Loon Populations Research Articles

Trends in Arctic-nesting loon (Gavia spp.) populations in North America

Trends in Arctic-nesting loon (Gavia spp.) populations in North America

Interrelated impacts of climate and land-use change on a widespread waterbird.

Together climate and land-use change play a crucial role in determining species distribution and abundance, but measuring the simultaneous impacts of these processes on current and future population trajectories is challenging due to time lags, interactive effects and data limitations. Most approaches that relate multiple global change drivers to population changes have been based on occurrence or count data alone. We leveraged three long-term (1995-2019) datasets to develop a coupled integrated population model-Bayesian population viability analysis (IPM-BPVA) to project future survival and reproductive success for common loons Gavia immer in northern Wisconsin, USA, by explicitly linking vital rates to changes in climate and land use. The winter North Atlantic Oscillation (NAO), a broad-scale climate index, immediately preceding the breeding season and annual changes in developed land cover within breeding areas both had strongly negative influences on adult survival. Local summer rainfall was negatively related to fecundity, though this relationship was mediated by a lagged interaction with the winter NAO, suggesting a compensatory population-level response to climate variability. We compared population viability under 12 future scenarios of annual land-use change, precipitation and NAO conditions. Under all scenarios, the loon population was expected to decline, yet the steepest declines were projected under positive NAO trends, as anticipated with ongoing climate change. Thus, loons breeding in the northern United States are likely to remain affected by climatic processes occurring thousands of miles away in the North Atlantic during the non-breeding period of the annual cycle. Our results reveal that climate and land-use changes are differentially contributing to loon population declines along the southern edge of their breeding range and will continue to do so despite natural compensatory responses. We also demonstrate that concurrent analysis of multiple data types facilitates deeper understanding of the ecological implications of anthropogenic-induced change occurring at multiple spatial scales. Our modelling approach can be used to project demographic responses of populations to varying environmental conditions while accounting for multiple sources of uncertainty, an increasingly pressing need in the face of unprecedented global change.

Plunging floater survival causes cryptic population decline in the Common Loon.

Populations of many vertebrates are declining and geographic ranges contracting, largely as a consequence of anthropogenic threats. Many reports of such decline, however, lack the breadth and detail to narrow down its causes. Here we describe population decline in the Common Loon (Gavia immer), a charismatic aquatic bird, based on systematic resighting and measurement of a marked population. During our 27-year investigation, age-adjusted chick mass has fallen by 11%, mortality among young and old chicks has increased by 31% and 82%, respectively, and fledging success has declined by 26%. Meanwhile, the return rate of marked nonbreeders ("floaters") has plunged by 53%, and the adult population overall has declined by 22%. Consistent with the thinning ranks of floaters, the rate of territory eviction has decreased by 52% during the study. Despite the decline in floaters, territory occupancy remains unchanged. However, a matrix model, updated with recent estimates for breeding success, juvenile survival, and senescence, yields a recalculated deterministic population growth rate (λ) of 0.94 for our study population, which suggests that declines in vital rates could lead to a loss of 52% of the current population and a decline of 37% in territory occupancy by 2031. Lack of data on floaters in other upper Midwest and New England loon populations leaves their status in doubt.

Drivers of declines in common loon (Gavia immer) productivity in Ontario, Canada

Common loons (Gavia immer) are top predators that depend on lake food webs to successfully fledge chicks. Common loon reproductive success is consequently recognized as an important indicator of aquatic ecosystem health. Existing evidence points to long-term declines in productivity in portions of the common loon range; however, the reason for these declines is not well understood. Our objectives were to define underlying baseline patterns of loon reproductive success in Ontario, Canada, and to identify drivers of temporal changes in loon productivity. We analyzed 38 years of reproductive data from over 1500 lakes using data from the Canadian Lakes Loon Survey, a citizen science loon monitoring program managed by Birds Canada that has run annually in Ontario since 1981. Overall, we estimated a declining trend in common loon reproductive success of −0.10 six-week-old young per pair per year in Ontario between 1981 and 2018. We assessed the influence of 14 factors on loon reproductive success. We identified low pH and associated higher mercury as factors linked to loon productivity declines. We also demonstrated that lake area, longitude, and April temperatures can predict the number of six-week-old young per pair per year. We hypothesize that climate change-induced stress, acting through multiple interacting pathways involving mercury acidity, fish abundance, lake size, and geographic location, may account for declining loon productivity. These results will be important for focusing future research and conservation efforts to help understand and mitigate threats to common loon populations.

The influence of chick production on territory retention in Arctic-breeding Pacific and Yellow-billed loons

Abstract Adult birds may use the production of offspring as a measure of habitat quality when prospecting for territories, increasing competition for productive territories. We evaluated the impact of breeding success on territory retention of Pacific (Gavia pacifica) and Yellow-billed (G. adamsii) loons in the National Petroleum Reserve-Alaska on the Arctic Coastal Plain of northern Alaska using mark–resight data and multi-state modeling. We also used behavioral observations of brood-rearing adult loons to quantify the frequency of visits by prospecting loons. We hypothesized that increased competition for productive territories would result in a decrease in territory retention rates. Territory retention rates the year following successful breeding attempts were only slightly lower (0.90) than after failed breeding attempts (0.93), and few territories were consistently successful across years. Overall territory retention rates were high (0.92) and similar for both species, suggesting that adults were able to defend their territories successfully. Males had higher territory retention rates than females, but we found no influence of mass (a possible proxy for fighting ability) on territory retention. These observations, coupled with the high frequency of visits by prospecting loons, provide additional evidence that site familiarity may provide advantages to territory holders. Quantifying territory retention behaviors may also inform land management decisions for oil and gas development in areas where loons are present. High territory retention rates, frequency of visits by prospectors, and limited habitat where new territories can be established suggest that breeding habitat in northern Alaska is saturated and may be limiting Yellow-billed Loon populations. In contrast, Pacific Loons attempting to acquire a territory may be able to form new territories on smaller, unoccupied lakes.

Common Loons respond adaptively to a black fly that reduces nesting success

ABSTRACT Nesting birds must often cope with harassment from biting insects, but it is difficult to ascertain what effect such pests might have on breeding success and population dynamics. We tested the hypothesis that a black fly (Simulium annulus) that feeds on the blood of nesting Common Loons (Gavia immer) causes nest abandonment in this charismatic diving bird. In addition, we measured effects of fly-induced abandonment on a loon population, and examined potential predictors of fly abundance and nest abandonment. We also tested a second hypothesis, which holds that loon pairs that abandon a nest owing to flies should often remain at the site for their subsequent nesting attempt, since fly outbreaks last only 1–2 weeks. All predictions of the fly-induced abandonment hypothesis were supported, including strong correlations between fly counts and rate of abandonment, reduced incubation during severe fly years, and increased abandonment during cool springs, which promote longevity of the flies. The correl...

Genomic insights into natural selection in the common loon (Gavia immer): evidence for aquatic adaptation

BackgroundThe common loon (Gavia immer) is one of five species that comprise the avian order Gaviiformes. Loons are specialized divers, reaching depths up to 60 m while staying submerged for intervals up to three minutes. In this study we used comparative genomics to investigate the genetic basis of the common loon adaptations to its ecological niche. We used Illumina short read DNA sequence data from a female bird to produce a draft assembly of the common loon (Gavia immer) genome.ResultsWe identified 14,169 common loon genes, which based on well-resolved avian genomes, represent approximately 80.7% of common loon genes. Evolutionary analyses between common loon and Adelie penguin (Pygoscelis adeliae), red-throated loon (Gavia stellata), chicken (Gallus gallus), northern fulmar (Fulmarus glacialis), and rock pigeon (Columba livia) show 164 positively selected genes in common and red-throated loons. These genes were enriched for a number of protein classes, including those involved in muscle tissue development, immunoglobulin function, hemoglobin iron binding, G-protein coupled receptors, and ATP metabolism.ConclusionsSignatures of positive selection in these areas suggest the genus Gavia may have adapted for underwater diving by modulating their oxidative and metabolic pathways. While more research is required, these adaptations likely result in (1) compensations in oxygen respiration and energetic metabolism, (2) low-light visual acuity, and (3) elevated solute exchange. This work represents the first effort to understand the genomic adaptations of the common loon as well as other Gavia and may have implications for subsequent studies that target particular genes for loon population genetic, ecological or conservation studies.

Population‐level effects of lead fishing tackle on common loons

ABSTRACTPoisoning 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. © 2017 The Wildlife Society.

Yellow-Billed Loon Subsistence Harvest in Alaska: Challenges in Harvest Assessment of a Conservation Concern Species

Abstract The yellow-billed loon Gavia adamsii was designated as a candidate species for listing as threatened or endangered under the U.S. Endangered Species Act in 2009. Subsistence harvest was identified as a threat based on the 2007 harvest estimate for the Bering Strait region of Alaska. This estimate was unusually high and inconsistent with data on the species' abundance and distribution. We conducted this study in 2011–2012 on St. Lawrence Island, in the Bering Sea, to fulfill data needs related to this Endangered Species Act listing process. Our objectives were to clarify 1) loon species harvested, 2) numbers of loons harvested, and 3) loon harvest methods and uses by local subsistence communities. We conducted harvest surveys, ethnographic research, and shore-based bird counts. Loons were <1% of all bird harvest. Pacific loons Gavia pacifica were 96% of observed loons and likely comprised the majority of loons harvested. Local ethnotaxonomy grouped loons by size (large or small) and overall plumage (breeding or nonbreeding), differing from scientific taxonomy. We found no evidence that loon migratory aggregations occurred near St. Lawrence Island or that intense harvest effort targeted loons. We estimated that five yellow-billed loons were harvested annually in 2011 and 2012. Hatch-year loons were likely at least half of the loon harvest, lessening effects of harvest on loon populations. Our study exemplifies the importance of using multidisciplinary approaches and engaging subsistence users to improve harvest assessment and inform wildlife conservation policy.

Habitat use and population status of Yellow-billed and Pacific loons in western Alaska, USA

ABSTRACT Effective conservation of sympatric avian populations depends on unbiased estimates of population size, distribution, and habitat use. For populations of Yellow-billed Loons (Gavia adamsii) and Pacific Loons (G. pacifica) co-occurring in Arctic wetland communities in Alaska, USA, such data are limited and difficult to obtain, hindering population assessments and decision making. The Yellow-billed Loon is also under consideration for additional protections under the Endangered Species Act due to small global population size, specific habitat requirements, and low fecundity, further increasing the need for information at the landscape scale. To help evaluate the population status and habitat use of both species, we used repeated aerial surveys and a dynamic multistate occupancy modeling approach to jointly estimate 1) probability of lake use and 2) probability of use for nesting for Yellow-billed and Pacific loon populations at the landscape scale on the Seward Peninsula and Cape Krusenstern, Alask...

The Impact of Mercury Exposure on the Common Loon (Gavia immer) Population in the Adirondack Park, New York, USA

The Common Loon (Gavia immer), a top trophic-level piscivorous predator, was used as an indicator species to assess mercury exposure and risk in aquatic ecosystems in the Adirondack Park of New York State. Mercury levels in Common Loons were related to long-term reproductive success to evaluate the effects of mercury contamination on the breeding population in the Park and enable the development of a mercury hazard profile. Common Loons were sampled and monitored on selected study lakes from 1998–2007. Lake acidity correlated with Common Loon mercury levels, with more acidic lakes exhibiting higher mercury concentrations in Common Loons. Based on mercury body burden estimated by blood mercury exposure, 21% of males and 8% of females were at high risk for behavioral and reproductive impacts, while feather mercury exposure estimated that 37% of males and 7% of females were at high risk. Female and male Common Loons in the highest exposure category showed a 32% and 56% reduction, respectively, in the number of chicks fledged per year, compared to individuals in the lowest exposure category. Thirteen percent of the Adirondack Common Loon eggs sampled were at high risk for mercury exposure. Population model results indicated that the portion of the Adirondack Common Loon population with high mercury levels has a reduced growth rate (λ = 1.0005), compared to Common Loons with low body burdens of mercury (λ = 1.026). The results of this project will assist in the continued refinement of State and Federal policies and regulations that effectively address the ecological impacts mercury and other environmental contaminants pose to freshwater ecosystems. Received 21 January 2013, accepted 26 May 2013.

Landscape Assessment of Habitat and Population Recovery of Common Loons (Gavia immer) in Massachusetts, USA

Common Loons (Gavia immer) recolonized Massachusetts in 1975 from a single breeding pair on the Quabbin Reservoir. Since then, the population has grown to 33 pairs that occupy 14 lakes, but the full recovery potential of the population is unknown. This study analyzed population data and habitat suitability, as well as compared population dynamics, of the Common Loon population in Massachusetts to the Common Loon population in New Hampshire to determine if a recovery similar to the one seen in New Hampshire is possible. Results indicated that a large-scale recovery may be possible as enough suitable habitat exists to support about 300 pairs statewide. Current population stresses have not led to a decline; thus, management efforts can be increased to encourage further growth. Due to a small initial population, some aspects of a small population paradigm and an allee affect may have contributed to the slow population growth since 1975 as compared to Vermont and New Hampshire.

Parasites and Pollution: Why Both Matter to Marine Bird Conservation in the North

Parasites and Pollution: Why Both Matter to Marine Bird Conservation in the North

Juvenile survival in common loonsGavia immer: effects of natal lake size and pH

Survival is a vexing parameter to measure in many young birds because of dispersal and delayed impacts of natal rearing conditions on fitness. Drawing upon marking and resighting records from an 18‐yr study of territorial behavior, we used Cormack–Jolly–Seber analysis with Program MARK to estimate juvenile survival and its predictors in a population of common loonsGavia immer. In addition, we investigated predictors of chick mass, survival and inter‐sibling size disparity in two‐chick broods. Both small size and low pH of natal lakes predicted poor survival among chicks and juveniles; thus, features of the natal environment have both immediate and lasting effects on fitness. The pH × stage interaction retained in our MARK models indicates that the detrimental impact of lake chemistry on fitness diminishes with time; the retention of pH × lake size as a predictor of chick mass and condition pinpoints small lakes as those where acidity impacts chicks most severely. Our adjusted estimate of 0.53 probability of for survival to age 3 suggests that loon populations are healthier than often supposed.

Territory occupancy by common loons in response to disturbance, habitat, and intraspecific relationships

AbstractStructure and distribution of animal territories are driven by a variety of environmental and demographic factors. A peninsular population of common loons (Gavia immer) nests on lakes in northwestern Montana, but does not occupy all apparently suitable breeding territories, suggesting unexplained limitations on population growth. To evaluate territorial dynamics of breeding loons in Montana, we created and tested occupancy models that evaluated the hypothesized effects of disturbance, habitat, and intraspecific relationships on territory occupancy by common loons in Montana from 2003 to 2007. Model‐averaged results indicated that the abundance of feeding lakes within 10 km (i.e., forage quality) and the number of territorial pairs within 10 km (i.e., density of loons) were equally supported and related to probabilities of occupancy. We found substantial support that the population was in a state of equilibrium, with the numbers of occupied territories stable in time, but not space. We also found that density of territorial pairs was related to the likelihood that an existing territory would be abandoned, but did not influence the establishment of new territories, suggesting the presence of territorial pairs could be a stronger indicator of territory quality to loons than physical lake characteristics. Our index of human disturbance was not well‐supported compared to other factors. Our results suggest management for stable or growing loon populations could be achieved using long‐term monitoring and protection of occupied territorial lakes and nearby feeding lakes, because these factors most influenced the probability of occupancy of surrounding lakes. © 2011 The Wildlife Society.

Bi-phasic trends in mercury concentrations in blood of Wisconsin common loons during 1992–2010

We assessed the ecological risk of mercury (Hg) in aquatic systems by monitoring common loon (Gavia immer) population dynamics and blood Hg concentrations. We report temporal trends in blood Hg concentrations based on 334 samples collected from adults recaptured in subsequent years (resampled 2-9 times) and from 421 blood samples of chicks collected at lakes resampled 2-8 times 1992-2010. Temporal trends were identified with generalized additive mixed effects models and mixed effects models to account for the potential lack of independence among observations from the same loon or same lake. Trend analyses indicated that Hg concentrations in the blood of Wisconsin loons declined over the period 1992-2000, and increased during 2002-2010, but not to the level observed in the early 1990s. The best fitting linear mixed effects model included separate trends for the two time periods. The estimated trend in Hg concentration among the adult loon population during 1992-2000 was -2.6% per year, and the estimated trend during 2002-2010 was +1.8% per year; chick blood Hg concentrations decreased -6.5% per year during 1992-2000, but increased 1.8% per year during 2002-2010. This bi-phasic pattern is similar to trends observed for concentrations of methylmercury and SO(4) in lake water of an intensely studied seepage lake (Little Rock Lake, Vilas County) within our study area. A cause-effect relationship between these independent trends is hypothesized.

Red-throated loons ( Gavia stellata) breeding in Alaska, USA, are exposed to PCBs while on their Asian wintering grounds

Red-throated loons ( Gavia stellata) breeding in Alaska declined 53% during 1977–1993. We compare concentrations of environmental contaminants in red-throated loons among four nesting areas in Alaska and discuss potential ramifications of exposure on reproductive success and population trends. Eggs from the four areas had similar total polychlorinated biphenyl (PCB) concentrations, but eggs from the Arctic coastal plain had different congener profiles and greater toxic equivalents (TEQs) than eggs from elsewhere. Satellite telemetry data indicate that red-throated loons from the Arctic coastal plain in northern Alaska winter in southeast Asia, while those breeding elsewhere in Alaska winter in North America. Different wintering areas may lead to differential PCB accumulation among red-throated loon populations. For eggs from the Arctic coastal plain, TEQs were great enough to postulate PCB-associated reproductive effects in piscivores. The correlation between migration patterns and PCB profiles suggests that red-throated loons breeding in northern Alaska are exposed to PCBs while on their Asian wintering grounds.

Long term monitoring of the common loon (Gavia immer) population on 18 lakes in Kejimkujik National Park, Nova Scotia, Canada

Long term monitoring of the common loon (<i>Gavia immer</i>) population on 18 lakes in Kejimkujik National Park, Nova Scotia, Canada

Reproductive Advantages for Common Loons Using Rafts

Abstract:Artificial nesting islands, or rafts, are often deployed in common loon (Gavia immer) breeding territories to decrease negative impacts of mammalian predation and water‐level fluctuations on nesting success. The management value of rafts has been demonstrated in other studies; however, no published studies have quantified the use or associated reproductive benefits of rafts on lakes exhibiting water‐level fluctuations. These lakes constitute a major portion of loon nesting habitat in New England and the Midwest. We used long‐term data sets from loon survey and raft management efforts on lakes with stable (SWL) and fluctuating water levels (FWL) in New Hampshire and Maine, USA, to compare raft‐use patterns on both types of lakes. We then modeled the influence of percentage of nesting attempts on rafts, lake fluctuation type, and human development index on nesting success as a function of the number of nesting attempts. Loons used 76% of all rafts for nesting, and initial use patterns were similar between SWL and FWL lakes. Half (51%) of rafts used for nesting were first used during the initial year of deployment and 90% of those used were used by the third year. Based on our model, we would expect to see an 8.6% increase in nesting success associated with each successive categorical increase in raft use (0–33%, 33–60%, 60–100%). Nesting success varied with lake fluctuation type, increasing by 21.4% from FWL to SWL types. Our model estimated a 12.8% decrease in nesting success associated with an increasing human development index. Naturally nesting loons on FWL lakes are likely to display mean nesting success levels lower than those needed to sustain populations. We suggest that natural nesting habitat on lakes with fluctuating water levels during the loon nesting season may constitute an ecological trap warranting consideration of raft management. Findings in this study are germane for managing breeding loon populations, particularly those on reservoirs requiring permits from the Federal Energy Regulatory Commission.

Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish

Wild piscivorous fish, mammals, and birds may be at risk for elevated dietary methylmercury intake and toxicity. In controlled feeding studies, the consumption of diets that contained Hg (as methylmercury) at environmentally realistic concentrations resulted in a range of toxic effects in fish, birds, and mammals, including behavioral, neurochemical, hormonal, and reproductive changes. Limited field-based studies, especially with certain wild piscivorous bird species, e.g., the common loon, corroborated laboratory-based results, demonstrating significant relations between methylmercury exposure and various indicators of methylmercury toxicity, including reproductive impairment. Potential population effects in fish and wildlife resulting from dietary methylmercury exposure are expected to vary as a function of species life history, as well as regional differences in fish-Hg concentrations, which, in turn, are influenced by differences in Hg deposition and environmental methylation rates. However, population modeling suggests that reductions in Hg emissions could have substantial benefits for some common loon populations that are currently experiencing elevated methylmercury exposure. Predicted benefits would be mediated primarily through improved hatching success and development of hatchlings to maturity as Hg concentrations in prey fish decline. Other piscivorous species may also benefit from decreased Hg exposure but have not been as extensively studied as the common loon.