Hourglass dolphins were not given a classification until 1824 and were originally classified as Delphinus cruciger. The word cruciger is Latin for “cross-bearing” and is probably a reference to the hourglass pattern on the sides of these dolphins. This dolphin may also be classified as Lagenorhynchus wilsoni, for Edward Wilson, an Antarctic naturalist in the early 20th century.
Other names for this species are skunk dolphin, Wilson’s dolphin, and Southern White-sided dolphin.
Hourglass dolphins are found only in the polar regions Southern Hemisphere. They can be found as far south as the edges of Antarctica and range to the southernmost areas of Australia, New Zealand, and South America. Though some strandings of this species has been recorded in New Zealand, these dolphins prefer living offshore and are seen infrequently.
The hourglass dolphin is most easily recognized by its unique white “hourglass” marking against a largely black body. Its underside is also white, though both sides of the fluke are black. The two white patches that make up the hourglass shape are often connected by points or at least a thin white line, though in some individuals the two white patches do not touch. The forward patch extends to the melon region and often there is a thin white line circling the eye.
The rostrum is short and black in color. The dorsal fin is easily notable and concave, though in some individuals it becomes sharply hooked backwards. Pectoral flippers may also have a definite “elbow” and curve back sharply on their leading edge.
DIET & BEHAVIOR
Stomach contents of stranded hourglass dolphins has revealed that they feed on small fish, crustaceans, and squid.
Usually found in groups of 7-10, these dolphins are not at all shy when encountered and often bow ride, even approaching slower moving vessels. Sometimes they’ll spin while riding the waves. When they bowride, they swim in long low leaps and may resemble a porpoising penguin. They may also create a “roostertail” of spray when surfacing to breathe at high speeds.
REPRODUCTION & LONGEVITY
Since these dolphins are sighted irregularly, details on their lifespan and reproduction are unknown.
Though three hourglass dolphins were once accidentally ensnared in a gill net, their contact with human activities is very slight. They are not considered threatened.