Scientists Track Homing Pigeons with GPS

How do homing pigeons find their way?  Scientists are still not sure.  They know that the birds use a sun compass and magnetic fields, but what other cues guide them back to the specific roost they know as home?  A new study shows they are smarter than we thought.  They use multiple cues and weigh the reliability of conflicting ones.  Oxford scientists reporting in PNAS¹ tracked the birds with GPS and found some surprises – and more questions.
    The team outfitted 32 birds with 28-gram GPS loggers on their backs, attached to clipped feathers with glue and velcro.  As a control, they made them do training flights with dummy weights.  Some birds were very familiar with the route; others were novices.  This allowed the researchers to contrast the influence of landmarks (piloting) with compass-guided flight.  They tracked the flight paths on courses up to 10.6 km.
    Once the birds learned the way, the experimenters played tricks on them with sun-shifted release times.  They kept the pigeons in light-tight chambers for a week where the sunrise and sunset times were shifted by 4 hours, corresponding to a 90° shift in sun position.  They found that even when these jet-lagged birds started off perpendicular to the correct orientation, they quickly found parallel routes to the targets.  The scientists concluded that multiple cues are weighed by the birds when they encounter unexpected conflicting information.

Thus piloting birds continue to maintain memories of, attention to, compass information even after they apparently have the sufficient and necessary route-based information homeward guidance.  While it is possible that such compass memories are, and have always been, associated with representations of familiar visual landmarks as hypothesized here, also possible that they originate from an initial, and now residual, olfactory navigational map.  In addition, a potential role for magnetic compass acting as a backup to the sun compass when solar and landmark guidance cues are put in conflict (although apparently not otherwise; see ref. 9) still remains to be explicitly investigated.  Either way, our results clearly indicate that birds combining multiple sources of onward guidance information during the local homing task.  Both the origin of this compass information and the function of its integration with landmark guidance remain to be elucidated.

¹Biro, Freeman, Meade, Roberts and Guilford, “Pigeons combine compass and landmark guidance in familiar route navigation,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0701575104, published online before print April 23, 2007.

Homing pigeons have fascinated humans for thousands of years.  How do they do it?  Here we are in 2007, still trying to figure it out.  The birds are not just robots with a compass.  They have the ability somehow to choose what cues to follow when they are in conflict.  There’s more going on in a bird brain than we can fathom.  The “origin of this compass information” doesn’t really need to be elucidated (if by that they think a Darwinian answer is in the wings).  They know where it came from.  In plain English, design reveals a Designer.  Make sense e’en to Pidgin speakah.