Factors affecting the courtship performance of woodcocks (Philohela minor) and the accuracy of the annual Singing Ground Survey of the U. S. Fish and Wildlife Service were studied in 1963 and 1964. Woodcock courtship calls were counted at 2-min intervals, alternating each day between several areas of differing woodcock density. At the same time, cooperators made the standard Singing Ground Survey through the study area each evening. Climatic conditions were measured for each woodcock performance. The most stable courtship activity occurred from about April 15 to May 15 and appeared to be affected only by extremes in climatic conditions. The performance seemed to be initiated by light intensities averaging 2.1 footcandles, so that starting times were earlier in relation to official sunset when the cloud cover was heavier. Male activity increased briefly with the coincident appearance of many broods. As the density of performing males increased, the level of peenting activity per bird significantly decreased; courtship flight activity was less affected. As density increased, the probability of hearing individual males was reduced. The predawn performance was deemed unsuitable for surveys. Poor hearing ability of survey cooperators lowered the survey results significantly. The inclusion of flight songs was not detrimental to the daily tally, nor was the survey significantly affected by stage of the moon. Recommendations for singing ground survey changes are presented. Censuses of the American woodcock take advantage of the bird's spring courtship performances. These occur daily just before dawn and just after sunset on relatively open areas called singing grounds. The woodcock makes three principal sounds during its performance: a buzzing peent call, given on the ground, and during aerial displays a vocal chirping called the flight song, which is accompanied by a mechanical twittering made by the wings (reviewed by Mendall and Aldous 1943:57-61). Apparently, only males peent since, of 50 birds shot while peenting (Dr. F. W. Martin, personal communication, July, 1963), all were males. The Singing Ground Surveys of the U. S. Fish and Wildlife Service are made annually in selected woodcock areas throughout the eastern United States and southeastern Canada for a population index to help regulate woodcock hunting. A known singing ground is selected as the starting point and the census begins when the first male is heard. The observer travels by car over a planned route for 35 min at dusk, stopping at no less than 0.4-mile intervals, since it is believed that woodcocks may be heard for 0.2 mile. Stops may be made at greater intervals to avoid unsuitable situations such as busy road intersections. At each stop, the number of woodcocks heard performing during a 2-min counting period is recorded. Mendall and Aldous (1943) studied the ecology of the woodcock and initiated the survey method. Sheldon (1953) analyzed the Singing Ground Survey, studied the activities of single birds, and appraised trapping data in efforts to improve the survey. Goudy (1960) studied the effects of various factors on the survey results and attempted further refinement of the method. This study was conducted to determine what factors may influence the male mating performance and thus affect the population index as determined by the survey. Specifically, the purpose was to determine: (1) the most desirable daily and seasonal time for useful surveys; (2) the most desirable climatic conditions for useful surveys; (3) the effects of climatic and physical factors and population density on the courtship performance; (4) the effect of observer's hearing ability on survey accuracy; 1 This paper is based on a thesis submitted in partial fulfillment of the requirements for the M.S. degree in Fisheries and Wildlife, Michigan State University.
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Jan 1, 1977
M A Cantrell + 1
