The Status of Crawfish Frogs (lithobates areolatus) in Indiana, and a Tool to Assess Populations

Abstract

The conservation status of Crawfish Frogs (Lithobates areolatus) in Indiana has changed over the past several decades. Once described as being locally plentiful, declines led to the listing of Crawfish Frogs as a State Endangered Species in 1988. Several records for this species in Indiana are > 50 yrs old and have gone unconfirmed for several decades. However, recent surveys have confirmed the continued presence of Crawfish Frogs in parts of southern Indiana, redefining the perceived range of this species in the state. In an effort to increase survey efficiency in this species, I used automated recording systems and manual call survey techniques to examine the chorusing phenologies of Crawfish Frogs at two sites along the northern extent of their range. Detection probabilities were determined as they related to season and environmental variables and survey duration. I also examined the effect that distance from wetland and position (ground level vs. approximate human ear level) had on call detection in automated recording systems. Correlations between call rates (calls/min) and numbers of male Crawfish Frogs present were used to calculate population estimates at 10 uncensused sites. Detection probabilities were highest when the frogs were breeding and when air temperatures were ≥ 13° C. Initial detection of Crawfish Frogs most frequently occurred during the first five min of sampling. Calls on automated recording units lost resolution as distance from wetland increased, and calls recorded at all distances at human ear level were measurably louder (in decibels) except at the wetland edge. Population estimates at uncensused sites ranged from a low of four to a high of 48. Using call rates and numbers of male frogs present in wetlands, I present a “rapid assessment” tool that can be used to quickly calculate on-site estimates of Crawfish Frogs in field studies.