Fitting statistical distributions to sea duck count data: Implications for survey design and abundance estimation

Determining appropriate statistical distributions for modeling animal count data is important for accurate estimation of abundance, distribution, and trends. In the case of sea ducks along the U.S. Atlantic coast, managers want to estimate local and regional abundance to detect and track population declines, to define areas of high and low use, and to predict the impact of future habitat change on populations. In this paper, we used a modified marked point process to model survey data that recorded flock sizes of Common eiders, Long-tailed ducks, and Black, Surf, and White-winged scoters. The data come from an experimental aerial survey, conducted by the United States Fish & Wildlife Service (USFWS) Division of Migratory Bird Management, during which east-west transects were flown along the Atlantic Coast from Maine to Florida during the winters of 2009–2011. To model the number of flocks per transect (the points), we compared the fit of four statistical distributions (zero-inflated Poisson, zero-inflated geometric, zero-inflated negative binomial and negative binomial) to data on the number of species-specific sea duck flocks that were recorded for each transect flown. To model the flock sizes (the marks), we compared the fit of flock size data for each species to seven statistical distributions: positive Poisson, positive negative binomial, positive geometric, logarithmic, discretized lognormal, zeta and Yule–Simon. Akaike’s Information Criterion and Vuong’s closeness tests indicated that the negative binomial and discretized lognormal were the best distributions for all species for the points and marks, respectively. These findings have important implications for estimating sea duck abundances as the discretized lognormal is a more skewed distribution than the Poisson and negative binomial, which are frequently used to model avian counts; the lognormal is also less heavy-tailed than the power law distributions (e.g., zeta and Yule–Simon), which are becoming increasingly popular for group size modeling. Choosing appropriate statistical distributions for modeling flock size data is fundamental to accurately estimating population summaries, determining required survey effort, and assessing and propagating uncertainty through decision-making processes

Framework for assessing and mitigating the impacts of offshore wind energy development on marine birds

Offshore wind energy development (OWED) is rapidly expanding globally and has the potential to contribute significantly to renewable energy portfolios. However, development of infrastructure in the marine environment presents risks to wildlife. Marine birds in particular have life history traits that amplify population impacts from displacement and collision with offshore wind infrastructure. Here, we present a broadly applicable framework to assess and mitigate the impacts of OWED on marine birds. We outline existing techniques to quantify impact via monitoring and modeling (e.g., collision risk models, population viability analysis), and present a robust mitigation framework to avoid, minimize, or compensate for OWED impacts. Our framework addresses impacts within the context of multiple stressors across multiple wind energy developments. We also present technological and methodological approaches that can improve impact estimation and mitigation. We highlight compensatory mitigation as a tool that can be incorporated into regulatory frameworks to mitigate impacts that cannot be avoided or minimized via siting decisions or alterations to OWED infrastructure or operation. Our framework is intended as a globally-relevant approach for assessing and mitigating OWED impacts on marine birds that may be adapted to existing regulatory frameworks in regions with existing or planned OWED

Sea_Duck_Joint_Venture_2007_Recommendations_for_monitoring

Reference S4. Sea Duck Joint Venture. 2007. Recommendations for monitoring distribution, abundance, and trends for North American sea ducks

Data from: Wintering sea duck distribution along the Atlantic coast of the United States

Although monitoring data for sea ducks (Tribe Mergini) are limited, current evidence suggests that four of the most common species wintering along the eastern coast of the United States—long-tailed duck Clangula hyemalis, white-winged scoter Melanitta fusca, surf scoter Melanitta perspicillata, and black scoter Melanitta americana—may be declining, while the status of American common eider Somateria mollissima dresseri is uncertain. The apparent negative trends, combined with the fact that sea duck life histories are among the most poorly documented of North American waterfowl, have led to concerns for these species and questions about the impacts of human activities, such as hunting, as well as catastrophic events and environmental change. During winter, thousands of sea ducks are found along the U.S. Atlantic coast, where they may be affected by proposed wind-power development, changes to marine traffic, aquaculture practices, sand mining, and other coastal development. Possible impacts are difficult to quantify because traditional winter waterfowl surveys do not cover many of the marine habitats used by sea ducks. Thus, the U.S. Fish and Wildlife Service conducted an experimental survey of sea ducks from 2008 to 2011 to characterize their winter distributions along the U.S. Atlantic coast. Each year, data were collected on 11 species of sea ducks on >200 transects, stretching from Maine to Florida. In this paper, we describe distribution of common eider, long-tailed duck, white-winged scoter, surf scoter, and black scoter. Densities of the two species with the most northerly distribution, white-winged scoter and common eider, were highest near Cape Cod and Nantucket. Long-tailed duck was most abundant around Cape Cod, Nantucket Shoals, and in Chesapeake Bay. Surf scoter also concentrated within Chesapeake Bay; however, they were additionally found in high densities in Delaware Bay, and along the Maryland–Delaware outer coast. Black scoter, the most widely distributed species, occurred at high densities along the South Carolina coast and the mouth of Chesapeake Bay. Spatial patterns of high-density transects were consistent among years for all species except black scoter, which exhibited the most interannual variation in distribution. The distance from land, depth, and bottom slope where flocks were observed varied among species and regions, with a median distance of 3.8 km from land along the coastal transects and 75% of flocks observed over depths of <16 m. Common eider and long-tailed duck were observed closer to shore and over steeper ocean bottoms than were the three scoter species. Our results represent the first large-scale quantitative description of winter sea duck distribution along the U.S. Atlantic coast, and should guide the development of sea duck monitoring programs and aid the assessment of potential impacts of ongoing and proposed offshore development

Caithamer_et_al_2000_Sea_Ducks_in_the_Atlantic_Flyway

Reference S1. Caithamer DF, Otto M, Padding PI, Sauer JR, and Haas GH. 2000. Sea ducks in the Atlantic flyway: population status and a review of special hunting seasons. Laurel, Maryland: U.S. Fish and Wildlife Service

DataACWSDsurvey.zip

Data S1. All data for the analyses are contained in the zipped folder titled DataACWSDsurvey.zip. The file contains three comma delimited data files, CluterWeightsMatrix.csv, ObservationData.csv, and TransectInformation.csv, as well as a ReadMe text file describing all data fields for each data file

Sea_Duck_Joint_Venture_2003_Special_Status_Report

Reference S3. Sea Duck Joint Venture. 2003. Species status report. Continental Technical Team

Sea_Duck_Joint_Venture_2008_Strategic_Plan

Reference S6. Sea Duck Joint Venture Management Board. 2008. Sea Duck Joint Venture Strategic Plan 2008 - 2012. Anchorage, Alaska and Sackville, New Brunswick

Silverman_et_al_2012a_Annual_Survey_Report_for_2011

Reference S9. Silverman E, Leirness J, Saalfeld D, and Richkus K. 2012a. 2011 Atlantic coast wintering sea duck survey. Laurel, Maryland: U.S. Fish and Wildlife Service

Silverman_et_al_2011_Annual_Survey_Report_for_2010

Reference S8. Silverman E, Koneff M, Fleming K, and Wortham J. 2011. 2010 Atlantic coast wintering sea duck survey. Laurel, Maryland: U.S. Fish and Wildlife Service