Variation in Pine Siskins and the so-called “green morph”

Pine Siskins – streaky relatives of goldfinches – are so distinctive as a species that we tend to overlook their considerable individual variation. Siskins are unusual among the small finches in that males and females look nearly identical. Subtle individual differences in the amount or intensity of streaking, or in overall color, have no bearing on identification and we simply blend them all together in our minds as “typical siskin”. They do show one infrequent variation that is quite noticeable, however, the so-called “green morph”.

A lot has been written about the “green morph”, and a good recent summary with photos and links is by Mandelbaum and Young. They end with a statement of uncertainty: “Whether green morph Pine Siskins represent a true “morph,” aberrant plumage, or simply the result of variations between individual birds is a question open to further study.”

Looking carefully at the flock of siskins that frequented our feeders in Deerfield, Massachusetts this winter, it is clear to me that the “green morph” is neither aberrant nor a distinct color morph separate from all other Pine Siskins. It is simply the bright extreme of variation in male Pine Siskins. There is an unbroken cline of variation from normal looking birds, to many that show some subtle hints of green morph features, to a few that stand out with obvious green morph features, and a very few extremely bright birds. The number of individuals showing these features drops off as the features get more extreme. That is, birds with less obvious “green morph” features are more frequent than birds with more extreme features, and the most extreme variants are the rarest of all.

Once you start looking carefully, you will find that the more subtle “green morph leaning” variants are not rare at all (like variation C, below, which could be 5% or more of all siskins). In fact, if all “green morph leaning” birds are adult males (like all “green morph”), and assuming that adult males make up roughly 25% of all siskins in winter, then about 20% of all adult males could be “green morph leaning”, and 4% of adult males are full “green morph”.

There is still a lot to learn about variation in Pine Siskins, and lots of interesting questions about these brighter males, but it is clear that the “green morph” is simply the bright extreme of a wide range of variation in male Pine Siskins, and not a distinct color morph.

A: A typical female Pine Siskin. Note heavy dark streaking, almost no yellow visible in the wing and tail, and narrow whitish wingbars. Original art © David Sibley
B: a typical male Pine Siskin. Most males look something like this, and distinguishing males from females in the field is generally not possible with confidence. On average males have lighter streaking, a more obvious yellow patch at the base of the primaries, and broader yellowish-white wingbars. Original art © David Sibley
C: a relatively bright (lightly streaked and greenish) Pine Siskin. We might not call this a “green morph” but it’s definitely leaning that way, with lighter streaking, slightly cleaner face pattern, and a faint yellow cast overall. Birds matching this illustration are fairly frequent, accounting for at least a few percent of all siskins, but it’s impossible to assign a percentage number because this variation blends imperceptibly into many slightly drabber birds and a few brighter birds. Original art © David Sibley
D: a brighter male Pine Siskin, with very thin and pale streaking, clean yellow neck sides, broad yellow wingbars, lots of yellow at the base of the primaries and even showing yellow at the base of the secondaries (which adds to the wingbar), and a yellow suffusion overall. Most would call this a “green morph”, and it matches many of the photos identified as green morph in Mandelbaum and Young. Birds like this are infrequent but regular, about 1% of all siskins, depending on how generous you are with the category. Original art © David Sibley
E: a very bright male Pine Siskin. Everyone would call this a “green morph”, but this is just the yellow extreme, and birds at this extreme are quite variable. Some have more distinct streaking, some have grayish backs, some have less yellow in the wings or on the breast, etc. Extreme variations like this are quite rare, perhaps one in several hundred siskins. The yellow undertail coverts and bold yellow wing markings distinguish this from the superficially similar Eurasian Siskin. Original art © David Sibley

8 thoughts on “Variation in Pine Siskins and the so-called “green morph””

  1. While checking specimens at the LSU Museum years ago, I discovered that recently fledged juvenile Pine Siskins seemed to show somewhat consistently larger yellow patches on the wings, tail, and often a yellower suffusion in the overall body plumage as well. Granted, the sample size I had to deal with was small, but I wonder if some of the birds with yellower plumage features may actually be showing 1st year age-related characters?

    Also, it may be worth noting that the southernmost population presently assigned to Pine Siskin, subspecies perplexus, found in the mountains of Chiapas and Guatemala, seems to have a green morph that has been a puzzling plumage (as hinted by the name!), particularly given the rare Black-capped Siskin with which it overlaps in range. Whether this is simply the local expression of yellow-pigmented birds, or whether it is an indication of introgression between the two populations remains to be settled.

    1. Hi Dan,
      Thanks for commenting. There is a tremendous amount of subtle variation in siskins, and most of it seems independent. That is, a bird can be lightly streaked or heavily streaked, yellowish, gray, or rufous toned on the body, with more or less yellow in the wings and tail, and any combination of those features and more. Some of it might be age-related, but I couldn’t make much progress on that even with birds at close range on the feeders.
      And that’s an interesting point about the southern subspecies. The first place I noticed “green morph” type siskins was in the Chiricahua Mountains of Arizona, and there were several birds. I’ve always wondered if these bright variants are more frequent in the more southerly populations.

  2. I was originally skeptical of such individuals until I had an odd plumaged bird show up at my residence on 4 Jan. 2021. I have been birding for 49 years and had never seen one like this prior to 4 Jan. Below is my checklist:
    https://ebird.org/checklist/S78658930
    One thing I noticed but tried to ignore was the fact that this bird seemed to be slightly but noticeably larger than adjacent “normal plumaged” Pine Siskins. I had as many as 270 at my feeders in Dec. and every one was the same size except this odd plumaged bird. In investigating this bird, I read that the supposed “green morph” individual was supposedly slightly larger than “normal plumaged”- I got input from a few experts who agreed that this was likely a green morph individual. While I agree that there is a tremendous variation in the amount of yellow in Pine Siskins, I had never seen one with this much greenish yellow on the rump and lower back. In the one photo on my checklist the odd plumaged bird definitely seems larger. My conclusion was only based on what I had read and input from experts. So is this just one of the extremes of an abnormally fat individual?

    1. Hi Paul,

      Thanks for your comment, and congratulations on noticing one of these bright siskins at your feeders. I would also call that a “green morph” type, and it looks like a pretty close match to my illustration D above.
      On the question of size, I wouldn’t be too surprised if these bright birds were a bit larger than normal. If there’s a hormonal basis to the color, that could also lead to a difference in size. Also, all of the bright birds are males, and males do average a little larger than females. I can’t comment on the size of the bird in your photos. It’s in a different posture, with all of its feathers fluffed up, so it’s impossible to judge size compared to the birds around it.

  3. In central British Columbia, we start looking for a “green morph” around the first of February. This year we had lots of Pine Siskins but very few with any degree of yellow feathering. We did notice one exceptional “partial albino” that showed faintly all the Siskin markings but colors were all faded. ( (Picture available). As February progressed we noticed a considerable increase in potential “green morph” but came up with the same conclusion that “the variation in Pine Siskins is so considerable that a “green morph” is no more uncommon that a “gray backed” morph(picture available) or even perhaps a “pale” morph.
    Pasted pictures here

  4. Somehow, I can’t tell the difference between a pine siskin and a fox sparrow. They all look similar to me. But none appear near urban areas. 🙁

  5. When you say green morph about the Pine Siskin, the illustration you posted looks like a yellow morph.

    Please correct me if I am wrong, and please don’t take this badly.

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