The above image was taken from my car at almost minimal focus distance without disturbing the Black Drongo.
After constant effort and analysis, I learned that birds are not scared of Cars/Closed vehicles. They allow the vehicles to be as near as 4-5 feet.
I shot this shot from car (from road) without getting down http://www.indianaturewatch.
When they see humans even near 15-20 feet, birds fly away but not when in vehicles.
So if the place is approachable in a vehicle, better to go as much near as possible in the vehicle.
Please also make sure the environment is not spoiled due to the vehicle ride and enjoy some good full frame shots.