Ever since yesterday, he has been screeching around night time. The thing is, he only screeches at one side of the cage. He would run to the left side of the cage, stick his beak out, and screech towards the kitchen. Then, he'd run back to the right side quietly, and a few seconds later, he'd run back to the left side. Is this normal behavior? Or should I be concerned? He also seems frightened. Should I move his cage somewhere else?

Welcome to the forum !

Have you moved his cage recently? Installed a new piece of furniture? Is there a draft? A toxic substance like an air freshener? A shadow that passes noticibly through the kitchen?

So many things to consider! If nothing at all has changed in his routine or the house then I would suggest you take him to an avian vet for a check up as out of character behaviour can be a sign of illness.

Better to be safe than sorry!

I agree with Von... if nothing has changed in his environment then there may be something wrong.
Also does he have food when he does this?

Is there anyone in the kitchen when he does this?

Keep us informed.

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When you say stick his beak out are you placing a cover over the cage at night? Some birds do not like to be covered. How long have you had this bird? How old is the bird? Any new toys in the cage? Like Von said even the slightest changes around the room the cage is in can really frighten a bird.

I don't think anything has changed in his environment. He mostly screeches at 7-8 PM when the cage isn't covered yet. We've had him for almost a week and he is about 6 months old. When he starts to screech, someone is usually in the kitchen. But the screeching also continues even if the person has left. There is food in his cage when he is screeching though. There aren't any new toys in the cage and the screeching only stops about thirty minutes after we cover the cage with a blanket. Also, yesterday, he pooped when he was scared and the color was green-ish white. I'm not sure if that's normal either.

If he's screeching because he can't see the person who's left the room but can see a bit of the kitchen and knows that's where they've gone, it's the beginning of bonding lol. It's also common for conures to screech when someone comes back inside the room.

Birds like to know where their "flock members" are at all times!