Hunted a cattle ranch years back... Birds would gobble at the quads and UTV's...
I also noticed that birds would ignore trucks, quads, etc., as long as they did not slow down... If the vehicle stops, the birds will make haste.
If you go to an area that does not have much vehicle traffic, I do feel that especially quads/UTV's will have a more severe effect though. Cattle ranch with regular vehicle traffic, birds that run off initially will answer a call within 20 minutes or so....
Funny story... Hunting a bird on a cattle ranch... Birds were across a small jeep road coming right at me, and I see a ranch hand driving towards me on the jeep road (I am sitting against a tree along the road).
Tom with a hen are coming my way, with the hen leading the way obviously upset at my calling in her territory... Maybe 60 yards and closing. I am thinking that if the truck does not stop, it will not affect the situation.
Truck stops right in front of me, literally between the birds and myself, and the ranch hand gets out of the vehicle (so I know the jig is up). I assumed it was to talk to me, and as I sat there contemplating my poor luck, the driver walkd around to the back of the truck... At which time I stood up and said "Hello there."
He about had a heart attack... I think if he would have had a gun he would have shot me! Apparently stopped there out of pure coincidence and had no idea I was there. And he stated "I thought you were a dead body attacking me!"