© Alex Simpson/Project Jonah/AFP/Getty ImagesVolunteers try to refloat stranded pilot whales, mainly cows with calves, at Colville Bay
Hundreds of holidaymakers witnessed the birth of a long-finned pilot whale as they struggled to rescue an entire pod stranded on a treacherous beach in New Zealand.

The mother was among 63 whales, mostly cows with calves, that were beached at Colville Bay near Coromandel township early on Sunday. About two thirds of the animals, measuring up to 12ft (3.6m) long, were saved by residents and holidaymakers who kept them wet in the low tide until they could be refloated in the afternoon.

By yesterday a Department of Conservation boat, which had kept close to the pod to ensure that it did not return, reported that the whales were at least 20 miles out to sea, according to Mike Donaghue, a senior adviser at the department.

Ingrid Visser, of the Orca Research Trust charity, watched the calf being born. "It was an amazing sight to see the calf pop like a cork out of the water. We had only just refloated the calf's mother and once the calf was born the cow took it first to the group of whales nearest her, then to the other two. Within 15 minutes she had headed out to sea with the calf and the others had followed her."

She said that it was likely that the distressed mother had swum into the shallow bay for protection and her pod had followed her.

"I've seen this a lot. The key whales, by which I mean the whales who lead the stranding, are often cows in distress. They head into the shallow waters to get protection from predators and their pod follows. They all become disorientated in the shallows and beach themselves.

"This particular cow was desperately anxious to get off the beach and back into the water. She was actually dragging her rescuers along the beach with her. When we saw the calf pop its head up it all made sense."

Ms Visser added: "It was a major thing for us to see, not just as rescuers but as researchers. It was also such a heartening thing to see after the tragedy of watching all those animals dying."

The triumphant rescue came less than 48 hours after more than a hundred whales died in a separate stranding. Such accidents are common in New Zealand, with up to six mass strandings a year, but it is rare for two so close together.

Experts believe that a pregnant cow in distress may have led her pod to the shallow beach on the Coromandel Peninsula, on North Island.

"The majority of strandings involve pilot whales," Mr Donaghue said. "They are highly social whales and if one gets into trouble the others are reluctant to abandon it. If a sick animal goes into shallow water the others will follow it in. Once they're in shallow water their sonar doesn't work as the sand scatters their sonar waves and they become confused. This is what may have happened here.

"I have never seen a group so reluctant to go back to sea. Most of the time it takes a couple of minutes to refloat stranded whales but this time they kept milling about and squealing. I thought they were going to restrand, but they might just have been waiting for mummy to give birth."

Anton van Helden, the collection manager of marine mammals at the Museum of New Zealand, said that while this behaviour was a good survival strategy in the open sea, it could be suicidal in shallower water. "Because of their strong social bond they will respond to an animal in distress in a particular way," Mr van Helden said.

"I imagine that if these animals are out at sea and one animal calls for help or gets in trouble in some way, that it calls for other animals to come and assist it, which is a perfectly fine survival strategy out in the open ocean.

"But when you get into an inshore environment, particularly the sort of whale trap-type environments with these shallow grade beaches, that it's a survival strategy which just really doesn't work for the environment that they find themselves in," he said.

In the first incident 105 whales beached themselves south of Nelson at Farewell Spit, which is close to the whales' migration routes. It is known for trapping whales because of its sloping beach, where the tide recedes by as much as 4ยฝ miles (7km).

By the time the whales were spotted by a tourist aircraft most were dead. Only 30 were alive when staff from the conservation department arrived and all the adults were dead, Hans Stoffregen, biodiversity programme manager of nearby Golden Bay, said.

"They were in bad shape. By the time we got there two thirds of them had already died. We had to euthanise the rest," Mr Stoffregen told The Southland Times. The whales had been out of the water for a long time because two tides had come and gone.

"It has been quite hot and they were very distressed. You could see the pain and suffering in their eyes," he said. Four conservation department staff were called to the site and shot the surviving whales. Mr Stoffregen said: "It was horrible but nothing could have been done to save them. It was the most humane thing to do."

Scientists still do not know why whales beach themselves but the idea that it may be caused because pilot whale pods stick together when one gets into distress is gaining ground Professor Mark Hindell, of the University of Tasmania, believes that mass strandings may be cyclic. Professor Hindell, who has studied every whale-stranding in Tasmania and Victoria over the past 80 years, said that the strandings were linked to a climatic condition in which heavy winds pushed colder water from the sub-Antarctic.

"We've got very strong evidence now that [the winds] occur in a ten-year cycle, and you get a peak in the number of whales that strands every ten years or so," he told the ABC, Australia's public broadcaster, recently.

The 21 dead whales at Colville Bay were being watched over last night by the Maori tribe, Ngati Tamatera, before a burial ceremony today. David Hamon, an iwi (tribe) member, said that Maori would place the whales in graves at the northern end of the bay.

"It's a sad moment. Maori have a strong connection with whales. We treat them as we would our dead on the marae [sacred places]. You don't leave your dead by themselves."