Hi,
I, own a border collie that is a shadow chaser, acquired in 2006 at 3 years old, from a rescue centre. He is obsessed with shadows which mesmorize him in much the same way as a sheepdog with too much eye. The main difficulty is getting him to focus on me and not on the shadows. My dog was left all day in his previous home for 10 hours a day during the working week and I agree that the habit might have been a way of occupying himself when home alone. At some point, he has been well trained, so he probably did not always have this problem of lack of focus. I think that the shadow chasing could well be a coping mechanism when he is overwhelmed or in an unfamiliar environment.
Some beleive that the dog has been teased with torchlights or children's toy flaming swords and encouraged to chase the light and that it is a learnt behaviour. However, I have met other people with border collie shadow chasers that they have owned from puppies who can confirm that their dog has not been encouraged with torchlights, etc.
Car travel is problematic. When the car is stationery, he is quiet but as soon as the vehicle moves he barks continuously and tries to shadow chase as the light moves around the car. The noise is deafening and it difficult to do much about it because I have to concentrate on driving.
Originally, I had a plan to distract him by long walks and agility but the latter has not proved possible because of a leg injury that means he must not engage in high impact exercise. He has had two sheepdog assessments by experienced shepherds who both describe him as 'quirky' and exceptionally nice natured. He is naturally submissive and lacks confidence with other dogs apart from puppies and dogs he knows really well. Unfortunately, he is too nice and not assertive enough to make the grade as a sheepdog, an activity that I had hoped might distract him from shadow chasing.
I would be interested