Interesting paper and coverage in New Scientist:
Voelkl et al. (2015) Matching times of leading and following suggest cooperation through direct reciprocity during V-formation flight in ibis. PNAS, doi: 10.1073/pnas.1413589112
http://www.newscientist.com/article/dn26895-formationflying-birds-swap-places-to-share-out-lift.html?utm_source=NSNS&utm_medium=SOC&utm_campaign=twitter&cmpid=SOC%7CNSNS%7C2014-GLOBAL-twitter#.VNCf59KsUrV