Initial post-mortem tests show the animals were well fed and healthy
Post-mortem examinations of some of 26 dolphins found dead in Cornwall have revealed no clues as to the cause of a mass stranding.
They appear to have been well fed and there were no obvious signs of disease or poisoning, results showed.
The dolphins died when they became trapped in several different river creeks near St Mawes on Monday.
Confusing sonar signals from ships are among the possible causes being considered by wildlife experts.
And they are continuing to search the area in case there are more dolphins in trouble.
David Jarvis, from the British Divers Marine Life Rescue organisation, told BBC News there were several different theories about why the common dolphins ended up trapped in Porth creek.
"They could have been looking for food," he said.
"It could have been something to do with sonar, it could have been that there was a killer whale out there that frightened them."
He estimated that up to 76 dolphins were in the area at the time but said the "good news" was that at least 40 had been helped to safety in deeper waters.
Bodies of dolphins being taken to shore on Monday
The stranding has been described as the worst ever seen in the UK.
Some of the dead animals found on Monday are believed to have been pregnant. Two of them had to be put down.
Veterinary pathologist Vic Simpson, who performed some of the post-mortem tests, said: "It's quite unprecedented, we have never had anything of this magnitude."
Tom Hardy, Marine Conservation Officer for the Cornwall Wildlife Trust, said healthy common dolphins should normally be able to swim out of shallow creeks.
"There must have been another factor involved," he said.
The Royal Navy said there had been no vessels on training exercises in the area at the time.
A spokesman said the navy did not use low-frequency sonar in South West waters because of "environmental concerns" and because the water was too shallow.