I came across a herd of elk shortly after sunrise at Grand Teton National Park last month as they were on the move. I quickly parked the car in a pull-off and started taking photos from just outside the car.
They came out of the woods and into a clearing and this group of cows, with a calf, paused for just a moment to get a look around to see if there was any danger in the area.
I only had time to get a few frames before they were off again. It is for situations like this that when I am traveling through areas that may have wildlife, my 150-600mm lens is on my camera and next to me ready to go. If I had to take the time to switch lenses in this situation I would have missed the shot.