Lions breed better if living near joining rivers

A 45-year study of lions in Tanzania has revealed that prides which have the best breeding success have territories located nearest river confluences.

Of all the 36 species of wild cats, the lion is the only one to live in social groups, known as prides. What could possibly have led lions to live this way, and what impact could it have on their future?

The global lion population now stands somewhere between 25,000 to 40,000.

To better understand their unique way of life, Professor Craig Packer and his team at the Serengeti Lion Project in Tanzania have spent decades investigating the lion in incredible detail.

When Prof Packer began on his quest in 1978, he thought it would take no more than perhaps three years to reach a conclusion but he found lions were supremely adept at doing nothing.

"I had found lion research to be much less exciting than I'd expected - hours and hours of boredom punctuated by moments of sheer boredom, waiting for the lazy beasts to do something," he said.

The team persevered, spending hours in the field recording the movements of up to 28 prides and now have data on more than 5,000 individual lions.

They were one of the first animal research projects to use DNA fingerprinting techniques in wild animals so as to understand the relationships within a pride. They also had full-size dummy lions built which were used with real lions to understand how lions viewed each others' manes.

Investigating the evolution of the lion social structure in such detail, Prof Packer and his team have had to look closely at the many theories for this lifestyle that have been suggested over the years, such as co-operative hunting, communal suckling of cubs and defence of young against attack.

While they may seem attractive theories on the surface, on closer inspection the research team found they could not be the driving force in the evolution of the lion's social lifestyle.

Now the team at the Serengeti Lion Project believe they may finally have the answer.

Using their extensive data of the lions in the Serengeti and mapping reproductive success over the landscape in which the prides live, the team discovered that the prides which had the highest reproductive success held territories in very specific areas of the national park.

The territories all centred on areas where rivers came together, confluences, which give the lions living there an advantage.

These areas have access to year-round water, shade and good ambush points for prey. Such valuable areas require the strong defence enabled by a pride.

Lion prides in territories without a river confluence had much less reproductive success, the prides were smaller and tended to disappear after 10 years of futility.

Could the very landscape in which lions live be responsible for their social way of life?

Finally, using a computer model the team looked at what effect landscapes with widely different areas of potential reproductive success would have on the effectiveness and likelihood of sociality to evolve.

The results spoke for themselves.

In areas where there were marked differences in the "value" of a territory in terms of reproduction, being social was a good strategy.

The team recorded the movements of up to 28 prides

The territory was so good there was no determent to individual breeding success by being part of a pride, whilst the pride structure conferred an advantage in defending the territory from outsiders.

It is a striking piece of research and reveals just how important specific areas of habitat are for the success of a lion pride in particular but also the lion population in general.

As top predators, it is perhaps not surprising that the areas where lions do best, which drove the evolution of their sociality, are also areas coveted by humans.

And Prof Packer and others have become increasingly worried about this most iconic of cat species.

He said: "I often find it surprising that we somehow expect Africa to bear the brunt of living with a really difficult species... seems to me that that's the world's responsibility.

"If the lion was lost, that's something that belongs to all of us... it's part of our whole history."

Such is the concern that moves by Born Free and others are under way to have the lion moved from listed as a Vulnerable Species and instead listed as an Endangered Species under the Endangered Species Act, elevating it to the same category as tigers and snow leopards.

A situation that just 30 years ago would have seemed unthinkable.

The Truth About Lions is broadcast on Wednesday at 2100 GMT on BBC Two.