Division of Migratory Bird Management
American Woodcock Singing-ground Survey
Data contained herein is summarized at the route level only. We currently lack the ability to provide users with computer programs required to estimate trends from such data. To estimate state and regional trends, we calculate weighted averages from individual routes for each area of interest. We weight regional estimates by state and provincial land area. Current trend estimation procedures require at least 2 non-zero counts by the same observer for a route to be used in analyses. Extrapolating our estimated trend statistics (% change per year) over time (e.g. 30 years) may exaggerate the total change over time. More detailed information about survey procedures or analyses of these data can be found in the annual American Woodcock Population Status report in the "Reports" section of the Division of Migratory Bird Management web site. (http://www.fws.gov/migratorybirds/reports/reports.html)
POINT OF CONTACT
Duke, G. E. 1966. Reliability of censuses of singing male woodcock. J. Wildl. Manage. 30:697-707.
Goudy, W. H. 1960. Factors affecting woodcock spring population indexes in southern Michigan. M. S. Thesis. Michigan State Univ., E. Lansing. 44pp.
Kelley, J.R., Jr., R.D. Rau. 2005. American woodcock population status, 2005. U.S. Fish and Wildlife Service, Laurel, Maryland. 15pp. For current status information visit http://www.fws.gov/migratorybirds/reports/reports.html
Link, W. A., and J. R. Sauer. 1994. Estimating equations estimates of trends. Bird Populations 2:23-32.
Mendall, H. L., and C. M. Aldous. 1943. The ecology and management of the American woodcock. Maine Coop. Wildl. Res. Unit. Univ. Maine, Orono. 201pp.
Owen, R. B., Jr., J. M. Anderson, J. W. Artmann, E. R. Clark, T. G. Dilworth, L. E. Gregg, F. W. Martin, J. D. Newsom, and S. R. Pursglove, Jr. 1977. American woodcock (Philohela minor = Scolopax minor of Edwards 1974), Pages 149-186 in G. C. Sanderson, ed. Management of migratory shore and upland game birds in North America. Int. Assoc. of Fish and Wildl. Agencies, Washington, D.C.
Sauer, J. R., and J. B. Bortner. 1991. Population trends from the American Woodcock Singing-ground Survey, 1970-88. J. Wildl. Mange. 55:300-312.
Sauer, J. R., and P. H. Geissler. 1990. Estimation of annual indices from roadside surveys. Pages 58-62 in J. R. Sauer and S. Droege, eds. Survey designs and statistical methods for the estimation of avian population trends. U. S. Fish and Wildlife Service, Biol. Rep. 90(1). 166pp.
U.S. Fish and Wildlife Service. 1990. American woodcock management plan. U.S. Fish and Wildlife Service, Washington, D.C. 11pp.
Whitcomb, D. A. 1974. Characteristics of an insular woodcock population. Mich. Dept. Nat Resour., Wildl. Div. Rep. 2720. 78pp.
Each route should be surveyed during the peak time of singing activity. For editing purposes, "acceptable" times are between 22 and 58 minutes after sunset (or, between 15 and 51 minutes after sunset on overcast evenings). Due to observer error, some stops on some routes are surveyed before or after the peak times of singing activity. Earlier analysis revealed that routes with 8 or fewer acceptable stops tended to be biased low. Therefore, only route observations with at least 9 acceptable stops are included in the analysis. Data preceding 1987 does not take this into account. Therefore, the field woodcock heard on acceptable stops (Accpwdck) contains a blank or a zero, which indicates the field was not assessed to begin with. Routes for which data are received after the deadline are not included in the analysis but are included in future trend estimates. Surveyors not following the proper procedures outlined above, affect the number of acceptable stops and woodcock heard on those stops.
The survey consists of about 1,500 routes. In order to avoid expending unnecessary manpower and funds, approximately one half of these routes are surveyed each year. The remaining routes are carried as "constant zeros." Routes for which no woodcock are heard for 2 consecutive years enter this constant zero status and are not run for the next 5 years. If woodcock are heard on a constant zero route when it is next run, the route reverts to normal status and is run again each year. Data from constant zero routes are included in the analysis only for the years they were actually surveyed. Sauer and Bortner (1991) reviewed the implementation and analysis of the Singing-ground Survey in more detail.
Annual indices are calculated for each state and province that participates in the survey as well as for the 2 Woodcock Management Units (Eastern and Central). These indices are derived by finding the deviation between the observed count on each route and that predicted by the long-term (e.g., 1968-2002 trend for 2002 indices) regional or state/provincial trend estimate. These residuals were averaged by year and added to the fitted trend to produce annual indices of abundance for each region, state, and province. Yearly variation in woodcock abundance was superimposed on the long-term fitted trends (Sauer and Geissler 1990). Thus, the indices calculated with this method portray year-to-year variation around the predicted trend line, which can be useful for exploratory data analysis (e.g., observing periods of departure from the long-term trend). However, the indices should be viewed in a descriptive context. They are not used to assess statistical significance and a change in the indices over a subset of years does not necessarily represent a significant change. Observed patterns must be verified using trend estimation methods to examine the period of interest (Sauer and Geissler 1990, Link and Sauer 1994).
Again, more detailed information about survey procedures or analyses of these data can be found in the annual American Woodcock Population Status report in the "Reports" section of the Division of Migratory Bird Management web site. (http://www.fws.gov/migratorybirds/reports/reports.html)
DOWNLOADABLE FIELD DEFINITIONS
*The observer code is the 1st 3 letters of the observer’s last name. “ROU” is short for Route Not Run. “C-Z” is short for Constant Zero. “NEW” is short for New Route.