Of all the Orca behaviours I have been privileged to see, it is when they are in “resting lines” that I most transported into awe. It makes so clear how socially bonded the whales are and how coordinated their behaviours can be.
Science has determined that toothed whales like Orca do not sleep but only “rest”, shutting off one half of their brains at a time (scientifically known as “unihemispheric sleep”). They have to maintain this level of brain activity since they are voluntary breathers and must therefore consciously come to the surface to inhale and exhale.
Occasionally, Orca rest alone. They then float on the surface, motionless, blowhole exposed, “logging” for only a few minutes.
Far more often the Orca rest together, uniting in these very tight groups, fin to fin. This can happen at any time of day and I have witnessed resting line behaviour for up to 8 hours.
Once in resting line formation, the whales are usually silent (although there are a couple of matrilines that do occasionally vocalize) and move slowly forward, undertaking a remarkably synchronous and regular dive pattern. They often take short, shallow dives for around 2 minutes and then they all take a longer dive. When they resurface, their breaths are incredibly coordinated and their dorsal fins often line up perfectly.They are of course particularly susceptible to disturbance by boats when they are resting – both due to sound and proximity.
“We are one” the behaviour seems to display and I certainly believe that this resting is also of great social and cultural importance to Orca.
At its most simple level though, a resting line of Orca is truly . . . breath-taking beauty.
Photos below = resting line of members of the D, C, A5 and I15 matrilines in August 2020. All photos taken with a telephoto lens.