or can contain only juveniles or adult males ("bulls"); mixed groups can occur at any time of year. In the summer, several groups come together, forming larger aggregations which can contain 500 to over 1,000 individuals. Male narwhals have been observed rubbing each other's tusks, a behaviour known as "tusking".

When in their wintering waters, narwhals make some of the deepest dives recorded for cetaceans, diving to at least 800 m over 15 times per day, with many dives reaching 1,500 m. The greatest dive depth recorded is 2370 m. Dives