Routes are run after sunset under favorable conditions, i.e., relatively warm air temperature, wind <8 mph, and preferably high humidity. Most routes are 10-25 miles in length and take 2-3 hours to complete. At each station the observer listens for 5 minutes (or up to 10 minutes if necessary due to noise interference) and records one of the following call index values for each frog species heard calling:
- Individuals can be counted; there is space between calls (no overlapping of calls).
- Calls of individuals can be distinguished but there is some overlapping of calls.
- Full chorus. Calls are constant, continuous, and overlapping; individual calls can not be distinguished.
Because the annual calling period of each species is fairly short and is different from the calling period of other species, volunteers run each route a total of 3 times every year, once each during the following sampling periods:
- Early spring (April 8-30 and minimum water temperature of 50°F)
- Late spring (May 20 - June 5 and minimum water temperature of 60°F)
- Summer (July 1-15 and minimum water temperature of 70°F )
Water temperatures are recorded where feasible, and where they appear to represent the conditions in which frogs are breeding. Air temperature, wind speed (Beaufort scale), and sky condition are recorded at the beginning and end of each route. Volunteers are asked to comment on changes in wetland conditions, problems with background noise, etc., and are encouraged to take along at least one other reliable observer who can run the survey alone if the primary observer is unable to do so at any time.
