i have birds in my room aswell as a bonsai tree. i didn't even think that it might be dangerous until one of them landed on it after flying today

While I have not found anything on the bonsai tree in particular, there are many household plants that are very toxic to your birds. The link below has a good site listing many, many different kinds of toxic plants. It's good that you are wary of the possible affect that plants can have on your bird because many bird owners don't even think there could be a potential hazard! Some plants are so high in toxins that they can even kill your bird! (example is the Oleander) Now the bird COULD be a hazard to the tree... God knows how birds love to chew things, so you'll still need to watch them.

its just a plant... DUH! LOL, nothing will hurt a bird.. plus bonsai's arn't even that big. If anything the bird will kill the tree

Cocktiel's are normally very curious, especially with plants. Anything they see that they can possibly take a chew or two out of. Commonly, curious cockatiel's like to taste things, but I don't think you have anything to be afraid of with those type's of plants. On another note: It's not heard of that a Bonsi tree being toxic to birds. I believe you'll be fine. Below is a list that may help you out in the future!

Enjoy your cockatiel's. They're great pet's!