In their comment on our work (ArXiv:1912.07056v1), Cavagna \textit{et al.} raise several interesting points on the phenomenology of flocks of birds, and conduct additional data analysis to back up their points. In particular, they question the existence of rigid body rotations in flocks of birds. In this reply, we first clarify the notions of rigid body rotations, and of rigidity itself. Then, we justify why we believe that it is legitimate to wonder about their importance when studying the spatial correlations between speeds in flocks of birds.
@article{arxiv.1912.09202,
title = {Reply to "Comment on "Velocity and Speed Correlations in Hamiltonian Flocks"},
author = {Mathias Casiulis and Marco Tarzia and Leticia F. Cugliandolo and Olivier Dauchot},
journal= {arXiv preprint arXiv:1912.09202},
year = {2019}
}