The strange phenomenon was first observed in the 1980s. During the summer of 1987, entire flocks swam around with hats made of dead salmon, according to the popular science website Live Science.
The trend then died out – but now it's suddenly back. Last month, whale watchers and researchers observed orcas with dead fish on their heads off the coast of the US state of Washington. According to researchers, it may be the same orcas as nearly 40 years ago.
It seems possible that certain individuals who tried out the behavior the first time have picked it up again, says evolutionary ecologist Andrew Foote to the magazine New Scientist.
The cause behind the hat trend is unclear, writes Live Science. Researchers' best guess is that the phenomenon is linked to abundant food supply. When orcas are full, it may happen that they choose to save certain salmon – by balancing them on their heads.
