Mathematical analysis of the homing flights of pigeons based on GPS tracks
At the RIN 11 Animal Navigation Conference Ingo Schiffner, presented a paper: Mathematical Analysis of Pigeon Tracks, characterisation of the underlying Navigational Process and now he has produced another paper covering Mathematical analysis of the homing fights of pigeons based on GPS tracks. For me, this work begins to create an underlying mathematical basis for the ideas that all navigation requires as much information as possible, from as many resources as are available at the time. Besides, the information required for navigation changes over the course of the journey. Setting out in the right direction initially is wholly different from the information required nearing home.<<<
Pigeons are the masters of navigation, not only can they home with pinpoint accuracy, but they also have one of the most robust navigational systems. Today it is fairly well understood, that the pigeons navigational system is based on two components a map and a compass. While the compass is very well understood, i.e they have an innate magnetic compass and, as juveniles, learn to use the sun as a compass, we know very little about the components that make up their navbigational map. After all a compass is utterly usless without a map. In the course of the last century a great number of different navigational cues have been proposed as the sole navigational cue explaining why pigeons are capable of such extrordinary navigational prowess. These include cues such as visual cues (vision), olfactory information (smell), infrasound (hearing), but also cues which may seem a bit odd seen from a human perspective, such as magnetic cues and gravitational cues. While their is good evidence for any of these cues of some involvement of all of these cues, no single cue seems to be sufficient to explain it all. To test the involvement of these cues, scientists have gone to great lengths to deprive the birds of any of these cues. That means pigeons have been spun on disks to disturb their gravitational sense, had their nostrils anaesthetised to deprive them of olfactory information, had their beaks anaesthesised to deprive them of magnetic information, had to wear frosted lenses to deprive them of their sense of vision, just to name a few. One common result of all these experiments, however, was that the pigeons- in the end – managed to get home to their loft.
In the current study we revisited the idea of depriving pigeons of some of these cues, nameley their magnetic and olfactory sense and record their flightpaths using GPS recorders – technology that wasn’t available at the time when most of the original studies had been conducted – and used state of the art analytical methods derived from dynamic systems theory to not just look at the flightpaths, but reconstruct the underlying navigational system, through the so called method of time lag embedding. This method then allowed us to calculate the short-term correlation dimension, a variable that reflects the degrees of freedom and thus the number of factors involved in the navigational system. While we were not able to show an involvement of the upper beak -as suggested earlier- in magneto-sensing, we were, however, able to show that natural fluctuations in the earths magnetic field had an significant effect on the number of factors used for active navigation. Additionally we were able to show an significant involvement of olfactory factors in the navigational process as well, as well as interactions between olfactory and magnetic factors. All in all our data suggest an simultaneous involvement of magnetic cues and olfactory factors during the homing flight of pigeons and point to a robust, multi-factorial map that incorporates not just one but possibly many of the cues previously suggested to p[lay a role in pigeon navigation. With this knowledge the earlier findings, i.e. the very weak effects of any of the above mentioned deprivation experiments, don’t seem so damning anymore. If pigeons indeed rely on many of these factors they could work as independent layers of redundancy allowing the pigeons to voluntarily include or exclude factors from the navigational process and thus achive a robust system that is impervious to environmental changes.