New research from scientists in Russia shows that even killer whales like to socialize, creating and visiting social clubs just like humans do.
Until now, scientists never knew why up to 100 killer whales would meet in the Avacha Gulf off the coast of Russia, forming huge superpods despite the fact they typically live in smaller groups. But after studying the whales, the researchers discovered that these groups act as clubs in which the fish-eating killer whales (Orcinus orca) form and maintain social bonds.
Killer whales in the Avacha Gulf live in stable groups known pods, which contain an average of ten whales with up to 20 in the largest pods. However, researchers have seen up to eight of these pods joining together to form even larger aggregations of up to 100 whales.
These large gatherings of pods are seen in numerous places around the world, such as British Columbia, Alaska, Iceland and Antarctica, where large numbers of killer whales live.
Since killer whales have no natural predators, it is not likely the pods are joining together for protection.
Although scientists had speculated that the whales meet to boost their foraging success or to breed, the true underlying reasons for the behavior had not been identified.
To investigate the phenomenon, Olga Filatova of the Moscow State University and colleagues from the Far East Russia Orca Project studied and photographed whales in the Avacha Gulf.
"At first we might see just a few spouts on the horizon. Then quickly we move among them, keeping a distance of a hundred meters so as not to bother them," project co-director Erich Hoyt of the Whale and Dolphin Conservation Society (WDCS), which provided the majority of funding for the project, told BBC News.
"As far as the eye can see, in every direction you see groupings of two to six killer whales surfacing, spouting then dipping below the surface,” he said.
"Each grouping has a focal mother figure surrounded by her offspring, some of whom may be full grown males with up to 2m dorsal fins that tower over the females.”
The researchers also used a hydrophone, a special underwater directional microphone, to record the sound of the whale vocalizations. Each pod of fish-eating killer whales in the Avacha Gulf has a specific vocal dialect that could be identified by the hydrophone, while the shape of a whale’s dorsal fins and markings were used to distinguish individual whales to analyze their behavior.
The whales rarely forage and feed when they gather into their superpods, the scientists found, suggesting this is not the reason behind their aggregation. In fact, depending on the type of prey, forming a superpod might even lessen the feeding success of each whale, the scientists said.
What the researchers did find is that the whales interacted much more during these large gatherings, which lasted anywhere from a few hours to almost half a day.
When meeting whales from other family pods, they made contact with each other, swam in synchrony and rubbed flippers more frequently, the scientists said. Additionally, sexual activity increased, something that might suggest these large aggregations offer a chance to assess potential breeding partners.
But these behaviors likely have a greater purpose beyond reproduction, the scientists said, by enabling whales to establish and maintain social bonds. For that reason, the whales gather in core meeting areas and form large aggregations.
"The superpods are like big social clubs," says Hoyt. "These clubs could help them stay acquainted, could be part of the courting process but could have other functions that we need to learn about,” the researchers said.
Preserving social bonds is vital for many social mammals that live and hunt together, particularly critical for killer whales, which tend to live long lives in small communities with low birth rates. Killer whales also struggle with high calf mortality rates that can reach 50% in the first six months.
"Understanding more about their social lives, including their reproduction, will be crucial to our future understanding of them and our ability to keep their population healthy," Hoyt told BBC News.
The researchers have recently expanded their research outside of the Avacha Gulf, and are studying other killer whale groups further north and south along the Kamchatka coast and to the offshore Commander Islands.
The research is published in the Journal of Ethology.
On the Net:
* Journal of Ethology
* Moscow State University
* Far East Russia Orca Project