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Long-tailed Duck Research: Details
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Long-tailed Ducks landing on Nantucket Sound. Photo copyright Dave Larson. |
Background
In late 2001, Cape Wind wind energy project (WEP) was proposed for Horseshoe Shoal in Nantucket Sound (the Sound), and comprehensive environmental review process began almost immediately. During the scoping phase of this project, Mass Audubon and others recommended that the environmental review include comprehensive surveys of avian use of the Sound. One of the focal areas was the use by winter waterfowl of the Sound and the proposed project area in order to gauge the risk of the project to this particular group of birds. Mass Audubon conducted aerial surveys of the Sound during the winter months to supplement studies conducted by the applicant (e.g., Perkins, et al. 2004).
The view from the plane - thousands and thousands of ducks on Nantucket Sound (with closeup inset). Photo copyright Mass Audubon. (See full size image)
The Sound is the winter home of 100,000’s of sea ducks, particularly Long-tailed Duck, all three North American scoters, and Common Eider. For Long-tailed Duck, this wintering congregation also is thought to represent a large, but unknown, fraction of the total North American population of this species and is probably greater than 5% of the global population (del Hoyo, et al. 1992).
The land-based Christmas Bird Count on Nantucket Island, coordinated nationwide by the National Audubon Society, have counted as many as a half million individuals (525,505 in 2002). As the Sea Duck Monitoring Working Group noted in their recommendations for North American waterfowl, nearly every sea duck is inadequately monitored, and accurate estimates of the number of sea ducks in various “stocks” or “management units” are lacking.
The effect of wind turbines and wind energy projects on birds, particularly WEPs constructed offshore, is not well known. Studies of offshore wind facilities in Europe that are slightly smaller than the proposed WEP in Nantucket Sound indicate little direct mortality of sea ducks, but suggest that the turbines can cause behavioral changes such as alteration of offshore habitat use (e.g., Petersen 2005; Tulp et al. 1999); the European studies often had only one year of pre-construction survey data to compare with post-construction “response”. An understanding of the shifting geographic pattern of winter habitat use of sea ducks will improve our ability to understand the ecological significance of post-construction shifts.
The abundance of birds in the Sound indicates a need for a multi-year study to gather reliable baseline data in order to assess the impact of the construction and deployment of this WEP on the avian species that use the Sound for winter habitat.
Methods
Our telemetry methods required several steps: 1) capture of LTDUs, 2) surgical implantation of transmitters, 3) tracking of ducks, 4) mapping of locations of ducks.
1) CAPTURE OF WATERFOWL
Ducks were located from a boat with the use of powerful spotlights as the birds rested on the water at night. When a bright spotlight was trained on ducks in darkness, they became somewhat disoriented, making them easier to approach. Under these conditions, they were captured from the bow of the boat with large, long-handled hoop nets. The capture team consisted of at least one capture person, one assistant, and one boat operator.
2) TRANSMITTER IMPLANTATION
Once the ducks were captured, they were transported to a local veterinary clinic (MSPCA Animal Care and Adoption Center, 21 Crooked Lane, Nantucket, MA), where Dr. Glenn Olsen, USFWS veterinarian, performed surgical implantation of a transmitter in each of the ducks. Implantation (vs. an external harness) was necessary to prevent abnormal behavior that has been observed with other diving ducks rigged with external loop harnesses (see Perry et al. 2004 for more information on sea duck radio telemetry). Following the surgery, the ducks were kept for observation for at least one day, and then released during morning hours in roughly the same area in which they were captured.
3) TRACKING/LOCATING
Satellite tracking of instrumented ducks was performed by Argos, Inc. The number of data points (geographic fixes for each duck) was limited by the 400-hour “life” of each battery within each of the transmitters. Within that limitation, all the transmitters were programmed to perform identical “duty cycles” to maximize the number of data points collected during a 12-month period. The periodicity of the duty cycles was programmed to be different within two discrete tracking seasons: winter (December 1 – April 15) and migration/breeding (April 15 – November 15).
- During the winter tracking season each transmitter was programmed with a 52-hour duty cycle – 4 hours on and 48 hours off- for a total of 253 battery hours.
- During the spring migration, summer breeding, and fall migration seasons, each transmitter was programmed for one 4-hour duty cycle every 5 days, for a total of 120 battery hours.
Transmitters also provide information on the accuracy of the satellite fix and the internal body temperature of the instrumented duck. The recording of body temperature provides useful information on the physiological status of the duck, especially if the duck is still living. If the internal body temperature of the duck indicates that the duck has died, the satellite transmitter automatically begins transmitting, and the “radio-track” mode begins operating potentially enabling us to relocate the animal. We have successfully used this feature to relocate five transmitters.
4) LOCATION MAPPING
Geographical and diagnostic data (e.g., internal body temperature) were downloaded weekly from the Argos web site. Mass Audubon staff plotted the geographical coordinates of each duck using ArcGIS software to create distribution maps of the birds on a regular basis.
There are six codes denoting the accuracy of the location determined by the satellite transmissions, i.e., the true location was within an estimated distance of the reported location (in latitude and longitude). We plotted only those locations that had an accuracy code specifying the precision of the location estimate, generally within 350-1,000m.
Results
More than 650 satellite location fixes were mapped for six of the instrumented ducks:
This sample provided no direct evidence that LTDUs used Horseshoe Shoal as a nighttime roosting site. Two ducks were located within one to two miles of Horseshoe Shoal (Figure 2 and Figure 4), but that distance is well within the margin of error of the mapped locations.
Despite the limited sample size the data do provide definitive answers to several questions about LTDU habitat use. These conclusions are presented briefly below:
- Not all LTDUs commute on a regular basis. Some ducks rarely if ever made the commute (Figure 4 and Figure 5), and in some cases remained concentrated in a small area around Tuckernuck and Muskeget Islands for most of the winter (Figure 2 and Figure 5).
- It is hypothesized that LTDUs commute to Nantucket Shoals to feed during the day and return to the safety of Nantucket Sound at night, but it appears that LTDUs will spend the night on Nantucket Shoals.
- LTDUs use a wide area of southern and eastern Nantucket Sound. Individual ducks may have a “preference” for certain regions, but collectively the ducks appear to use the entire range of waters within 10-15 miles of Nantucket Island.
- The location data provide no evidence of major nighttime concentrations of ducks. As described in above, ducks are dispersed over 100’s of square miles of Nantucket Sound.
- Ducks do not return to the same locations on a regular basis. Individual ducks may vary their daytime and nighttime locations – tendencies toward certain large areas in the waters around Nantucket are visible, but the area used by individual ducks is substantial.
The six surviving instrumented ducks departed Nantucket Sound in mid-April 2008, traveled via the Gaspe Peninsula, Quebec, Canada, and Hudson Bay, and spent summer 2008 in areas north of Hudson Bay, presumably their summer breeding grounds (Figure 8). Two ducks (#35 and #37) returned to Nantucket Sound in the fall of 2008, and LTDU #37 continues to transmit every 4 days. The fate of the other four ducks is unknown, and they either perished on their breeding grounds or the batteries on the transmitters died.
Our success this past winter has encouraged us to tag additional ducks next winter season (2008-2009) in order to increase our sample size and to test the generality of the tentative conclusions listed above. In partnership with the Biology Department of Boston University we will conduct DNA analysis of instrumented ducks to determine the origin of wintering populations of LTDUs and to determine whether LTDU breeding populations can be delineated to specific geographic areas.
Literature Cited:
del Hoyo, J. A. Elliott, and J. Sargatal. 1992. Handbook of the Birds of the World. Vol. 1. Lynx Edicions, Barcelona, 696 pages.
Everaert, J. 2003. Wind Turbines and birds in Flanders: Preliminary study results and recommendations. Natuur. Oriolus 69(4): 145-155.
Janss, G. 2000. Bird behavior in and near a wind farm at Tarifa, Spain: Management Considerations. In: Proceedings of the National Avian-Wind Power Planning Meeting III, pp. 110-114, http://www.nrel.gov.
Langston, R. H. W. and J. D. Pullan. 2002. Wind farms and birds: an analysis of the effects of wind farms on birds, and guidance on environmental assessment criteria and site selection issues. BirdLife International and the Bern Convention, 38 pages
North American Waterfowl Management Plan (NAWMP). 1998. Expanding the Vision. 1998 Update. United States Department of Interior, SEMARNAP Mexico, and Environment Canada, 43 pages.
Orloff, S. and A. Flannery. 1992. Wind turbine effects on avian activity, habitat use, and mortality in Altamont Pass and Solano County Wind Resource Areas 1989-1991. Biosystems Analysis Inc. California Energy Commission, 160 pages.
Perkins, S., G. Sadoti, T. Allison, and A. Jones. 2004. Relative waterfowl abundance within Nantucket Sound, Massachusetts during the 2003-2004 winter season. Final report. Massachusetts Audubon Society, Lincoln, MA. 24 pp. http://www.massaudubon.org/PDF/advocacy/2003_2004Seaducks.pdf
Perry M.C, E.J.R. Lohnes, A. M. Wells, P. C. Osenton, and D. M. Kidwell. 2004. Atlantic Seaduck Project, USGS Patuxent Wildlife Research Center, Laurel, MD.
http://www.pwrc.usgs.gov/resshow/perry/scoters/default.htm
Petersen, I. K. 2005. Bird numbers and distributions in the Horns Rev offshore wind farm area Subtitle: Annual status report 2004. National Environmental Research Institute Ministry of Environment, 38 pp.
Sea Duck Joint Venture. 2005. Recommendations for monitoring North American sea duck populations. August 2005. Available at http://seaduckjv.org or U. S. Fish and Wildlife Service, Anchorage, Alaska or Canadian Wildlife Service, Sackville, New Brunswick.
Thelander, C. G. and Rugge, L. 2000. Avian risk behavior and fatalities at the Altamont wind resource area. National Renewable Energy Laboratory Report, 28 pages.
Tulp, I. H. Schekkerman, J. K. Larsen, J. van der Winden, R. J. W. van de Haterd, P. van Horssen, S. Dirksen, and A. L. Spaans. 1999. Nocturnal flight activity of sea ducks near the windfarm Tuno Knob in the Kattegat. IBN-DLO Report No. 99, 30 pages.
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