The 48-day dry spell saw water levels drop at the Lancashire Wildlife Trust nature reserve, in Rufford, and on other reserves in the North West.
It has meant problems for many wading birds that feed in mud, which is now rock solid, so they cannot find food with their long bills.
Less water in Mere Sands Woods lakes mean oystercatchers can get to freshwater mussels.
Expert on the history of the former Martin Mere lake, which once covered the area, Professor William Hale said: “Freshwater mussels are not normally available to oystercatchers because of the depth of water in which they usually occur.
“In the summer of 2010 and 2011 the water level in Mere Sands Wood was so low that oystercatchers were able to access the mussels which they found by probing. This appears to be the first record of oystercatchers feeding on freshwater mussels anywhere in the world. The only previous mentions were a record of a Dutch Oystercatcher attempting to break the shell of a freshwater mussel by dropping it on a road and a very dubious report of one being dissected from the gut of a dead oystercatcher in Russia.
“Oystercatchers break into the shell of mussels on the shore from the point of where the two valves of the shell come together opposite the hinge. They then, in some cases, sever the adductor mussel, which opens and closes the valves, but this may not be deliberate.”
Prof Hale noticed that the Mere Sands Wood oystercatchers had tried to sever the adductor muscle but said: “Shells were usually broken into from the side by hammering the thinner part of the shell, often with the shell under water.
The contents were then usually removed through the hole produced by the hammering.”
Mere Sands Reserve Manager Lindsay Beaton said: “We have found shells with the sides broken and we have had an influx of oystercatchers over the dry period.
“Most of our fish-eating birds are doing well, because we still have the same amount of fish in the lakes but a lot less water.
“But the waders who usually delve in the mud with their bills have been struggling because it is bone dry.”
And Mere Sands Wood has been a hotspot for kingfishers over the last couple of months, with fledglings being fed close to Rufford Hide. Lindsay said: “I am delighted to say that the parents have now cast the young kingfishers free and they are still hunting around the reserve.”
Brockholes has also been affected by the dry weather with water levels at their lowest since the reserve opened in 2011. However, there have been good news stories too with terns breeding on tern rafts for the first time.