By James Painter: Samiria River, Peruvian Amazon
Pink dolphins are intelligent like their distant cousins, the sea dolphins
Several months ago, parts of the Amazon rainforest were in the grip of one of the most severe droughts on record.
River levels were at historic lows and the impact on wildlife was severe.
The number of pink river dolphins in a remote part of the Peruvian Amazon dropped by nearly half in October compared with 2009, as the level of the Samiria River, a major tributary of the Amazon, fell.
Along a 20km (12 mile) stretch of the river, a population of 250 declined to about 140.
But now a team of conservation experts working in the region has found that many species have recovered more quickly than expected.
This includes the pink dolphins, which, according to surveys conducted in March, have seen their numbers increased by nearly 10%, compared to the same period last year, prior to the drought.
The number of grey dolphins is also up from March 2010 - by 30%.
"This is a very good sign and suggests that the Samiria River is recovering from the drought of 2010," says Dr Richard Bodmer from the University of Kent, who has published extensively on the area for the last 25 years.
The research is being carried out in the Pacaya Samiria national reserve in the upper reaches of the Amazon, an area covering more than 20,000 sq km (700 sq miles).
It falls within one of the three regions worst affected by the 2010 drought, when parts of the Amazon and its tributaries reached their lowest levels for half a century.
"This reserve is a flooded forest, where we get high levels and low levels in the rivers every year," says Dr Bodmer.
"But the 2010 drought and the record floods the previous year were much worse."
Now the water levels are extremely high again and local officials have declared a state of emergency.
"We are being hit on both sides - extremely high levels of water or droughts," says Dr Bodmer.
Dr Bodmer and his team of Peruvian researchers, backed up by volunteers from the conservation organisation Earthwatch, are monitoring the effect of these weather extremes on the pink dolphins and other wildlife.
Conservationists regard pink dolphins as a remarkable species - partly for their colour, which no-one can explain for sure.
But they are also the only species of dolphin able to move their neck horizontally as well as vertically. This enables them to find their way underwater between tree roots.
Several of them played around the boat when we visited a favourite spot of theirs on the River Samiria in late March.
You could glimpse sudden movements of pink, but it was easier to hear them than see them. They expel air loudly like old men with a smoker's cough.
They are apparently curious and intelligent, like their distant cousins the sea dolphins. Between 10 million and 20 million years ago, their ancestors were trapped when this region of the Amazon formed part of a large inland sea area.
Other species appear to have recovered well, too, but the picture is not entirely positive.
Chestnut-fronted macaws had apparently left the reserve or died in significant numbers during the 2010 drought. The latest figures suggest their numbers have recovered strongly now that the rivers are back to high levels.
However, the spectacled caiman, a smaller relation of the crocodile, continues to be a cause for concern. Its numbers in the first three months of 2011 were still 60% lower than in 2010.
Several communities of Cocama Indians live on the river banks of the Samiria within the reserve. They are still talking about last year's drought, and fear it may be repeated in the future.
Tedy Yuyarima, a 42-year-old shaman from San Martin de Tipishca, says the drought was the worst he has ever known.
"Our community depends on fish like the piranha both to eat and sell," he says.
"During the drought it was very difficult to travel for several months because the river was so low. We had to push our boats through less than 20cm of water."
The fish were left stranded in packed, rotting piles. The cormorants and other birds just picked out the best flesh and left the rest.
"We couldn't eat the fish as they had infected abscesses," says Mr Yuyarima.
The community is still worried the fish stocks may not build up again in 2011. But the early signs from Dr Bodmer's team suggest that fish numbers are recovering.
The Cocama Indians are involved in projects to manage the forest in a sustainable way, but extreme weather makes this more difficult, says Mr Yuyarima.
A team of British and Brazilian researchers recently confirmed that the 2010 Amazon drought was more widespread than the one in 2005, which was regarded as "a once in a century event".
The two droughts have been associated with warmer waters in the North Atlantic off the Brazilian coast, caused by warmer global temperatures.
Some computer models suggest that the Amazon could suffer more droughts as the planet warms.
"We cannot ignore these larger global events, which are impacting the local ecosystems and people here, and testing the resilience of the wildlife," says Dr Bodmer.
"At the moment, these impacts worry me, but they are not as dramatic as they could be. But if these weather extremes continue in the future, this will change."