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Identifying Male from Female


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#1 GargoyleStalker

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Posted 27 August 2006 - 05:34 PM

Is there any good way to tell the difference between a male and female Blue Jay? All the ones I have studied at my feeders seem to have very little, if any, difference that I can tell to distinguish a male from a female.

I also have trouble telling the difference between a mature male and female Osprey. All the field guides I have read tell me that the female will usually have more brown streaks on her chest and will be slightly larger than the male. But I have a pair of Osprey that live in a nest on a cell tower near me that I am having trouble identifying. I can sometimes see the difference in their sizes if they are perched on the cell tower together but if they are alone, I can't tell one from the other. One seems to have a darkish chestband - not really streaks but more like a band - high up on the chest. The other one seems to have a less obvious chestband. Could this be the brown "streaks" the guides refer to on the female?

Thanks.

Still learning and loving it!

Susan



#2 David Lukas

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Posted 27 August 2006 - 07:21 PM

There is no difference between male and female Blue Jays. You might notice that the size and shape of the black bridle on the face varies between birds, but biologists believe that the jays use this for recognizing individuals not male or female differences.

Yes, the field guides tell you that you can separate Ospreys, but I seem to recollect that all the professional hawk watchers I've worked with (people who count migrating hawks for a living) say that those features don't actually work to separate the sexes and is unreliable. You might be able to do it based on size if you see the members of a pair perched together, but as you noted even that is difficult.

David Lukas



#3 joshc

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Posted 28 August 2006 - 09:49 AM

Although we can not distinguish male from female, the birds can.  They see ultraviolet light, and that is how they tell male from female.  Take the Blue Tit for example.  The crown and cheeks glow in ultra violet light, and the males are brighter than the females.  This is a picture modified to simulate what the tit sees. 

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#4 GargoyleStalker

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Posted 28 August 2006 - 06:55 PM

Joshc,

Great simulation! Maybe I should carry around an ultra violet light with me so I can identify the males and females, also!

Thanks for the reply.

Susan



#5 joshc

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Posted 28 August 2006 - 07:13 PM

Ya, that might work! 

And in Budgerigars, their feet and a patch on their cheeks glow.






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