Fig 1.
These six evenly spaced ridges in the ear of a big brown bats (Eptesicus fuscus) form an array containing five grooves.
Fig 2.
Diffraction effects from optical transmission gratings occur when light waves pass through slits.
Each slit produces wavelets that create interference patterns which become more distinct as increasing groove numbers contribute to the effects. Multi-frequency waves such as depicted here with white light are broken into separate frequencies because the different wavelengths emerge at different angles. The same effect would occur with an acoustic frequency modulated (FM) sweep in bat ears deflecting from grooves (image courtesy of Pasco Scientific).
Fig 3.
Constructive and destructive interference effects occur when two waves meet.
Constructive interference will retain the frequency and double the amplitude when two identical waves of the same period and amplitude that are completely in phase meet. Destructive interference occurs when identical waves meet that are completely out of phase because it cancels the signal frequency and the amplitude to zero.
Table 1.
Bat guild description.
Table 2.
Guild, number of grooves, average groove separation, and ear length of 120 bat species included in the study.
Table 3.
Groove number is related to ear length in some bat guilds.
Fig 4.
Distribution of groove number for species in each bat guild.
1—open space, aerial; 2—edge space, aerial; 3—edge space, trawling; 4—narrow space, flutter detecting; 5—narrow space, passive gleaning; 6—narrow space, active/passive gleaning. The sample size is given above the boxes for a total of 119 species within the six guilds. Guild 7 was not included in the analysis because it only contains one species.
Table 4.
Results of AIC and log likelihood ratio tests to determine the model that best explains the number of grooves in bat ears.
Table 5.
Results of Mann-Whitney U tests for difference in groove number between all pair combinations from six guilds.
See Table 1 for guild definitions and sample sizes.
Table 6.
Mammal species (other than bats) with grooves in their ears.
Fig 5.
The phenomenon of sound waves of different frequencies creating a beat frequency is called superposition.
For example, a frequency of 100Hz integrates with a frequency of 110Hz to form a 10Hz beat frequency [13]. Image courtesy of SFU School of Communication.
Table 7.
Frequencies of echolocation calls of groove-less species.