Offshore wind energy development in the United States is projected to expand in the upcoming decades to meet growing energy demands and reduce fossil fuel emissions. There is particular interest in commercial offshore wind development within Federal waters (i.e., > 3 nautical miles from shore) of the mid-Atlantic. In order to understand the potential for adverse effects on marine birds in this area, information on distribution and behavior (e.g., flight pathways, timing, etc.) is required for a broad suite of species. In areas where offshore wind development is likely to occur, such information can be used to identify high use areas during critical life stages, which can inform the siting of offshore facilities. It can also be used to provide baseline data for understanding broad changes in distributions that occur after offshore wind developments are constructed in a specific area.
The primary objective of this study was to determine fine scale use and movement patterns of three species of diving marine birds, Red-throated Loon (Gavia stellata), Surf Scoter (Melanitta perspicillata), and Northern Gannet (Morus bassanus), in Federal waters of the mid-Atlantic U.S. during migration and winter. These species are each found in relatively large numbers and represent a cross-section of marine birds within mid-Atlantic U.S. waters during this time period. They are all considered species of conservation concern, and also exhibit traits that may make them vulnerable to the adverse effects of offshore wind development.
Additional objectives included: 1) linking areas used by each species across seasons (e.g., delineating source breeding population s); 2) designing and testing externally mounted transmitter attachment techniques, and assessing improved tracking technology on focal species, with goals of increased tag longevity, reduced bird mortality, and a more continuous record of movement pathways; and 3) developing winter capture techniques for Northern Gannets, which had not previously been targeted for at-sea capture during winter. This study also examined practices during tag attachment that could cause capture stress, and post-tagging mortality, in an effort to reduce such impacts.
In order to determine use and movement patterns of our three study species, we tagged 239 adult birds, primarily in bays and near-shore waters from New Jersey to North Carolina, between 2012 and 2015, and tracked them with Platform Terminal (satellite) Transmitters (PTTs). An additional 109 Surf Scoters, and 38 Northern Gannets tagged with PTTs as part of prior field efforts from other studies were also added to our analyses. Tracking data were analyzed using dynamic Brownian bridge movement models to develop spatial utilization distributions for each species. In winter, and in general, all three species exhibited a largely near-shore, coastal, or in-shore distribution within our study area (southern Long Island to the southern border of North Carolina). Habitat use was concentrated in or around large bays (e.g., Delaware, Chesapeake, Pamlico Sound), with the most extensive use at bay mouths. Northern Gannets ranged much farther offshore than the other two species, and covered a much larger area (including instances of individuals using both the Gulf of Mexico and the mid-Atlantic within a single season). Differences among species distributions were likely due to differences in motility and distribution of their preferred prey. For example, Surf Scoters, which left bays the least during winter, target largely sessile prey in shallower waters. Winter distributions of all three species were primarily inshore of current federal Wind Energy Areas (WEAs) and Lease Areas. However, WEAs and/or Lease Areas overlapped with portions of Northern Gannet distributions throughout the study area, whereas the winter home range distributions of Surf Scoters and Red-throated Loons showed a much more limited overlap (primarily off of Massachusetts, New Jersey, and Delaware).
Resource selection analysis indicated that core use areas for all three species were associated with shallower, colder, and more productive waters, compared to other locations within each of their winter home ranges, further supporting the idea that distributions were linked to forage resources. There was variation, however, in the range of values associated with the habitat characteristics we measured within the winter core use and home range areas, which differed for each species.
All three study species used Federal offshore waters substantially more during migratory periods than in winter. Offshore use during migration was particularly extensive for Northern Gannets, with WEAs and Lease Areas overlapping their fall and spring distributions more than the other species. Red-throated Loons and Surf Scoters exhibited more coastal use than Northern Gannets during migration, and WEAs and Lease Areas generally overlapped with their distributions less extensively. The greatest overlap of WEAs and Lease Areas with Red-throated Loon and Surf Scoter distributions occurred during spring migration, and was concentrated in the northern half (MD –NJ) of our study area, and the area immediately to the north (e.g., Cape Cod and Islands), with some additional overlap of Red-throated Loon distribution further south along the North Carolina coast. Red-throated Loons and Surf Scoters often migrated overland in fall resulting in less overlap with WEAs and Lease Areas during this period. Despite the increased use of Federal waters and consequent increased potential for exposure to future offshore wind development in WEAs and Lease Areas during migratory periods, the overall area of overlap and potential exposure generally made up a very small percentage of the overall distributions of our study species during this period (< 5%), and occurred during a brief portion of the annual cycle.
Fall migration was more prolonged, and less synchronized across species than spring migration. Northern Gannets were the first to arrive in the study area in fall, starting in early October, followed by Surf Scoters in mid to late October, and Red-throated Loons in mid-November. All three species began to depart the study area by mid-April and the vast majority of individuals had departed the study area by mid-May. Differences in average dates of arrival and departure in the study area between males and females were noted for Red-throated Loons and Northern Gannets, with females generally arriving earlier and departing later. No such difference was noted for Surf Scoters.
Most of our deployed satellite tags transmitted long enough to identify the wintering area and breeding area for each individual, establishing a connection between birds wintering in the mid-Atlantic, and their source populations. Locations of and distances to breeding areas varied widely among the three species. Red-throated Loons had the longest migration and most dispersed breeding distribution, with breeding birds spread across the Arctic and Subarctic from the Northwest Territories to northwest Greenland. Surf Scoters also widely dispersed to breeding grounds, primarily in middle and eastern portions of Subarctic Canada. Tagged Northern Gannets associated with five of the six North American breeding colonies, all of which occur in Atlantic Canada. Most of the tagged Northern Gannets associated with Bonaventure Island, which supports by far the largest breeding colony in North America. Major stop-over sites included the Gulf of St. Lawrence for all three species, the St. Lawrence River for Red-throated Loons and Surf Scoters, Hudson Bay and James Bay and the eastern Great Lakes for Red-throated Loons, and the Northumberland Strait for Surf Scoters. A subset of 38 juvenile Northern Gannets tagged on breeding colonies in Newfoundland, dispersed much farther offshore during their fall migration than adults.
The mortality rate of all birds tagged with PTTs during our study (2012 to 2015) was slightly under 20%, with the highest rate in Red-throated Loons, and the lowest in Northern Gannets. Several medical (e.g., surgeon experience, distance between capture and deployment sites, use of midazolam, presence of captivity-related injuries) and non-medical factors (e.g., weather during and immediately after release; bird age, sex, and mass; sea surface temperature) were examined to better understand how the surgical implant procedure may have affected their survival. Surprisingly, few of these factors were found to be correlated with survival. In Red-throated Loons, north-south wind speed and extant medical issues were significant factors affecting post release survival, while in Northern Gannets, only time under anesthesia was a significant factor. No variables examined corresponded with post-tagging survival in Surf Scoters.
In an effort to increase tag longevity, reduce bird mortality, and increase retention times over PTTs attached with existing tagging methods (surgical implants, and tail tape for some Northern Gannets), we tested novel external harness attachment methods on over 25 birds in captivity (mostly scoters) during 2013 and 2014. A newly-developed silicone harness proved the most promising and was tested on all three species in the field during 2015 and 2016 (n = 38). Tagged birds, however, experienced poor tag retention and notable impacts on behavior and mortality. While effectiveness varied among the species, these issues likely resulted from intolerance of the harnesses, buoyancy issues at dive depth, harness breakage during normal preening behavior, hydrodynamic drag while pursuing prey, or a combination of all of these factors. Therefore, although using silicone harnesses to attach external transmitters to marine birds shows some promise, their use remains inadvisable without further refinement of the harness design.
A new tracking technology (solar GPS-GSM) was tested in 2015 and 2016, in conjunction with the experimental silicone harness techniques. In addition, 10 GPS-GSM tags were attached to Northern Gannets using a tail tape attachment (limited tag retention of 2-4 months) in 2016. GPS-GSM tags provided location data at a greater precision and frequency than PTT tags. Although finding an ideal external attachment method is still an issue with these tags, we present a pilot analysis of migration data showing how GPS-GSM technology may be used in future studies to provide a more complete understanding of fine-scale movement patterns of marine birds.
Overall, this study tracked movements of over 400 individuals of three species over the course of five years; one of the most comprehensive satellite tracking studies of marine birds ever conducted in Atlantic North America. Results provide a better understanding of how diving birds use offshore areas of the mid-Atlantic U.S. and beyond, and, in combination with results from other types of research (e.g., surveys, other tracking work), can be used to inform placement and pre-and post-construction impact assessments of offshore energy infrastructure. Additional work is needed to put the extensive quantity of information collected on birds in the offshore environment into a common analytical framework for undertaking the most informed management decisions (see Chapter 7).