By Matt Walker
Editor, Earth News
The greatest battle of all...
It is the greatest animal battle on the planet, and it has finally been caught on camera.
A BBC natural history crew has filmed the "humpback whale heat run", where 15m long, 40 tonne male whales fight it out to mate with even larger females.
During the first complete sequence of this behaviour ever captured, the male humpbacks swim at high speed behind the female, violently jostling for access.
The collisions between the males can be violent enough to kill.
The footage was recorded for the BBC natural history series
"Even though this is one of the most common of the large whales, very little is known about its actual sexual behaviour," says Life producer Dr Ted Oakes.
"One of the most interesting things is that humpbacks have never been seen to mate."
But what has been filmed is the epic battle between males to get mating access to the female whales.
Up to 40 males swim behind a single female at speeds of up to ten knots, each jostling to obtain a dominant position.
"It's the closest we're ever going to get to dinosaurs fighting. It's the largest battle in the animal kingdom and it feels like something out of Jurassic Park," says Dr Oakes.
Migrate to mate
Most humpback whales spend their summers feeding in polar regions.
During the winter, they migrate thousands of miles to warmer tropical waters.
While there is little food in the tropics, females move there to give birth, as the warmer water helps smaller baby whales better regulate their body temperature.
Males follow the females to the tropics, hoping to find mates.
How the heat run was filmed
To film the whales' heat run, the Life team travelled to the southern Pacific waters around the archipelago of the Kingdom of Tonga.
"In order to capture the sequence we had to film from a helicopter, a boat and from underwater," says Dr Oakes.
"Each of those was really difficult, and we had to get them all together. It was a big challenge."
Running the gauntlet
When a female humpback comes into heat, she alerts males by making sounds, such as slapping the water surface. She may also release scent into the water to signal her status.
"The males all gather around the female, she hangs there, and then swims away. That's when it kicks off," says Dr Oakes.
"It is kind of like a gauntlet. She swims away at speed and the males then fight for pole position directly behind her tail."
As they chase the female, the males escalate their conflict.
First they lift their bodies out of the water, slapping the bottom of their huge feeding pouches onto the surface. They also slap their long pectoral fins onto the water.
The males then vocalise loudly and blow bubbles underwater, a threat display among many marine mammals.
Listen to a male humpback whale singing at BBC Wildlife Finder
"When they blow these huge streams of bubbles, in this context it means there's going to be an almighty fight'," says Dr Oakes.
The males then start colliding, hitting one another and even jumping out of the water and onto rivals.
Considering that each male humpback can weigh 40 tonnes, such collisions must hurt, says Dr Oakes.
"It's a violent behaviour. So violent that there are records of males killing one another."
Cameraman Mr Roger Munns filmed most of the underwater footage of the heat run for the BBC.
Mr Munns had to freedive whilst holding his breath to get shots of the whales swimming past him at speed, as the use of scuba tanks would disturb the humpbacks.
"We had to find the whales when they are on the heat run, which is hard," says Dr Oakes.
"Then we had to position the diving team in front of the charging pack of whales for them to have any chance."
"At one point I think Roger had the female and seven or eight males go past him. He said it was the most incredible experience of his life. Like standing in the middle of a motorway."
The "humpack heat run" is broadcast within the Mammals episode of the BBC series
Life at 2100BST on BBC One on Monday 26th October.