Create an empty GameObject and call it GameState and attach your TrackItems script to it.
Set the tag of the GameState object to "GameController" in the inspector.
Your feather object must have a collider set as a trigger.
Attached this script to the feather:
//get the itemTracking Script
var itemTracker;
function Start()
{
itemTracker = GameObject.FindWithTag("GameController").GetComponent(TrackItems);
}
function OnTriggerEnter ()
{
itemTracker.feathers -= 1; //subtract 1 from feathers in TrackItems
Destroy(gameObject);
}