Population observations and microhabitat use of Isthmohyla tica (Anura: Hylidae) in San Ramón, Costa Rica

Abstract

Isthmohyla tica, the Tica Frog, is a critically endangered species endemic to Costa Rica and supposedly Panama that has only been seen in a few sites in recent decades. To aid in its conservation, we assessed the population status and microhabitat preferences of this frog in a section of the Danta stream at Rancho Alegre farm, San Ramón, Costa Rica. We conducted 18 nocturnal surveys and collected data on perch types, vegetation associations, stream characteristics, and environmental variables for each sighting of the Tica Frog. To identify potential microhabitat preferences, we compared these features between sites with or without frogs as well as between sites with juvenile or adult individuals. We recorded 13 individuals, comprising three juveniles and 10 adults. Nine adults were male and one female, with the disparity likely due to the conspicuous vocalizations of males. Juvenile and adult frogs occupied areas with similar stream widths (t = 0.91; p = 0.38). However, juveniles were found closer to the water (t = 5.14, p = 0.01) and adjacent to shallower areas of the stream compared to adults (t = 2.50, p = 0.03). Frogs predominantly perched on Piper sp. (30.7%) and on the upper surface of leaves (69.2%). The height at which the Tica Frog was recorded (0.1 to 2.2 m) was similar for both age groups (t = 0.86, p = 0.44). We did not find significant differences in canopy cover (average = 74.6%), diameter at breast height (≤ 3.14 cm), vegetation density (5.0 plants/m²), or plant richness (1–4 species) between juveniles and adults. Similarly, we did not observe differences in environmental variables between these groups. Furthermore, vegetation characteristics and environmental variables did not differ between sites with the Tica Frog and nearby sites without them. Our findings suggest that the measured variables do not significantly influence the microhabitat selection of the Tica Frog. This novel information on the population status and microhabitat use of I. tica is needed for the development of management strategies for the conservation of this critically endangered species.