A little greenery?

  

This morning (20 December 2020) a large flock of Pine Siskins (Spinus pinus) was feeding on sweet gum seed pods in our front yard.  I'd estimate there were ~30 individuals, so it was a good opportunity to look at color variation.  

Because so many siskins have been coming to our bird bath this fall, I'd been noticing that there's quite a range in how much yellow there is on each bird — some are primarily brown with barely any yellow visible, while others have bright yellow in the wings which is apparent from a distance.  I had been wondering about this variability (e.g., does color vary with age, or whether the birds are male or female?), when I read that there is also a "green morph" — although rare, some siskins show much more yellow/green coloration.

Today I was taking advantage of being able to look at a lot of siskins up close.  I was taking photos of different birds from different angles.  There was a variable amount of yellow in the wings (some were more buffy than yellow), but most had brown backs:

 

 

 

 

 

And then I noticed this bird:

 

 

 

 

The base color of the back feathers was noticeably yellow/green rather than brown.  The yellow in the wings was extensive and bright:

 

 

 

 

 

The brown streaking on the underparts wasn't as prominent, and the yellow appeared along the sides and on the undertail coverts, too:

 

 

 

 

Based on what I've read, this individual probably matches the description of a "green morph" Pine Siskin.  It's not known whether this color variation is based on genetics or environmental factors (e.g., diet when the birds are molting).  If you're seeing siskins in your neighborhood this winter, it might be fun to watch for greenish individuals: