In all honesty, I think the only way a person can tell if an animal has a autism-like condition is if they show truely abnormal behaviors. I've only read one animal story ever on this site where I strongly suspected the animal had a form of autism, and that was a cat and that was over a year ago.
If I had to draw up diagnostic criteria, they would be almost identical with the human criteria:
Does the animal display abnormal behaviors that have been present from very young? (This would exclude an adult getting a head injury or virus that creates off behavior.)
Does the animal display odd stereotopies (such as repeating a certain behavior over and over and over, for no known reason, and not caused out of mental deprivation or pain.)
Does the animal fail to display normal species-specific social regulatory behaviors or even ignore's another of it's kind (or a human) completely? Is he/she often attacked or shunned?
Does the animal react abnormally to environmental stimuli, either by engaging in a stereotopy or becoming abnormally transfixed?
Once engaged a stereotopy or by a certain stimuli, does the animal act abnormally aggressive if they are prevented from reingaging in that behavior?
This is by no means perfect, but I drew it up from what I remember the human diagnostic, plus I removed the parts that animals wouldn't be able to do anyway such as speaking. I also emphisized the stereotopies and abnormal behavior parts more because most times animals will act shy, and many breeds of dogs have some of their social regulatory behaviors bred out. Also arranging of objects might be a form of nesting behavior in species that normally do nesting. However it isn't normal to see a cat jumping back and forth for hours on end and most social species will not find an inanimate object more fascinating then their own kind. Also most of these would have tp be present from a very young age, as it would remove any likelihood of it being a 'copycat' behavior caused by deprivation or disease.
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Crispy Pickles!!