By Alex Kirby
BBC News Online environment correspondent
A study of African elephants suggests they may be more numerous than they were four years ago, scientists say.
The news may not be as good as it seems
They think there are from 400,000 to 660,000 elephants across the continent, with large numbers in southern Africa.
But the scientists, from IUCN-The World Conservation Union, are interpreting their findings with extreme caution.
They say one explanation may be that the elephants are fleeing to protected areas to try to escape human pressure, thus giving an unduly hopeful picture.
They say habitat loss and competition between people and elephants for resources remain among the principal challenges in elephant conservation.
The scientists are members of IUCN's African elephant specialist group, and their study, the African Elephant Status Report, updates one produced in 1999.
More questions than answers
It is the latest in a series derived from a database on African elephants which since 1986 has been compiling information from the 37 countries where the animals live.
The 1999 report concluded there were at least 300,000 elephants in Africa, and possibly as many as 487,000.
Ivory poachers remain a potent threat
The updated version says the higher figures may be partly explained by reported increases in savanna elephant populations in Botswana, Tanzania and Zimbabwe.
But one of the report's authors, Julian Blanc, said the increase revealed little about how populations were faring at the continental level.
He suspected there could be a more worrying explanation for the apparent population growth - that the elephants were crowding together for safety.
He said: "Most elephant surveys are restricted to protected areas, and it is precisely to protected areas that elephants flock when their range is compressed by expanding human populations.
"A high concentration of elephants in protected areas can give a misleading impression of increasing numbers."
This crowding under pressure, known as "hyper-aggregation", occurs in some other species, and was identified among North Atlantic cod shortly before the collapse of Canada's Grand Banks fishery in the early 1990s.
The authors say there are other possible reasons for caution in interpreting the figures: one is that they are based on data from just over half the total area where elephants may live.
There are still gaps in scientists' knowledge
So much more work needs to be done in the unsurveyed areas to arrive at an accurate picture of changes in population.
Julian Blanc said: "We now have estimates covering a much larger area than we did five years ago - and that alone can go a long way in explaining differences in numbers - but there are still huge gaps in our knowledge."
The update's regional estimates show a wide variation, and considerable uncertainty:
Julian Blanc told BBC News Online: "We know there are large, stable - in places perhaps increasing - elephant populations in southern and eastern Africa, where the amount of monitoring effort is greatest.
- Southern Africa: from 246,000 "definite" to a "speculative" total of 300,000 animals
- Eastern Africa: at least 118,000 elephants, and possibly 163,000
- Central Africa, with huge expanses of unprotected elephant range: somewhere between 16,500 and 196,000 animals
- West Africa: perhaps only 5,500 elephants, and at most 13,200.
"But even in these two regions there are countries - notably Sudan and Angola - with large areas of possible elephant range but about which we have virtually no information.
"This uncertainty not only applies to numbers. Although we have reported an important contraction and increased fragmentation in elephant range in many parts of the continent, it is impossible to say whether this is a recent phenomenon or simply the result of the availability of better information.
"At this stage, even with better information, it remains very difficult to disentangle real changes from perceived changes in elephant populations."