Study of Life Cycle of Tree Frogs (Hyla savygnyi) in Semi-Arid Habitats in Northern Israel

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The life cycle of tree frogs (Hyla savygnyi) in various localities and habitats in northern Israel in the Upper Galilee and Golan Heights (annual rainfall range of 500–1000 mm) and the Hula Valley, ranging from 212 to 740 m above sea level, was studied. Tree frogs were observed around winter rain pools, springs and streams. Fifty-one different breeding sites were monitored. The frogs forage on land. During the breeding season, adults forage periodically on the shore and on high plant stems above the water surface. Only ponds and springs with stable, non-flowing water are used by tree frogs for reproduction and this is where the larvae can metamorphose. The male call at the breeding site attracts the female, who then comes to the male, and breeding occurs underwater. Breeding time in Israel varies according to location and geographical and ecological conditions. It takes place in March–April in northern Israel, the Upper Galilee, the Golan Heights and the Hula Valley. In various breeding sites, larvae grow between April and June. Apparently, tree frog larvae adapt to breeding sites where stable water is found, such as in ponds or springs, but not to breeding sites with flowing water such as streams or rivers. Various anuran and Urodela larvae were found in the same breeding sites as the larvae of H. savygnyi, including Pseudepidalea viridis, Rana bedriagae, Pelobates syriacus, Salamandra infraimmaculata and Triturus vittatus. Following metamorphosis, H. savygnyi adapts to terrestrial life in semi-arid habitats, and is found on plants or in hiding places under rocks and in holes to prevent dehydration, particularly during hot and dry weather. The ability to change color helps the frogs hide in various substrates. The rate of water loss for terrestrial H. savygnyi during dehydration is around 50% of body weight. Plasma osmolality increases from 200 mOsm/kg to about 450 mOsm/kg, which helps the tree frog survive in semi-arid habitats.