White-winged Choughs (Chough is pronounced
chuff) are birds of dry open eucalypt forests and woodlands. Highly social
birds with fascinating group behavior they spend much of the day fossicking in
ground litter for food. At this time of year the young are out of their large
mud bowl nests, following the adult birds of their extended family group about,
begging incessantly to be fed.
The white patches on their wings are only
visible when the wing is opened in flight or when displaying or grooming.
An adult White-winged Chough - note white wing panels in flight feathers. |
Adult choughs have a red eyes, the iris is
orange, while young birds have a brown iris.
Adult bird excavating hole in soil under ground litter to uncover insect larvae. Note the red eye. |
The choughs on our property are used to
humans and are quite confiding, allowing close approach for observation and
photos.
I have noticed in the past that the red eye
of adults sometimes appears larger than normal and until now had not given it
much thought or looked closely to see how this is achieved. Choughs are highly
excitable birds sometimes responding to disturbances within or external to the
group by spreading their wings, fanning their tail and also by enlarging their
red eyes.
The following two enlarged shots show first
a calm bird feeding with normal eye appearance and then an excited bird with an
enlarged red eye.
Enlarged photo of adult bird from feeding shot above showing close up of head and the normal elliptical eyelid position of a calm bird. |
One field guide states that the outer eye
ring flushes brighter red giving the impression that there is a colour change
to the eye. The above photos show that rather than the eye changing colour, the
bird achieves an enlarged red eye by uncovering the eye by expanding the
surrounding eyelid. The eyelid is normally held in an elliptical shape and is opened out to a circular shape when the bird becomes excited.
The field guides describe a red eye and from a distance the eye does appear to be red however on closer examination the iris is orange and the surrounding eye ball is pink.
If you have ever wondered about the Chough’s
expanding red eye, now you know how it is achieved. For those readers who
already knew this I hope you enjoy the photos.
Another really interesting post. Hasn't digital photography changed some things about birding?
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