Citizen science reveals broad-scale variation of calling activity of the Mediterranean tree frog (Hyla meridionalis) in its westernmost range

Population monitoring is essential to determine different aspects of the ecology and conservation of the species. In anurans, recording the acoustic activity of choruses allows surveying populations. Therefore, knowing the timing of male calls is fundamental to achieve this goal. Here we monitored calling activity of the Mediterranean tree frog (Hyla meridionalis) at eight localities in southern Iberian Peninsula and western North Africa in the frame of a citizen science program. Subsequently, after summarizing call activity with Non-metric Multidimensional Scaling, we aimed to identify the geographic and environmental variables that associate with the calling activity of frogs. The results of the 258-hour census showed that male tree frogs called mainly from December to July, although the duration and intensity of choruses varied, depending on the elevation and seasonality of the water bodies. Males sang earlier and had more durable call activities at lower elevation sites, which are sites with higher and more stable ambient temperatures. Also, calling activity was lower in sites where water fluctuates more over the annual cycle. Our results provide a first overview of the calling activity of the Mediterranean tree frog over a relatively large set of populations encompassing a wide variety of environmental conditions in its westernmost range of distribution. However, further studies relying on more intensive sampling, likely using automatic recorders, would be desirable to achieve a full understanding of the calling activity of tree frogs in the region.