Pods of blue whales have found a unique home in the tropical waters of Sri Lanka. The island’s geology and climate create conditions that allow these gentle giants to stay close to shore almost year-round.

The continental shelf surrounding Sri Lanka is unusually narrow. A continental shelf is a geologic feature that extends from a shoreline to a steep drop-off known as a shelf break. A narrow continental shelf means large, deep-water species such as blue whales can safely swim very near the shore.

Two climate conditions also favor Sri Lanka’s blue whales. The first is upwelling, an underwater process in which cold, nutrient-rich water from the deep ocean is forced toward the surface. Upwellings fill the ocean around Sri Lanka with krill, the staple of a blue whale’s diet. The second climate condition that creates such a rich environment for blue whales around Sri Lanka is the “double monsoon.”

A double monsoon describes seasonal climates impacted by strong, predictable changes in prevailing wind patterns (monsoons). The summer monsoon brings winds from the hot, humid southwestern Indian Ocean. The summer monsoon is associated with torrential rainfall and warm surface waters. The winter monsoon brings cooler, drier air from the Himalayas, far to Sri Lanka’s north. Winter monsoons are much, much less powerful than summer monsoons in Sri Lanka, but the mixing of ocean waters creates opportunities for upwelling and creates a diverse marine ecosystem in which the blue whale thrives.

Watch the video, from the Nat Geo WILD series “Destination Wild,” to learn about other environmental conditions that allow southern Sri Lanka to support one of the world’s largest populations of pygmy blue whales.

Use the Fast Facts tab to learn some interesting facts about this distinct subspecies. Be sure to listen to vocalizations in the video, and see if you can answer questions about blue whale “songs” in the Questions tab.