In my last blog I told you that the mountain chicken is listed as
Critically Endangered, which means it is facing the threat of going extinct
very soon unless something is done. But why is this amazing frog so close to
going the way of the dodo?
To understand the whole story we must first go back in time. Hundreds
of years ago before Christopher Columbus discovered the Americas and Europeans
began to arrive, the mountain chicken was found on 7 different islands in the
Caribbean instead of the 2 it is today. As Europeans arrived and settled on the
various islands of the Caribbean they brought with them, either deliberately or
unintentionally, species that did not exist there before. These included rats,
cats and small Indian mongoose.
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| Red islands where the mountain chicken is still found. Blue Islands where it is now extinct |
Mongooses will eat pretty much anything, including frogs and is a
successful predator. The native animals would never have seen a mongoose (or a
cat or rat) so would not know how to react. On all the islands where mongooses
were introduced the mountain chicken went extinct suggesting it was a main reason. Only Montserrat and Dominica
have never had mongoose and it is no coincidence that they are the only two
islands on which the mountain chicken still survives.
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| Small Indian mongoose - probably the main reason why the mountain chicken went extinct on the five other islands |
So why if there are no mongooses on these two islands have the numbers
of mountain chickens dropped by over 90% in the last 15 years? Local people did
hunt the mountain chicken for food but not in the numbers to cause such a huge drop so quickly.
Was it loss of habitat? Not really as they were quite happy in gardens on these islands although a volcano on Montserrat erupting did not help! No the
answer is disease. In this case a particularly nasty, amphibian killing disease
called chytridiomycosis or chytrid (pronounced ki-trid) for short.
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| Healthy mountain chicken (Photo: S-L Adams) |
Chytrid isn’t caused by a virus or bacteria but by a fungus that infects the skin of amphibians. Unlike reptiles, amphibians have permeable skin, which they use to help absorb gases and water many species use their skin to help them breathe. When the fungus infects the skin it can inhibit these processes causing many problems for the animal and eventually death. Some of the visual signs of chytrid in mountain chickens are animals looking lethargic (tired), reddening of the belly and legs and skin peeling off.
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| Mountain chicken infected with chytrid (Photo: S-L Adams) |
Are there groups of scientists currently working on finding a cure for chrytridiomycosis?
ReplyDeleteYes there are lots of groups working on it at the moment all around the world both in the field and in laboratories and Universities. Chytridiomycosis is the biggest disease threat facing any living animal group and scientists and conservationists are very concerned about it. However there are so many questions and unknowns about it, that different groups of scientists are working on different aspects. This is important as the more we learn about the disease the more likely we are to find a cure or a way to effectively treat it.
ReplyDeleteChytridiomycosis is the disease that is caused by a type of fungus whose scientific name is Batrachochytrium dendrobatidis, commonly called Bd or chytrid. This fungus infects the skin of amphibians and the amount of it is measured in zoospore counts. When these zoospores reach a threshold number, susceptible species start showing signs of illness.
ReplyDeleteIt is believed that chytridiomycosis affects the natural functions of the skin in relation to breathing, electrolyte exchange, thermoregulation. This causes behavioural changes such as lethargy, failure to seek shelter, loss of appetite and eventually causes death.
However not all amphibians develop chytridiomycosis from having chytrid. Why this is, is still a mystery.