s up symmetrically to 90 degree for µ 0, and closes symmetrically to the line /3 = a for µ —) co. In this last case, the mixed region disappears. Doebeli 1996, Nakamaru & Sasaki 2003), which is given by the payoff matrix H D H b / D 0 The two strategies are hawk (H) and dove (D). While hawks escalate