pacing behavior

Question
I received a pair, both male, of cockatiels about five years ago.  they were friends.  At the time, I already had a cockatiel, another male, and I put all three in the same cage.  they have co-habited without inccident for the past five years.  two months ago, one of the two I received as gifts died.  Several weeks ago, his "friend" began rapidly pacing back and forth on his perch.  Other than that he appears to be fine, even making some overtures toward friendship with the third cockatiel...even though both the grays ignored the yellow until one gray died.  What does this behavior mean?  Thank you for your answer.
Sue  

Answer
Hi Sue,

Your sweet little bird is grieving..which is stressing him out a little bit,it's fantastic that he is trying to befriend your yellow bird now as this means he is starting to come to terms with his loss.
Just keep an eye on him and make sure he doesn't start picking his feathers obsesively or pulling them out this means he's severely stressed and you will have to take him to the vet for medication.