A workshop titled The Status of Gavia: Conservation in Black and White was held at the 5th North American Ornithological Conference on 14 August 2012, in Vancouver, British Columbia. The last such North American meeting focused on loons was at the American Ornithologist's Union meetings in Minneapolis in 1997. During the interim 15 years, our knowledge of this group of diving birds in North America has increased significantly. From the 2012 workshop, as well as from contributions of authors unable to attend, 15 papers are presented in this special issue under five broad headings: behavior, life history and population ecology, movements and migration, habitat and landscape requirements and contaminants. Some highlights include the first data on sex ratios in Common Loon (Gavia immer) chicks, the first adult survival estimates for Red-throated Loons (G. stellata), and first reports of mercury exposure in Yellow-billed Loons (G. adamsii) from Alaska and Canada. In addition, a new long-distance migration record for the Common Loon, a landscape assessment of Common Loons in Massachusetts, and oil concentrations in loons wintering in Barataria Bay, Louisiana (one of the areas hit hardest by the Deepwater Horizon Oil Spill) are documented. We hope this collection of papers will be useful to researchers and wildlife managers in North America and abroad.

We used a polymerase chain reaction (PCR)-based sex identification technique to evaluate the sex ratios of pre-fledged juvenile Common Loons (Gavia immer) from three breeding populations in northern Michigan and northern Wisconsin, and of dead adult Common Loons migrating through Lake Huron. Results of these analyses show that more juvenile males than females fledged from all three breeding populations, although none of these biases differed significantly from parity. The sex ratio of migratory adults was at parity. No parental or territory quality indicators were significantly associated with the sex of chicks fledged from one intensely studied northern Michigan population at Seney National Wildlife Refuge. A significant male bias in adult re-observation of Common Loons banded as juveniles at the wildlife refuge was not solely attributable to the modest male bias recorded at fledging, and thus suggests a pattern of female-biased post-fledging mortality and/or female-biased adult dispersal in Common Loons.

Pacific (Gavia pacifica) and Yellow-billed (G. adamsii) loons nest sympatrically in Arctic regions. These related species likely face similar constraints and requirements for nesting success; therefore, use of similar habitats and direct competition for nesting habitat is likely. Both of these loon species must select a breeding lake that provides suitable habitat for nesting and raising chicks; however, characteristics of nest site selection by either species on interior Arctic lakes remains poorly understood. Here, logistic regression was used to compare structural and habitat characteristics of all loon nest locations with random points from lakes on the interior Arctic Coastal Plain, Alaska. Results suggest that both loon species select nest sites to avoid predation and exposure to waves and shifting ice. Loon nest sites were more likely to be on islands and peninsulas (odds ratio = 16.13, 95% CI = 4.64–56.16) than mainland shoreline, which may help loons avoid terrestrial predators. Further, nest sites had a higher degree of visibility (mean degrees of visibility to 100 and 200 m) of approaching predators than random points (odds ratio = 2.57, 95% CI = 1.22–5.39). Nests were sheltered from exposure, having lower odds of being exposed to prevailing winds (odds ratio = 0.34, 95% CI = 0.13–0.92) and lower odds of having high fetch values (odds ratio = 0.46, 95% CI = 0.22–0.96). Differences between Pacific and Yellow-billed loon nesting sites were subtle, suggesting that both species have similar general nest site requirements. However, Yellow-billed Loons nested at slightly higher elevations and were more likely to nest on peninsulas than Pacific Loons. Pacific Loons constructed built up nests from mud and vegetation, potentially in response to limited access to suitable shoreline due to other territorial loons. Results suggest that land managers wishing to protect habitats for these species should focus on lakes with islands as well as shorelines sheltered from exposure to prevailing wind and ice patterns.

Animal signals play an important role in mate attraction and territory defense, and animals may benefit by adopting signaling strategies that maximize effective communication in the face of changing environmental conditions. In this study, a custom-designed microphone array was used to collect landscape-scale recordings of the acoustic signaling behavior of Common Loons (Gavia immer) along a 10-km transect spanning three lakes in eastern Ontario, Canada. Recordings were collected during the early part of the breeding season during two consecutive years (2008–2009). Analyses focused on understanding how the vocal output of Common Loons varied with time of day, time of year, and in response to variation in weather. Common Loons showed significant diel variation in vocal output, producing more wail, yodel, and tremolo calls at night than during the day. Common Loons showed significant seasonal variation in vocal output, producing fewer wail, yodel, and tremolo calls as the first month of the breeding season progressed. Common Loons showed significant differences in vocal behavior with changing weather conditions, producing more calls at cold temperatures, with low wind speed and air pressure, and when rain was light or absent. Microphone array recordings were used to estimate signal transmission properties of Common Loon vocalizations, demonstrating that wail, yodel, and tremolo calls transmit significantly farther at night than during the day. These results provide quantitative details of Common Loon vocal signaling strategies, revealing that this species calls when abiotic conditions are ideal for long-range signaling.

Unlike most waterbirds, Common Loons (Gavia immer) have a dynamic vocal repertoire that includes the high-amplitude wail, tremolo, and yodel. This paper is a review of the acoustic structure of the yodel, an aggressive warning signal only given by male Common Loons. The context in which males yodel is described along with the possible adaptive functions of this signal. The yodel is the most acoustically complex vocalization of the Common Loon and contains a wealth of information about the signaler. Suites of frequency and time elements of the yodel appear to communicate information about the identity of the signaler, which may be important for neighbor-stranger, mate, and kin recognition. The peak frequencies of the final note of the introductory phrase and repeat phrases also appear to communicate the condition-dependent fighting ability. Finally, the number of repeat phrases a male adds to its yodel appears to communicate the aggressive motivation, or the willingness a male Common Loon has to escalate a contest. Under various contexts not necessarily unique to Common Loons, these functions may be mutually beneficial to signalers and conspecific and heterospecific receivers, and evoke a number of interesting questions regarding the function of this dynamic signal. Such dynamic vocal signals are rare among waterbirds, and among ornithologists and behaviorists alike elicit questions regarding the conditions that maintain signal honesty among birds communicating fighting ability and aggressive state within the same vocal signal.

Common Loon (Gavia immer) migration pathways have been previously identified using resightings, band recoveries, and satellite tracking with platform terminal transmitters, but there remains much to be learned. No band recoveries or resightings of Common Loons from Louisiana have been documented to date, and it is unclear where Common Loons from this region migrate and breed. On 29 March 2011, as part of a pilot study, we implanted two platform terminal transmitters in Common Loons wintering off the Louisiana coast. Both individuals migrated to Saskatchewan, Canada. Previous research using satellite telemetry on migrating Common Loons in the western USA states (Nevada and Montana) showed they migrated to Saskatchewan, but wintered at Lake Mead, Nevada, the Gulf of California and the Pacific Ocean. Our findings are of interest as Common Loons from the same breeding area in Saskatchewan overwinter in different regions of North America.

Yellow-billed Loons (Gavia adamsii) breed in lakes in the treeless Arctic and are globally rare. Like their sister taxa, the well-documented Common Loon (G. immer) of the boreal forest, Yellow-billed Loons exhibit strong territorial behavior during the breeding season. Little is known about what size territories are required, however, or how readily territories are retained from year to year. An understanding of territory dynamics and size is needed by management agencies as most of the U.S. breeding population of Yellow-billed Loons resides in the National Petroleum Reserve-Alaska where oil and gas development is expected to increase in the next few decades. Using locational data from a set of Yellow-billed Loons marked with satellite transmitters, we quantified an index of territory radius for each of three breeding populations: two in Alaska and one in Canada. The mean territory radius was 0.42 km for Yellow-billed Loons summering on lakes within the Seward Peninsula in northwest Alaska, 0.69 km for Yellow-billed Loons within the Arctic Coastal Plain of Alaska (encompasses the National Petroleum Reserve), and 0.96 km for Yellow-billed Loons within Daring Lake in mainland Canada. In this study, the mean territory radius on the Arctic Coastal Plain was about half the distance identified in stipulations for industrial development in the National Petroleum Reserve. The range in territory size among areas corresponded to a gradient in size of lakes used by Yellow-billed Loons with territories at the two Alaska sites on lakes averaging < 200 ha while territories in Canada were generally on much larger lakes. In the year after capture, 71% of Yellow-billed Loons retained territories that were held the previous year. Most Yellow-billed Loons that lost their territories wandered over a large area within 6 km of their prior territory. No Yellow-billed Loons occupied new territories, though one reacquired its prior territory after a 1-year hiatus. Retention of a territory in a subsequent year was positively related to early arrival dates at the breeding site. For Yellow-billed Loons on the Arctic Coastal Plain, this relationship was quite strong with a week lag in arrival decreasing the probability of retaining a territory by 80%. These collective observations, in combination with theoretical studies of population regulation by floaters (non-territorial birds), suggest that lake habitat suitable for breeding Yellow-billed Loons may currently limit population size in this species.

During 25 field seasons between 1988 and 2012, Biodiversity Research Institute captured and uniquely color-banded 2,730 adult Common Loons (Gavia immer) on breeding territories in 11 States and seven Provinces throughout North America. Body mass was obtained from each individual; tarsus and bill measurements were obtained from more than half the birds banded. Clinal variation in body mass, tarsal width and bill length was observed. Body mass varied from 2,700 g to 7,600 g; loons from populations in the upper Great Lakes and central Canada were smallest, and size increased to the east and west. Examination of band return and satellite tracking data resulted in three migration distance groups: < 1,500 km; 1,500–3,500 km; and ≥ 3,500 km. Body mass was inversely related to migration distance. Males were significantly larger (> 20%) than associated females, and withinpair differences increased with decreasing migration distance (i.e., males from coastal States were proportionally larger than their mates compared to interior State pairs).

Estimates of wildlife population viability through measurements of contaminant stressors, such as water mercury concentrations, were modified with variables specific to New York’s Adirondack Park to develop a wildlife criterion value for the Common Loon (Gavia immer). Biotic and abiotic samples were collected for mercury analysis on 44 Adirondack lakes over a 2-year period (2003 to 2004). From 1998 to 2007, Common Loon blood samples were collected for mercury analysis from the 44 lakes, loon feather samples from 40 lakes, and nonviable eggs from 29 lakes. It was determined that 2.00 ng Hg/L or less in the water was small enough to prevent male Adirondack Common Loons from accumulating mercury in levels high enough to impact reproductive success and behavior, while a water sample of 1.69 ng Hg/L or less was small enough to not cause impacts to female Common Loons. These wildlife criterion values are greater than the wildlife criterion value of 1.30 ng Hg/L applied to avian species by the Great Lakes Water Quality Initiative. The Common Loon-based wildlife criterion value provides a valuable estimate of the mercury thresholds associated with biotic impacts due to mercury contamination in aquatic ecosystems, enabling legislators to integrate these standards into policies that better protect environmental quality. Based on the water samples collected, it was estimated that the wildlife criterion value accurately predicted the protection of 61% of female and 73% of male Adirondack loons. More rigorous sampling of the abiotic compartment over a wider temporal and spatial scale is necessary to fully understand how water quality parameters relate to Common Loon reproductive success.

On 20 April 2010, the Deepwater Horizon oil drilling rig located 66 km southeast of the Louisiana coast exploded and, by the time the pipeline was capped in July, estimates of 4.9 million barrels of oil were released in the northern Gulf of Mexico. Polycyclic aromatic hydrocarbons make up a small percentage of petroleum (< 5%), but are the most toxic with known negative impacts on wildlife and humans. Because of their lifestyle and trophic standing, seabirds are often impacted by marine spills. To test for the presence of polycyclic aromatic hydrocarbons, we captured and tested blood in Common Loons (Gavia immer), a winter migrant that spends 4–5 months in the Gulf of Mexico. Common Loons were captured at night, using spotlighting and a large dip net off the Louisiana coast, during January–March in 2011 and 2012. A total of 38 Common Loons were caught and sampled (17 in 2011 and 21 in 2012). Both the concentrations and frequency of polycyclic aromatic hydrocarbons present in Common Loons appear to be increasing between years; however, concentrations were low (< 10 ppb). In 2012, petrogenic alkyl polycyclic aromatic hydrocarbons, those derived from petroleum, were significantly higher than pyrogenic polycyclic aromatic hydrocarbons, derived from combustion and anthropogenic sources. It remains unknown if current levels have any adverse impacts on Common Loon health, reproduction and survival.

The effects of lakeshore development on reproductive success of Common Loons (Gavia immer) were examined in New York State’s Adirondack Park. It was hypothesized that loon reproductive success would be negatively affected by the increased amount of shoreline development that has been occurring in the Park in recent years. Additionally, it was further hypothesized that the average distance from the nest site to the nearest point of development would be greater for successful nests than for failed nests. Historical nest productivity data collected from banded Common Loons on 53 lakes over a period of 7 years were evaluated along with residential development data collected during two field seasons in 2004 and 2005. Mean distance from successful nests (n = 28) to the nearest shoreline development unit (442.7 m, Range: 41.4–1,540.0 m) was greater than the mean distance from failed nests (n = 32) to the nearest shoreline development unit (343.1 m, Range: 2.2–1,222.9 m). Presence of nesting pairs was significantly related (R² = 0.25, P = 0.001) to increased shoreline length and decreased amount of development. Common Loon chick hatching success was significantly related to the density of development on small lakes (P = 0.033), but not on large lakes (P > 0.05). Our results indicate that the amount of development on lakes is not as important to nesting Common Loons as the placement of development in clusters along lakeshores. The clustering of development on one part of the lake will allow Common Loons to nest a distance away from developed areas. Thus, this study provides additional support for the buffering of loon nesting areas from development as a conservation/ management tool to enhance their reproductive success.

Shoreline attributes and extensive field surveys of aquatic vegetation and animal presence were used to determine probabilities of Common Loon (Gavia immer) nesting for segments of lakeshore on 35 lakes in north-central Minnesota. Model development used both a general linear mixed model and random forest classifier approach. The resulting nesting habitat models were used to predict nesting sites for a small set of independent lakes. Shoreline segments with low mean fetch and littoral slope, fewer developed shoreline parcels, and higher aquatic plant richness had higher probabilities of nesting. In addition, significantly more nesting sites were on islands than on mainland shoreline segments. The locations of predicted nesting sites on the independent lake set compared favorably to the locations of observed nests. The ability to predict suitable Common Loon nesting sites should lead to the greater protection or restoration of these valuable areas and enhance conservation efforts across the state.

Large variations in the summering population size of Red-throated Loons (Gavia stellata) have occurred in recent decades in Alaska. Little information exists about annual or seasonal survival rates of adult Red-throated Loons. This study used tracking data from satellite transmitters implanted into 33 Red-throated Loons captured on breeding areas in Alaska to estimate annual survival with the sampling effort split between two study periods: 2000–2002 and 2008–2010. Mortality was inferred from transmitted sensor data that indicated body temperature of the Red-throated Loon and voltage of the transmitter's battery. Two definitive mortalities occurred, resulting in an annual survival estimate of 0.920 (SE = 0.054). The fates of two additional Red-throated Loons were ambiguous and, when treated as mortalities, the annual survival estimate was 0.838 (SE = 0.074). All four putative mortalities occurred during the non-breeding season in the early study period. Oceanic conditions, indexed by the Pacific Decadal Oscillation, appeared to differ between the study periods with higher Pacific Decadal Oscillation values associated with the early study period. Given that high values for Pacific Decadal Oscillation were also associated with the large decline of Red-throated Loons observed in Alaska during 1977–1993, this study suggests that survival of adult Red-throated Loons may vary in relation to the state of the marine ecosystem and thus contribute to long-term variation in population trends.

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.

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.

The Yellow-billed Loon (Gavia adamsii) is one of the rarest breeding birds in North America. Because of the small population size and patchy distribution, any stressor to its population is of concern. To determine risks posed by environmental mercury (Hg) loads, we captured 115 Yellow-billed Loons between 2002 and 2012 in the North American Arctic and sampled their blood and/or feather tissues and collected nine eggs. Museum samples from Yellow-billed Loons also were analyzed to examine potential changes in Hg exposure over time. An extensive database of published Hg concentrations and associated adverse effects in Common Loons (G. immer) is highly informative and representative for Yellow-billed Loons. Blood Hg concentrations reflect dietary uptake of methylmercury (MeHg) from breeding areas and are generally considered near background levels if less than 1.0 µg/g wet weight (ww). Feather (growrn at wintering sites) and egg Hg concentrations can represent a mix of breeding and wintering dietary uptake of MeHg. Based on Common Loon studies, significant risk of reduced reproductive success generally occurs when adult Hg concentrations exceed 2.0 µg/g ww in blood, 20.0 µg/g fresh weight (fw) in flight feathers and 1.0 µg/g ww in eggs. Contemporary mercury concentrations for 176 total samples (across all study sites for 115 Yellow-billed Loons) ranged from 0.08 to 1.45 µg/g ww in blood, 3.0 to 24.9 µg/g fw in feathers and 0.21 to 1.23 µg/g ww in eggs. Mercury concentrations in blood, feather and egg tissues indicate that some individual Yellow-billed Loons in breeding populations across North America are at risk of lowered productivity resulting from Hg exposure. Most Yellow-billed Loons breeding in Alaska overwinter in marine waters of eastern Asia. Although blood Hg concentrations from most breeding loons in Alaska are within background levels, some individuals exhibit elevated feather and egg Hg concentrations, which likely indicate the uptake of MeHg originating from eastern Asia. Feather Hg concentrations tended to be highest in individuals overwintering farthest west (closer to Asia). A retrospective analysis of museum specimens (n = 25) found a two-fold increase in Yellow-billed Loon feather Hg concentrations from the pre-1920s (as early as 1845) to the present. The projected increase in Hg deposition (approximately four-fold by 2050) along with the uncertainty of Hg being released through the thawing of permafrost and Arctic sea ice suggest that Hg body burdens in Yellow-billed Loons may increase. These findings indicate that Hg is a current and potentially increasing environmental stressor for the Yellow-billed Loon and possibly other Nearctic-Palearctic migrant birds.