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the Decline of Giraffe
and Frog Populations 百科知识
CNN Student News - December 14, 2016
Examining the Decline of Giraffe and Frog Populations
Up next, are giraffes going extinct?
The International Union for the Conservation of Nature, this is a network of environmental organizations, recently listed the giraffe as vulnerable, meaning it`s threatened with extinction. Why?
The group estimates that in 1985, there were more than 150,000 giraffes in the world. Last year, there were fewer than 98,000. The reasons: poaching, the illegal hunting of giraffes. Also, lost of habitat as people expand farms and mines. These factors are reportedly destroying populations and this may not be the only species that`s disappearing.
JOHN STUTTER, CNN COLUMNIST:
In the Costa Rican rainforest, it`s sound not sight that`s helping some researchers track the disappearance of amphibians. These creatures are vanishing at an alarming rate and their plight may be a window into the troubled future of all species on earth.
Out here in the Costa Rican rainforest, ecologist Bryan Pijanowski is setting up high tech microphones to listen for the sound of extinction.
What sort of frogs that you expected to hear?
BRYAN PIJANOWSKI, PROFESSOR, PURDUE UNIVERSITY:
A lot of tree frogs out here, probably strawberry and dark frogs. I`m listening to what I call a rhythm of nature or its tempo of the amphibians and the insects. And if they`re there, it tells me that it`s basically healthy ecosystem. If they`re not there, I get to be very worried.
STEVEN WHITFIELD, CONSERVATION ECOLOGIST, ZOO MIAMI:
In the past 30 years or so, we`ve seen really dramatic, really rapid extinctions for frog populations all over the world. Many of these extinctions are due to habitat loss. But other extinctions have occurred in pristine rainforests like this, places that look healthy, but the frogs are telling there`s something clearly wrong.
For frogs, climate change and a killer fungus called Chytrid which humans helped spread around the world are causing much of the problem.
There are several poisoned frogs calling right around here. We can go and try to track one down.
To try to understand it, Steven Whitfield spent years walking through the rainforest here at La Selva biological station.
Oh, here it is.
Counting and observing frogs.
What is the sounds you hear?
There`s a frog up, that clack, clack, clack, that`s a frog that you can hear from a fairly long distance. There we go again.
I`ll be the first to tell you that it`s not easy work.
There have been many occasions where I`m doing surveys for frogs and I`ll hear one call and spend half an hour or more looking into a small patch of vegetation, knowing that it`s right there and that I need to find it, but unable to see it.
That`s when Pijanowski comes in. He and collaborators from around the world have been installing microphone sensors on the forest floor and up high in the canopy. The goal: listen for changes that biologists like Whitfield might not be able to see.
How many of these sensors are on the forest here?
At the height of our study, we had 34.
It could become a record of extinction. Pijanowski has audio recordings for these forests dating back to 2008. And already, he`s hearing signs of trouble.
He showed me how he uses his computer algorithms to analyze the sound and pick out the species trends. He visualizes these massive audio files in charts called spectrograms.
When you`re in the tropics, you look at a spectrogram, it`s full. It`s rich, because we have thousands of animals here. But when I see something like a spectrogram like this, where we have this large gap and it`s dark, these kinds of differences are ones that you began to ask for serious questions.
But there are some trends so obvious that Pijanowski hears them before the computers do. He tells me that in 2015, he was alarmed at how quiet the forest sounded. Take a listen to this file from 2008.
(AUDIO FILE PLAYS)
And then another from 2015, recorded in similar conditions.
(AUDIO FILE PLAYS)
Those are just two moments, but look how clear the difference becomes when you look at nearly a year`s worth of recordings. You can see the animals making more noise in red. Again, here`s 2008 and 2015. Pijanowski says it`s too early to draw scientific conclusions, but he is frightened.
I`m worried that these would potentially become acoustic fossils. In other words, the animals that are in these files are no longer alive and the only record that we have of some of their presence is in an audio recording. That is somewhat disturbing to me as a scientist, and that`s also as a citizen of this planet.
What happens if they`re gone?
I mean, some of theoretical work that we`re doing in ecology suggests that we could have ecosystem collapse and that`s not good. You don`t want to start removing organisms and expect the ecosystem to survive and function in a healthy way.
Do you feel like you`ve already heard this extinction starting?
I think so. You know, I`ve been only listening for about 15 to 20 years and making a record through these recordings. There is evidence of that. There is evidence all around the world in just about every ecosystem.
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