Blanchard’s Cricket Frogs May be on the Comeback Trail in Western Ohio
Scientist Rick Lehtinen and colleagues find that the tiny amphibians are holding their own
WOOSTER, Ohio — The once-declining cricket frog population in western Ohio appears to have stabilized and may even be making a modest leap forward in some areas, according to a recent study by scientists at The College of Wooster.
Richard Lehtinen, associate professor of biology, and James Witter, a former student now with the Wood County Park District, have published their findings in the December issue of the journal Herpetological Conservation and Biology.
"The last comprehensive study of Blanchard's Cricket Frog in Ohio was 1946," said Lehtinen, who had conducted similar studies in Michigan where the creature has all but disappeared. "Much has changed since then, and I thought [a follow-up study] was long overdue."
The primary objective of the Lehtinen-Witter study was to provide robust estimates of occupancy in these areas over time and to assess the conservation status of the species in Ohio.
Cricket frogs are easier to hear than see. The tiny amphibian makes a distinctive mating call, which Lehtinen describes as "the sound of two pebbles being knocked together" Thus, the researchers are able to track their presence through sound instead of sight.
"We gathered information by listening for the mating calls of the male frogs near ponds, lakes, streams, and rivers to determine whether they were present or absent at a particular location," said Lehtinen. "We conducted more than 1,800 eight-minute listening surveys over a five-year period (2004-2008)."
The researchers also used an instrument to measure such variables as temperature, wind speed, and humidity during the exhausting but productive listening sessions, which yielded a hearty sample size.
Similar studies had been conducted by other researchers in neighboring states (Michigan, Iowa, Illinois, etc.), and all suggested that the species was declining, if not disappearing, from the landscape, so there was considerable interest in determining its status in Ohio.
"This isn't just important to scientists; it is also important to conservationists," said Lehtinen, who was one of those researchers in Michigan where the cricket frog is almost completely gone. "If the populations are declining, we want to ask ourselves why, and whether there is anything we can do (to prevent a further decline)."
Lehtinen and his student researchers referenced digitized topographic maps of western Ohio to identify listening areas using a random method so that there would be no bias in the site selections.
A total of 312 sites were chosen in three clusters: one in northwest Ohio (Wood and Hancock counties); another in the southwestern part of the state (Clinton, Greene, and Warren counties); and a third in west central Ohio (Champaign, Logan, Miami, and Shelby counties). The reason that all of the research was done in western Ohio is that there are no longer any cricket frogs in the eastern two-thirds of the state.
In order to effectively analyze the data, Lehtinen had to learn some new techniques. "I had to re-educate myself," he said. "It slowed the overall process, but it enabled me to use the most current and accurate methods."
What they found was that the greatest proportion of occupied sites was consistently present in the northern monitoring area, with the central and southern monitoring areas having somewhat fewer populations in all years. The proportion of extant populations was stable in the northern monitoring area and increasing in the central and southern monitoring areas.
They also learned that broadcasting breeding vocalizations strongly increased detection probability, but that other variables, such as barometric pressure and moon phase were not significant in influencing the probability of detecting the species using calling surveys.
The most significant finding in the study is that based on five years of data, the current outlook the cricket frog is promising in the western part of Ohio. "At a time when most amphibian conservation news is sobering, it is encouraging that populations of Blanchard's Cricket Frogs in western Ohio are not continuing to decline, and there is even some evidence of recovery, at least as of 2008," wrote Lehtinen and Witter in the concluding remarks of their paper. "However, this conclusion was only reached after substantial field effort utilizing modern analytical techniques to correct for variation in detection probability. While these data provide an important historical baseline, detecting future changes in space and time will require additional monitoring work, and we encourage these activities throughout the range of this species."