Amphibians play an important role in the food
chain. During spring and summer many thousands are eaten by predators
such as otters, foxes or herons.
Out of a clump of spawn containing 2,000 eggs,
95% of the eggs may hatch. Only 1-5% of the tadpoles make it
through metamorphosis and only a handful of the original 2,000
reach sexual maturity. If spawn is laid early in the season,
hard frost may kill it, especially in shallow water. Tadpoles
may also die if their aquatic habitat dries out before they have
metamorphosed. In addition to natural threats, frogs are endangered
by human activities.
 UV
Radiation
Herpetologists blame increasing UV radiation levels and the resulting
damage to the ozone layer for amphibian declines since 1989.
UV radiation damages DNA causing cell mutations and death. Frogs
have very low levels of the necessary enzyme, photolyase, to
repair the damage, and it is believed that this is a large contributor
to their demise.
Fire
An extensive danger to frogs is that of accidental fires. In
any hot dry summer there are inevitably going to be accidental
fires which can result in the loss of habitat. Another threat
for the common frog is from deliberate regular burning of bogland
in the belief that this improves the grazing for farm stock.
Pollution
Exposure to chemical fertilisers, pesticides and herbicides can
cause frogs agonising deaths. Ammonium nitrate granules can kill
a frog within 5 minutes. It is thought that the chemicals are
absorbed into the skin and affect the balance of chemicals in
the moist tissue. They then suffer a massive toxic attack.
Water polluted with heavy metals such as Aluminium,
Cadmium, Zinc, Copper and Iron are toxic to frogs. Lead from
car exhausts may be important even in rural areas. Acid rain
can also increase the
toxicity of metals in ponds causing further threats to frog populations.
Road Migration Deaths
During a few warm, damp nights in spring, thousands of amphibians
follow traditional migration routes on their way back to spawning
ponds. Unfortunately, hundreds can be squashed and killed by
traffic on intervening roads as they make for a suitable pond.
 Habitat
Destruction
Over 50% of Ireland's amphibian wetlands have been lost to drainage,
industrial peat extraction, pollution and natural senescence
in the past 100 years. The terrestrial habitat of frogs is also
important. Unfortunately just as wetlands are being drained,
hedgerows are also being destroyed to make way for industrial
farming methods.
Fatal Infections
The fungus Batrachochytrium dendrobatidis parasitises amphibians
and has caused frog and toad population declines throughout the
world since the 1980's. The fungus destroys the skin pigment
keratin in amphibians. Frogs infected appear emaciated and lethargic,
often with abnormalities of the skin or eyes. The fungus has
caused the extinction of the Costa Rican golden toad (Bufo periglenes)
and serious frog kills in Panama, Australia and the U.S. The
rapid spread of the fungus at 42km per year, has been blamed
on ozone depletion and loss of forest cover, which change the
habitats of sensitive amphibians.
Several mass deaths of frogs have been blamed
on a disease known as "red leg". A British study has
uncovered a new virus - Ranavirus which is responsible for killing
frogs by the hundred.
 Food
and Pets
Europe imports hundreds of millions of frogs from Indonesia,
India and Bangladesh, threatening some species. Millions of South
African frogs have been exported to the U.S. as pets. The American
bull frog, a pet in Britain is a danger to native frogs. Once
these or others escape they displace natural amphibian populations
by hunting them or mating and producing hybrids. The release
of exotic species into the wild is an offense under the Wildlife
Act.
What you can do?
1 Make a garden pond to encourage frogs to breed.
2 Frogs spend most of their lives on land so give them long grass,
leaf and log piles, trees and shrubs in your garden to feed and
hibernate under.
3 Pass on your knowledge of frogs to others.
4 Do not keep endangered frog species as pets and never release
a pet frog into the wild.
5 Organise a clean up of rubbish from local ponds and streams.
6 Take part in the Hop To It Irish Frog Survey and help us learn
more about the status of frogs in Ireland.
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