Homing pigeons can return home over hundreds of kilometres. For a long time people argued about what serves as their "compass and map": the sun, the magnetic field, smells. One of the most intriguing hypotheses is that part of the map they build from infrasound.
The riddle of the "dead zones"
For decades pigeon fanciers had noticed that in certain places whole flocks inexplicably get lost. The geologist John Hagstrum, examining such cases in the United States, spotted a pattern — the navigation failures coincided with conditions in which infrasound from the home loft did not reach the birds because of temperature and wind layers in the atmosphere.1
The home's "acoustic map"
According to Hagstrum's hypothesis, every locality constantly radiates faint infrasound (microseisms, reflections from the terrain), and a loft has its own unique "acoustic signature". A pigeon memorises it and, once airborne, uses the echo to work out the direction home. Modelling of sound propagation in the atmosphere explained well where and when the birds went astray.1
The infrasound model elegantly explains the anomalies, but it has not been definitively proven. Today most scientists believe that bird navigation is multisensory: the magnetic field, the sun, smells and, possibly, sound work together. Infrasound is a strong candidate, but not the only answer.
- There are persistent "dead spots" where whole pigeon races regularly get lost — for years this was a mystery.
- The anomalies coincided with days when infrasound from the home loft did not reach the birds because of atmospheric layers.
- Bird navigation is almost certainly multisensory: the magnetic field, the sun, smells and, possibly, sound — all together.
- It is not only pigeons that use infrasound: cassowaries produce the lowest-frequency bird call known (~23 Hz; Mack & Jones, 2003).
- Peacocks generate infrasound during the tail-rattling display — and peahens detect it (Freeman & Hare, 2015).
The story of the pigeons shows that even very faint, background infrasound carries information about space. That is inspiring — it means a sensitive network can "read" the surrounding landscape from sound we cannot hear.
Sources for this article
- peer-reviewed Hagstrum J.T. (2013). Atmospheric propagation modeling indicates homing pigeons use loft-specific infrasound for navigation. Journal of Experimental Biology 216(4). journals.biologists.com
- peer-reviewed Mack A.L., Jones J. (2003). Low-frequency vocalizations by cassowaries (Casuarius spp.). The Auk 120(4). doi.org
- peer-reviewed Freeman A.R., Hare J.F. (2015). Infrasound in mating displays: a peacock's tale. Animal Behaviour 102. doi.org