Ouaouaron

The frog-bull , frog mugissante , wawaron (Québécisme) or ouaouaron (Québécisme) is the largest species of Grenouille of North America. It was introduced into many countries of the world and is today described as invasive Espèce.

Morphology

length of the body (muzzle-cesspool): 15 to 20 cm
length of the posterior legs in extension: up to 25 cm
adult weight: ~ 600 G (exceptionally up to 1 kg)
color of the back: vary green olive with brown dark with often of the spots darker
color of the abdomen: cream moucheté of gray
sexual dimorphism:

male: gorges with yellow color, diameter of the tympanum equivalent to the double of that of the eye
Femelle: gorges with cream-coloured color, diameter of the tympanum equivalent to that of the eye

distinctive character of the Espèce: absence of dorso-side fold, cutaneous fold only around the tympanum
Tadpole: reached 7 to 15 cm before the metamorphosis, color green variable and punctuated small black spots on the body and the tail

The adult frogs have an osseous skeleton; the ends of certain bones maintain a cartilage clean with the larval phase (when the skeleton was cartilagineux). The osseous structure accounts for 6,5% of the weight living of the animal.

Physiology

larval life: 1 to 3 years (in France)
sexual maturity: 2 to 4 years after the metamorphosis
many eggs/laying: 3000 to 24000
many layings/year: 1 to 2
longevity:

free: 8 to 9 years
captive: up to 16 years

song: serious and slow, in series from 5 to 6 deaf meuglements

Behavior

The males are aggressive and territorial, especially for the period of reproduction. Their territory can cover 3 to 35 meters of banks. They produce a serious and sound call which can be connected with the lowing of a Taureau.

During the Fall, the adults enter in Hibernation. They can take refuge in the mud and build a kind of small cave to protect itself. They take again their activities when the temperature of water is higher than 13°C and that of the air with 20-24°C. The tadpoles do not hibernate: they remain active throughout the year.

Thanks to its strong legs, this Grenouille can traverse long distances as well in water as on ground. The widest trajectories observed by Raney (1940) are those carried out of night and after strong rains. In addition, he notices an important interindividual variation, certain individuals carrying out of great displacements and others adopting a more sedentary behavior.

Food mode

The Frog bull is a Prédateur Opportuniste. It is sustained of all the alive preys which it is able to capture and to control. It drives out with the mounting and is active of day like night. Its principal preys are: Frog S, Tadpole S, small Poisson S and crayfish S (cf appears opposite)

The youthful ones eat various Arthropodes (mainly Insectes), Mollusques, Têtard S, other small Grenouille S as well as small Poisson S.

The Têtard is Omnivore (eggs of fish, and others Amphibians, Invertébré S, remains Végétaux, dejection, corpses).

The principal predatory ones of the Frog bull are: the Poisson S carnivores, the Snake S, the Duck S, the wader S, the crow S, the Raptor S, the Insect S watery, Mammalian S carnivores and others Frog S of sound Species (cannibalism).

General habitat

The frog bull is pledged in the aquatic environments but is not very demanding with respect to the quality of sound habitat. It occupies of the mediums lentic such as Lacs, Mare S, ditches, gravel pits in Eau or of the artificial basins. However, it is also able to use running water to move.

Distribution

Rana catesbeiana is originating in the east coast of the the United States, of the Mexican border with the area of the Big lakes and the south of the Canada. It was introduced voluntarily into many parts of the world. Several countries are thus concerned in Europe: Germany, Belgium, Spain, France, Italy, the United Kingdom…

Invading exotic species

The Frog bull is described as invasive Espèce. Originating in the East of North America, it was introduced into many countries of the world where it disturbs natural balances then and threatens mainly the other species of Amphibien S.

The introduction of the Frog bull

The Frog bull was introduced voluntarily by the man into many countries. This for various reasons:

the breeding (human consumption)
the use as a play or pet (contest of jump)
like agent of control of Insect S ravageurs and others Plague S.

Involuntary introductions can also occur via the market of the pets (eggs stuck to the plants intended for the Aquariophilie for example or Têtard S directly).

The species thus appeared in many European countries such as Germany, Belgium, Spain, France, Greece, Italy, the Netherlands or Royaume+Uni. It is also found in China and in Japan like in many Pacific Islands, the Greater Antilles and certain countries of South America: Brazil, Colombia, Cuba.

In France, the 19th century, various tests of introduction probably failed. However, at least an introduction succeeded in 1968 in the Gironde: a private individual reported of North America ten individuals for his basin of ornamentation. Some of these individuals moved then and colonized the adjacent water points. The size of the population increased considerably and the species extended on many sites in Aquitaine.

Mechanisms of the invasion

In order to counter the effects of a strong pressure of Predation in its surface Natural of distribution, Rana Catesbeiana developed a capacity of high reproduction (great number of eggs per laying) and an important rate of survival of the larvae.

So in the mediums of introduction, the absence of Prédateur S natural makes it possible the species to proliferate and makes it more competitive than the close species autochtones (other Amphibians). This Batrachian having of more than good adaptabilities and an important capacity of displacement, is then very prolific in the mediums where the introduction succeeded.

On a whole scale of sites, the assumption of the expansion of the Frog bull in France corresponds to a process in 2 phases:

occupation of spaces with weak interspecific Competition, generally of the mediums subjected to strong disturbances of origin Anthropique
migration S and colonization of the Wetlands close when the population becomes too important

Impacts on the colonized mediums

The Frog bull upsets the natural ecosystem S and threat incontestably the fauna of the wetlands. It is indicated like a species being able to involve biological imbalances and its Importation is prohibited in the Europeans worldwide.

The introduction of this frog caused in many countries:

the Regression of populations indigenous S
the disappearance of several species Indigenous S (particularly of the species of Amphibians)

It can also be vector of agents Pathogène S exotics which the species autochtones cannot fight.

Remark : it is essential to note that in many cases, the populations indigenous S are threatened beforehand by disappearance of the wetlands and various Pollution S of origin Anthropique.

Example of measurement against the invasion

Natural Cistude association in Aquitaine set up a multiannual program (2003-2007) having to allow the development of a plan of eradication of this invading species. It consists in studying the biology of the Frog bull and testing methods of Capture and elimination in order to propose effective techniques.

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