This is the short edition of Morales, first broadcast on the BBC World Service.

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Hello, this is more or less on the BBC World Service. I'm Wesley Stevenson.

Let's take a trip into the jungle.

And if the WWF and the Zoological Society of London are right, there are now fewer animals here than there were 40 years ago and they fallen by an average rate of 50%.

In fact, it's not just in the jungles but all over the world.

This news prompted startling headlines and it also got the more or less inbox buzzing.

We've had a lot of emails like this one from Steve Welsh.

The headline figure of wildlife falling by half seemed immediately suspicious.

And I see from the text that only some types of animals are included.

For example, there are no insects.

But what does falling by an average of 52% mean? Please enlighten us.

More or less listeners are a skeptical lot.

So let's have a look at what the figure means and how it was arrived at.

It came from the recently released Living Planet Index and the project manager is Louise McCray from the Zoological Society of London.

The exact figure is 52% and this is a decline in the size of vertebrate populations over 40 years.

The way we came to this figure was that we gathered over 10,000 different population trends from over 3,000 species.

And what we've done is we've calculated an average of these trends to get this figure.

Now what it means is that it's the rate of decline.

So it means that populations have roughly halved over this period.

So does it mean that if you counted all the vertebrates in 1970 and counted them all in 2010, the number is 50% less?

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