DELINEATING BREEDING POPULATIONS AND TRACKING NIGHT-TIME MOVEMENTS OF LONG-TAILED DUCKS WINTERING IN NANTUCKET SOUND
Massachusetts Audubon Society (MAS), USGS Patuxent Wildlife Research Center, and Boston University propose to instrument a minimum of 11 adult long-tailed ducks (LTDUs) with satellite transmitters in December 2008. The study will track diurnal movements in and around Nantucket Sound and track instrumented ducks to Arctic and sub-Arctic breeding grounds. This study will obtain evidence regarding the relationship of wintering ducks to their breeding grounds and to thereby delineate populations of this important species (e.g., NAWMP, 1998).
DNA will be obtained from blood and feather samples collected from instrumented ducks and from additional captured ducks (n = 40) to estimate population parameters such as historical changes in effective population size and whether LTDUs in Nantucket Sound comprise genetically differentiated breeding populations. The resulting genetic database may then be used in the future to determine the origin of other wintering populations of LTDUs. This is a multi-year study using satellite telemetry and DNA genetic anslyses to delineate breeding populations and understand migration movements of ducks wintering in Nantucket Sound. Such studies are important in understanding the ecological impact of potential changes in the habitat quality of Nantucket Sound. Local movement data is critical to understanding the impacts that a proposed wind turbine project in Nantucket Sound will have on wintering LTDUs.
Dr. Matthew Perry with instrumented long-tailed duck
Nantucket Sound is the winter home of 100,000’s of sea ducks, particularly common eider, all three North American scoters, and the LTDU. The latter is the most abundant species and land-based Christmas Bird Counts of LTDUs from Nantucket Island have exceeded one-half million individuals. Best estimates put the overall North American population of LTDUs at 3-4 million (del Hoyo et al. 1992). Therefore, the numbers of LTDUs that use the Sound each winter might represent up to one sixth of the entire continental population of this species. The Monitoring Working Group of the Sea Duck Joint Venturehas presented draft recommendations for priorities in monitoring North American Sea Ducks, and the LTDU ranks near the top in priority (SDJV 2005).
Between 2003 and 2006, MAS conducted winter waterfowl surveys within the Sound and in the waters immediately outside the Sound. These surveys provided more detailed information on the local abundance and distribution of eiders, scoters, and LTDUs. The surveys were conducted in the context of contributing to the risk assessment of a proposed 130-turbine wind farm in Nantucket Sound. The effect of wind turbines and wind farms on ducks, particularly wind farms constructed offshore, is not well known. Studies of offshore wind facilities in Europe that are slightly smaller than the proposed wind farm in Nantucket Sound indicate little, if any, 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).
Long-tailed ducks overhead at Nantucket
Photo by Vernon Laux
As a result of three years of study of avian distribution and abundance in Nantucket Sound, Mass Audubon outlined remaining data gaps that needed to be filled in order to complete the environmental review of the Cape Wind project. One major data gap involved the nighttime distribution of LTDUs in Nantucket Sound and the relationship of this distribution to the Cape Wind project area, Horseshoe Shoal. LTDUs typically depart en masse from Nantucket Sound at dawn each day to feeding areas primarily in and around Nantucket Shoals southeast of Nantucket Island, and then return to the Sound at dusk to nocturnal locations. The exact location and use (feeding or roosting) of these dirunal and nocturnal sites is not well documented.
A second important knowledge gap relates to the delineation of the breeding populations that constitute the wintering populations in Nantucket Sound. LTDUs have a circumpolar breeding distribution, but it is unknown which of the possible breeding populations between arctic Alaska, Canada, Greenland, Iceland, Scandinavia, and Siberia are represented in the hundreds of thousands of ducks overwintering in Nantucket Sound. Although the proposed wind farm has been an important driver of our investigations, the question regarding population delineation is of general interest in understanding the ecological impact of changes in the quality of the LTDU wintering habitat of Nantucket Sound. Whether this impact is the direct effect of collision mortality at the proposed wind farm (if constructed), or the indirect effects due to loss of habitat or decline in habitat quality is unknown. It is difficult to interpret the ecological significance of these effects without accurate definition of the origin of the breeding populations for LTDUs. For example, habitat quality of the wintering range may be a limiting factor for some breeding populations but not others. This possible difference is crucial in understanding whether factors affecting the wintering habitat of seaducks in Nantucket Sound are of concern to the breeding populations present in this area.
Industrial and urban development on Cape Cod and the Islands may result in the degradation of habitat quality in wintering areas, but the effects of this habitat degradation on sea duck populations are also unknown. Development pressures on these wintering areas will continue to increase. Our results could be utilized to inform natural resource policy and management decisions, including efforts to reduce winter mortality, if ecologically significant, and resulting mitigation if the wind farm is constructed.
Lines of long-tailed ducks overhead at Nantucket
Photo by Vernon Laux
We are conducting a multi-year study of winter seaducks in Nantucket Sound and are currently focusing on LTDUs. We are using satellite telemetry to track the movements of wintering LTDUs in the waters around Nantucket, and to track the movements of instrumented ducks as they migrate between their wintering grounds and their breeding grounds. Last winter (December 2007), we captured and instrumented ten ducks (seven males and three females), and the six surviving instrumented ducks provided new data on diurnal and nocturnal movements, which allowed us to better understand the winter nocturnal movements and habitats used by the ducks (see http://seaduckjv.org/ssna.html). Our primary objectives this winter season are to add to our sample size, to obtain more data on nighttime locations of instrumented LTDUs in Nantucket Sound, and to further our understanding of LTDU movements back to their breeding grounds.
We have expanded our study to include DNA analyses on the ducks instrumented and a larger sample of non-instrumented ducks to learn more about the origin and genetics of this unusually large population of LTDUs. We will attach satellite transmitters to 11 LTDUs and draw blood samples from these 11 ducks and up to a total of 40 ducks for DNA analysis. Our total sample of instrumented ducks will be 17 (six ducks survived the full winter season) for the first two years. Our intention is to continue this project in winter 2009-2010 adding an additional 10-15 ducks to our sample size of instrumented ducks as funds are available.
Questions about LTDU use of Nantucket Sound, migration routes, and possible breeding grounds have been posed and some preliminary answers are available based on our first year of telemetry. The results of the first season of telemetry work provide some tentative answers to the following questions that we hope to address with our research:
- Many ducks demonstrated the pattern of diurnal migration so often observed, but ducks do not make this journey every night. Some ducks appeared not to migrate but stay in one location both day and night. Other ducks apparently spent the night on Nantucket Shoals, not returning to Nantucket Sound at night.
- Initial results suggest that instrumented LTDUs used a broad area of Nantucket Sound for nighttime roosting sites, and that the roosting locations changed during the winter season.
- None of the instrumented ducks were recorded roosting on Horseshoe Shoal, although the ducks could have been on the Shoal on nights when the transmitters were in the “off” portion of the winter season duty cycle
- It is too early to tell from our limited sample of the four ducks that continued transmitting after migration to return to breeding grounds, but the surviving ducks were located in a large region north of Hudson Bay in an area encompassing approximately 20,000 sq. miles (see figure). Instrumented ducks followed similar paths to their putative breeding locations, spending some weeks in and around the maritime provinces of Canada.
- We are tracking the surviving ducks to determine whether they will all return to Nantucket Sound for this winter or whether they select another wintering ground. One instrumented female duck arrived in the Sound on October 26, 2008.
- Results from this winter’s telemetry will test the generality of the above results as well as provide additional information on breeding ground locations of LTDUs.
Long-tailed ducks moving fast at dusk, Nantucket
Photo by Vernon Laux
Our primary study area is Nantucket Sound, an approximately 163 square mile body of water off the south coast of Cape Cod, Massachusetts, where nocturnal locations of LTDUs will be determined by satellite telemetry. Satellite telemetry will also be utilized to determine the locations of the LTDUs’ Arctic breeding grounds and DNA analyses will be used to link genetic “identity” of instrumented ducks to specific geographic locations. Several steps are required to complete this project: 1) capture of LTDUs, 2) surgical implantation of transmitters, 3) taking blood samples for DNA analyses, 4) activating satellite transmitters and downloading location fixes, and 5) mapping of locations of instrumented ducks
1) CAPTURE OF WATERFOWL
Our team now has extensive experience capturing LTDUs in Nantucket Sound using a high-speed boat and night-lighting. Last winter we caught 16 ducks and instrumented ten ducks in approximately eight hours of boat time over two evenings. We will continue to use these methods that have worked successfully.
2) TRANSMITTER IMPLANTATION
Once the ducks are captured, they are transported to a local veterinary clinic (MSPCA Animal Care and Adoption Center, Nantucket, MA), where Dr. Glenn Olsen, USFWS veterinarian, performs surgical implantation of a transmitter in each of the ducks. http://www.pwrc.usgs.gov/resshow/perry/scoters/Surgery.htm
Dr. Glenn Olsen preparing for surgery and after surgery with an instrumented male LTDU
External attachment is considered inappropriate for diving ducks (Perry et al. 1981). Following surgery and to reduce stress (and increase survivability), ducks are kept for observation for at least one day, kept hydrated, and then released during morning hours in roughly the same areas in which they were captured. As we describe below, we initially focused on instrumenting male LTDUs. Males are larger than females, don't have egg laying stress, and may be better able to handle the extra weight of the transmitter. However, during the 2008-09 winter we will instrument females, as we now know that some adult males do not go to breeding areas, whereas we feel all adult females do.
Satellite tracking of instrumented ducks is performed by Argos, Inc. (Largo, Maryland). The number of data points (geographic fixes for each duck) is determined by the 400-hour “life” of each battery within each of the transmitters. Within that limitation, all the transmitters are programmed to perform identical “duty cycles” to optimize the number of data points collected during two seasons that we have defined over a 12 month period. The periodicity of the duty cycles is different within these two discrete tracking seasons: winter (December 1 – April 15) and migration/breeding (April 15 – November 15).
During the winter tracking season we propose to program each transmitter with a 52-hour duty cycle – 4 hours on and 48 hours off- for a total of 253 battery hours. This program will provide us with a maximum of 61 fixes during the winter season. These fixes will indicate whether we have instrumented ducks that conduct the daily “commute” between the Ocean and the Sound and where their nighttime locations are within Nantucket Sound.
During the spring migration, summer breeding, and fall migration seasons, each transmitter will be programmed for one 4-hour duty cycle every 5 days, for a total of 120 battery hours. These fixes will indicate where each bird spends the summer, and, assuming they survive migration and the breeding season, whether these ducks return to Nantucket Sound the following winter.
We instrument only healthy, breeding-age LTDUs (determined by body mass and from several identifiable characteristics) in order to maximize our chances of tracking ducks to their true breeding grounds. We do not assume that the sexes behave in the same manner, so as mentioned above, to maximize our sample size we initially emphasized instrumenting breeding age males. In addition to the factors cited above, males also go to molting areas shortly after nesting so this provided us with information about a second important habitat. During future work in the winters of 2008-09 and 2009-10, we will instrument only females to determine differences in nesting habitat and timing and direction of migration.
Group of long-tailed ducks over Nantucket
Photo by Vernon Laux
4) LOCATION MAPPING
Location "fixes" are downloaded from the Argos web site. Massachusetts Audubon GIS staff map the location coordinates with Google Earth graphics. Graphics of movements are presented below. Lines connect locations recorded at different times during migration and end points in northern Canada suggest breeding locations. However, lines may not represent the exact route.
Winter movements on long-tailed ducks near Nantucket
Spring movements to Canada by long-tailed ducks
Locations of LTDUs as September 15, 2008.
Routes to and from long-tailed duck breeding areas, November 20, 2008
5) DNA ANALYSES
Unpublished genetics work suggests that LTDUs form one large intermixed North American population. Blood and feather samples will be collected from instrumented ducks during surgery and from ducks that are only banded. Genomic DNA will be isolated from each sample and subjected to enzymatic amplification and sequencing of both mitochondrial and nuclear genes. The Sorenson lab at Boston University has conducted similar analyses on other waterfowl species and has developed PCR and sequencing primers for an array of nuclear sequence loci, many of which have already been sequenced for a single LTDU sample as part of a systematic analysis of seaducks.
Data from multiple genetic loci for a sample of individuals will enable estimation of population parameters such as historical changes in effective population size using analyses based on coalescent theory. We will also test whether LTDUs in Nantucket Sound comprise a mixture of individuals from genetically differentiated breeding populations using genetic clustering methods implemented in the software STRUCTURE. If so, the genetic data may allow assignment of individual wintering ducks to breeding areas once those areas are identified and defined with telemetry data. DNA sampling from additional LTDUs on the wintering grounds (total sample size equals 40) and tissue samples from other geographical areas obtained from the Burke Museum collection at the University of Washington, Seattle, WA (availability of samples has been confirmed) will enable us to develop a more accurate delineation of possible breeding populations that winter in Nantucket Sound. The resulting genetic database could then be used in the future to determine the origin of other wintering populations of LTDU.
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