Last month, scientists and whale watchers spotted orcas (Orcinus orca) in South Puget Sound and off Point No Point in Washington State swimming with dead fish on their heads.

This is the first time they’ve donned the bizarre headgear since the summer of 1987, when a trendsetting female West Coast orca kickstarted the behavior for no apparent reason. Within a couple of weeks, the rest of the pod had jumped on the bandwagon and turned salmon corpses into must-have fashion accessories, according to the marine conservation charity ORCA — but it’s unclear whether the same will happen this time around.

Researchers think the orcas sporting salmon hats now may be veterans of the trend when it first appeared nearly 40 years ago. “It does seem possible that some individuals that experienced [the behavior] the first time around may have started it again,” Andrew Foote, an evolutionary ecologist at the University of Oslo in Norway, told New Scientist.

The motivation for the salmon hat trend remains a mystery. “Honestly, your guess is as good as mine,” Deborah Giles, an orca researcher at the University of Washington who also heads the science and research teams at the non-profit Wild Orca, told New Scientist.