critical calls: circadian and seasonal periodicity in vocal activity in a breeding colony of Panamanian golden frogs (<em>Atelopus zeteki</em>)

The Panamanian golden frog (Atelopus zeteki) is a critically endangered species and is currently believed to survive and reproduce only in human care. Panamanian golden frog males are considerably vocal, which may be an important component in their successful reproduction, though little is currently known about their calls. To better understand the behavior and vocal patterns of this species and to improve breeding efforts in the assurance colony, we employed individual sound recordings of male advertisement calls and acoustic monitoring of a breeding colony to investigate variation in the vocal behavior of Panamanian golden frogs. The goal was to capture variability within and among frogs as well as patterns of periodicity over time. First, the advertisement calls from individual male Panamanian golden frogs were recorded, and acoustic parameters were analyzed for individual differences. Results suggest that male advertisement calls demonstrate individual- and population specificity. Second, data collected through a year-long acoustic monitoring of the breeding colony were investigated for circadian and circannual periodicity. Male vocal activity revealed a circadian periodicity entrained by the daily light schedule. Seasonal periodicity was also found with highest vocal activities between December and March. The finding of a seasonal periodicity is worth noting given that the population had been bred for 20 years under constant environmental conditions. Finally, results suggest that vocal activity was responsive to daily animal care activity. Vocal activity decreased substantially when personnel entered the room and engaged in animal husbandry activities. The findings illustrate the usefulness of acoustic monitoring to provide insight into animal behavior in a zoo setting in a key breeding colony of endangered animals, and calling pattern observations may be utilized to modify husbandry practices to improve Panamanian golden frog breeding success and general care. Methods To investigate whether calls show individual differences, sixteen males were randomly selected for recording. Males were singly housed in a tank of identical composition and care as their home tank. During the single housing experiment, the experimental tank was flanked by tanks housing groups of females that were within potential line of sight of the males. The singly-housed males were given 24 hours to acclimate in the tank. Each male was then sound recorded for 48 hours. Sound was recorded with a condenser microphone (AKG C417 L Omnidirectional Lavalier Microphone; frequency range 20Hz-20kHz) attached to the lid of the tank. The sound signal was recorded at a sample rate of 44.1 kHz directly onto a computer using Avisoft Recorder software (Avisoft Bioacoustics, Berlin, Germany). Of the sixteen frogs monitored, three frogs did not call during observations, leaving us with collections of 20 or more call recordings from 13 singly-housed males (6 from the A- and 7 from the S-population). For each frog, 20 calls were randomly selected, and five acoustic parameters (fundamental frequency, call duration, pulse interval, first and second dominant frequency) were measured and analyzed. Acoustic analyses were performed using PRAAT sound analysis software (version 5.3.80 for Windows; www.praat.org). Fundamental frequency was measured in the middle of the call as the inverse of an average pulse duration. Call duration was measured as the interval between the first and last pulse of a call. Pulse interval was measured as the ratio between call duration and the total number of pulses. The first and second dominant frequencies were estimated from a short 50-ms segment from the middle of a call using linear predictive coding (LPC) function in PRAAT.