An interesting example of sexual dimorphism in eye-colour, in this case
coupled to many other differences, is the Ferruginous Duck Aythya nyroca in
Eurasia, by the way also a crepuscular species. Here the dark brown males
have a conspicuous white eye (the species is called Witoogeend (=White-eyed
Duck) in Dutch), while the duller brown females have dark eyes. Of course
in ducks, where the males display and compete for females and thus need to
be conspicuous, and the females breed on the ground, and thus need to be
inconspicuous, such a difference is easier tio understand.
Eye-colour is always a most fascinating subject. I have earlier inquired
on the possible reason why so many Australian birds have white eyes or
eye-rings (many more than here in Europe), but at that time did not get any
answers at all. Several of the white-eyed species have dark eyes when
immature (a good example here in Europe is the Jackdaw Corvus
monedula); this may be to curb aggressiveness towards the younger birds in
the adults, maybe?
Questions are easy, answers much harder.
Wim Vader, Tromsø Museum
9037 Tromsø, Norway
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