It’s a hilarious party trick that never seems to get old. But scientists didn’t make an alligator inhale helium just for scientific jokes: they wanted to find out why these vocal creatures are so noisy.
Both males and females loudly inform the world of their presence year-round using calls known as bellows, although they churn them out more frequently during the mating season. Such long-distance vocalizations have been known to convey certain physical characteristics about the caller, like sex and body size, which is important for both courtship and territorial behavior.
For example, in crocodilians – alligators, caimans, crocodiles and the gharial – females will only mate with males that are larger than them. And males obviously don’t want to go round picking fights with males that are substantially bigger. So it makes sense that these animals would use these vocalizations to inform others of such features, but no one had actually investigated this. In comes the helium.
The reason helium makes our voices go Donald Duck style is that it’s lighter than air, which means that sound waves travel much faster through it and thus the frequencies of resonances are increased. This doesn’t actually alter the pitch, but rather changes the timbre.
The researchers used this feature of helium to their advantage, recording the vocalizations produced by a female Chinese alligator after inhaling either normal air or a mix of helium and oxygen, heliox. Of course, this didn’t involve a balloon, but instead an airtight chamber.
Although the vocalizations actually sounded deeper in the heliox condition, after performing an acoustic analysis on the recordings they discovered an upward shift in frequency. As reported in the Journal of Experimental Biology, this indicates that the animals use resonances in the vocal tract, which have never been documented in non-avian reptiles before. The scientists therefore conclude that these vocalizations could help to convey body size. And since birds and crocodilians share a common ancestor with dinosaurs, perhaps dinosaurs used similar communication systems.
[H/T Washington Post]