We investigated both social and foraging plasticity in a population of Common Loons (Gavia immer) that overwinter inland on Lake Jocassee Reservoir, South Carolina, using transects and time-activity budgets from 4 Jan-10 March 2017. Loons were observed as either solitary individuals (65%) or in groups (35%, i.e., within < 5 body lengths of another loon). Loons were more social (i.e., in groups) on transects with a river mouth (40.9% + 7.1) than on transects without a river mouth (24.2% + 5.4). The average (+ SE) dive duration for solitary loons was 71.3 + 7.7s (n=46, range 15-219s) and several dives exceeded 2 min (22.2%, 10/46). In contrast, fifteen foraging flocks were characterized by numerous shallow dives of < 20s. The average group size (+ SE) was 6.9 + 0.8 individuals and group foraging bouts lasted 8.3 + 1.2 min. In addition, Horned Grebes (Podiceps auritus) and Ring-billed Gulls (Larus argentatus), joined loons forming multispecies foraging flocks, 26.7% and 13.3% of the time. These data indicate Common Loons wintering at Lake Jocassee are social and exhibit foraging plasticity.

The Natural Resource Damage Assessment and Restoration Trustees for the Deepwater Horizon oil spill assessed the external oiling of migratory bird species dependent on open water in the Gulf of Mexico following the aforementioned spill. The assessment was designed to evaluate birds that use open water during the winter within 40 km of the Gulf shoreline. We focused on the American white pelican (Pelecanus erythrorhynchos), common loon (Gavia immer), and northern gannet (Morus bassanus). Point counts (pelican, loon) or strip transects (gannet) were used and each target species was assessed for oiling (unoiled, trace, light, moderate, or heavy amounts) and photographed. Due to distance at sighting and/or poor visibility, not all visible birds were assessed. The percentage of birds oiled varied by species, with the common loon being the highest (23.6%), followed by American white pelican (16.9%), and northern gannet (6.9%).Most of the American white pelicans and common loons had trace (83% and 72%, respectively) or light levels (11% and 24%, respectively) of oiling...

We captured 93 wintering adult and subadult Common Loons (Gavia immer) in coastal Louisiana from 2011 to 2015 following the Deepwater Horizon oil spill. We tested blood samples for exposure to polycyclic aromatic hydrocarbons (PAHs) and measured physiological variables including hematocrit, hemoglobin and total blood protein. PAH concentrations in loon blood differed from year to year and by age class. High PAH concentrations were significantly related to lower body masses in both adult and subadult birds and higher serum protein levels in adults only. PAH concentrations had marginal relations with both hematocrit and hemoglobin levels. The types of PAHs detected also underwent a major shift over time. The PAHs detected in 2011, 2012, and 2015 were primarily low molecular weight (three carbon rings); however, in 2013, most detected PAHs were high molecular weight (four carbon rings). It is unclear what events led to the increase in PAH concentrations and the shift in type of PAHs over time.

In many avian species, breeding site fidelity has been more thoroughly investigated than winter site fidelity, yet the latter may have a greater impact on survivorship. The Common Loon (Gavia immer) is an example of a species whose breeding site fidelity has been well established, but whether it exhibits winter site fidelity remains unknown. Because Common Loons primarily winter in marine waters off coastal shores, winter site fidelity has been challenging to document. We investigated winter site fidelity in Common Loons across North America using satellite transmitters, recaptures, and resightings of previously color-marked individuals. Color-marked adults returned in consecutive years to the same coastal wintering locations in California, Washington, Louisiana, Maryland, and Massachusetts, USA. We estimated adult annual apparent survival as 77% (0.48–0.93) and adult winter site fidelity as 85% (0.35–0.98). This finding has important conservation implications in the aftermath of recent marine oil spills; if Common Loons return to the same contaminated wintering areas annually, decreased fitness and survivorship could result in population-level effects.

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 loons from Louisiana have been documented to date and it is unclear where loons from this region migrate and breed. This of particular interest due to the Deepwater Horizon Oil Spill in April 2010. 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. Previous research using satellite telemetry on migrating loons in the western states (Nevada, Montana) showed they were migrating to Saskatchewan, but wintering at Lake Mead, Nevada, the Gulf of California and the Pacific Ocean. Our findings are of interest because loons from the same breeding area in Saskatchewan are wintering in different regions of North America.

A workshop titled The Status of Gavia: Conservation in Black and White was held at the 5th North American Ornithological Conference on August 14, 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 chicks (Gavia immer), 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.