There's no place like home – no doubt a sentiment that any homing pigeon would agree with. These talented pigeons can be released far away from their loft and yet quickly develop, and remember, distinct homeward-bound routes. For many years, scientists have been releasing these intelligent birds individually to determine exactly how they develop these stable routes. While much progress has been made by these solo releases, Andrea Flack, a PhD student from the University of Oxford, UK, points out that pigeons ‘are clearly attracted to each other when they navigate and have a strong tendency to fly in flocks.’ So, with the help of Robin Freeman from University College London, UK, and her other two co-supervisors, Tim Guilford and Dora Biro from Oxford, Flack decided to see how well pigeons would learn to navigate in small flocks. (p. 1434)

First the team decided to test the navigational skills of pigeons released in the smallest flock size, releasing eight pairs of pigeons at a site 7 km away from their roost. ‘We suspected that pairwise-trained birds would behave similarly to individuals and that they would develop routes, but we didn't know how they would develop their routes, or whether they would develop them faster or slower’, recalls Flack. At first, it seemed as if the birds might not co-navigate home together, with the pairs frequently splitting up while homing. However, by the third release, the birds perhaps became less wary of their assigned companion and started to home together. After six releases the winged duos had established stable flight paths, which had, in the end, developed just as quickly as in individually released birds.

After the birds had settled into the habit of homing as pairs, the team then challenged the pigeon by increasing the size of the flock, releasing them with another pair. Flack explains that ‘If you pair up individually trained birds, then you find these interesting outcomes; sometimes one individual leads the other along its own route, other times they fly along a compromise route.’ Are birds trained in pairs as equally amenable to adjusting their routes when flying with others? The results suggest that training in pairs actually promotes compromise, with these birds flying along a middle-ground path more frequently than singly trained birds. Whereas individually trained birds will only compromise if their respective paths were less than 600 m away, pairwise-trained birds compromised even when the two routes lay at a distant 1.5 km away. Homing birds rely on landmarks to guide them home and singly trained birds might compromise when routes are within visual range of their guiding landmarks. Flack suggests that pairwise-trained birds may be more willing to compromise at farther distances by relying less on landmarks for reassurance and instead drawing comfort from the presence of their training partner. Certainly, when the team looked at how closely the four-birded flock flew, they did find that pairs stuck together and flew closer to their partner than to the other pair.

Despite overall increased compromise in pair-trained birds, some combinations did fall into a leader–follower pattern, with some pigeon pairs emerging more frequently as leader pairs. It is possible that these leader pairs preferred to lead because they weren't able to draw as much confidence from their partnership with the other pair, and still preferred to rely more on landmarks. Either way, regardless of whether the pairs compromised, Flack's study clearly highlights the important role that social bonds between birds play on collective decisions taken by flocks. This give-and-take attitude has its benefits, with the team finding that homing efficiency increases in flocks. So, sticking together is worth it!

Pairs of pigeons act as behavioural units during route learning and co-navigational leadership conflicts
J. Exp. Biol.