private void giveBirth(List<Actor> newBears)
    {
        // New bears are born into adjacent locations.
        // Get a list of adjacent free locations.
        Field field = getField();
        List<Location> free = field.getFreeAdjacentLocations(getLocation());
        int births = breed();
        for(int b = 0; b < births && free.size() > 0; b++) {
            Location loc = free.remove(0);
            Bear young = new Bear(false, field, loc);
            newBears.add(young);
        }
    }