Feather arrays are patterned by interacting signalling and cell density waves by Ho, WKW, Freem, L, Zhao, D, Painter, KJ, Woolley, TE, Gaffney, EA, McGrew, MJ, Tzika, A, Milinkovitch, MC, Schneider, P, Drusko, A, Matthäus, F, Glover, JD, Wells, KL, Johansson, JA, Davey, MG, Sang, HM, Clinton, M, Headon, DJ