Frogs

Common Frog (Rana temporaria)

The common frog is the most frequently encountered amphibian.  Its length ranges from 6 to 10cm, the male being smaller than the female.  It has a smooth, moist skin which is very variable in colour, the background usually ranging from olive, yellow or brown to grey.  Some females are russet in colour with small bumps under the skin.  The back, head and flanks has a very variable pattern of brown or black splotches, some individuals even lacking these blotches completely.  The majority have stripes or bars across their legs.

Frogs have prominent eyes with a speckled yellowish/brown iris and slightly oval pupil.  They also have highly visible circular eardrums located behind the eyes and surrounded by a triangular dark patch.

They have longer back legs than toads making them strong swimmers and enabling them to jump six times their own body length when disturbed.  The front legs are much shorter and in males have a thickened white pad on the first finger.  These nuptial pads become dark and roughened in the breeding season and enable the male to hang on to the female during mating.

Frogs feed on slugs, snails, beetles, earthworms and flies, so should be a welcome resident in any garden.

Life cycle +

Common frogs mostly spend the winter in hibernacula on land, usually under piles of stones or logs, sometimes in the compost heap, although many males hibernate in the silt the bottom of the pond, absorbing oxygen from the water through their skin.  When the pond is iced over for long periods this may lead to frogs suffocating, so it is important to maintain a holier the ice in garden ponds.  Amazingly frogs can survive being frozen for a short time.

In February or March on mild wet nights frogs emerge from hibernation and migrate to their breeding ponds, where males congregate in large numbers waiting for the arrival of the females.  The low purring croak of large numbers of male frogs is a sound well known to owners of even very small garden ponds.

Once the females arrive the males struggle and jostle with each other to grab a female which they then cling to in an embrace known as amplexus.  They remain together until the female spawns and the clump of 1000 to 2000 eggs is fertilised by the male.

The round, black eggs are surrounded by transparent jelly which absorbs water and swells to four times the original size, providing protection against predators.  Usually frogs spawn within a few days of each other, in the warmer shallow edges of the pond.  Spawning may be spread over several weeks, especially if interrupted by freezing temperatures.  After spawning most of the adults leave the pond and seek refuge on land.

On hatching the tiny black tadpoles remain in the disintegrating jelly for a few days before dispersing, when groups of them can often be found in sunny spots grazing on algae.  s they grow they spend more time at the bottom of the pond and their skin becomes a speckled greenish brown in contrast to toad tadpoles which remain jet black.  Unlike toad tadpoles frog tadpoles do not have a toxic skin and are eaten by a large number of aquatic species such as dragonfly nymphs, water beetles and fish.  At night newts can often be seen amongst the spawn preying on eggs and tadpoles.

By May or June complete their development into froglets, and hundreds may be seen leaving the water.  At this stage they are very vulnerable and are heavily preyed on by many species, including herons, crows, blackbirds, grass snakes, foxes and hedgehogs.

Habitat +
Frogs can breed in a wide variety of waterbodies from very small ponds to the shallow edges of large lakes.  Occasionally spawn is even found in tractor ruts, although breeding in such sites tends to be unsuccessful due to desiccation.  The best ponds for frogs are shallow, preferably covering a large area.  Scrapes and hollows in marshland are ideal.  Large populations may also occur in garden ponds, particularly where there is not undue predation from newts.  Unlike newts, frogs do not seem to avoid ponds with fish.

After breeding they need damp terrestrial habitat for shelter, shrubby borders, rock piles and dry stone walls provide refuge.  In the wider landscape they favour rough grassland and woodland.Many male frogs overwinter in ponds.

 

 

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