What causes a taildragger to lift its tail during the takeoff roll?
Yes, when the plane exceeds a certain speed (known to the pilot!), the pilot then pushes the stick slightly forward and this lifts the tail off the ground. This reduces rolling drag and sets up the angle of attack of the wing for takeoff. For very powerful airplanes, the tail will sometimes come up on its own and surprise the pilot during the takeoff roll.
In some planes, the resulting angle of attack is enough that the plane will fly itself off the ground and begin climbing when it has picked up enough speed in the roll. In other designs, the pilot will wait for the right speed and then gently pull back on the stick to increase the AoA a bit and the plane then takes off.