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Bird 1 - Intergrade - This HY (hatch year) male was captured summer of 2019 in Edness Kimball Wilkins State Park near Casper, Wyoming.

Note the two-toned malar stripe and red crescent on the nape. The face is a mixture of buffy and gray, though this will change some with age.

The orange rectrices (tail feathers) might be confused for red from a distance.

The red remiges (wing feathers) might be confused for reddish from a distance.
Bird 2 - Intergrade - This adult male is one of the parents of birds 1 and 3.

Check out the pattern of the colors on this malar! Bird 1 was black in front and red in back. This individual is red on top and black on the bottom! WHOA! Also, check out that buffy face.
Bird 3 - Intergrade - This HY female was captured summer of 2019 in Edness Kimball Wilkins State Park near Casper, Wyoming.

This face might not be enough to identify an intergrade. Which is why the next shot is so helpful!

Additional Intergrade - This male was captured summer of 2016 in Edness Kimball Wilkins State Park near Casper, Wyoming.

If you zoom in, you can see the black to red malar stripe. This individual does not show much of a red crescent.
All these individuals came from Edness Kimball Wilkins State Park in Casper, Wyoming. It seems highly likely, there are very few pure RSFL or YSFL in the state park any longer. Though, more study is usually needed to make such a bold statement!