Every year, blue whales sing lower

For decades, blue whale populations around the world have been singing songs at lower fundamental frequencies each successive year. Although scientists aren’t sure why this is happening, they’ve proposed a number of hypotheses, including noisier oceans and sexual selection.

Barlow et al. presented further evidence of this lowering. They documented the decline in song frequency of a blue whale population off the coast of New Zealand from 1964 to 2025.

“The blue whales we studied add another piece to this global phenomenon that has been documented across decadal scales and in many different places,” said author Dawn Barlow. “This work emphasizes the value of acoustic monitoring, because there’s a lot you can learn by listening to the oceans through time. Blue whales are ecosystem sentinels that can tell us a lot about the health of ocean ecosystems.”

Uniquely, the authors were able to listen to this population year-round. They found that the whales’ songs vary not only year to year, but also within a year. More songs were recorded from February to June, a period that is thought to coincide with their breeding season, and the songs were at higher frequencies.

“If these songs are in fact related to their ability to successfully reproduce, listening to these songs can help us understand if and how they’re recovering from the impacts of commercial whaling, as well as how they are impacted by modern human threats and global climate change,” Barlow said.

In addition to songs, blue whales produce other calls. The authors plan to see if these other calls are also changing in frequency while continuing to monitor the songs over time.

Source: “Inter- and intra-annual variation in the frequency of blue whale songs in Aotearoa New Zealand,” by Dawn Renee Barlow, Holger Klinck, and Leigh Gabriela Torres, JASA Express Letters (2026). The article can be accessed at https://doi.org/10.1121/10.0041948 .