While working on squirrel calls, I found that the frequency of the sound produced by individuals from mean sea level is quite more than the same from an elevation of about 2000 metres. Does the frequency depends upon the elevation of habitat and changes with change in the height or their is something else behind the aforesaid phenomenon.
Hello Anish; There are a number of mammalian traits (body mass, fur color for instance) that vary with elevation and latitude, but I've never seen anything in the literature like what you have observed. Try the study over a wider range of elevations with more species. You might be onto something! Best regards, Jim Des Lauriers
Sound arises from the vibration of a source. The larger the source, the longer the potential wavelength. Ergo, for any given species, a larger individual has the anatomical potential to produce a lower frequency signal than a smaller counterpart of the same genus. This is a general statement of course. If the highland animals are physically smaller than their lowland counterparts, then it is reasonable to conjecture that they may have higher frequency signals. i am happy to look at some signals in more detail if you would like further thought.
Hello Anish, interesting question!
Did you consider checking if the environmental background noise differs between those elevations? It is not rare for birds in urban areas to shift their vocalizations to higher frequency to avoid behind overlapped by lower-pitched city noise. One can expect coastal area to be more artificially "noisy" than high elevations?
See for example:
https://www.nature.com/articles/424267a
Article Experimental evidence for real-time song frequency shift in ...
A gradient between different elevation, controlling for the urbanization level would be a very good way to test that.
@Abel Souriau
The environmental noises were certainly different among the two places. One was from a urban area and another from a hill station. The hill station was having comparatively less city noise but in both the cases the recordings were from human settlements. So certain anthropogenic noises were present in both the cases.
@Edward Pedersen
The results just contradict the general statement. Since no morphometric studies were done, the body size comparison is not clearly known. But so far the results are concerned, the frequency of the individuals from.higher elevation were found to be lower than that of the plains.
Hi Anish,
It is interesting that vocalization frequency tends to get lower as one proceeds up an altitudinal gradient. Moreover, dominant frequency also decreases with increasing body size. For many animals, body size also increases as one proceeds up an altitudinal gradient, due to harsher conditions at higher altitudes. Harsher conditions favor larger animals with smaller surface area-to-volume ratios.
In a study (refernce below) we did on hearing in tropical treefrogs found along an altitudinal gradient in Puerto Rico, we concluded:
"We suggest that the animal’s body size determines the frequency particulars of the call apparatus and the inner ear."
Meenderink SWF, Kits M and Narins PM (2010) Frequency matching of vocalizations to inner-ear sensitivity along an altitudinal gradient in the coqui frog. Biol Letters 6: 278-281. doi:101098/rsbl20090763.
I hope this helps,
Peter
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