Before revision:  Numerical simulations of self-propelled particles flocks in the same size range as the empirical data fully support our theoretical results . The match of field empirical data , theory and simulations over such an extensive range of sizes suggests that the novel speed control we propose is the most economic theoretical mechanism able to reproduce all key experimental traits of real flocks .
After revision:  Numerical simulations of self-propelled particles in three dimensions. We validate the theoretical as well as the numerical predictions of this analysis by comparing our results with field experimental data on starling flocks having group sizes spanning an unprecedented interval of over two orders of magnitude .