What I don't understand is:
-putting bird in a cage on the seat. Bird is high enough to see out the windows. Bird gets enrichment from seeing trees and people and whatever else is out there. Bird is a little bit safer in a crash. If seatbelt is around cage then a little bit safer still. Bird is near owner so feels good! Bird is restrained if it displays an unexpected or new behaviour. Carrier may pop and lead to escape anyway.
Bird loose in car- bird is high enough to see out windows. Bird gets enrichment from scenery/people outside car. Bird is near owner so is happy. Bird is at higher risk of injury or escape from a crash. Bird may distract driver- just once is enough. You can never 100% predict animal behaviour. If your driving and concentrating on the road then your not watching your birds body language and are even less able to predict the unexpected.
Both methods have the same benefits but only one reduces the negatives.
There are no benefits to having your bird loose while the car is in motion. Stationary is a different matter and I do have Ollie out when parked up.






