Wood Frog Population Trends
Wood frog is the most difficult of the relatively common species to monitor, because it is hard to time surveys to
coincide with the species' early, short, explosive breeding season. Because of this difficulty and annual variations
in wood frog breeding activity, year-to-year variation is generally high on individual routes and in regional or
statewide data. Several cooperators mentioned that their ability to time the first survey run for wood frogs improved
with experience. This factor undoubtedly contributed to the significant annual increases statewide and in the North-
central Forest and Central Sands; as did the fact that in 1991 we extended the starting date of the early spring
sampling period from 15 April to 8 April because several cooperators reported that wood frog activity had waned by
15 April in some years. The trend plot shows a sharp decline during 1984-86 (beginning prior to the onset of
drought conditions) followed by a small peak in 1987, then a gradual increase (beginning before the survey period
was modified) to a level not quite that of 1984. A more thorough analysis is needed to evaluate the relative effects
of bias, drought, and other factors on this trend.