The massive region of clear-water channels and some 50,000 islands is considered to be one of the most bountiful wildlife areas on Earth.

But a survey commissioned by Botswana wildlife authorities has found that 11 species are in serious decline, according to the report, which appeared in South African online newspaper Mail & Guardian (M&G)

The survey, undertaken by two members of an organisation called Elephants Without Borders, compared present wildlife numbers with those of a decade ago.

One of the men, Michael Chase, told the M&G: "There’s a catastrophic loss of wildlife.

"We cannot be certain about why, but one thing is clear from the survey - the Delta’s wildlife is in trouble:.

The article suggests that human encroachment, poaching and widespread fires during last year’s dry season are partly to blame.

But "the most potent factor", the M&G says, is seen to be drought.

Though the Delta has experienced torrential rain and flooding this year, the decline in animal numbers has coincided with a dry spell which began in 1980 - the severest ever recorded in the region.

The article has some good news.

It says elephants and hippos are bucking the downward trend. Hippos are increasing at a rate of 6% a year and elephant numbers are holding.

There are said to be 130,000 elephants in northern Botswana.