If they are touching the tip of the syringe. I would not use the same one for each bird. I would use separate syringes for each bird and a clean one for each dose after cleaning. Or just use once and toss disposable. If you are treating for something highly contagious. I would use once and dispose.
Agreed. I will reuse syringes when I am worming, I don't have any illness in my flock. If I had, or suspected that I was treating something viral or bacterial, I would not reuse between birds. Better safe than sorry.