The pool frog often referred to as the northern pool frog, is a medium-sized frog belonging to the genus Pelophylax. Lorenzo Camerano, an Italian herpetologist, gave the binomial name in honour of well known Italian zoologist Michele Lessona. Pool frog is one of the four amphibian species that are protected by the Biodiversity Action Plan of the UK government. In the early 1990s, the wild population of pool frog was believed to have extinct in England.
Species: P. lessonae
The scientific name for Pool Frog is Pelophylax lessonae.
The size of adult pool frogs can be up to 6 centimetres in length. They generally have a bulky body, and adults weigh around 70 to 80 grams. Females tend to be a little larger than males.
The color of this frog species is variable. Individuals can be yellowish-green, green, olive-green, brownish-green, greyish-green or brown. They have dark splattered blotches on it’s back that differ in arrangement, size and number. They have light yellow stripes on either side of its back. The color of the underpart is greyish-white, or yellowish-white with no spots. One of pool frog’s unique identification feature is its sharply pointed snout. They have webbed hind feet that help them in swimming. They have vomerine teeth, and the pupil of its eye is horizontal. Males and females can easily be distinguished as males have a pair of vocal sacs on each side of its mouth; and nuptial pads on its first finger.
Pool frogs prefer to inhabit un-shaded, permanent puddles, ponds, or marshes with densely vegetated areas nearby.
At times, they can also be seen around slow flowing streams or calm rivers. Researchers have noticed that Pelophylax lessonae thrives in places where many waterbodies are in close proximity to each other. During the non-breeding season, they disperse from the waterbodies and take shelter in woodlands and grasslands.
Isolated population of pool frogs are scattered much across central and northern Europe, primarily in Norway and Sweden. There has been a lot of debate as to whether Pelophylax lessonae was an introduced frog species in UK, or a native one. Although there have been recorded introductions in the past, yet recent verification suggests that pool frog is indeed native in some parts, especially in the east of England. Fossil studies, as well as vocalization and genetic analysis, suggest that the pool frogs in Britain are related to the populations found in Scandinavia.
Pool frogs are known to spend much time of the year in or around waterbodies. Even on very hot days, they have a tendency to bask under the sun. They do not have an insatiable appetite like the ecologically and taxonomically similar marsh frog. However, at times, they feed small amphibians and juvenile grass snakes. Their hibernation starts in fall and goes on till spring. They hibernate on land, mostly under logs, or inside tree cavities.
Unlike common frogs, pool frogs breed much later in the year. Males start mating chorus somewhere around May, mostly coinciding with the commencement of warm comfortable nights. Breeding takes place in still waterbodies.
Females lay eggs that float on water surface in a sticky cluster, which are smaller than the cluster laid by common frog. Average clutch size can be 400 to 4000 depending on a lot of factors (such as temperature). Eggs tend to be yellowish below and brown above. After hatching, tadpoles drop under water, where further development goes on. Metamorphosis starts around August to September. Sometimes, the tadpoles overwinter attaining a large size. They become sexually mature in their 2nd or 3rd year.
Pool frogs are carnivorous. Adults primarily feed on invertebrates, such as insects and worms. At times, they also feed on aquatic organisms like gerridae, dytiscidae etc. Tadpoles eat algae (such as chlorophyta, cyanophyta etc.), while juveniles feed on fly and fly larvae.
Because of its semi-aquatic lifestyle, pool frogs are preyed upon by various types of animals. Their common predators include mammals such as cats, dogs and foxes among others. They also fell victim to large birds of prey.
Pool frog’s lifespan is believed to be 6 – 12 years in the wild. Their lifespan varies depending on geographical location.
In the United Kingdom, the last wild sighting was in 1994 (before the reintroduction). Even to this day, pool frog is a rare species found in the British Isle. Reintroduction programs are now currently underway in several undisclosed locations throughout the British Isle. Pool frog’s reintroduction in the UK started in 2005. The initiative was started by the Amphibian and Reptile Conservation Trust and their partners. They utilized wild-to-wild translocation method to restore a population at a specially prepared site. The specimens were collected from Sweden. The Amphibian and Reptile Conservation Trust is still working to institute a new population depending on head-starting instead of wild-to-wild translocation process.
The IUCN Red List of Threatened Species has listed this little frog species in the “Least Concern” category.
Pelophylax kl. esculentus (edible frog) is a fertile hybrid of Pelophylax ridibundus (marsh frog) and Pelophylax lessonae (pool frog). Its reproduction occurs by hybridogenesis (hemiclonally). Pelophylax lessonae are often easily confused with Pelophylax ridibundus and Pelophylax kl. esculentus.
In the United Kingdom, pool frog’s habitat had been destroyed, in the past, in order to create housing estates. Air pollution that led to over-nitrification of waerbodies has played a role in its sharp decline.
The UK reintroduced population are mostly brown with black spots on the back, with yellow stripe.
The last captive pool frog specimen named’Lucky’ died in 1999. It was captured from the Norfolk site.
Pool frog’s call is quite loud. The vocalization is akin to the quacking call of a duck.
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