My male cockatiel is about 2 years old and really enjoyed mirrors when I first got him. He still loves them but now he is acting differently. He is now hopping around looking at his own reflection, and sometimes sings to himself, what does this mean?
(He is also with 2 different other species of birds so I don't believe he is lonely)
I do not believe in most cases that being with other species equals not being lonely....
I have 3 lone/single male birds all of different species (macaw, sulfur crested cocky and a budgie) and not one of them has any interest at all in the others but when I play videos or even just the sounds of their own kind all of them change automatically and become interested in where that bird is, they even call out to the bird on the screen and become excited, I believe this is because they speak the same language as birds the same species as them but body language and vocals of other species are basically like you trying to understand a language you have never heard before.
If he is getting desperate or wound up (like it sounds like he may be) then the mirror is not a helpful thing, it is a thing of frustration. I have seen birds who do well with a mirror and I have seen birds get frantic because of a mirror- most birds do not understand what a mirror is, they seem to think the bird in the mirror is leading them on or is defective and it causes frustration and annoyance. The description you give about your bird with the mirror suggests to me that he is maybe desperate for communication with his own kind and the mirror bird is tormenting him by not responding as a real bird would.