Can Bird Twitter Using Different Sound?

Saw this bird hang out around my company for many months twittering for someone
I guess he is twittering for the bird infront of the mirror.
Which is himself XD

I have heard a lot different sound from the same bird.
This proof that bird do twitter differently like us~!
Do follow my twitter @TianChad

Getting new on twitter and need you guys to teach me how to use it ;p
How do you read twitter message?
Through Website? PDA? Handphone?
And what software do you use?

Thanks in advance~
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Two days left!