here, we describe a rapid and low‐cost approach for identifying the origins of birds sampled across their annual cycle that is robust even when DNA quality is poor. We illustrate the approach in the common loon (Gavia immer), an iconic migratory aquatic bird that is under increasing threat on both its breeding and wintering areas. Using 300 samples collected from across the breeding range, we develop a panel of 158 single‐nucleotide polymorphisms (SNP) loci with divergent allele frequencies across six genetic subpopulations. We use this SNP panel to identify the breeding grounds for 142 live nonbreeding individuals and carcasses. For example, genetic assignment of loons sampled during botulism outbreaks in parts of the Great Lakes provides evidence for the significant role the lakes play as migratory stopover areas for loons that breed across wide swaths of Canada, and highlights the vulnerability of a large segment of the breeding population to botulism outbreaks that are occurring in the Great Lakes with increasing frequency. Our results illustrate that the use of SNP panels to identify breeding origins of carcasses collected during the nonbreeding season can improve our understanding of the population‐specific impacts of mortality from disease and anthropogenic stressors, ultimately allowing more effective management.

Bald Eagles (Haliaeetus leucocephalus) and Common Loons (Gavia immer) have been the subject of intensive recovery efforts over 4 decades in New Hampshire. In the last 2 decades, eagles have increased from 1 to 40 territorial pairs, and loons have increased from 208 to 284 territorial pairs. Eagle predation of loons and loon eggs has been documented in a limited but increasing number of cases. We looked for evidence that this predation has begun to limit loon productivity or provoke territorial shifts to avoid predation during the initial period of Bald Eagle population recovery (1998-2013). Using 16 yr of breeding census data, we found support for the prediction that eagle nest proximity may be contributing to >3% of observed loon nest failures. Our findings indicate that eagles may already be exerting a measurable predation pressure. However, at current eagle densities, this pressure does not explain observed local declines in loon abundance. Our counterfactual analysis identified subsets of the data (e.g., loon nest sites on islands) where eagle nest density had the strongest negative association with loon productivity; it may be a useful tool for similar ecological models. Received 28 February 2018. Accepted 18 November 2018.

Mercury (Hg), a neurotoxic pollutant, can be transported long distances through the atmosphere and deposited in remote areas, threatening aquatic wildlife through methylation and bioaccumulation. Over the last two decades, air quality management has resulted in decreases in Hg emissions from waste incinerators and coal-fired power plants across North America. The common loon (Gavia immer) is an apex predator of the aquatic food web. Long-term monitoring of Hg in loons can help track biological recovery in response to the declines in atmospheric Hg that have been documented in the northeastern USA. To assess spatial patterns and temporal trends in Hg exposure of the common loon in the Adirondack Park of New York State, we analyzed Hg concentrations in loon blood and egg samples from 116 lakes between 1998 and 2016. We found spatially variable Hg concentrations in adult loon blood and feathers across the Park. Loon Hg concentrations (converted to female loon units) increased 5.7% yr−1 from 1998 to 2010 (p = 0.04), and then stabilized at 1.70 mg kg−1 from 2010 to 2016 (p = 0.91), based on 760 observations. Concentrations of Hg in juvenile loons also increased in the early part of the record, stabilizing 2 years before Hg concentrations stabilized in adults. For 52 individual lakes with samples from at least 4 different years, loon Hg increased in 34 lakes and decreased in 18 lakes. Overall, we found a delayed recovery of Hg concentrations in loons, despite recent declines in atmospheric Hg.