I have a great Shephard mix who chases lights and shadows incessantly. If I take him over to the off-leash doggie park, he will stare at the ground for a long long time and will prance onto shadows or flickering lights he sees on the ground. He is fully capable of doing this hours on end.

When the sun is not out due to overcast, or during his night time walks, he is a normal happy pup. Other times he is also distracted and will play normally depending on his 'mood'. Some times there is no way to take him away from that behavior.

Does anyone know what is causing this and if there is anything we can do to get him from taking these obsessive behaviors? He is such a nice dog and thoroughly enjoys playing with other dogs which is much healthier for him compared to the endless staring into the ground.

Thanks,
Martin