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Amphibian Surveys Overview

For decades, scientific studies have shown that amphibian populations have been in steady decline across North America, and particularly in the heavily populated and industrialized Great Lakes region. Amphibians are very sensitive to environmental stresses, such as air and water pollution, thus their decline or disappearance in a region is indicative of environmental degradation. Consequently, the presence or absence of amphibians in marshes is a good indicator of marsh habitat health. The Marsh Monitoring Program (MMP) uses aural (hearing-based) surveys to detect the presence or absence and relative abundance of calling amphibians (frogs and toads). Data collected by MMP volunteers are used to determine relative annual population trend changes for calling amphibians at local, regional, and Great Lakes basin levels.
To conduct amphibian (frog and toad) surveys, volunteers:

  • Survey three times per year between April and July 5th, with at least 15 days between each survey;
  • Begin surveying one half-hour after sunset and end by midnight during evenings with little wind and minimum night air temperatures of 50C (410F), 100C (500F) and 170C (630F) for each of the three respective survey periods. These temperature requirements are in place because amphibian calling intensity is strongly associated with season, time of day, and weather conditions;
  • Establish monitoring stations at least 500 meters (550 yards) apart in order to minimize the possibility that calls or choruses are double-counted between adjacent survey stations. Unlike marsh bird survey stations, amphibian survey stations can be placed back-to-back because the amphibian survey protocol is entirely passive (i.e. call responses are not elicited through the use of a call broadcast tape/CD;
  • Conduct surveys using an unlimited distance semi-circular sampling area. However, in order to associate calls heard within the defined 100 meter (110 yard) area surveyed with habitat composition within these same areas, surveyors are asked to ascertain and record whether calls were heard outside the 100 meter (110 yard) radius or within this radius;
  • Complete a 3-minute survey at each station. Call level codes are assigned to all calling frog and toad species:
  • Code 1: individual calls do not overlap and calling individuals can be discretely counted;
  • Code 2: calls of individuals sometimes overlap, but numbers of individuals can still be estimated;
  • Code 3: overlap among calls seems continuous (full chorus), and a count estimate is impossible;


Finding and Protecting Western Chorus Frogs

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