What are Amphibians?
The amphibians were the first group of animals with a backbone to live on land but never became independent of the water environment due to two factors – one, they never developed a watertight skin and two, their eggs never developed a waterproof shell. So, amphibians loose moisture through their skins and thus need to replenish their water supplies by returning to a moist environment.
Typically, amphibians have a two-phase life cycle, spending much of their early life in water and most of their adult lives on land. Eggs are laid in water and develop into tadpoles, which then undergo a series of transformations, known as metamorphosis, to prepare for a largely terrestrial life as juveniles and adults. In winter the newts, frogs and toads find frost-free refuges under tree stumps, in stacks of peat or in rock piles, where they become torpid (inactive) until the following spring.
Amphibians are protected under the Wildlife Acts (1976 and 2000). Under this legislation a licence is required from the National Parks and Wildlife Service to take these animals from the wild or to disturb their habitat. The Common Frog is also listed in the Red Data Book.
The Smooth Newt
It is generally believed that the Smooth Newt is a native species, in that it colonised Ireland naturally after the last Ice Age some 10,000 years ago. Newts are fairly widespread in Ireland. However they are very secretive animals and are normally only encountered when pond-dipping.
They may grow up to 100mm in length with the tail accounting for 50% of that. The colour of the topside of the Smooth Newt varies from olive-brown to black and may be with or without spots, the underside is paler with black spots on males and dark speckles on females. During the breeding season males develop an orange belly, a large crest along the middle of their backs, and a blue stripe appears on the tail.
In Ireland newts have been called ‘man-keepers’, ‘man-creepers’ or even ‘man-eaters’ in the belief that a newt would run down your throat if you drank pond water. Newts normally breed in well-vegetated ponds and stagnant ditches. Ponds in old deserted quarries are often particularly successful breeding sites. Long grass, woodland or scrub around the breeding pond to provide cover is also important.
Newts normally emerge from winter torpor in February and migrate immediately to their breeding pond. The breeding season is often protracted and adult newts may spend several months in water. The male newt employs an elaborate underwater courtship dance to coax the female to breed.
A successful display ultimately involves the transfer of a package of sperm (spermatophore) to the female. During the breeding season a female newt may lay 200-300 eggs, each one wrapped individually in the leaf of a water plant.
Like frogs, they have a tadpole stage (called an eft), but unlike frogs the tadpoles develop their front legs before their back legs. The tadpoles which develop from the eggs become active, free-swimming predators, but are themselves preyed upon by fish and aquatic carnivorous beetle larvae. The adults normally leave the breeding pond in July, foraging on land mostly at night in autumn. They usually hibernate on land during winter.
The tadpoles metamorphose during July and August, and like their parents they feed on land before they all enter winter torpor (inactive period). Juveniles spend two or three years on land and may wander up to a kilometre from the breeding pond. After three or four winters, they are ready to breed and will seek out a suitable breeding site. Herons, crows and mammalian predators may eat adult newts, but survivors can live up to seven years.
The Common Frog
It appears the Common Frog was introduced in Norman times, perhaps for food. The Common Frog is the most widespread of our amphibians and is found in all parts of the country from suburban gardens and lowland farmland to mountain bog and forestry plantations.
It is an adaptable animal and will breed in all types of still water bodies. Like the newt, scrub, woodland or long grass with undisturbed piles of stones and rotting logs are ideal terrestrial habitats for the adults.
Their colour varies enormously depending on the primary colour of the surrounding habitat, from pale yellow to dark purple on top; the underside is usually paler and sometimes speckled. This adaptation helps the frogs avoid the ever-present danger of predation by Otters, Foxes and Grey Herons. Adults measure 60-80mm in length.
Frogs become active in late January or early February when males call from the breeding ponds to attract females. In contrast to the elaborate courtship of the newt, frogs use a straightforward approach. When the females arrive, they are grasped by the waiting males in a hold known as amplexus. The female carries the male around in this piggyback style and, as she lays her eggs, the male emits a stream of sperm, which fertilises them. The breeding may only last a few nights after which the adults move away from the pond to forage on land for food, eating beetles, slugs, snails, caterpillars and flies. Both male and female frogs return to the same pond year after year.
Back in the pond, the eggs rapidly develop into tadpoles, which feed largely on microscopic algae. Within a couple of months, the tadpoles metamorphose into juvenile frogs called froglets, gradually developing legs and losing their fish-like tail. Juvenile frogs spend one or two years on land feeding and growing before reaching sexual maturity. However few survive to this stage. Less than half of the spawning sites are able to support tadpoles to metamorphosis. In the sites which are suitable, predation and food shortage may account for the loss of a large proportion of the developing tadpoles. Predation of juveniles on land and of adult frogs by Otters, Foxes and Grey Herons can also have a significant impact on survival rates. However, adult frogs can live for seven or eight years and female frogs can lay several thousand eggs in a lifetime. Only a tiny portion of these eggs (less than 1 in 10,000!) need to survive to maintain population numbers.