University of Hawaii researchers using underwater recorders say they’ve discovered humpback whales are spending the winter in the Northwestern Hawaiian Islands in addition to the main Hawaiian Islands.

Scientists from the Hawaii Institute of Marine Biology and the National Oceanic and Atmospheric Administration recorded humpback whale songs, which are an indicator of winter breeding activity, in both areas.

They found the whale songs were prevalent throughout the Northwestern Hawaiian Islands and that demonstrated trends very similar to those in the main Hawaiian Islands.

The researchers published their study in in the current issue of the journal Marine Ecology Progress Series.

There are about 20,000 humpback whales in the North Pacific. About half this population is believed to come to the Hawaii each winter to breed and calve.