Why do shrews twitter? Communication or simple echo-based orientation.

Area of Science:

• Behavioral Ecology
• Bioacoustics
• Sensory Biology

Background:

• Shrews are highly vocal mammals, producing high-frequency laryngeal 'twittering' calls.
• The precise function of these shrew vocalizations remains largely undetermined, with possibilities including communication or sensory orientation.
• Understanding shrew vocalization function is key to comprehending their ecological niche and sensory world.

Purpose of the Study:

• To investigate whether shrew 'twittering' calls are used for communication or for echo-based orientation.
• To determine the behavioral responses of shrews to varying environmental acoustic properties.
• To assess the acoustic feasibility of echo orientation in shrew habitats.

Main Methods:

• Behavioral experiments were conducted on representative shrew species from major phylogenetic groups.
• Call rates were measured under manipulated substrate densities and varying conspecific presence likelihoods.
• Acoustic feasibility was tested by ensonifying shrew habitats with an 'artificial shrew' speaker and microphone system.

Main Results:

• Shrew call rate significantly correlated with substrate density, indicating adaptation to habitat clutter.
• Call rate was not affected by the likelihood of conspecific presence, suggesting a non-communicative primary function in exploration.
• Acoustic modeling demonstrated that shrew-like calls can provide useful echo information for close-range habitat assessment.

Conclusions:

• Shrew vocalizations likely serve an echo-based orientation function, analogous to bat echolocation.
• Shrews may use sound echoes to navigate complex environments and assess habitat characteristics.
• The utility of echo orientation is limited to ranges within the shrew's vibrissae, suggesting integration with tactile sensing.