Budgie has turned up feathers

by mainsqueen
(Scotland)

I found a Budgie in my garden four weeks ago and she has been very quite. but has now started to scratch and pluck at her feathers her feathers are turned up at the neck area why is this,and she is very nervous of human contact but she is nosy and likes to watch me when i am on pc but when i turn to look at her she hides behind her cover