Amphibian Survey
A pond survey carried out by Hertfordshire County Council in 1986 revealed that nearly half of Hertfordshire's ponds had disappeared at a rate calculated as the equivalent to one every ten days! Among the species that are declining with them are the amphibians that rely on ponds for breeding.
Amphibians are an important indicator of habitat quality and environmental change. They are also beneficial in terms of garden pest control as well as providing a food supply for other species such as grass snakes, herons, owls, foxes and even otters. Dense tadpole populations also provide food for dragonfly and beetle larvae. Perhaps, I should add here, however, that not all amphibians are tasty. Toads, their eggs and tadpoles contain substances which make them unpalatable to many predators.
Five species of native amphibians are found in Hertfordshire: common frog Rana temporaria, common toad Bufo bufo, great crested newt Trituris cristatus smooth newt Triturus vulgaris and palmate newt Triturus helveticus. Non-native introductions include marsh frog Rana ridibunda, midwife toad Alytes obstetricans and alpine newt Triturus alpestris. Frogs and toads are most easily recorded when they return to water to breed in the spring and newts are best seen after dark by shining a torch into the edge of the pond.
The phone has already been ringing with reports of frog spawn (first reported early March) and frogs with problems. Unusual frog mortality has been investigated by the organisation Froglife who set up a Frog Mortality Project ( Tel : 01986 873733 ) a few years back now.
A viral disease, originating from North America, was found to have caused the death of thousands of frogs across Britain particularly in the south-east. This virus can lead to skin ulceration and haemorrhaging. The term "red-leg" has commonly been applied to frogs who generally show these haemorrhagic symptoms. Frog deaths however can also be caused by numerous other reasons.
Problems can occur when frogs and toads spawn early in the season, especially in shallow water. A sudden freeze may cause the surface water and spawn to freeze over. Spawn may remain unfertilized and not develop , or become subject to fungal infections especially in cold weather. It is probably just as well that amphibians compensate for a high mortality rate by the large number of eggs they produce.
Each adult female amphibian can lay hundreds (newts) or even thousands (frogs and toads) of eggs each year. A word of caution, if you think you have too much frog spawn in your garden pond, don't be tempted to transport it to another pond. By taking spawn or adults to another pond you may increase the risk of spreading disease and there may be a danger of introducing the animals to an unsuitable area.
Newly constructed ponds or ponds which are relatively poor in nutrients may have little food available for the emerging tadpoles. This may lead to slower growth and later emergence , sometimes even causing the tadpoles to remain in the pond over the winter. Low water temperatures or low oxygen levels similarly may cause slow growth and other problems.
Survey is essential to both the understanding of amphibian ecology and the implementation of conservation measures. Location of amphibian sites allows the distribution of the species to be determined and gives an insight to the factors that may limit their range.
To investigate more about Hertfordshire's amphibians, the Hertfordshire Natural History Society in partnership with the Hertfordshire Biological Records Centre is hoping to expand on their amphibian site database. This dataset has already proved invaluable in ensuring that many ponds are safeguarded from development and also managed appropriately.
We are hoping to increase our amphibian recorder network and have produced a survey pack, which includes survey forms and brief identification guides. A pond survey form is included in this newsletter but if you would also like to have a survey pack , please contact Jenny Jones at HBRC, Environment Department, County Hall, Pegs Lane , Hertford, SG13 8DN (tel 01992 556156).
This year's survey will be seen as a pilot to the setting up of a regular surveillance programme targeted at registered sites. People who contribute to the survey project will be provided with a report of the current status of amphibians in Hertfordshire. I am also compiling a register of Toad Crossing sites. Each spring , toads follow traditional migratory routes to their spawning ponds and many get killed on the roads during this migration.
The Toad Crossing site organised by June Crew at Stansted Abbotts is well recorded but there may be others. I currently have 6 known sites on the register. If you know of
such a site and would like it to be registered please get in contact. If your site is considered suitable for Toad Signs it will be registered with DEFRA.
Remember recording is fundamental to the protection and conservation of our wildlife. Wishing you happy amphibian spotting!
Jenny Jones
County Amphibian and Reptile Recorder
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