birding-aus

Re: Birds' eyes

To: Shane Raidal <>
Subject: Re: Birds' eyes
From: James Davis <>
Date: Fri, 27 Mar 1998 16:33:58 +1000 (EST)
Shane: Has anyone identified any function for "hippus"?  Why only parrots?
Cheers, Jim

Dr. Wm. James Davis
e-mail 

> The regular fast opening and closing of the iris is called "hippus" and the
> best example of this in Aus birds that I can recall is the rainbow lorikeet
> but most lorikeets and other psittacine birds display hippus.  Unlike
> mammals the avian iris contains striated muscle which means they have more
> "control" over the pupil diameter.  They can probably alter the pupil much
> in the same way we wink.  
> 


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