I apologize but most of the answers here seem to be missing the very straightforward reason. Let's start with the estimates that say the stray dogs:human ratio is about 1:36 in India (I am assuming the question pertains to observation in India). read more
Also, this behaviour is not limited to rag-pickers. Stray dogs sometimes bark at or chase delivery guys who carry a big bag with them. Like this. read more
Interestingly, dogs without a home (sometimes known as stray dogs) are more likely to chase cars than dogs with a home. The reason for this is training - or lack thereof. If a dog has never take a ride in a car, they are more likely to see the moving vehicle as pray or as a type of game. read more
The fetching game that the dogs find entertaining is inclined towards this particular prey instincts and this is true with dogs chasing cats, kids, squirrel and other dogs. Sometimes out of boredom the stray dogs chase something that is getting away from it playing an exciting game to pass the time. allindiaroundup 2. read more