Environmental determinants of acoustic activity in Iberian anurans

Abstract

We monitored acoustic activity of populations of anurans (genera Hyla and Alytes) in the Iberian Peninsula (Spain and Portugal) in localities at thermal extremes of their distribution. Logistic and linear regression models revealed that the major social and environmental determinants of calling behavior (chorus recruitment and chorus duration) were similar over most populations. Chorus recruitment was less dependent on environmental factors than chorus duration, which was also influenced by chorus size. Seasonal variation of night temperatures in populations of Hyla showed wide overall ranges (above 11 °C) and gradual increases of the nightly mean (3-12 °C), which was positively associated with the day number in the breeding season. Within days, temperatures were typically close to their daily maximum at sunset, the initiation of calling activity. We compared ranges of calling temperatures among species, populations, and seasons over three years. We showed that calling temperature changed when anuran populations were subjected to different thermal environments. Species had wide calling temperatures ranges across their distribution. Interannual comparisons showed that both terrestrial and aquatic breeding anurans were active during extremely hot breeding seasons. Lower thermal thresholds for the onset of calling were different between conspecific populations, suggesting that other factors are needed to trigger reproduction.