The bird

To test the atmosphere. Miners would take a caged bird into mines and if there was a lack of oxygen to breathe the bird would die or freak out first and alert the miners.

I don't believe the explained it. My take is that it was there for the traditional reasons of bringing a bird into a questionable space, which is to test the air for things that kill you.

The film also used the bird to enhance excitement, showing it jumping around more excited when things in the film were getting more tense. So in that respect, the bird was just a device.

I gotta say, I had a problem with the bird.
I understand that its intent was to telegraph atmospheric conditions to the scientists. But in this age of technology thats pretty silly.
But my main issue is that if the purpose of contact was for the humans to interact with the aliens in order to develop a codified language bringing along another communicating animal is simply foolish. How would they know that the bird and alien wouldn't communicate with one another better?
In addition, the hazmat suits weren't sealed, you can plainly see the two access holes for external respirator lines on the back of the suit in the beginning. I recently used a similar suit and they would not be appropriate in a condition like that. They should be using radiation suits which are pretty similar looking but sealed all around.
In terms of story though I liked the film.
Maybe one day we will have a phrase that will unite us all. "I love you" doesn't seem to have any "punch" anymore.
That you imdb for removing a forum that allows us to communicate with one another. Great job. I love you guys.

As others have stated, it was to make sure the air is okay to breathe. The characters did the same in Close Encounters of the Third Kind.