A new paper has just been published on the vocal responses of grey whales to underwater noise.
This new study has shown evidence for the Lombard effect in grey whales. The Lombard effect is the involuntary response of animals to change their vocalisations in louder environments. There are different ways that animals can change their vocalisations in order to be heard. For example, they can vocalise louder, change the pitch of their vocalisations, vocalise more often or change the duration of vocalisations. The Lombard effect has been shown in other marine mammal species. For example, check out our previous blog post on the communication space between mother and calf North Atlantic Right Whales and how they could adapt the amplitude (volume) and frequency (pitch) of their calls in response to shipping noise.
This new paper is the first evidence of the Lombard effect in grey whales. The study involved projecting both natural and man made noise into the water and monitoring how grey whales changed their calls in response to the noise.
Marilyn Dahlheim (lead author) said:
“We used underwater hydrophones to both collect and project natural and man-made noise into the waters of San Ignacio Lagoon to see how the whales would react. When we projected a variety of different sound sources into the environment, whales were documented to alter the timing and structure of their calls. Acoustic response varied depending on the type of the noise played back. Calling behavior also was documented to change depending upon the duration of the noise (i.e., short versus long-term playback periods).”
The study found that in response to noise the whales were observed to change their calls by increasing calling rates, call received levels, frequency-modulated signals, number of pulses per call, and call repetition rates. Interestingly, they found that in response to oil drilling noise the whales responded by stopping their calling altogether. This is also seen in grey whales in response to predator sounds from killer whales, which means that the grey whales may go silent if they perceive the noise source as a threat.
Check out the full paper here.
So, why is this important to know?
Vocalisation is vital for marine mammals and it is involved in critical activities including foraging, socialising and reproducing for many species. If noise sources decrease the vocal range of marine mammals and they have to adapt by modifying their vocal behaviour in order to make themselves heard, this could have potential implications on their critical activities such as foraging and reproducing, which could in turn lead to changes in survival rates.
Photo: Merrill Gosho, NOAA Fisheries Gray whale breaching