My 17 mo old Australorp hen has all of a sudden gone listless. She is not eating, and spent most of the day sitting. She has yellow - white sticky poo covering her tail feathers. She walks only very occasionally, and very slowly. We have introduced some leghorn and rhode island red "teenagers" (well, 3 month olds now) about a week ago (they have been free ranging together for 2 months, but only recently gone in the coop). The australorp didn't go into the coop last night, but stayed outside underneath it. One of our 2 month old Dorkings got taken by a cat yesterday -- not sure if she was around that. They are on sawdust shavings in the coop, free range over about an acre of forest and grass, and eat an organic layer feed usually. There is some wet "grower" food on the grass, because we've bee moving the young one's coops around. Her crop seems normal. Any tips would be appreciated!