One of our chickens died this evening. She'd been loosing feathers around her bottom for a week or two but no recognisable reason why - no pecking, no lice/mites etc. Also a bit sporadic on laying this last week (but again, not unusual as all young birds). Perky and happy running around the garden yesterday. This morning however she was hunched and not moving much; not eating or drinking. Left her for a bit then checked her over this afternoon - big squishy balloon-like crop so checked books and treated her for sour crop. Lots of fluid came out of her mouth - all pretty yukky. Popped her back in the run after but when we checked a couple of hours later she'd collapsed; by the time I'd got DH to go down in order to 'dispatch' her so not to let her suffer any more she'd died. 
Chicken experts amongst you - does this sound like just sour crop? If not, what else could it be? If it was sour crop, what typically causes this so we know how to avoid the others suffering similarly. Was there something else we could have done?
We've only had them a month but got very attached and DDs were quite distraught tonight. Can currently hear DD2 down the monitor talking to her toys about it in bed
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