Assessment of the calling detection probability throughout the day of two invasive populations of bullfrog ( Lithobates catesbeianus ) in Uruguay

Abstract

Bullfrog invasion is a major conservation concern in South America, so there is an urgent needto detect and monitor its many invasion foci. Amphibian sampling methods commonly usecalling display, specifically the nuptial calls of males. With the aim of obtaining the better dayperiod to sample and monitor Lithobates catesbeianus presence, we recorded its calls at threeponds in two invaded localities in Uruguay (Acegua, Cerro Largo, and San Carlos, Maldonado)during the reproductive season. Then, we studied the records, obtaining a subsample of callingintensity at the first 5 minutes for each hour. We detected that vocalization intensity remainedalmost constant between 20:00 and 05:00 h. Detection probability remained high and constantduring this period, and then decreased. Therefore, bullfrog displays a constant calling activityduring the nights of its reproductive period, even longer than native anurans. This long callingperiod facilitates its detection during nocturnal sampling.