Some of the orcas off North America鈥檚 west coast have taken to wearing dead salmon on their heads, resurrecting a curious trend that was first reported in the 1980s.
Local photographers noticed the 鈥� and so did researchers. , science and research director for the non-profit organisation Wild Orca, was observing the marine mammals in South Puget Sound in south-west Washington a few weeks ago. 鈥淲e saw one with a fish on its head,鈥� she says. 鈥淪o that was fun 鈥� it鈥檚 been a while since I鈥檝e personally seen it.鈥�
We still don鈥檛 understand why the聽orcas 鈥� or killer whales 鈥� behave this way. 鈥淗onestly, your guess is as good as mine,鈥� says Giles. But that doesn鈥檛 mean we will never find an explanation.
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This trend seems to be specific to the west coast orcas, and given their long lifespan, it could have spread through the same whales that wore fish as hats decades earlier. 鈥淚t does seem possible that some individuals that experienced [the behaviour the] first time around may have started it again,鈥� says at the University of Oslo, Norway.
But why do orcas wear salmon hats in the first place? One possibility is that the behaviour re-emerges periodically because it is useful when food is particularly plentiful. It might be that the orcas have so much to eat that they have prey to spare, so they balance unneeded food on their heads in case they feel peckish later.
This theory is in line with current conditions in South Puget Sound, where the water is teeming with chum salmon that local orcas prey upon. 鈥淭hey鈥檙e calling it a bumper crop,鈥� says Giles.
It also matches another behaviour observed in orca populations. 鈥淲e鈥檝e seen mammal-eating killer whales carry large chunks of food under their pectoral fin, kind of tucked in next to their body,鈥� says Giles. Salmon may be too small to tuck securely beneath the fin, encouraging orcas to store the food on their heads instead.
Crucially, we now have the technology to test this idea. When orcas first began wearing salmon hats in the 1980s, it wasn鈥檛 easy to follow them. But today, Giles and other researchers can use camera-equipped drones to keep up with the whales.
鈥淥ver time, we may be able to gather enough information to show that, for instance, one carried a fish hat for 30 minutes or so, and then he ate it,鈥� she says.
Of course, the drone footage may instead reveal that the orcas wear fish hats for a while and then simply abandon them. In that case, the researchers would have to go back to the drawing board to figure out another explanation for this curious behaviour.
