Journal Club: Modelling of bone conduction in otic bullae of Baloon whales.

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Today's journal article

Cranford TW, Morris MA, Krysl P, Hildebrand JA. Colossal ears? How baleen whales hear low-frequency sound. 

Why I picked this article

Some animals communicate across extraordinary distances, and baleen whales are a classic example. Many species use low-frequency calls that can travel far through seawater. That same feature makes them vulnerable to human-made noise that also carries long distances. So the basic question of “what can they hear, and how?” matters for both biology and conservation.

What makes baleen whale hearing especially interesting is the apparent mismatch between sound and anatomy. Low-frequency sounds have very long wavelengths. Yet the ear structures in baleen whales are not proportionally huge. This research takes a computational modelling and structural analysis of the whale's inner ear to understand whether the skull itself can act as the main sound receiver, and whether the bony ear complex can amplify those vibrations. 


From Fig3 Cranford et al. 2025. Blue part is the otic bullae - which contains the middle ear structures.

Some of the research findings

Model and whale bone material: 
  • Natural juvenile grey whale skulls were scanned with CT, and were also physically prepared to document the anatomy. 
  • Finite element modelling was developed to analyse the vibratory property of the otic bullae with low-frequency sounds. CT data were used to generate mashes. 
  • Vibroacoustic experiments were conducted using the specimen. This is published in more detail in Morris et al. (2025), https://www.nature.com/articles/s41598-025-98100-1
Key findings: 
  • Incident low-frequency sound is proposed to induce skull vibrations. 
  • Those vibrations are transferred to the tympanoperiotic complex (TPC), the bony ear complex in baleen whales. 
  • The researchers describe amplification within the TPC, especially involving the tympanic bullae and associated structures. 
  • The pedicles (thin bony connections suspending the bullae from the periotic) are highlighted as key dynamic elements. 
  • The suggested role of the pedicles is mechanical amplification of low-frequency vibration delivered from the skull. 
  • Vibrations of the dynamic bony elements (including bullae and middle ear ossicles) are linked to the displacement of inner-ear (cochlear) fluids. As such, the authors argue that this skull-driven pathway is central for understanding mysticete low-frequency hearing and related natural history.

Haruna's takeaway

I have to say, I realised that I don't know enough about whale ear to understand this publication!! What's in the otic bullae of aquatic mammals? I had thought that ossicles are in place and identifiable as landmarks, but they must be more like evolutionary remnants; however, according to my quick search, it seems that air space does exist in even deep-diving aquatic mammals. It would be so interesting (for me) to find some middle-ear publication and really start with outer and middle ear components to understand whale and dolphin hearing. Thinking about different animal models is fascinating - I sometimes wish I had studied ecology!

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This is Haruna's 84/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.