Not to be confused with the killer whale, the hourglass dolphin is recognizable by black and white markings across its body that makes a “cross-bearing” or hourglass pattern. Hourglass dolphins swim where few other cetaceans go, in the cold waters surrounding Antarctica. This species will frequent waters as cold as -0.3 degrees Celsius, or about 31 degrees Fahrenheit. Their icy range, coupled with their distinctive coloring, makes misidentification of hourglass dolphins rare by researchers.
The hourglass dolphin's body is short and stocky, while the dorsal fin is tall and curved, sometimes even appearing bent towards the body in adult males. Their body narrows near the mouth where one of the dolphin's white patches begins, extending over the eye and tapering off at the dorsal fin. The dolphin's second white patch begins where the other ends and narrows at the tail, creating the iconic hourglass illusion. The hourglass dolphin is the only small dolphin that swims south of the Antarctic convergence where cold Antarctic waters meet the slightly warmer waters of the sub-antarctic. The largest concentrations of hourglass dolphins have been sighted in Drake Passage, which lies between the tip of South America and Antarctica.
Similar to other cetaceans, hourglass dolphins swim in groups called pods that can reach up to 100 individuals. However, the average hourglass pod is closer to 14 or less individuals. Swimming at speeds of up to 22 km/h, hourglass dolphins are notorious for riding the waves of fast boats and spraying the surface with sea water as they come up for air. Hourglass dolphins live on a diet of fish, squid and crustaceans and feed at the surface, which often draws a crowd of sea birds and helps research vessels spot the groups of dolphins. The reproductive habits of hourglass dolphins have not been observed, but relatives of this species, like the Pacific white-sided dolphin and the dusky dolphin, give birth every 28 months between August and October.
An estimated 144,300 hourglass dolphins remain south of the Antarctic convergence. There are no direct threats to this species, largely because their remote habitat is rarely visited by humans. However, climate change could still pose a threat to hourglass dolphins in the near future. Climate change has the potential to raise sea temperatures significantly, which could disrupt vital marine ecosystems that have adapted to the cold water.
1. Hourglass dolphins are named after the distinct, hourglass-shaped white markings on their sides.
2. Hourglass dolphins are known for bow riding (leaping through waves) in front of ships and whales.
3. Hourglass dolphins have been spotted in groups of up to 100, but typically stay in smaller groups of about 8 dolphins.
4. Hourglass dolphins reach a maximum known length of 6 feet (1.8 m).1
5. The hourglass dolphin is the only small dolphin species found in Antarctic waters.2
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