• Adult Survivorship and Juvenile Recruitment in Populations of Crawfish Frogs (Lithobates Areolatus), with Additional Consideration of the Population Sizes of Associated Pond Breeding Species

      Kinney, Vanessa C. (2011-07-19)
      Crawfish Frog populations have declined significantly in both the northeastern and southwestern portions of their range, and are listed as state endangered in both Iowa and Indiana. They are animals with a secretive nature, and comparatively little is know about their basic life history and natural history. To address this gap, and to obtain the information necessary to manage for this species in areas of decline, I studied the breeding biology of two Crawfish Frog populations during 2009 and 2010. Using data collected from drift fence and pitfall trap arrays around breeding wetlands, I estimated breeding population sizes, operational sex ratios, breeding adult size ranges, egg and larval survivorship, juvenile recruitment, and adult within-season and between-year survivorship. I also documented the timing of breeding and metamorphosis, spatial patterns of immigration and emigration from breeding sites by adults and recently metamorphosed juveniles, and the diversity and abundance of associated pond breeding species. Crawfish Frog sex ratios were approximately 1:1 (M:F), with male-biased operational sex ratios. Adult sizes were comparatively larger than those reported in other areas of their range, as were sizes of newly metamorphosed juveniles. Breeding occurred from March through May during both years, and metamorphosis occurred from June through August. The number of eggs deposited per wetland ranged from 45,000 to 189,000. Thirteen associated amphibian species (18,109 individuals) and 14 reptile species (435 individuals) were captured at the breeding wetlands. Crawfish Frog survivorship estimates suggest that mortality is high during the larval stage and relatively low during the egg, juvenile and adult stages. Thus, the adult population is likely regulated by larval survivorship. To help manage for declining populations, captive rearing of larvae could be used to help offset the high mortality experienced during the larval stage and be used to help restore and/or repatriate populations at suitable sites.
    • Breeding Migrations, Survivorship, and Obligate Crayfish Burrow Use by Adult Crawfish Frogs (Lithobates Areolatus)

      Heemeyer, Jennifer L (2011-07-19)
      Movements are risky behaviors to animals, and amphibians are no exception. Being unable to cover long distances quickly, amphibians may find migrations challenging, yet many if not most species exhibit cyclic annual migrations. Crawfish Frogs (Lithobates areolatus), are a relatively understudied species of North American amphibian listed as endangered in Indiana and Iowa, and considered a species of conservation concern throughout much of their range. To better understand the biology of this species, and in particular, to assess the role that movements play in affecting survivorship, I radio tracked 48 Crawfish Frog adults, in 2009 and 2010. My study encompassed a total of 7,898 telemetered-frog days; single frogs were tracked for up to 606 days. These data demonstrate two behaviors previously undocumented in this species: 1) migration distances that averaged nearly ½ km, and for one frog was > 1,187 m; and 2) fidelity to upland burrows excavated by crayfish. Together, these findings indicate that Crawfish Frogs have a remarkable ability to home to distant upland burrow sites. Burrow fidelity in Crawfish Frogs involves, in part, frogs following similar migration routes to and from breeding wetlands. Burrow fidelity also occurs after ranging movements, and often involves individual frogs following the same circuit across years. Further, I demonstrate that movements are risky for Crawfish Frogs (about 12 times riskier than burrow dwelling), and therefore have survival consequences. My data also suggest that adult Crawfish Frogs are likely not dispersing to colonize new sites; instead, it seems more likely that juveniles represent the dispersing stage. To ensure the least impact to Crawfish Frog populations several conservation measures should be taken. First, core habitat and buffers should be established that exclude or limit roads for at least a 1.1-km radius around breeding wetlands. Secondly, burrow destruction should be minimized by limiting new cultivation and other ground disturbance within the core habitat and buffer. Thirdly, prescribed burns should be avoided from mid-March to mid-May, when frogs are out of their burrows migrating to and from wetlands.
    • The Status of Crawfish Frogs (lithobates areolatus) in Indiana, and a Tool to Assess Populations

      Engbrecht, Nathan J. (2011-03-16)
      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.