For the past month, dolphins have been beaching themselves along the southern shore of Massachusetts at an unprecedented pace.

Scientists say it's the largest beaching by a single species in history. It's happening on the bay side of Cape Cod. Dolphins are dying en masse and researchers don’t know why. Since mid-January, more than a 160 common dolphins have been stranded on the shores.

This isn't a new phenomenon, per se, and Cape Cod is known for the number of beachings its sees every year. But this year is different. It's happening in great numbers and with just a single species.

Once they're on-shore, time is critical if they're to be saved. Volunteers and staff members from the International Fund for Animal Welfare carry the dolphins to a special marine mammal ambulance. Rescuers draw blood, look for injuries on the animals, some of which are eight feet long and weigh 500 pounds. They also tag dorsal fins with GPS devices, so staff can track the dolphins when they’re released into the ocean.

Some 60 dolphins have been rescued by the volunteers. But more than 100 have died on the Massachusetts shores.

Some scientists think bacterial or viral infections, toxins, or loud noises that interfere with the dolphin’s sonar could play a role in strandings. But at this point, there's no clear answer.

Oceanographer C. T. Harry has another idea. He believes a climate phenomenon may be a factor.

Harry, assistant stranding coordinator for the International Fund for Animal Welfare, said his research shows a correlation between increased strandings with fluctuations of the North Atlantic oscillation.

"If you can imagine the atmospheric system almost as like a sea-saw going back and forth oscillating between a high and low pressure system," Harry said. "Those fluctuations or oscillations do a number of things to alter the atmosphere and then from that can change various types of oceanographic parameters."

It can alter current patterns, circulation and basic physical properties of the water, like temperature and salinity. That can alter various biological systems and creatures, like phytoplankton, zooplankton, fish, all the way up to, potentially, cetaceans, he said.

"I can’t prove causation, but I do think that there are some basic kind of intuitive principles in the sense that anything that alters the ocean, specifically on a more regional scale, can then potentially alter what lives in it," Harry said.

He said that could be altering where prey species, like dolphins, are hunting. He said the particular breed of dolphins that are beaching are the type that typically live offshore and may not be used to encountering a landmass like the cape.

I mean, it’s basically a natural hook," he said. "Cape Cod is filled with those little nooks and crannies. And so, if there’s fluctuations of the North Atlantic oscillation that might create conditions to where the animals are closer to shore, that then can put them in an area that would make them more likely to strand."

Harry said the past weeks have been taxing, as far as trying to save the animals, and dealing with those who have died.

"You’re trying to reduce the amount of stress that these animals are already under. Their bodies aren’t used to having any type of kind of intense internal pressure on their organs," he said. "They’re in literally life and death situations. If you can get to them quick enough, and have the proper equipment and also a dedicated group of volunteers, you can provide immediate rescue and response to these animals. But, animals die. Some obviously are stronger than others."