A homing pigeon carrying a GPS sensor and an accelerometer to detect motion. Photo credit: Lucy Taylor.
Each homing pigeon embarking on a lengthy homeward journey is following in the wingbeats of the human tradition of pigeon keeping dating back thousands of years. Equipped with internal compasses for guidance, young pigeons gradually build up a picture of the terrain surrounding their loft, which they eventually call on when displaced further. However, Dora Biro and Lucy Taylor, from the University of Oxford, UK, were curious to learn more about how pigeons build confidence as a route becomes more familiar. ‘When I think about how I move when navigating, I move differently if I am not sure where I am going compared to when I am walking a known route’, says Taylor, adding, ‘We imagined the same may also be true for birds’.
Teaming up with biomechanics expert Steven Portugal, from Royal Holloway, University of London, UK, Taylor and Biro attached accelerometers, which detect motion, coupled with GPS sensors to young pigeons to monitor their wingbeat patterns and routes as the aviators became increasingly familiar with the return journey home from two locations, 3.85 and 7.06 km away. ‘The pigeons were very cooperative’, says Taylor, recalling that they were content to be held while the motion sensors were secured to their backs before being released individually. However, Taylor had to be prepared for the notoriously unpredictable British summer. High winds, cloud, rain and extreme heat can affect a bird's ability to navigate home, so Taylor was on standby for much of the season to catch the few days when the conditions were ideal and the team could fit in two homing flights per day. Then, having collected 200 acceleration readings each second during flights lasting 5 min up to several hours, Taylor was faced with the colossal task of synchronising over 48 million data records to build a complete understanding of each homing flight as the birds gained in confidence.
After analysing the immense data set, the trio was able to identify clear patterns in the pigeons’ behaviour. As the birds became more experienced, their routes meandered less and became more direct until they converged on an efficient flight path by the sixth return journey. In addition, the animals flapped their wings harder (their torsos bobbed up and down more) and increased their speed as they became more confident of their path. Summing up their observations, Taylor says, ‘Pigeons flap their wings differently depending on how well they know a landscape’, adding that early flights from unfamiliar locations are likely to be more energetically costly as the pigeons fly more slowly and take less direct routes.
Reflecting on the study, Taylor says, ‘We didn't know at the start whether the birds would flap differently depending on how well they know a terrain’, and she and her colleagues are now optimistic that their observations could help other scientists investigate how animals navigate. ‘[These] flight characteristics may be used as “signatures” of birds’ familiarity with a navigational task… that could be utilised to provide new insights, through non-invasive methods, into the decision-making and navigational strategies of birds’, says Taylor.
