The Peruvian government claims that nearly 900 dolphins died of natural causes. A separate study disagrees.
At night, bottlenose dolphins at the Planète Sauvage aquarium in France sound like they are mimicking recorded humpback whale songs.
In Peru, more than 3,000 dolphins have washed ashore dead on the north coast beaches so far this year.
The survival rate of the rare Hector's dolphins in the protected area increased by 5.4 percent over the past 21 years.
NOAA biologists believe that the 714 dead dolphins found since February 2010 represents only a fraction of the actual death count and has declared the die-off an "Unusual Mortality Event."