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Variation between the male and the female

by Bob Sallinger

kgw.com

Posted on March 28, 2009 at 2:04 PM

Updated Wednesday, Nov 4 at 2:39 PM

Hawks day 2-27-07 026.JPG

Adults copulating 2007 by Dieter Waiblinger

Question: Can you tell us how we can determine the male from the female? We've noticed that one seems to have a "foo-man-choo", while the other does not. Is this so, or is this just our imagination?

Answer: Most of the time we are watching the female because she does the majority of the incubation. The easiest way to tell them apart when they are both visible on raptor cam is that the male is significantly smaller than the female. Red-tails have what we call "reverse sexual dimorphism"---a fancy way of saying that the female is bigger than the male. This is true for many raptor species. The females can be up to a third larger than their mates. The male tends to look kind of long and skinny while the female is rounder and more full bodied. There are also variations in the coloration between individuals. In fact red-tails have some of the greatest color variations of any raptor species. Their body feathering can range from very, very light to nearly entirely chocolate brown. These two birds have the most common color patterns found in red-tails with dark heads, light chest and a darker belly band. However their are subtle differences. For one thing the female appears to have more white on the back of her head than the male. I have not noticed the "foo-man-choo" described above, but keep watching an write in as you notice variations that will allow us to discern one from the other. This picture above taken by Dieter Waiblinger (who used to work in the office next to the nest) while the birds were copulating in 2007 demonstrates the size variation between the two birds and if you look closely you can can also see the female has more white on the back of her head.

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