Humpback whales are famous for their complex and beautiful songs, which they produce mainly during their breeding season.
These songs are thought to play a role in attracting mates, communicating with other whales and maintaining social bonds.
But how do humpback whales deal with noise in their environment, such as wind and boat engines, that could interfere with their singing?
A team of researchers from the University of Queensland has investigated this question by recording humpback whales off the Queensland coast during their southward migration from the Great Barrier Reef to Antarctica.
They found that humpback whales sing louder when the wind is noisy, but not when boat engines are noisy.
This suggests that humpback whales have different strategies to cope with natural and man-made noise sources.
Wind noise: A natural challenge
Wind noise is a natural source of noise that humpback whales have evolved with over millions of years. Wind noise can vary depending on the wind speed, direction and sea state. It can affect the transmission and reception of whale songs by masking (covering up) or distorting them, as per Phys.org.
The researchers found that humpback whales increase the source levels (loudness) of their songs when the wind noise increases, which is a common behaviour among many animal species to maintain effective communication in noisy environments. This behaviour is known as the Lombard effect.
By singing louder, humpback whales can increase the signal-to-noise ratio (the difference between the sound of interest and the background noise) and make their songs more detectable and intelligible to other whales.
However, singing louder also has costs, such as increased energy expenditure, increased predation risk and increased exposure to potential competitors or enemies.
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Boat noise: A man-made threat
Boat noise is a man-made source of noise that humpback whales have not evolved with and may not be well adapted to, as per The Royal Society.
Boat noise can vary depending on the type, size, speed and distance of the boat. It can also affect the transmission and reception of whale songs by masking or distorting them.
The researchers found that humpback whales do not increase the source levels of their songs when boat engines are noisy, which is a surprising finding given that boat noise has a similar frequency range to wind noise.
This suggests that humpback whales do not perceive boat noise as a communication challenge or that they are unable to cope with it.
The researchers propose that humpback whales may use other strategies to compensate for boat noise, such as spatial release from masking (the ability to discriminate between sounds coming from different directions) or comodulation release from masking (the ability to discriminate between sounds and noise when the noise has distinctive frequency components that do not overlap with the sounds).
Alternatively, humpback whales may simply ignore boat noise or reduce their communication efforts when boat noise is present. This could have negative consequences for their reproductive success and social interactions.
Implications for conservation
Humpback whales are exposed to increasing levels of noise in their habitats due to human activities such as shipping, fishing, tourism and exploration.
Noise pollution can have detrimental effects on whale health, behaviour and population dynamics.
Understanding how humpback whales respond to noise is important for developing mitigation measures and policies to protect them and their acoustic environment.
The researchers suggest that more studies are needed to assess the long-term impacts of noise on humpback whale singing and breeding.
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