Before revision:  Long-range correlations and limited speed fluctuations set conflicting constraints on the mechanism controlling the individual speed of each bird, as the factors boosting correlations also tend to amplify speed fluctuations and vice versa.
After revision:  Long-range correlations and limited speed fluctuations set conflicting constraints on the mechanism controlling the speed of each bird, as the factors boosting correlations also tend to amplify speed fluctuations and vice versa.