Zebra Finch growth.

Question
I have a three zebra finches and one is the father of the two.  Karl has a growth on his back, right above where his little hip would be, it started in the summer and I wasn't worried but now it seems to be bigger.  He is about 7 years old, is acting fine, grooming, eating, drinking, normal poop, not aggressive.  He can move and fly around perfectly fine and I was wondering what your opinion would be.  It is very traumatic to try and take him to a vet.  I live in the country and the closest bird vet is 45 minutes away.  I do not believe he is suffering but if you believe it may be serious than I can try and take him.  I do not want him to be suffering!
Thanks,
Samantha and Karl

Answer
It's hard to say what it may be. If it's hard getting to a vet then you may not want to bother, seven is old for a finch considering the average lifespan of a finch is 5-6 years. If it isn't bothering your birdie in any way I wouldn't worry about it too much.