Vomerine teeth present. Tongue more or less free posteriorly. Pupil of the eye horizontal. Toes webbed. Tips of fingers and toes expanded into discs. Tympanic membrane smaller than eye. When the hind leg is stretched along the body, the tibio-tarsal articulation commonly reaches the anterior edge of the eye. Dorsal skin smooth, ventral skin granular. Dorsal coloration varies from green to light-grey, brown, or almost black depending on substrate color and temperature. Coloration changes depending on substrate. No dark spot below the eye. Ventral surface white or yellowish. Dorsal surface divided from ventral surface by thin, dark, uninterrupted band with outer white edging. This band usually forms an inguinal loop, except for some individuals of H. arborea schelkownikowi. If the inguinal loop is absent, the dark band reaches the inner surface of the groin. A light line bordering lips. Male differs from female by having a large guttural vocal sac (visible externally) which is distinguished by darker skin folds and wrinkles on the throat.
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Albania, Armenia, Austria, Azerbaijan, Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Czech Republic, Denmark, France, Georgia, Germany, Greece, Hungary, Israel, Italy, Liechtenstein, Lithuania, Luxembourg, Moldova, Republic of, Montenegro, Netherlands, Poland, Portugal, Romania, Russian Federation, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, Ukraine. Introduced: United Kingdom.
The subspecies H. arborea arborea inhabits almost all of Europe. The northern margin of the range runs approximately from Denmark (Aarhus and Jutland), Sweden (Scania) and the southern shore of the Baltic Sea in Lithuania (Vilnius City: 54º41'N, 25º17'E) through Byelorussia (approximately on the line: towns of Oshmyany - Uzda - Slutsk) to southern Russia. From there, the margin runs south- and south-eastwards approximately along the line Bryansk Province - Kursk Province - west of Byelgorod Province (Shebekino District), then southwards in Ukraine from Kharkov City to Dnepropetrovsk Province to Donetsk Province. In Crimea, the frog is known from the southern shore and the extreme northwest of the peninsula. The frog is absent from eastern and southern parts of the Iberian Peninsula and Southern France. H. arborea schelkownikowi lives in the Caucasus. Its northern range runs in Russia approximately from Krasnodar Region along the line Abrau Peninsula in Novorossiik District - Goryachii Klyuch Town - Maikop Town - Stavropol Region (Stavropol City: 45º03'N, 41º59'E). From there, the margin runs in Stavropol Region to the south-east and then to the east: North Ossetia to Chechnya to Daghestan. The subspecies is absent in the highlands of the Great Caucasus. The eastern part of the southern margin of the range runs from the Northern Turkey to Georgia and Azerbaijan. The southern margin of the range is insufficiently known. H. arborea kretensis lives in Crete, Rhodos, Aegean, Peloponnese and the west of Asia Minor; H. arborea molleri in Northwestern Spain and Portugal; H. arborea sarda in Corsica, Sardinia and Elba.
The Common Tree Frog inhabits well-illuminated, broad-leafed and mixed forests, bushlands, gardens, vineyards, orchards, parks, lake shores and stream banks. Dark and dense forests are avoided. Meadows are primarily used for reproduction. In the southern areas of the European part of the range, i.e. in the forest steppe zone, the tree frog inhabits insular forests and dense vegetation of floodplains. In mountains, it lives only in forests and in more or less wet transformed landscapes, and sometimes penetrates the subalpine belt. Spawning occurs in stagnant waters such as lakes, ponds, swamps and reservoirs, sometimes even in ditches and puddles.
Life History, Abundance, Activity, and Special Behaviors
In suitable habitats in the southern part of the range this is a common amphibian. For example, in the south of the former Soviet Union up to 20 specimens per 100 m of pond shore may be counted in spring. After reproduction, the population density is maximum in river valleys covered with broad-leafed trees.During the day, H. arborea usually sit on the stems and broad leaves of trees, bushes and large herbaceous vegetation. The frog is active primarily in the evening and at night, when it comes down to the ground from vegetation to forage and to rehydrate. During the autumn migration to hibernacula, H. arborea are active during the day. Hibernation occurs on land from September - December to February - early May, on land (in soil, burrows, heaps of stones and holes in trees). Reproduction occurs from April - May, but sometimes in March, June or even late July. As a rule, more males are found in breeding pools than females. Females enter pools after males and leave immediately after breeding. Clutch contains about 200-2000 eggs deposited in portions, usually having the form of small rounded clumps containing from 3 to 100 eggs. Metamorphosis occurs from June to September, depending on the geographic position of a locality. In some cases, the larvae overwinter and complete transformation the following summer. Young froglets in the first time remain on the shore climbing grass and small bushes. Hyla arborea prey mainly on insects. Its ability for long leaps makes it possible to forage on fast flying insects, which comprise a considerable proportion of its food. The frogs forage on land. During the breeding season, adults forage periodically on the shore and on high plant stems above the water surface.
Trends and Threats
The tree frog displays a considerable decline and extinction in the West and Central Europe. It is caused by loss of breeding habitats, habitat isolation and fragmentation, pollution and collecting by people, as well as climate changes. However, in many large areas of its southern part of the range, e.g. in Ukraine and the Caucasus, the species is not rare and does not display population declines.
Relation to Humans
Although some kinds of human activity lead to decline and extinction of populations of H. arborea (see above), construction of a system of fish ponds, ditches, channels etc. sometimes cause local increase in the number of this species.
Possible reasons for amphibian decline
General habitat alteration and loss
Local pesticides, fertilizers, and pollutants
Long-distance pesticides, toxins, and pollutants
Climate change, increased UVB or increased sensitivity to it, etc.
Protection of habitats seems to be the most important method of conservation of H. arborea.
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Written by Sergius L. Kuzmin (ipe51 AT yahoo.com), Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow
First submitted 1999-11-10
Edited by Meredith J. Mahoney
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