[penly]

I have a 4 yr old female Hahn's and a 2 year old female Caique. They both get along fine with other birds but do not like each other. They both can get very jealous when I give attention to the other. Maybe that is what your Caique is reacting to. He may not want to share. I find most birds will be mean to the person they love the most if they are unhappy about something. Caiques are very smart sensitive birds. So is the Macaw.
How old are they? If either or both are @ 2 years old they are reaching sexual maturity and can be moody and bitey. My Hahn's is very cage protective and will bite if you mess around inside her cage. Once she is out she is always sweet. My caique can be snappy and possessive regarding certain toys.
Have the birds had health checks? Sometimes health problems cause bad behavior.
You have to watch them and observe what sets him off and makes the Caique bite.
It is not an easy question to answer without more information.
One thing I can say for sure is, they are two birds with totally different personalities. They couldn't be more opposite.