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Case Study: Red-throated Loons
Case Study: Red-throated Loons

Context

The Red-throated Loon is the most widespread member of the loon family, with a circumpolar distribution. Red-throated Loons were a focus of this study in the mid-Atlantic because European studies have indicated that they experience long-term, localized disturbance and displacement from wind energy facilities, as well as related activities such as vessel traffic.

 

Download Mid-Atlantic Wildlife Studies: Distribution and Abundance of Wildlife along the Eastern Seaboard 2012-2014. This 32-page summary publication explores aspects of the mid-Atlantic ecosystem; describes our survey and analytical approaches; and presents a range of results, featuring several case studies on specific species or phenomena.

The Executive Summary for the technical report is also available here.

 

Take Home Messages

  • The greatest overlap between Red-throated Loon distributions and mid-Atlantic WEAs occurred during migration periods, when movements tended to be located farther offshore.
  • In winter, Red-throated Loons were most commonly located west of the WEAs.
 

Background

Red-throated Loons are long-lived and experience high adult survival. In North America, they breed primarily on freshwater or brackish ponds and small lakes on the Arctic tundra. They likely form monogamous pairs and often return to the same nest site over multiple years.

Red-throated Loons spend winter in temperate coastal ocean waters, migrating singly or in small groups within a few miles of the coast. They primarily eat fish on the breeding grounds, in addition to aquatic invertebrates and an occasional frog. Red-throated Loons are the only loon species to forage in marine habitats year-round.

The Red-throated Loon has a Conservation Status of Least Concern from the International Union for the Conservation of Nature, due to its broad range and large population size, despite a population trend indicating a decline. Fisheries are a major source of adult mortality, via bycatch of birds in nets.

 

Distribution and Abundance

Winter utilization distribution for satellite-tagged Red-throated Loons (n=23; data are preliminary).
Winter utilization distribution for satellite-tagged Red-throated Loons (n=23; data are preliminary).
 
Predicted abundance of Red-throated Loons for a given day in winter 2013-2014. Model outputs combine observation data from boat-based surveys with environmental covariate data to predict Red-throated Loon abundance across the study area. The highest abundance of Red-throated Loons was predicted to occur close to shore and in regions with cooler water and high primary productivity.
Predicted abundance of Red-throated Loons for a given day in winter 2013-2014. Model outputs combine observation data from boat-based surveys with environmental covariate data to predict Red-throated Loon abundance across the study area. The highest abundance of Red-throated Loons was predicted to occur close to shore and in regions with cooler water and high primary productivity.
 

Behaviors and Habitat Use

Red-throated Loons were most consistently observed within within approximately 20 km of shore. This differed from Common Loons, which were more widely distributed across the study area. Telemetry data indicated that Red-throated Loons preferentially used shallow nearshore waters over flat sandy substrates while wintering in the mid-Atlantic, particularly around the mouth of Chesapeake Bay and south along the Virginia and North Carolina coasts. Modeled boat survey data indicated that proximity to shore was the strongest predictor of Red-throated Loon abundance, followed by relatively cold sea surface temperature, and primary productivity (low in spring, high in winter).

Satellite tagged individuals left the study area between late March and early May, largely following the coast north to breeding grounds. Greatest offshore movements occurred during this departure from the study area. During fall migration, loons arrived in the study area between mid-November and late December. Most individuals stopped over in Hudson Bay and moved either to the Gulf of St. Lawrence or the Great Lakes before flying to Delaware Bay and following the coastline south.

 

Temporal Variation

Red-throated Loons were most commonly observed on the boat-based and digital aerial surveys between November and May. No individuals were observed in July-August from either survey method.

Satellite tracked Red-throated Loons arrived in the study area between mid-November and late December, and departed beginning in late March, with all birds gone by May. A time variant kernel density model of satellite telemetry data was developed to improve our understanding of the species’ use of the landscape through time. The movement video generated from this model is shown here.

 

For More Information

For more information, see Chapters 12, 17, 21, and 23 in the technical report.

Telemetry data were gathered as part of a longer-term study of Red-throated Loons funded by multiple agencies and organizations.

Funders and collaborators for this effort are listed on the study methods page.

 

References

  • Barr JF, Eberl C, McIntyre JW (2000) Red-throated Loon (Gavia stellata), in: Poole A (ed) Birds of North America Online. Cornell Lab of Ornithology, Ithaca, NY
  • BirdLife International (2015) IUCN Red List of Threatened Species. Version 2015.2. www.iucnredlist.org Accessed 09 July 2015
  • Kaufman K (1996) Lives of North American Birds. Houghton Mifflin Co., Boston, MA. 675 pp.
  • Langston, R. H. W. 2013. Birds and wind projects across the pond: A UK perspective. Wildlife Society Bulletin 37:5–18. doi: 10.1002/wsb.262
  • Petersen I, Fox A (2007) Changes in bird habitat utilization around Horns Rev 1 offshore wind farm, with particular emphasis on Common Scoter. Report commissioned by Vattenfall A/S. National Environmental Research Institute. 36 pp
 
Photo Credits: Header photo © Ken Archer; Maps © BRI
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