Amphibians depend on suitable freshwater habitats in which to breed and to pass the early stages of their life history. Britain’s three species of newt, two toads and single native frog (plus two introduced species) all face severe loss of breeding habitat and, to a lesser extent, increased man-made barriers to migration and dispersal. Their conservation is usually best served by the creation and maintenance of ponds, pools and ditches, with surroundings free from public pressure and provided with suitable shelter and hibernation sites. It is generally not recommended to transport spawn to unpopulated waters since the fact that amphibians do not occur in a given location may indicate that conditions there are unsuitable. Extra care is necessary with species having limited or scattered distributions, especially the natterjack toad, which occurs only on a few sites, mainly sand dunes. The edible and marsh frogs are introduced species and are concentrated near London and in Romney Marsh respectively and should not be deliberately transferred elsewhere. Although amphibians are in general rather sedentary, individuals wandering at random allow the gradual natural colonisation of suitable new sites within a mile or two of existing populations.
Life history
Management work may be very destructive to amphibians if carried out at the wrong time of year. Dredging, pumping, extensive aquatic weed control and other severe disturbance of ponds and ditches should be avoided during the breeding season and until the tadpoles have metamorphosed and left the water. Derelict ponds and marginal areas are usually dug out in winter, but this may expose and kill hibernating adults. Where it is known that a species occurs on site, it may be possible to time management to accord with its life history outlined in the table on the following page. Details are given in Macan and Worthington (1972, pp209-17).
| Name | Hibernation (1) | Mating and spawning (1, 2) | Tadpoles leaving water |
|---|---|---|---|
| Warty newt (Triturus cristatus) | late October - mid March | mid March - mid July (early August) (3) | late August - late October |
| Smooth newt (Triturus vulgaris) | mid October - end Feb | early March - early June (early August) (3) | late June - mid October |
| Palmate newt (Triturus helveticus) | mid October - end Feb | March - | |
| Common toad (Bufo bufo) | mid October - mid March | mid March - end April (4) | late May - late July |
| Natterjack toad (Bufo calamita) | late October - late Feb | mid April - end June (5) | early June - mid August |
| Common frog (Rana temporaria) | mid October - end Feb | early March - end April | end May - mid August |
| Edible frog (Rana esculenta) | early Nov - early April | early May - mid June | mid August - end October |
| Marsh frog (Rana ridibunda) | early Nov - early April | late May - early June | late August - early Nov |
| Notes: 1 Dates vary from year to year, depending on weather conditions. 2 Some species remain in or near the water most of their active adult life. Others are highly terrestrial except at the indicated season. 3 Dates in brackets indicate extended aquatic llife of adults after spawning. 4 Spawns in deeper water than frogs, though it may share the same pond. 5 Spawns in very shallow water in areas which often dry up in summer. | |||
Predation
Amphibians are relatively defenceless against predators. Newts have considerable regenerative powers throughout their lives and toads and frogs can regenerate at the tadpole stage. The warty newt is generally left alone because of its poisonous skin; the common toad also secretes a distasteful fluid but many predators have learned to eat it and leave the skin.
All amphibians are most at risk in the early stages, when they fall prey to water beetles, dragonfly larvae and sticklebacks as well as to the larger fish, snakes and water birds which eat them as adults. Frogs and toads are easily caught when they gather in large numbers to breed. When on land, newts are eaten by hedgehogs, stoats, weasels and rats. The common toad is preyed on by crows, magpies and grass snakes, and the natterjack toad by voles and herons. Toads secrete a poisonous substance in their skin, which reduces the number of predators to those which can either skin or disembowel them. Frogs do not have this ability, and therefore have more predators than do the toads.
Man, while not directly a predator, takes his toll. Thousands of frogs and toads are run down each year while crossing roads to return to their spawning ponds.
Amphibians, like fish, depend on their great fecundity to persist. In special circumstances it may be necessary to discourage predators, such as herons which frequent natterjack spawning pools, but protection from human disturbance and provision of habitat at all stages of the life history is usually the best way to ensure their survival.
