Kyriakopoulos, NikosGinelli, FrancescoToner, John2016-07-272016-07-272016-07-20Kyriakopoulos, N, Ginelli, F & Toner, J 2016, 'Leading birds by their beaks : the response of flocks to external perturbations', New Journal of Physics, vol. 18, 073039, pp. 1-14. https://doi.org/10.1088/1367-2630/18/7/0730391367-2630http://hdl.handle.net/2164/6266Acknowledgments We have benefited from discussions with H Chaté and A Cavagna. We acknowledge support from the Marie Curie Career Integration Grant (CIG) PCIG13-GA-2013-618399. JT also acknowledges support from the SUPA distinguished visitor program and from the National Science Foundation through awards # EF-1137815 and 1006171, and thanks the University of Aberdeen for their hospitality while this work was underway. FG acknowledges support from EPSRC First Grant EP/K018450/1.141022396engactive matterflockingresponse theoryemergent behaviorrenormalization groupQC PhysicsEngineering and Physical Sciences Research Council (EPSRC)EP/K018450/1QCJournal article10.1088/1367-2630/18/7/07303918