European tree frog
|European tree frog|
European tree frog ( Hyla arborea )
|( Linnaeus , 1758)|
The European tree frog ( Hyla arborea ) is a frog that belongs to the family of tree frogs in the broader sense (Hylidae) and to the genus of tree frogs ( Hyla ). It is the only Central European representative of an animal family that is spread almost worldwide (but mainly New World ), which with a good 700 species is one of the richest in amphibian forms . For the year 2008 the European tree frog was elected amphibian of the year by the German Society for Herpetology and Terrarium Science (DGHT) .
The head-trunk length of the European tree frog is 3 to 4.5 centimeters, in females also up to 5 centimeters. The body weight of the male can vary from 3.5 to 7 grams, the female frog between 6 and 9 grams, depending on the season. The head is wider than it is long; the sides of the head drop off steeply, the snout is correspondingly obtuse-angled. The strongly protruding eyes have horizontal elliptical pupils, the sometimes dark speckled iris shines golden yellow. In the dark, the pupils dilate in such a way that they fill almost the entire visible eyeball. The eardrum is clearly visible and about half the size of the eye. Ear gland bulges ( parotids ), such as those in the common toad , are missing. The front limbs are quite short and each have four fingers with adhesive discs (see below) at the ends, the hind feet each have five toes. The throat of the males is yellow to yellow-brown in color and wrinkled, that of the females is whitish to light gray and slightly granular. Males have a large, yellow or brownish, throaty vocal sac .
The surface of the skin is smooth and can shine noticeably, especially when sunbathing. The top is usually colored bright green. The abdomen and the inner surfaces of the extremities are predominantly white to light gray and granular. On both sides of the flanks, a dark stripe runs from the nostril over the eardrum to the groin region. There it arches upwards and forms a so-called hip loop. Especially in the area of this hip loop, the flank strip runs a little differently for each individual. The hip loop is also called a groin brace, because the black side stripe ends in the groin region and does not form a loop. The light green skin color is caused by the absorption of long-wave light by dark skin pigments, e.g. B. of melanophores ( melanocytes ). Short-wave light, on the other hand, is reflected by yellow skin pigments ( xanthophores ) as blue interference light, which appears as a strong green with the help of lipophores . The occasional occurrence of blue-colored tree frogs is proven to be due to a lack of yellow skin pigments and thus represents a pigment disorder in the skin. Reports on albinotic specimens of Hyla arborea are extremely rare and mostly refer to tadpoles or freshly transformed juveniles. Such a completely yellow-colored young animal was documented in the summer of 2007 in Holtum (Geest) in the district of Verden .
Tree frogs can take on quite a different colored appearance in quick succession. The variation ranges from light gray to yellowish to dark green. One often reads in this context that the frog adapts its skin color to the color of the ground on which it is currently located. This contradicts an experiment by the physiologist Biedermann, in which light green hylids did not turn dark after surgical removal of the eyes. Rather, tactile stimuli emanating from the surface have a significant impact on the animal's skin color. If you put light green tree frogs in a container with a floor and walls covered with felt or wire gauze, the animals quickly turn dark. On the other hand, they remain light green on smooth structures such as glass. These reactions are independent of color and brightness. In nature, a tree frog stays green on a smooth leaf, but on rough tree bark it sometimes turns brown or gray. The ambient temperature plays a certain role in the coloration. Basically, the higher the outside temperature, the lighter the skin.
The skin of Hyla arborea is extremely rich in glands. In general, a distinction is made between two types of skin glands in adult amphibians: mucous and venom glands. Their number varies depending on the type and body region. The way of life and the current location (water, land) of the animal also play a role. Mucous glands are usually distributed over the entire surface of the skin in different densities. Secretion occurs through contraction of the muscles attached to the gland and is subject to nervous regulation. The closer the mucous glands are to one another, the greater the moisturizing of the skin and thus the protection against drying out. On the other hand, the secretion increases the internal, physiological dehydration. If you stay in the water for a long time, the slime acts as a protective layer against the penetration of liquid. In Hyla arborea , which as a bush and tree inhabitant differs from other amphibians in its way of life, anatomical peculiarities can be found in the structure and function of the glands. They can be closed as protection against drying out. Each mucous gland cell has its own special locking device that can regulate the secretion processes.
In tree frogs with a body length of 4.5 cm, the brain is 9-10 mm long, measured from the front edge of the Lobi olfactorii to the rear end of the nerves of the vagus group. The greatest width is in the area of the Lobi optici and is around 4 mm. This means that the brain is almost as big as that of a pond frog with a body length of 6.8 cm.
The upper part consists of the three semicircular canals, each with an ampulla, followed by the utriculus and the large sacculus, which has three relatively small bulges equipped with sensory cells: papilla amphibiorum, papilla basilaris and lagena. The two papillae perceive sound. The papilla amphibiorum in male tree frogs has an average of 70.5 sensory cells, and in females 77.8 sensory cells. It reacts to sound waves up to around 1000 Hz. The basilar papilla contains around 11.2 sensory cells in male tree frogs and 16.3 in female sensory cells and reacts to sound waves above 1000 Hz. The audible range extends from 100 Hz to 6500 Hz at 20 ° C. The hearing threshold is lowest at around 3000 Hz, from 4000 Hz the threshold rises steeply. If the temperature falls below 20 ° C, the hearing sensitivity decreases; if it rises above it to 28 ° C, there is no improvement.
Tree frogs have excellent adhesive and climbing abilities. Other amphibians are also able to climb a little on smooth surfaces, even on glass panes - they attach themselves to the respective surface by means of adhesive forces of the moist abdominal skin and the underside of the limbs. As an adaptation to the climbing way of life, tree frogs also have rounded adhesive balls on the tips of their fingers and toes, which are easy to see with the naked eye. When climbing on smooth surfaces, the flexible end link of the fingers is pressed onto the surface and fixed by pulling gently backwards. At the same time, tissue fluid is expelled, which remains as tiny, sticky footprints on the surface as the frog moves forward. Under the scanning electron microscope (SEM), the surfaces of the adhesive disks turn out to be a complex combination of numerous small sub-units, which are reminiscent of a honeycomb-like pattern. At a higher magnification it can be seen that these fine structures are built up from small, pentagonal , sometimes hexagonal columns. Presumably for reasons of stability, they show an irregular, staggered arrangement. The complex interaction of these substructures enables the tree frogs to climb effortlessly even on mirror-smooth surfaces.
1960 were u. a. Mertens and Wermuth believe that there is only one species of tree frog in Europe, Hyla arborea , with six subspecies: H. a. arborea , H. a. kretensis , H. a. meridionalis , H. a. molleri , H. a. sarda and H. a. schelkownikowi . Hyla intermedia was considered a synonym for H. arborea . Further subspecies were H. a. savignyi in the Middle East and H. a. japonica in Japan. The poorly differentiated classification was based on morphological features that show slight differences in the tree frogs.
This systematic structure subsequently underwent radical changes. They were obtained by comparing the display calls that represent specific characteristics of the species and, more recently, by analyzing mitochondrial DNA ( mtDNA ) and nuclear DNA ( nDNA ).
Due to the differences in the announcement calls, the Mediterranean tree frog, H. meridionalis , the Middle Eastern tree frog, H. savignyi , and the Tyrrhenian tree frog, H. sarda , received the status of separate species. The subspecies H. a. kretensis , H. a. molleri and H. a. schelkownikowi as well as with H. intermedia , on the other hand, there were no definite differences compared to the announcement call of H. arborea .
Analyzes of the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA) confirmed the species status of H. meridionalis and H. savignyi . At the same time, these investigations revealed previously overlooked, as yet unnamed species such as H. felixarabica from southern Arabia. The tree frogs in southern Italy and Sicily are now considered a separate species, H. intermedia . A closely related, as yet unnamed species has been found in southern Switzerland. Also H. Mølleri awarded species status; its distribution covers a large part of the Iberian Peninsula. In addition, H. orientalis , which over a large area in parts of the Ukraine, Bulgaria, Russia, northern Armenia and a small part of Iran as well as in the European part of Turkey and in almost all of Anatolia, was delimited from H. arborea .
The announcement calls of the tree frogs in western Turkey and in northern Armenia, which are now assigned to H. orientalis , show almost identical characteristics to those of H. arborea in southwest Germany. The same applies to H. molleri and H. arborea , and also to H. intermedia and H. arborea . It is not unusual for two species to have identical announcement calls as long as they are not sympatric and there is no possibility of confusion when finding a partner.
Calls and call behavior
The display calls of the males are described as "äpp ... äpp ... äpp ... äpp" and consist of uniform groups of impulses that are clearly separated from each other by intervals (see illustration). A series of such impulse groups forms a call. Most calls are made up of 15 to 30 impulse groups, long calls with up to a hundred or even more impulse groups are given by the tree frogs during the main spawning season. The impulse groups always begin with a very quiet impulse, mostly nine impulses build a group, deviations are small. The frequency range extends from 400 to 6000 Hertz and has two dominant ranges at 400 to 1200 and from 1600 to 2400 Hertz. At a distance of 50 centimeters from a calling male, volume levels of up to 87 dB were measured.
The lower call threshold is 8 ° C air temperature, the upper 20 to 22 ° C. The two call characteristics duration of the pulse groups and interval are correlated with the air temperature, they decrease with increasing temperature. At 8 ° C air temperature, the pulse groups last an average of 100 milliseconds, at 20 ° C 65.7 milliseconds. The intervals measure 180 milliseconds on average at 8 ° C, and only 82 milliseconds at 20 ° C. If the temperature rises by 12 ° C from the lower to the upper call threshold, the pulse groups are shortened by about a third and the intervals by more than half. The number of pulses per group does not change. The changes in calls under the influence of temperature can be easily detected while listening.
Calling males usually sit on the bank in shallow water, so that the back legs are covered by the water. Other males have chosen call places on plants or branches or they lie in the water and hold on to plants with their forelegs. They rarely float freely on the surface of the water. On rainy days, calling males sit one to two meters away from the shore on the wet ground. Often two males make alternating calls for minutes. The two males set their impulse groups exactly in the intervals of the partner. Usually neighboring males make alternating calls, with little call activity they can be ten meters or more apart.
Another characteristic call type is the district call. If male tree frogs have chosen their call places in the evening, they show territorial behavior towards other migrating males. As soon as these start to call and are less than 30 centimeters away from the placeholder, it gives district calls that sound growling. Under the influence of the territorial calls, the tree frogs, mostly the newcomers, keep a greater distance. According to previous results, the males use the volume of the calls to determine the distance from one another.
Annual and daily profile of call activity
In south-west Germany in the Neckar Valley area, male tree frogs start calling in the first days of May and end around mid-July. The daily course of call activity is determined by the air temperature and the brightness.
The males begin to call when the brightness has dropped to at least 260 lux in the evening. This is the case at the beginning of May around 7:45 p.m. Chorus calling, in which ten males call at the same time for the first time, starts at less than 60 lux. This corresponds to an advanced dusk. As the length of the day increases, the start of calling shifts continuously to a later point in time and is at 9 p.m. in mid-June. If the day length then decreases again, the tree frogs do not follow, but stop calling the current season around mid-July. In the course of the calling period, which lasts more than two months, the start of calling is thus postponed by more than an hour.
In spring, the air temperature in the evening is still a little above the lower call threshold of 8 degrees and falls relatively quickly below it. The males' calling phase is short on such days. If, on very cool days, the air temperature in the evening has already dropped below the lower call threshold at the time the call usually begins, the tree frogs will not call. With increasing daily warming in the following time and the now slow drop in air temperature to below the lower call threshold, the daily call phases last up to two hours. In summer, when the air temperature no longer falls below the lower call threshold, the tree frogs stop calling around midnight and migrate again. During the main breeding season, isolated males call throughout the night.
The female tree frogs are mostly mute or only able to make insignificant noises (soft squeaking).
In late summer and autumn - until the beginning of winter dormancy around mid / late October - so-called autumn calls can be heard. Unlike the courtship calls, these are uttered out of hedges and bushes on sunny days (“ Indian summer ”!) And sound more like “croaking” or “creaking”. With a corresponding population density, brief concerts of several males can result. The meaning of these vocalizations is unknown.
The nocturnal calls in spring, on the other hand, are clearly interpreted in terms of their function: females are to be attracted that migrate from their winter quarters to the spawning waters. If a female approaches a courting male (the most powerfully voiced specimens are probably preferred by the females), the latter interrupts its croaking and immediately tries to climb the female's back and clasp it in the armpit area ( amplexus ). It remains there until the spawning process occurs hours or sometimes days later. Here, the males inseminated the straight out of the cloaca exiting the female spawning.
Calling males have a distinctive demeanor. The front legs are straight so that the body is erect. The body and the individual vocal sac in the throat are inflated because the males have taken in a lot of air into the lungs and vocal sac to call. When calling, air is moved between the lungs and the sound bladder in the rhythm of the impulse groups, and the airflow from the lungs into the sound bladder forms the sound. During the calling period the skin of the throat is yellow in the males, while in the females it is white.
The larynx with the vocal cords is important for voice training. It connects directly to the oral cavity and is immediately followed by the lungs, as there is no windpipe. The larynx consists of a ring of cartilage and two movable cartilage plates that close the entrance. In the rear part there is a pair of vocal cords in the form of tight ligaments. Four pairs of muscles in the larynx open or close its entrance, or tighten and relax the vocal cords. The larynx is larger in the males than in the females. The length of the larynx is 9.5 millimeters in a 48 mm male and 3.1 millimeters long in a female of the same size. Vocal cords are present on the larynx of females, but they are bulges made of soft tissue.
The fine structure of the four larynx muscles of the males is identical. All of the characteristics identify them as fast muscles: the muscle fibers and myofibrils are thin, the content of lipoids and glycogen is high, and the number of motor end plates and mitochondria is large. In the females, however, the larynx muscles are poorly developed. They also have the same fine structure, but lack the characteristics of fast muscles.
The different structure is reflected in the performance, for which the fusion frequency is a measure. When a muscle is electrically stimulated, the fusion frequency is reached when the muscle goes into continuous contraction (tetanus). The higher the fusion frequency, the faster the muscle works. The fusion frequency increases with increasing temperature. In the male tree frogs, all four larynx muscles have identical fusion frequencies. At 10 degrees Celsius it is on average 73 Hertz (= stimuli per second) and increases to 206 Hertz at 22 degrees. In the females, the fusion frequencies of the four larynx muscles are also the same, but they are noticeably lower than in the males. At 10 degrees it is on average 31, at 22 degrees 96 Hertz.
In the lower temperature range of 5 to 8 ° Celsius, the heart rate is between 10 and 20 beats per minute and increases sharply as the temperature rises. At 10 ° Celsius the beat frequency is on average 22 beats per minute and increases to an average of 69 beats per minute at 21 ° Celsius. The increase in this temperature range follows an equation of the first degree. The further increase in temperature initially leads to a slowdown, then to sudden, strong changes in the beat frequency and finally to thermal paralysis of the heart.
The electrocardiogram (EKG) was recorded on the open heart. Using the terms customary in the electrocardiogram of humans, the electrocardiogram of the tree frog and other frog auger shows the P, R, S and T peaks, while the Q peaks are absent. When the temperature rises, all parts of the electrocardiogram shorten, the spikes considerably less than the time between them.
Egg-laying takes place mainly in April and May, the earliest observations of spawn are from the end of March, the latest from June. The often somewhat misshapen spawning balls, which can swell up to the size of a walnut in the water , are attached to the water vegetation in shallow places, such as submerged stalks. The number of eggs per bale is between 30 and 80, rarely up to 100. However, a female can wean several dozen of them in one night, so that a total of between 150 and 1100 per female can be laid within one spring. The eggs are yellowish to light brown on the top and creamy white on the underside. The egg diameter is 1.5 to 2 millimeters, the surrounding gelatinous shells measure three to four millimeters.
After laying the eggs, the eggs in the spawning ball align themselves in such a way that the yellowish-brownish pigmented animal pole points upwards and the whitish, unpigmented vegetative pole points downwards. The development time of the clutches varies according to the prevailing ambient and water temperatures. In spawning balls that sink to the bottom of the water, the embryos develop much more slowly than in clutches that are directly exposed to sunlight below the surface of the water.
Hatched larvae are initially about three to five millimeters long and light yellow in color, which changes to an olive green overgrown with gold with increasing age. For larval development to metamorphosis , they need between 50 and 80 days, depending on the water temperature and nutritional status. Shortly before the transformation, the tadpoles are between 35 and 50 millimeters in size. They have a long, strong oar tail with noticeably wide fin seams. The upper hem extends between the eyes - an important determinant for field herpetologists . When viewed from above, the eyes are far apart on the sides of the head. Tree frog tadpoles are excellent swimmers and can quickly evade enemy attacks. Your skin surface shimmers gold-green in the sunlight. The breathing opening of their inner gills ( spiraculum ) is on the left flank of the body. The upper lip has two rows of teeth, the lower lip three.
The adhesive disks are made fully functional in the last stage of the larval phase. In Central Europe, the transition to rural life occurs mainly in July and August. If the weather conditions are favorable, the first freshly metamorphosed young can be found on land as early as mid-June. If the summer months are predominantly cool and rainy, it can also happen that the tree frog larvae have not yet completed their development in October. Such specimens then hardly have a chance of survival, since the overwintering of the larvae in this amphibian species is usually not successful, also because the animals are particularly sensitive to low temperatures.
During the development of germs in the egg, but also in the attachment stage after hatching, the larvae feed on the yolk stored in the body . As soon as the tadpoles are free to swim, they start actively searching for food. In general, they eat unselectively organic material that comes in front of their rasp teeth and horny jaws. These are predominantly microscopic algae ( green algae , diatoms ) as well as protozoa and detritus from their direct environment. Plants, stones and other surfaces are grazed for such food particles. Older larvae also nibble on animal carcasses, such as dead fish and amphibians, as well as drowned mollusks and land insects. When finding such food sources, the tadpoles are evidently guided by smells or flavors. Like many amphibian species, the tree frog completely changes its diet after metamorphosis.
Adolescents, like adult tree frogs, usually go for food at dusk. Prey animals are mostly found on the ground or in its vicinity - but flying and walking insects are not spurned on the raised day sitting areas either. The decisive visual stimulus is created by the movement of the victim; motionless small organisms are not perceived. The sticky tongue plays an important role in overpowering the food animals. This is fused and compressed on the front floor of the mouth. If the victim is within reach, the tongue pops out and carries it into the mouth. Often the frog moves its body in the direction of the prey or actually jumps at it. In general, the amphibian uses its rich repertoire of mobility. Fast, sometimes long hopping, as well as agile running, are used both horizontally and vertically. Climbing and shackling - even upside down - are normal movements for Hyla arborea . In the absence of teeth, the food animal is swallowed whole; With larger chunks, the drawing in of the eyeballs supports the work of the throat muscles.
The duration of nocturnal activity is largely determined by the respective environmental factors such as temperature and humidity. Insects of almost all species are eaten , as well as spiders and, in exceptional cases, small nudibranchs . Exact nutritional studies are available from U. Tester (1990) and H.-J. Clausnitzer (1986). Accordingly, the main part of the diet consists of beetles (Coleoptera, 34.2%) and two-winged animals (Diptera) such as flies and mosquitoes (47.2%); Spiders ( Araneae , 4.3%), ants (Formicidae, 1.6%), butterflies (Lepidoptera, 1.1%) and cicadas (Cicadina, 1.1%) only made up small proportions in these studies.
By delimiting the eastern tree frog as an independent species, Hyla orientalis , the area of H. arborea experienced a considerable reduction. It encompasses western and central Europe, southern Sweden, stretches in the east into central Poland, includes the western part of Ukraine, as well as the western Balkans, Greece and Crete. The species is absent in the British Isles and the Baltic Republics.
The nominate form of the European tree frog occurs (or occurred) in all federal states and prefers to inhabit flat to wavy areas of the lowlands and the hill country (planar-colline elevation). For the warmth-loving amphibian species, this altitude level is obviously a climatic limitation. Even in the rather cool summer landscapes near the North Sea ( East Frisia , Emsland , Lower Elbe ) there are probably natural gaps in occurrence. In most western federal states, however, the distribution is discontinuous and isolated, mainly due to the sharp decline in populations, while in the eastern federal states it is sometimes even more constant. Notable current areas of distribution of the tree frog are among others in parts of Mecklenburg-Western Pomerania , in the Middle Elbe lowlands of Saxony-Anhalt and Lower Saxony as well as in the area of the Leipzig lowland basin. After targeted species protection measures through new water bodies and biotope maintenance, in some regions, for example in the Westphalian Münsterland , previously heavily reduced stocks have recently recovered somewhat. Forty locations are recorded in Hesse, with a focus on the Darmstadt-Dieburg district , where experts counted 1200 males, Bingenheimer Ried in the Wetterau and the Werra-Meißner district .
Swiss and Austria
The species was once widespread in Switzerland, especially in lower altitudes. The decline of this species was even faster here than in Germany. The tree frogs in Ticino belong to the species Hyla perrini , which was only separated in 2018, and were previously classified as the Italian tree frog .
In Austria, the current stocks are difficult to assess; an important distribution center is the area around Lake Neusiedl .
Depending on the seasonal activity, tree frogs require very different aquatic and terrestrial sub-habitats. The following biotope types and structures are relevant for a successful and sustainably secured life cycle:
Aquatic sub-habitats - reproductive habitats
- Fish-free, sunlit small bodies of water (ponds, ponds, pressurized / smoke water areas, bracks, flood troughs and backwaters in floodplains and brooks, temporarily flooded grassland depressions, also bodies of water in mining pits)
- Amphibious shallow and alternating water zones rich in vegetation (as a metamorphosis and maturity habitat for juvenile specimens)
- Aquatic and marsh plant communities made of spawning herbs ( Potamogeton spec.), Floodplain (above all Glyceria fluitans ), sour grass beds ( sedges , rushes ) and reeds .
Terrestrial partial habitats - day hiding places, feeding habitats
- Extensively managed wet and wet meadows as food habitat for growing and adult specimens
- Strips of wood, reed beds and tall perennial corridors accompanying the water as sitting and call waiting areas outside the mating season and as biotope network structures (see below)
- Riparian forests , field trees , sunlit, moist coppice forests , land reeds on locations close to the groundwater.
In addition to shrubs and even treetops, various herbaceous plant species are chosen as sitting areas by adults and growing animals. Blackberry bushes are often mentioned in the literature; According to our own observations, the large leaves of burdock ( Arctium spec.) are also particularly popular for sunbathing. In the case of the example, however, it is unclear whether these structures are specifically preferred by the frogs or whether they are simply discovered more easily on the large leaf surfaces.
Accompanying species of tree frogs in spawning habitat are sorted (based here in Germany) to natural environment and the region more or less regularly: frog , moor frog , spadefoot , toad , green toad , natterjack toad , pond frog , newt , smooth newt and - though rare - Rotbauch- and yellow-bellied toads . At higher altitudes, tree frogs sometimes share the spawning waters with the mountain newt. The syntopic occurrence in a habitat is not an expression of a symbiotic interrelation, but results from common demands on habitat qualities (for example: heavily sunlit, herbaceous shallow waters without fish; see below). The different amphibian species coexist more or less peacefully in spawning waters, but can also appear as competitors for resources and as mutual predators. Larger frogs prey on smaller specimens of their own or other species and newts are considered spawning and larvae predators. The common spadefoot toad tadpoles is also said to have decimated the smaller tree frog larvae.
As a cold-blooded (poikilothermic) animal, the tree frog basically needs frost-free, terrestrial wintering places such as burrows, large piles of leaves, gap systems in the root area of deciduous trees as well as stone and floor crevices. (Because of their high content of acidic humic substances, soils under conifers are rather unsuitable for wintering.) Occasionally, voles and mole burrows are also used as roosts. Visiting the winter quarters depends on the prevailing weather conditions. In Central Europe, the tree frog usually goes to hibernation during the month of October - in the Upper Rhine Plain this happens around the same time as the yellow-bellied toad .
Tree frog larvae reach metamorphosis in significant numbers only in waters with relatively low enemy pressure and sufficient water plants. In particular, fish, including so-called “ non-coarse fish ” such as carp , reduce the spawn and larvae of the amphibian population considerably, so that such waters are usually not reproductive waters in a metapopulation of the tree frog.
Predatory water bugs and swimming beetles as well as their larvae (e.g. Dytiscidae , including the " yellow fire beetle "), larger water bugs (e.g. scorpion bugs ( Nepidae ), back swimmers , row bugs ) and the larvae of dragonflies ( Anisoptera ) are predators ( Predators ) of tree frog larvae. The larvae of the blue-green mermaid ( Aeshna cyanea ) swim to the tadpoles from below, grab them by the base of their tail with their capture mask and eat them up to the spiral intestinal tract.
Numerous bird species such as herons , white storks , purple heron , night heron , Rallenreiher and various corvids are known as predators. Every now and then remains were of tree frogs in Gewöllen of owls detected.
(For amphibians as predators, see the section on socialization .)
Both as larvae and as adults, tree frogs harbor a large number of parasites . Sun can be found in the intestine and liver of the tadpoles, the amoeba Entamoeba ranarum and Entamoeba histolytica and the ciliates Opalina ranarum . The pathogenic modes of action of E. histolytica (pathogen causing amoebic dysentery ) are, in contrast to humans, almost harmless in amphibian organisms . The tadpoles are infected through food intake.
External organs such as skin and gills of amphibian larvae are, among others, by the ciliates polypinum Charchesium and trichodina pediculus populated. A high infestation density of Ch. Polypinum can lead to death. Trichodina lives on the skin of tadpoles and occasionally migrates into their host's urinary bladder. When fish and amphibian larvae occur together, the carp louse ( Argulus foliaceus ) can occasionally be observed as a skin parasite on tree frog larvae .
Almost all amphibians are infested with parasitic trematodes ( flukes ), the adult stages of which often live in the respiratory and excretory organs as well as in the digestive tract ( endoparasites ). Flukes have hook-shaped abdominal suction cups for attachment, but cause only minor damage to their natural host. They become a serious threat either in mass infestations or when they occur in species that normally do not act as hosts. One of the most common amphibian parasites among the trematodes is Polystomum integerrimum , which can also be found in the urinary bladder of tree frogs. This suction worm has precisely synchronized its life cycle with the biorhythm of its host. The parasites also stop their reproduction stages in the period in which the host animals are also laying their eggs. This means that parasite larvae ( miracidia ) and tadpoles enter the same body of water together. The miracidia attach themselves to the gills of the tadpoles and feed on mucus particles there. In the course of metamorphosis, when the tadpole becomes a frog and loses its gills, the trematode larvae migrate into the urogenital system via the food duct and reach the urinary bladder. After three years, the parasites become sexually mature there and the cycle can begin again.
In the intestinal area, Acantocephalus ranae is a typical representative, which can also occur more frequently in tree frogs. For the spread and reproduction of this parasite, intermediate hosts such as water isopods , amphipods and ostracods ("mussel crabs") are required. If there is a mass infestation, the parasites break through the intestinal wall of the host and often penetrate the body cavity. Acantocephalus ranae occurs preferentially in tree frogs with weakened health.
Hazard and protection
Causes of the hazard
With the drainage of fens and bodies of water and the straightening of most streams and rivers, the extensive loss of suitable habitats began as early as the beginning to the middle of the 20th century. Habitat fragmentation through more and more structural measures (road construction, settlement construction) as well as intensified agriculture with accompanying phenomena such as surface drainage, pond filling, hedge clearing, huge fields, pesticide use, etc. increased the decline in the tree frog population in Central Europe after the Second World War - this downward trend continues to this day in many regions. The release of fish in small bodies of water can also have negative consequences for the amphibian population. In addition to the actual loss of habitat, tree frogs are also endangered by the fact that they frequently switch between the seasonal sub-habitats. The frogs also fall victim to road traffic when they migrate. Young animal migrations in particular suffer considerable losses.
The islanding of formerly networked habitats is particularly fatal for the relatively short-lived tree frog. To understand this relationship, the so-called “ metapopulation model” is used in animal ecology . The graphic on the right is intended to illustrate this: The large blue circles represent optimal biotopes that function as refuges and centers of expansion for “surplus populations ” rich in individuals. By migrating from there, suboptimal secondary colonies ("N") in their vicinity are stabilized, so that smaller populations can be maintained there despite high individual mortality rates. In addition, “stepping stone biotopes” (“TB”), which are less suitable as permanent habitats, serve as biotope-networking temporary locations for individuals who wander around in the otherwise intensively cultivated area. Via secondary colonies and stepping stone biotopes, there are at least indirect population-ecological interrelationships between the optimal biotopes. The prerequisite for the functioning of this model is, among other things, the "biological permeability" of the landscape: amphibians "friendly" line structures (hedges etc.) play an essential role. The graphic also shows that the elimination of individual side or stepping stone biotopes can seriously impair or interrupt the network. If even an optimal biotope is destabilized or destroyed, the entire directly linked environment is affected. The risk of extinction increases considerably because of the lack of immigration, although there have been no qualitative changes there.
Protective measures and resettlement
As a popular figure among the population and in nature conservation, the tree frog fulfills important criteria of a “ lead species ”, which is promoted on behalf of entire communities with similar demands. Preservation of the existing reproductive waters is a priority for protection. But tree frogs can also be supported by creating new small bodies of water in the field as well as in gravel and clay pits. Optimal waters are exposed to south to south-west, so they should be exposed to sunshine for several hours at least from the late afternoon. This favors both the development of the larvae and the adult animals that need warmth. In the northern edge of the spawning area, we recommend planting bushes such as sloe , hazel or blackberries . They serve as hiding places and at the same time as protection against cool north winds. A planting with conifers is not advisable, as this is usually not typical of the natural area and is avoided by the frogs.
In general, it can be said that several smaller spawning waters in close proximity are more useful in promoting the population than a single large, possibly quite deep body of water. In order to enable good spawning conditions for head-strong subpopulations , these bodies of water should each have a minimum size of 100 m² and have extensive shallow and alternating water zones . The creation of water bodies of different water depths (differences between 20 and 50 cm water depth) has proven its worth here, since this can guarantee both the spawning site suitability in dry periods (fluctuating groundwater level) and the regular absence of fish (drying out / freezing through). Since the animals are only temporarily in the partial habitats, a locally coordinated biotope management is necessary for effective tree frog protection. The following landscape conservation measures are associated with this:
- Securing small bodies of water
- Cutting back trees on the banks of the spawning waters (to avoid shading)
- Preservation / promotion of a biotope network system (line-like fringing structures such as shrub hedges and rows of trees)
- Maintenance concept for the preservation of damp and wet meadows (targeted area mowing in terms of timing and execution)
For example, unused wet meadows often tend to become reed, especially when the soil is rich in nutrients. In order to maintain or restore an at least partially open grassland character, the high growth is initially cut twice a year. To protect juvenile, freshly metamorphosed tree frogs, however, the first mowing date should not be made before July. The second cut takes place in October. After a significant reduction in the dynamics of the reed and tall herbaceous growth, the annual mowing can be dispensed with. A cycle with intervals of two to three years is usually sufficient. No further maintenance measures are required where land reed stands are to be preserved. This is the case, for example, where reed belts act as a buffer zone between agricultural areas and endangered or protected waters.
The maintenance measures mentioned as examples are complex and, depending on the size of the living space to be protected, also machine and cost-intensive. For endangered occurrences, ongoing care and documentation ( monitoring ) of the “current situation” can be a helpful means of averting the extinction of a population. Here the official and voluntary nature conservation (associations, groups) are equally required.
If tree frogs live in areas that are strictly protected by law ( nature reserve , natural monument , national park core zone, biosphere reserve core zone, FFH area ), detailed “maintenance and development plans” must also be drawn up. Particular attention must be paid to adequate protection of buffer zones in these areas.
It is also important that no chemical agents (fertilizers, pesticides ) are used in the immediate vicinity of tree frog habitats . If such areas are privately owned, the willingness of the respective users is most likely to be achieved by offering financial compensation for toleration of maintenance measures (state extensification programs, landscape conservation guidelines), contractual nature conservation agreements or a land purchase by the public sector or nature conservation associations he follows.
In addition to efforts to protect existing occurrences, there are also regional attempts to reintroduce tree frogs in former areas of distribution. The prerequisite for the success of such, not unproblematic measures, however, is always the provision of suitable habitat structures (aquatic as well as terrestrial) in appropriate dimensions and good spatial networking.
Protection status and red list classifications
Legal protection status (selection)
- Fauna-Flora-Habitat Directive (FFH-RL): Annex IV (species to be strictly protected)
- Federal Nature Conservation Act (BNatSchG): strictly protected
Red list classifications (selection)
- Red list of the Federal Republic of Germany: 3 - endangered
- Red list of Austria: VU (corresponds to: endangered)
- Red list of Switzerland: EN (corresponds to: highly endangered)
- IUCN red list (world inventory): LC (corresponds to: not endangered)
Previous scientific synonyms are:
- Rana arborea Schwenkfeld, 1605
- Ranunculus viridis Gesner, 1617
- Rana viridis Linnaeus, 1746 (FS ED. I)
- Calamita arboreus Schneider, 1799
- Hyla viridis Daudin, 1803
- Calamitas arborea A. Risso, 1826
- Hyas arborea Wagler, 1830
- Raganella arborea Bonaparte, 1830
- Dendrohyas arborea Tschudi, 1839
- Dendrohyas viridis Fitzinger, 1843
In German-speaking countries, the tree frog is also known as the "hedge frog", "green rock" or (now rarely) the " weather frog ".
Closely related to the European tree frog are the following species of the Palearctic :
- Hyla heinzsteinitzi Grach, Plesser & Werner, 2007
- Italian tree frog , Hyla intermedia Boulenger, 1882
- Japanese tree frog , Hyla japonica Günther, 1858
- Mediterranean tree frog , Hyla meridionalis Boettger, 1874
- Portuguese tree frog , Hyla molleri Bedriaga, 1890
- Hyla perrini Dufresnes et al., 2018
- Tyrrhenian tree frog , Hyla sarda (De Betta, 1857)
- Middle Eastern tree frog , Hyla savignyi Audouin, 1827
The Italian tree frog ( Hyla intermedia ), which occurs in Italy (including Sicily ) and Switzerland ( Ticino ) , has only recently been listed as a separate species and is very similar to the European tree frog. The Portuguese tree frog ( Hyla molleri ) was previously considered a sub-species or variety of Hyla arborea , but has been postulated as a separate species by some authors since 2008 based on molecular genetic studies. In the Mediterranean tree frog ( Hyla meridionalis ), which lives in southern France, northwest Italy, Spain, Portugal and northwest Africa, the dark flank strip ends directly behind the base of the upper arm. The Tyrrhenian tree frog ( Hyla sarda ), which occurs on Corsica , Sardinia , Elba , Capraia and some other Mediterranean islands, has a lateral stripe that runs to the middle of the body and then dissolves into individual stripes and spots. There are also dark green spots on the back and limbs and the skin is less smooth. Its snout is slightly shortened, which makes the head appear wider.
- Josef Blab, Petra Brüggemann, Harald Sauer: Animals in the landscape of civilization. Part 2. Integration of space and use of biotopes for reptiles and amphibians in the Drachenfelser Ländchen. Federal Research Institute for Nature Conservation and Landscape Ecology , Bonn-Bad Godesberg 1991, ISBN 3-88949-175-8 .
- Christa Clausnitzer, Hans-Joachim Clausnitzer: First results of a resettlement of the tree frog Hyla arborea (Linnaeus, 1758) in the district of Celle (Lower Saxony). (Salientia: Hylidae). In: Salamandra, DGHT, Rheinbach 1984, 20 (1), pp. 50-55, ISSN 0036-3375 .
- Hans-Joachim Clausnitzer: On the ecology and nutrition of the tree frog Hyla a. arborea (Linnaeus, 1758) in the summer habitat (Salientia: Hylidae). In: Salamandra, DGHT, Rheinbach 1986, 22, pp. 162-172, ISSN 0036-3375 .
- Hans-Joachim Clausnitzer, Friedo Berninghausen: Long-term results from two reintroductions of the tree frog with suggestions for species protection. Nature and landscape, Kohlhammer, Stuttgart 1991, 66 (6), pp. 335-339, ISSN 0028-0615 .
- Eduard M. Egiasarjan & Hans Schneider: The mating calls of tree frogs in Armenia (Anura, Hylidae). In: Zoologischer Anzeiger. Volume 225, 1990, pp. 113-122.
- Irenäus Eibl-Eibesfeld: Comparative behavioral studies on anurs. 1. The mating biology of the tree frog. In: Zeitschrift für Tierpsychologie. Volume 9, Parey, Berlin / Hamburg 1952, pp. 382-395, ISSN 0044-3573 .
- Arno Geiger (Ed.): The tree frog ( Hyla arborea L.). Ecology and species protection. Mertensiella, Vol. 6, Rheinbach / Bonn 1995, ISBN 3-9801929-5-4 .
- Dieter Glandt: The tree frog - a king is looking for his kingdom. Zeitschrift für Feldherpetologie, Laurenti, Bochum 2004, supplement 8, ISSN 0946-7998
- Wolf-Rüdiger Grosse: The tree frog. (= Die Neue Brehm-Bücherei. Volume 615). Westarp, Magdeburg 1994, ISBN 3-89432-407-4 .
- Wolf-Rüdiger Grosse, Rainer Günther: Tree frog - Hyla arborea (Linnaeus, 1758). In: Rainer Günther (Ed.): The amphibians and reptiles of Germany. G. Fischer, Jena 1996, ISBN 3-437-35016-1 , pp. 343-364.
- Wolf-Rüdiger Große, Marcel Seyring: European tree frog - Hyla arborea (Linnaeus, 1758). In: The amphibians and reptiles (Amphibia et Reptilia) of the state of Saxony-Anhalt. Reports of the State Office for Environmental Protection Saxony-Anhalt 4, 2015, pp. 291–312.
- Václav Gvoždik: Second species of tree frog Hyla orientalis (formerly H. arborea), from Iran confirmed by acoustic data. In: Herpetology Notes. Volume 3, 2010, pp. 41-44.
- Uğur Kaya, AM Simmons: Advertisement calls of tree frogs Hyla arborea and Hyla savignyi (Anura, Hylidae) in Turkey. In: Bioacoustics. Volume 10, 1999, pp. 175-190.
- Uğur Kaya: Morphological investigation of Turkish tree frogs Hyla arborea and Hyla savignyi (Anura, Hylidae) in Turkey. In: Israel Journal of Zoology. Volume 47, 2001, pp. 123-134.
- Rafael Márquez: Hyla arborea (Linnaeus, 1758). Ranita de San Antón. In: JM Plegezuelos, R. Márquez, M. Lizana (eds.): Atlas y libro rojo de los anfibios y reptiles de España. Madrid, 2nd edition, 2002, ISBN 84-8014-450-5 , pp. 114-115.
- Robert Mertens, Heinz Wermuth: The amphibians and reptiles of Europe. Waldemar Kramer Verlag, Frankfurt am Main 1960, 264 pp.
- Andreas Nöllert, Christel Nöllert: The amphibians of Europe. Kosmos nature guide. Franckh-Kosmos, Stuttgart 1992, ISBN 3-440-06340-2 .
- Hans Schneider: The mating calls of native frogs (Discoglossidae, Pelobatidae, Bufonidae, Hylidae). In: Journal for Morphology and Ecology of Animals. Volume 57, 1966, pp. 119-136.
- Hans Schneider: Calls and call behavior of the tree frog Hyla arborea arborea (L.). In: Journal of Comparative Physiology. Volume 57, 1967, pp. 174-189, ISSN 0044-3638 .
- Hans Schneider: Morphology of the larynx by Hyla a. arborea (L.) and Hyla meridionalis Boettger (Amphibia, Anura). In: Journal for Morphology of Animals. Volume 66, 1970, pp. 299-309.
- Hans Schneider: The control of the daily call start with the tree frog, Hyla arborea arborea (L.). In: Oecologia (Berl.) . Volume 8, 1971, pp. 310-320.
- Hans Schneider: Structure of the mating calls and relationships of the European tree frogs (Hylidae, Anura). In: Oecologia (Berl.), Volume 14, 1974, pp. 99-110.
- Hans Schneider: Bioacoustic demonstration of Hyla a. arborea in western Turkey (Anura: Hylidae). In: Zoology in the Middle East. Volume 21, 2000, pp. 77-85.
- Hans Schneider: The range of Hyla arborea and H. savignyi (Anura: Hylidae) on the south coast of Turkey. In: Zoology in the Middle East. Volume 23, 2001, pp. 61-69.
- Hans Schneider: The tree frog, Hyla arborea: calls, behavior, systematics. In: Dieter Glandt and Andreas Kronshage (eds.): The European tree frog (Hyla arborea). In: Journal of Field Herpetology. Supplement, Volume 5, 2004, pp. 9-26.
- Hans Schneider: Bioacoustics of the Froschlurche - native and related species. With audio CD. Supplement to the Zeitschrift für Feldherpetologie 6. Laurenti Verlag, Bielefeld 2005, ISBN 3-933066-23-9 (audio examples 8.1-8.4.).
- Hans Schneider, Ulrich Sinsch: Contributions of bioacoustics to the taxonomy of the Anura. In: Harold Heatwole, Michael J. Tyler (Eds.): Amphibian Biology. Volume 7, Systematics, 2007, pp. 2893-2932. Chipping Norton NSW, Australia, (Surrey Beatty & Sons).
- Hans Schneider, Wolf-Rüdiger Große: Hyla arborea (Linnaeus, 1758) - European tree frog In: Kurt Grossenbacher (Hrsg.): Handbook of the reptiles and amphibians of Europe. Volume 5 / II Froschlurche (Anura) II (Hylidae, Bufonidae). 2009, ISBN 978-3-89104-655-5 , pp. 5-83.
- Matthias Stöck, Sylvain Dubey, Cornelya Klütsch, Spartak N. Litvinchuk, Ulrich Scheidt, Nicolas Perrin: Mitochondrial and nuclear phylogeny of circum-Mediterranean tree frogs from the Hyla arborea group. In: Molecular Phylogenetics and Evolution. Volume 49, No. 3. Elsevier, December 2008, pp. 1019-1024, doi : 10.1016 / j.ympev.2008.08.029 (PDF, 1.2 MB).
- Matthias Stöck, Christophe Dufresnes, Spartak N. Litvinchuk, Petros Lymberakis, Sébastien Biollay, Matthieu Berroneau, Amaël Borzée, Karim Ghali, Maria Ogielska, Nicolas Perrin: Cryptic diversity among western palearctic tree frogs: postglacial range expansion, range limits, and secondary contacts of three European tree frog lines (Hyla arborea group). In: Molecular Phylogenetics and Evolution, Volume 65, 2012, pp. 1-9.
- Urs Tester: Ecology of the tree frog ( Hyla arborea ) relevant to the protection of species . Inaugural dissertation natural science. Univ. Basel, 1990.
- ↑ European Tree Frog - Frog of the Year 2008 ( Memento of the original from May 16, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. , Article accessed May 30, 2008
- ↑ Hans Schneider, Wolf-Rüdiger Große: Hyla arborea (Linnaeus, 1758) - European tree frog In: Kurt Grossenbacher (Hrsg.): Handbuch der Reptilien und Amphibien Europa. Volume 5 / II Froschlurche (Anura) II (Hylidae, Bufonidae). 2009, ISBN 978-3-89104-655-5 , pp. 5-83.
- ↑ Website with photos of a yellow albino tree frog (young animal) ( Memento from April 19, 2014 in the Internet Archive )
- ↑ Andreas Knorr, Hans Schneider: Contribution to the morphology of the brain of Hyla arborea arborea (L.) (Hylidae, Anura). In: Bonn zoological contributions, Volume 26, 1975, pp. 370–382.
- ↑ Bernd Alfs, Hans Schneider: Comparative anatomical investigations on the labyrinth of central European frogfish species (Anura). In: Zeitschrift für Morphologie und Ökologie der Tiere, Volume 76, 1973, pp. 129-143.
- ↑ Ludger Hubl, Hans Schneider: Temperature and auditory thresholds: Bioacoustic studies of the frogs Rana r. ridibunda, Hyla a. arborea, and Hyla a. savignyi (Anura, Amphibia). In: Journal of Comparative Physiology, Volume 130, 1979, pp. 17-27.
- ↑ Robert Mertens, Heinz Wermuth: The amphibians and reptiles of Europe. Waldemar Kramer Verlag, Frankfurt am Main, 1960. 264 pp.
- ^ A b Matthias Stöck, Sylvain Dubey, Cornelya Klütsch, Spartak N. Litvinchuk, Ulrich Scheidt and Nicolas Perrin: Mitochondrial and nuclear phylogeny of circum-Mediterranean tree frogs from the Hyla arborea group . In: Molecular Phylogenetics and Evolution . tape 49 , no. 3 . Elsevier , December 2008, ISSN 1055-7903 , p. 1019-1024 , doi : 10.1016 / j.ympev.2008.08.029 ( PDF, 1.2 MB ).
- ↑ Matthias Stöck, Christophe Dufresnes, Spartak N. Litvinchuk, Petros Lymberakis, Sébastien Biollay, Matthieu Berroneau, Amaël Borzée, Karim Ghali, Maria Ogielska, Nicolas Perrin: Cryptic diversity among western palearctic tree frogs: postglacial range expansion, range limits, and secondary contacts of three European tree frog lines (Hyla arborea group). In: Molecular Phylogenetics and Evolution, Volume 65, 2012, pp. 1-9
- ↑ Hans Schneider: Bio-acoustic studies on the Mediterranean tree frog. In: Journal for Comparative Physiology, Volume 61,! 968, pp. 369–385.
- ↑ Hans Schneider, Eviatar Nevo: bio-acoustic study of the yellow-lemon treefrog. Hyla arborea savignyi Audouin. In: Zoological Yearbooks, Physiology Department, Volume 76, 1972, pp. 497-506
- ^ Hans Schneider: Structure of the mating calls and relationships of the European tree frogs (Hylidae, Anura). In: Oecologia (Berlin), Volume 14, 1974, pp. 99-110.
- ^ Hans Schneider, Ulrich Sinsch: Contributions of bioacoustics to the taxonomy of the Anura. In: Harold Heatwole and Michael J. Tyler (Eds.): Amphibian Biology, Volume 7, Systematics. 2007, pp. 2893-2932. Chipping Norton NSW, Australia, (Surrey Beatty & Sons).
- ↑ Václav Gvoždik, Jiřŕ Moravec, Cornelya Klütsch, Petr Kotlik: Phylogeography of Middle Eastern tree frogs ( Hyla , Hylidae, Amphibia) as inferred from nuclear and mitochondrial DNA variation, with a description of a new species. In: Molecular Phylogenetics and Evolution, Volume 55, 2010, pp. 1146-1166.
- ↑ Václav Gvoždik: Second species of tree frog Hyla orientalis (formerly H. arborea ), from Iran confirmed by acoustic data. In: Herpetology Notes, Volume 3, 2010, pp. 41-44.
- ↑ Uğur Kaya, AM Simmons: Advertisement calls of tree frogs Hyla arborea and Hyla savignyi (Anura, Hylidae) in Turkey. In: Bioacoustics, Volume 10, (1999), Volume 10, pp. 175-190.
- ^ Hans Schneider: Bioacoustic demonstration of the tree frog, Hyla arborea , (Amphibia, Anura) in western Turkey. In: Zoology in the Middle East, Volume 21; 2000, pp. 77-85.
- ^ Hans Schneider: Calls and call behavior of the tree frog Hyla arborea arborea (L.). In: Journal for Comparative Physiology, Volume 57, 1967, pp. 174-189, ISSN 0044-3638
- ↑ Hans Schneider and Institute for Scientific Film: Acoustic orientation in the female of the Mediterranean tree frog. Film C 1500 of the IWF, Göttingen 1983. Publication by H. Schneider, Publ. Wiss. Film, Sekt. Biol., Ser. 17, No. 21 / C 1500, 1985. 13 pp.
- ^ Hans Schneider, E. Nevo, G. Heth, S. Samson, J. Brzoska: Auditory discrimination tests of female near eastern tree frogs and reevaluation of the systematic position (Amphibia, Hylidae). In: Zoologischer Anzeiger, Volume 213, 1984, pp. 306-312.
- ↑ a b c d e f Hans Schneider: Calls and call behavior of the tree frog Hyla arborea arborea (L.). In: Journal for Comparative Physiology, Volume 57, 1967, pp. 174-189, ISSN 0044-3638
- ↑ Hans Schneider: Bioacoustics of the Froschlurche - native and related species. With audio CD. Supplement to the Zeitschrift für Feldherpetologie 6. Laurenti Verlag, Bielefeld 2005. ISBN 3-933066-23-9
- ^ A b Hans Schneider: The control of the daily call beginning with the tree frog, Hyla arborea arborea (L.). In: Oecologia (Berlin), Volume 8, 1971, pp. 310-320.
- ↑ Hans Schneider: Morphology of the Larynx by Hyla a. arborea (L.) and Hyla meridionalis Boettger (Amphibia, Anura). Journal for Morphology and Ecology of Animals, Volume 66, 1970, pp. 299-309.
- ↑ Helga Eichelberg, Hans Schneider: The fine structure of the larynx muscles of the tree frog, Hyla arborea arborea (L.), compared to a skeletal muscle. In: Zeitschrift für Zellforschung, Volume 141, 1973, pp. 223-233.
- ↑ Helga Eichelberg, Hans Schneider: The fine structure of the larynx muscles in female tree frogs, Hyla a. arborea L. (Anura, Amphibia). In: Cell and Tissue Research, Vol. 152, 1974, pp. 185-191.
- ↑ Rolf Manz: The fusion frequencies of the larynx muscles and a leg muscle as a function of the temperature in European frogs (anura). In: Zoological Yearbooks, Department of General Zoology and Physiology, Volume 79, 1975, pp. 221–245.
- ↑ Erich Rüth, Hans Schneider: The influence of body temperature on the heart rate of some European frogs. In: Pflügers Archive, Volume 337, 1972, pp. 45-52.
- ↑ Christoph Riegler: European Tree Frog - Hyla arborea (LINNAEUS, 1758) at herpetofauna.at, Amphibians and Reptiles Austria, 2002–2015, accessed on November 3, 2015
- ↑ The tree frog should croak more often again.
- ↑ Susanne Lenné, Hans Schneider: The sea frog in Northern Hesse: evidence, calls, call behavior. In: Hessische Faunistische Briefe , Volume 14, 1995, pp. 51-62.
- ↑ Christophe Dufresnes, Glib Mazepa, Nicolas Rodrigues, Alan Brelsford, Spartak N. Litvinchuk, Roberto Sermier, Guillaume Lavanchy, Caroline Betto-Colliard, Olivier Blaser, Amaël Borzée, Elisa Cavoto, Guillaume Fabre, Karim Ghali, Christine Grossen, Agnes Horn, Julien Leuenberger, Barret C. Phillips, Paul A. Saunders, Romain Savary, Tiziano Maddalena, Matthias Stöck, Sylvain Dubey, Daniele Canestrelli and Daniel L. Jeffries: Genomic evidence for cryptic speciation in tree frogs from the Apennine Peninsula, with description of Hyla perrini sp. nov. Frontiers in Ecology and Evolution 6: October 144, 2018, doi: 10.3389 / fevo.2018.00144
- ↑ European tree frog at www.wisia.de
- ↑ Federal Agency for Nature Conservation (ed.): Red list of endangered animals, plants and fungi in Germany 1: Vertebrates. Landwirtschaftsverlag, Münster 2009, ISBN 978-3-7843-5033-2
- ↑ Online overview at www.amphibienschutz.de; incl. table with red lists of the federal states
- ↑ Hyla arborea in the endangered Red List species the IUCN 2008. Posted by: Böhme, W., Kuzmin, S., Tarkhnishvili, D., Ishchenko, V., Tuniyev, B., Papenfuss, T., Anderson, S. , Sparreboom, M., Ugurtas, I., Beja, P., Andreone, F., Nyström, P., Schmidt, B., Anthony, B., Ogrodowczyk, A., Ogielska, M., Bosch, J. , Vogrin, M., Tejedo, M., Cogalniceanu, D., Kovács, T., Kiss, I., Puky, M., Vörös, J., Lizana, M., Martínez-Solano, I., Salvador, A., García-París, M., Recuero Gil, E., Marquez, R., Cheylan, M. & Haxhiu, I., 2006. Retrieved March 11, 2009.
- Photos of the European tree frog on www.herp.it
- Information and photos at www.herpetofauna.at
- Information at www.amphibienschutz.de (including Red Lists D, A, CH, federal states)
- A tree frog protection project in Lower Saxony at www.laubfrosch-hannover.de
- NABU project to protect the tree frog in the Münsterland "A king seeks his kingdom"
- Audio sample of a tree frog call