Blue whales are known to create the loudest noises of any living thing to communicate across vast distances. Now,a new study has found that they can also hear sounds beyond their vocalisation range.
In their study,researchers at the Scripps Institution of Oceanography observed the response of blue whales in the Southern California Bight to mid-frequency sounds created by military sonar,which occur between 1000Hz to 8000Hz,much higher than blue whale calls,which are 100Hz and lower.
They collected thousands of hours of recordings over two summers,and found that,when mid-frequency active (MFA) sonar (which is used to find submarines) was active in the region,blue whales’ low-frequency vocalisations,known as “D-calls”,dropped by almost half,the ‘Discovery News’ reported.
The researchers say it’s a sign that despite being well outside the whales’ vocalisation range,such relatively high- frequency sounds are within their hearing range.
One possible explanation for being able to hear sounds of such high frequency,lead researcher Mariana Melcon suggest,”is that it may be advantageous,for instance,to hear their predators,ie,killer whales,which vocalise in the same frequency range as MFA sonar.”
Conversely,when confronted with the noise of shipping,which does largely fall within their vocalisation range,the whales increased their D-calls — which,the researchers say “may be the vocal response of the animals to overcome the noise”.