I don't know if this was mentioned by anyone yet, but you shouldn't have them in the same room for the first 30 days anyway, as the new bird needs to be quarantined in a totally separate room for the health and safety of your first bird. Not only is this the standard quarantine protocol for whenever you bring home a new bird and you already have a bird (so you don't infect your current, healthy bird with anything that the new bird might have that is airborne), but also because this will provide a buffer and time for your first bird to adjust to the idea of another bird being in your house...
By just putting the new bird in the same room as your first bird right off the bat the way you did, you've totally invaded his "safe space" with a new bird that he doesn't know, and now this new bird is in his territory. Parrots are extremely territorial, and your first bird is now feeling jealous, angry, and extremely possessive of BOTH HIS HOUSE/ROOM/CAGE AND OF YOU! That's why he's biting you, he's trying to "protect" you from the new bird. That's a very common reaction for them in this situation, and the way to avoid stressing him like this is to slowly ease the new bird into "his" house, his room, his family, instead of just putting the new bird down in his room and going "okay, here's your new friend. Love him!". That typically doesn't work out well, as you're finding out, and forgetting his reaction to the new bird, more importantly you're putting his health at risk by putting them together in the same room right away...
***Just an FYI: Even if the breeder, pet shop, or prior owner that you got the new bird from gave you a "Health Certificate" with him or they told you that he was taken to an Avian Vet for a "wellness exam" and he "checked out fine", that still does not EVER eliminate the need for a full 30-day quarantine for any new bird you bring home in a completely different room of your home from your current bird(s). The reason for this is because as I'm sure you know, all birds possess a natural, innate survival instinct that enables them to hide any and all outward signs and symptoms of illness, injury, pain, etc. for as long as they possibly can, up to several months to even a year or more depending on what the illness/disease is. As a result, we as people usually do not have any idea that our birds are sick or in pain until they've already been infected and actively sick for months. And even a Certified Avian Vet can't tell if a bird is actively infected with a bacterial or fungal infection, a viral infection, or any number of serious diseases which are contagious and airborne, as the bird will be displaying no outward signs or symptoms, and they sometimes can even hide regular, bodily responses to illnesses to some point. So the bottom-line is that unless the Avian Vet actually runs multiple cultures (fecal, crop, sinus, etc.), does routine blood-work including a CBC, Chem7, Coag, and liver/kidney functions, etc., they have no way of knowing whether a bird is suffering from an active infection or whether or not they currently have a disease that is contagious to your current bird. And during a routine "wellness exam" that pet shops and breeders get done so that they can give customers a Health-Certificate, they don't typically do ANY diagnostic testing at all due to the cost, unless the customer buying the bird specifically requests them and is paying for them up-front.
**So it's extremely important that you get the new bird in a totally different room from your current bird ASAP, and keep him there for 30 days, until you will have had at least a chance for outward signs/symptoms of the new bird being ill with an infection or contagious disease to show-up. This will not only keep your first bird from contracting any active-infections and/or diseases that the new bird may have, but in this particular situation it will also give BOTH BIRDS time to adjust to this new living/family situation. Your first bird is most-likely extremely stressed-out right now because the new bird just suddenly appeared and took up residence in "his" room and with "his" person/people, so he needs to be slowly introduced to this new arrangement, as does the new bird as well. Usually it's the bird that was already living in the home and not the new bird that has the most issues with this, because they have already established their territory, and now the new bird is invading it. But honestly the risk of spreading any illnesses to your first bird is the biggest reason to ALWAYS do a 30-Day Quarantine with any new birds your bring home in a totally different room and behind a closed door if possible.
Just as a side-note, there are some extremely nasty diseases that birds can pass-on to each other, of course the big one that always comes to mind first is PBFD, and then you always have to worry about Chlamydia/Psittacosis. But it typically isn't the "big" fatal diseases like these that usually get passed-on from a new bird that is brought home and not quarantined in a separate room from any current birds, it's the bacterial, fungal, and viral infections that are very common and actively passed around aviaries and the homes of breeders if they aren't responsible about things like sterility, which you'd never know, and of course pet shops are a nightmare...There are some extremely serious bacterial and fungal infections that are HIGHLY CONTAGIOUS AND AIRBORNE, and that are often fatal even with immediate medical treatment by a CAV...The one of these that comes to mind immediately is Aspergilliosis (upper respiratory infections and lung infections in-general are extremely common in this situation).
You can't do anything about your new bird already having an active infection or disease, all you can do about that is get them to a CAV immediately upon seeing any outward signs/symptoms that he's sick and get him diagnosed and treated. HOWEVER, you CAN prevent your healthy, happy bird that you've had for 4 months already from contracting anything that this new bird might have. So please, move the new bird's cage into a totally separate room of your home that has a door that can be shut, or if that room is the only one with a door that can be shut then leave the new bird in there and move your first bird out of that room and into another area of the house. This will help your biting issue as well, because he's going to hear the new bird and he already knows that the new bird is in the home, but this will allow him to get used to the idea, and they will no-doubt start talking back and forth to one another even though they can't see each other. This much more gradual approach to introducing the new bird will go much more smoothly than just putting the new bird in the same room as him did last night.
