It sounds like your bird has two problems: 1) carsickness and 2) vomiting as a reaction to extreme stress.
The only reason why I know a bird can actually vomit as a result of stress is because my green cheek conure does it. I asked my vet last week if she'd ever heard of that before and she said no. However, there is no question that on a few occasions he has vomited from stress.
Once years ago we had to evacuate our apartment in the middle of the night due to a fire somewhere else in the complex and I put him in his travel cage and took him outside and within minutes he was vomiting. He vomited the whole time we were outside but eventually we were able to return to our apartment and when I put him back in his cage he stopped vomiting immediately. In the past 6 weeks I have had to take him to the vet multiple times and while he was good at first during last week's visit he started vomiting when the vet walked into the room (which he has never done before) and there's no doubt it was the stress.
He also gets carsick as well but like your Quaker he has in the past actually started vomiting when placed IN the car but BEFORE the car even moves. Sometimes he starts vomiting before I even start the car!
Regarding the carsickness there's a few things you can try: feeding ginger may help (although my bird wouldn't eat the ginger when I tried this). You can ask your avian vet to prescribe anti-nausea medication. You can try
Rescue Remedy Pet or
Avicalm and if the sickness is just due to nerves or stress it may prevent it. As a note I have tried all these things with no success but that doesn't mean they won't work for you.
marie83 wrote:In addition to the other reply, I would also try to desensitize his thoughts on linking the carrier to always traveling, practice taking him in and out with rewards and take him out before he has chance to be sick if possible, also you can work up towards letting him have a few of his meals in there. This way if he is linking the cage to being sick in the car it will hopefully weaken the association if you do it reguarly enough.
+1
The other thing you need to do is, as Marie suggests, try to break the link between the carrier and traveling. Yes, you'll still have to use it for travel but if you can get to the point where you usually use it
without traveling he'll probably stop getting sick upon seeing it (from stress).
At one point my conure would get sick when I just placed him in his travel cage (before I could even get to the car) and the way I eventually stopped this was to use the travel cage very frequently without taking a car trip. I'd just put him in it and give him a treat, and let him out immediately. Once he would tolerate that I'd put him in, give him a treat, leave him there for a few minutes, and give him another treat before letting him out. Now I take him outside 2 - 3 times a week for ~30 min. in the cage and he gets a small treat every 5 min. or so while he is outside in the cage and although he still gets car sick he no longer gets sick from just being in the travel cage.
If your bird is vomiting when he just sees the cage you're probably not going to be able to start by putting him in it and giving him a treat. You're going to have to determine how close you can put the cage before he vomits and then just put the cage in the room and give him a treat when he sees it but doesn't get sick. You can slowly put it closer and closer and then give him a treat for standing on top of it and eventually for being inside of it.