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Changing Tunes

CHIME IN Some whale species are communicating more quietly each year. BARCROFT MEDIA/GETTY IMAGES

Blue whales love to sing. Males sing to communicate across long distances. Scientists use special audio equipment to study the songs. Over many decades, they’ve noticed something. The songs have gotten lower in pitch. Pitch describes how high or low a sound is.

Emmanuelle Leroy and a team of scientists think they know why the pitch has dropped. They studied more than a million whale songs. The songs were recorded in the Indian Ocean over a period of seven years. The team’s report was published in the Journal of Geophysical Research: Oceans. It sheds light on why the pitch of whale songs has changed: Whales aren’t singing as loudly as they used to.

Why So Low?

Leroy’s study presents two hypotheses hypothesis RICHARD T. NOWITZ/GETTY IMAGES a possible explanation based on research (noun) Scientists have many hypotheses about why dinosaurs became extinct. . The first is that there are more whales. In the past, some whale species nearly went extinct. But commercial whale hunting was banned in 1985. The whale population has increased. Whales have begun to live closer together. And because the whales are closer together, they don’t have to sing as loudly to communicate.

The study’s second hypothesis is that the pitch of whale songs has dropped due to climate change. An increase of carbon dioxide in the atmosphere has made ocean water more acidic. This changes the water’s acoustics acoustics ATSUO WATANBE/GETTY IMAGES a place’s effect on the quality of sound heard there (noun) The theater's acoustics make it the perfect place for a piano recital. . Now the songs can be heard farther away. So the whales don’t have to sing as loudly.

“In whale communication, this is good news,” Leroy told TIME for Kids. “But for the environment, it’s not good at all.” Water that’s more acidic could be damaging to some marine life.

Leroy says more research needs to be done to confirm either hypothesis. Scientists will continue to study whale songs. Each study adds to our understanding. “Maybe our hypotheses will be proven in 10 years,” Leroy says. “Science is often a journey.”

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