WEBVTT 00:00:08.460 --> 00:00:11.090 Communicating underwater is challenging. 00:00:11.090 --> 00:00:16.650 Light and odors don't travel well, so it's hard for animals to see or smell. 00:00:16.650 --> 00:00:21.840 But sound moves about four times faster in water than in air, 00:00:21.840 --> 00:00:23.440 so in this dark environment, 00:00:23.440 --> 00:00:28.351 marine mammals often rely on vocalization to communicate. NOTE Paragraph 00:00:28.351 --> 00:00:32.057 That's why a chorus of sounds fills the ocean. 00:00:32.057 --> 00:00:32.822 Clicks, 00:00:32.822 --> 00:00:33.522 pulses, 00:00:33.522 --> 00:00:34.544 whistles, 00:00:34.544 --> 00:00:35.431 groans, 00:00:35.431 --> 00:00:36.281 boings, 00:00:36.281 --> 00:00:37.080 cries, 00:00:37.080 --> 00:00:39.791 and trills, to name a few. 00:00:39.791 --> 00:00:42.291 But the most famous parts of this underwater symphony 00:00:42.291 --> 00:00:48.111 are the evocative melodies, or songs, composed by the world's largest mammals, 00:00:48.111 --> 00:00:50.741 whales. NOTE Paragraph 00:00:50.741 --> 00:00:54.602 Whale songs are one of the most sophisticated communication systems 00:00:54.602 --> 00:00:56.472 in the animal kingdom. 00:00:56.472 --> 00:00:59.181 Only a few species are known to sing. 00:00:59.181 --> 00:00:59.924 Blue, 00:00:59.924 --> 00:01:00.832 fin, 00:01:00.832 --> 00:01:01.701 bowhead 00:01:01.701 --> 00:01:03.181 minke whales, 00:01:03.181 --> 00:01:06.282 and of course humpback whales. 00:01:06.282 --> 00:01:08.032 These are all baleen whales 00:01:08.032 --> 00:01:12.921 which use hairy baleen plates instead of teeth to trap their prey. 00:01:12.921 --> 00:01:16.322 Meanwhile, toothed whales do use echolocation, 00:01:16.322 --> 00:01:19.182 and they and other species of baleen whales 00:01:19.182 --> 00:01:23.871 make social sounds, such as cries and whistles, to communicate. 00:01:23.871 --> 00:01:28.292 But those vocalizations lack the complexity of songs. NOTE Paragraph 00:01:28.292 --> 00:01:29.992 So how do they do it? 00:01:29.992 --> 00:01:34.988 Land mammals like us generate sound by moving air over our vocal cords 00:01:34.988 --> 00:01:38.114 when we exhale, causing them to vibrate. 00:01:38.114 --> 00:01:42.262 Baleen whales have a U-shaped fold of tissue between their lungs 00:01:42.262 --> 00:01:47.492 and their large inflatable organs called laryngeal sacs. 00:01:47.492 --> 00:01:49.705 We don't know this for sure 00:01:49.705 --> 00:01:53.115 because it's essentially impossible to observe the internal organs 00:01:53.115 --> 00:01:55.104 of a living, singing whale, 00:01:55.104 --> 00:01:57.333 but we think that when a whale sings, 00:01:57.333 --> 00:02:00.113 muscular contractions in the throat and chest 00:02:00.113 --> 00:02:06.023 move air from the lungs across the U-fold and into the laryngeal sacs, 00:02:06.023 --> 00:02:08.483 causing the U-fold to vibrate. 00:02:08.483 --> 00:02:14.163 The resulting sound resonates in the sacs like a choir singing in a cathedral 00:02:14.163 --> 00:02:19.194 making songs loud enough to propagate up to thousands of kilometers away. 00:02:19.194 --> 00:02:21.765 Whales don't have to exhale to sing. 00:02:21.765 --> 00:02:25.334 Instead, the air is recycled back into the lungs, 00:02:25.334 --> 00:02:27.984 creating sound once more. NOTE Paragraph 00:02:27.984 --> 00:02:31.763 One reason whale songs are so fascinating is their pattern. 00:02:31.763 --> 00:02:36.615 Units, like moans, cries, and chirps are arranged in phrases. 00:02:36.615 --> 00:02:39.674 Repeated phrases are assembled into themes. 00:02:39.674 --> 00:02:44.553 Multiple themes repeated in a predictable pattern create a song. 00:02:44.553 --> 00:02:47.115 This hierarchical structure is a kind of grammar. 00:02:47.115 --> 00:02:50.842 Whale songs are extremely variable in duration, 00:02:50.842 --> 00:02:54.135 and whales can repeat them over and over. 00:02:54.135 --> 00:02:59.954 In one recorded session, a humpback whale sang for 22 hours. NOTE Paragraph 00:02:59.954 --> 00:03:01.564 And why do they do it? 00:03:01.564 --> 00:03:05.155 We don't yet know the exact purpose, but we can speculate. 00:03:05.155 --> 00:03:09.315 Given that the singers are males and they mostly sing during the mating season, 00:03:09.315 --> 00:03:12.266 songs might be used to attract females. 00:03:12.266 --> 00:03:17.036 Or perhaps they're territorial, used to deter other males. NOTE Paragraph 00:03:17.036 --> 00:03:21.155 Whales return to the same feeding and breeding grounds annually, 00:03:21.155 --> 00:03:24.966 and each discrete population has a different song. 00:03:24.966 --> 00:03:31.196 Songs evolve over time as units or phrases are added, changed, or dropped. 00:03:31.196 --> 00:03:35.020 And when males from different populations are feeding within earshot, 00:03:35.020 --> 00:03:37.300 phrases are often exchanged, 00:03:37.300 --> 00:03:41.855 maybe because new songs make them more attractive to breeding females. 00:03:41.855 --> 00:03:45.586 This is one of the fastest examples of cultural transmission, 00:03:45.586 --> 00:03:49.470 where learned behaviors are passed between unrelated individuals 00:03:49.470 --> 00:03:51.520 of the same species. NOTE Paragraph 00:03:51.520 --> 00:03:54.507 We can eavesdrop on these songs using underwater microphones 00:03:54.507 --> 00:03:56.406 called hydrophones. 00:03:56.406 --> 00:04:02.007 These help us track species when sightings or genetic samples are rare. 00:04:02.007 --> 00:04:04.897 For example, scientists have been able to differentiate 00:04:04.897 --> 00:04:10.335 the elusive blue whale's populations worldwide based on their songs. 00:04:10.335 --> 00:04:14.946 But the oceans are getting noisier as a result of human activity. 00:04:14.946 --> 00:04:15.676 Boating, 00:04:15.676 --> 00:04:16.756 military sonar, 00:04:16.756 --> 00:04:18.127 underwater construction, 00:04:18.127 --> 00:04:22.156 and seismic surveys for oil are occurring more often 00:04:22.156 --> 00:04:25.347 which may interfere with whale's communication. 00:04:25.347 --> 00:04:28.667 Some whales will avoid key feeding or breeding grounds 00:04:28.667 --> 00:04:31.298 if human noise is too loud. 00:04:31.298 --> 00:04:34.557 And humpback whales have been observed to reduce their singing 00:04:34.557 --> 00:04:38.898 in response to noise 200 kilometers away. 00:04:38.898 --> 00:04:41.557 Limiting human activity along migratory routes 00:04:41.557 --> 00:04:43.617 and in other critical habitats, 00:04:43.617 --> 00:04:46.437 and reducing noise pollution throughout the ocean 00:04:46.437 --> 00:04:49.987 would help ensure whales continued survival. 00:04:49.987 --> 00:04:52.838 If the whales can keep singing and we can keep listening, 00:04:52.838 --> 00:04:56.537 maybe one day we'll truly understand what they're saying.