What is green thin poop a symptom of?

[AlpineButterfly]

I have one hen who has been having thin green poop over the last week or so (photo below).
She is a 9 year old bantam Easter egger, and one of the smallest of the flock of five assorted hens. The other hens seem to have normal poop. She seems to be acting normally as far as I can tell, although may be thinner than normal.
What could this be a symptom of?

 

[Wyorp Rock]

The color of poop can vary.
If she's acting normal, then I don't know if I'd be too worried.

You can give her a basic check for lice/mites, see that her crop is emptying and watch to see that she's eating/drinking well.

Getting a fecal float to check for worms is another thing you can do.

At 9 years of age, she may process foods a bit differently. Yellow urates could indicate some liver involvement. She's lived a long time and hopefully has a few more years left in her.