Dave, thank you for your excellent comparison of markings, a fine discussion and the two helpful photographs. If I may further add to your description, as a falconer and someone who has worked with males and females of both species:
I've been told by several experienced raptor watchers who've seen the Ft. Collins gyrfalcon in person that it is a male. If the prairie falcon appears to be about the same size when looking through binoculars, or even with the naked eye, then it is likely a female. The healthy flying weight of a female prairie falcon is in the range of 27-30 oz. The equivalent for a male gyrfalcon ranges from about 32-37 oz. Two falcons so close in weight would almost certainly appear to be the same size when viewed perched on a pole, etc. My point being, this can definitely be a tough call if lighting and other conditions aren't ideal…and both falcons are very close in size. Good birding to all, ~Anne Price Littleton, JeffCo -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/CY4PR07MB2743B7A286CD98CFBF68C051CF100%40CY4PR07MB2743.namprd07.prod.outlook.com.
