Sexing Red-tails by the sub-terminal band?

posted by Jerry Liguori at
on Tuesday, February 4, 2014 

Does that title capture any attention? Well, I've been looking at ways to sex adult Red-tailed Hawks by plumage since the late 1980's, and guess what....YOU CAN'T! I checked thousands of adult Red-tails from the East and West and came up with some differences, but they don't hold enough water to make even a half-definitive statement about sexing -- did I waste all that time or what? What I found I will share anyway for fun. One thing to remember, when you have a bird in-hand, size is evident, so if tail patterns match with the smallest or largest individuals, it lacks great significance anway, but if it's a bird in flight or a bird in a photo, it could be fun to notice tail patterns. 

I looked at the width of the sub-terminal tail band on adult Red-tails as well as the darkness to the red color and found that the smallest Red-tails (ones that take 7A bands and weighed under 900 gms healthy) tended to have broader sub-terminal bands and darker reddish tails than "large" Red-tails (weighing over 1200 gms and requiring 7D bands). The real issue (besides overlap in these traits) is that most Red-tails fall between these measurements and show a sub-terminal band intermediate in width! Another issue arises when comparing light-morph to dark-morph birds, birds from different geographic locations, or factors that could effect tail color (fading, etc.).

By the way, there is overlap in the sub-terminal tail band width of adult male and female Swainson's Hawks as well, so do not use that trait on its own to sex Swainson's Hawks, especially when sexing dark-morph birds! I should also mention that there is a paper on sexing Western Red-tailed Hawks using a combination of measurements authored by Kara Donohue that you can download here:

 Presumed male Eastern
 Presumed male Western
 Presumed female Eastern
  Presumed female Eastern
Anonymous Anonymous said...

Interesting as always Jerry. Is there anything you haven't studied? I love the blog, please keep it going.

Dave C.

February 4, 2014 at 3:27 PM  
Blogger Jerry Liguori said...

Thank you Dave

I plan to blog until I run out of things to say....

February 4, 2014 at 3:29 PM  
Anonymous Anonymous said...

Jerry, why do you caution "especially dark morph birds" when sexing Swainson's Hawks? Can they really be sexed by the band on the tail?

February 5, 2014 at 6:13 AM  
Blogger Jerry Liguori said...

Anonymous - There are average measurements for the sub-terminal tail band width of Swainson's Hawk, but there is overlap as well and dark birds tend to have broader bands than light birds so dark males will fall into the female measurement fairly often. It is similar to plumages of adult Swainson's, there are general differences between adult male and female, but plumage overlaps. It's like trying to age female Kestrels based on the width of the black band at the tail tip, the overlap is too great! That is why I ignore previous literature at times until I have studied something in depth myself.

February 5, 2014 at 6:31 AM  
Blogger Bryce said...

Interesting and useful. Thanks for sharing.

February 5, 2014 at 11:36 AM  
Anonymous Hatem Gomaa said...

Damn red tails! This species never makes it easy, does it? So Jerry, if you have a photograph of an adult (and it's probably easier with eastern birds) and you noticed the sub terminal band is pretty narrow, what's the percentage that it's a female? And vice versa, if it's slightly wider, what percentage would you say it's a male? Would it be going out on a limb to say "75% chance that bird is a male"? Or is it best to just stay the heck away from that?!

I also noticed some of those western birds that have heavily banded tails have a very wide sub-terminal band, compared to say the eastern birds. Does that sub-t band width for Carulus aslo follow the "tentative" rule of wider = male and narrower = female?

February 6, 2014 at 3:03 AM  
Blogger Jerry Liguori said...

I wouldn't say a % because even though I looked at a good number of birds, there are a million Red-tails out there, so any number I give would be misleading

February 6, 2014 at 7:23 AM  
Anonymous Hatem Gomaa said...

Chucks! You're too smart for our own bad.

February 6, 2014 at 5:27 PM  
Anonymous Ron Dudley said...

Yes, that title did "get my attention"! I was hoping for a magic bullet...

But I came away impressed with your logical thought process and your reluctance to jump to conclusions. Every time I visit here I'm more impressed by how well you know your stuff, Jerry. Thanks to you there's hope that I will eventually get red-tails figured out to some small degree...

February 19, 2014 at 5:26 AM  
Blogger Jerry Liguori said...

Thanks Ron....that is a nice compliment, especially coming from you.

February 19, 2014 at 7:22 AM  

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