Feather Identification Tips, Leucism

Unusual Blue Jay feathers: part two

I recently had the opportunity to revisit the Blue Jay I wrote about in this post after consulting with the Delaware Museum of Natural History’s Dr. Jean Woods (Curator of Birds). She recommended that I examine a larger sample size and allowed me to go upstairs into the collections (only one of the coolest places in the world if you ask me)! Drawing from the museum’s collection of Blue Jay spread wings and study skins, I looked for any specimens that shared the unusual patterns.

Asymmetrical Patterning?

I took more detailed photographs of the unusual white patterning, which made me notice how my initial assumption that the secondaries were symmetrically patterned was not entirely correct. Here are some comparison photos so you can see what I mean. (Note: secondary wing feathers are labeled from the outside in. As you get closer to the body of the bird, the numbers go up).

The same feathers were affected on each wing, but I found the variation in pattern within each corresponding pair, particularly the S4’s, interesting. Birds rarely have asymmetrical patterns, and if anything, asymmetry often results from abnormalities such as gynandromorphism or leucism. Basically, it tends to indicate that something’s wrong. For this reason, I believe that leucism is still a possibility.

Normal, but Uncommon.

As I looked through the museum’s thirty-five Blue Jay spread wings, I found that seven (20%) had white patterning on their secondaries similar to the pictures above. Each had somewhere between two to five secondaries affected. All of the affected feathers were grouped next to each other and included S1. This made it seem as if the pattern was simply a continuation of the white patterning that normally occurs on the primaries; nothing unusual, just an example of individual variation in an uncommon trait.

The one thing I couldn’t tell from the spread wings is whether they had symmetrical or asymmetrical patterning. Only one wing from each individual was collected, while the other wing’s feathers were discarded. Therefore, it’s difficult to tell whether asymmetry can be attributed to a naturally-occurring trait or an abnormality like leucism.

Here’s a closeup of the white rump–note how extensive it is. Dr. Woods said that while rump and lower breast feathers on study skins can sometimes be switched around, these were well anchored to the rump, making it unlikely that the white rump was due to faulty taxidermy or out-of-place feathers. As we looked through some different Blue Jay study skins, some had a few white feathers on their rump, but none had a patch quite as exaggerated as this. Still, that means that white rumps are not necessarily out of the ordinary for Blue Jays.

Overall, the unusual Blue Jay’s wing feathers (top) look paler in comparison to the other spread wings. In most bird specimens, that could be easily attributed to pigment degradation over the years. However, blue feathers do not actually contain any blue pigment–they are structurally colored instead. While pigments may suffer damage from sunlight, the actual keratin structure in the feathers remains intact and preserves any structure-based color long after the pigments fade. So in this case, the pale coloration cannot be attributed to post-mortem fading–this is what it looked like at least at the time of its death.

The unusual Blue Jay’s color fit within the range of colors I saw in the museum’s Blue Jays, but the fact that it falls on the lighter end is curious since its other “quirks” also have to do with the absence of color.

A match?

While there were seven wings that had white-patterned secondaries, only one, specimen #79244, had five feathers affected like the unusual Blue Jay. Here’s what it looked like:

The white patterning was much less extensive than the unusual jay’s, but of the seven spread wings that had any patterning at all, this one made the best match.

The unusual jay’s wing color (top) still paled in comparison to this “matching” wing, which is unsurprising considering that very few specimens in the collections even approximated its lightness.

Essentially, the unusual Blue Jay’s patterning shows up in other Blue Jay individuals, but none truly match it in intensity.

Aging the Specimens

Dr. Woods suggested trying to identify the age of the birds to see if there were any trends based on maturity/immaturity. According to Peter Pyle’s Identification Guide to North American Birds, Blue Jays can be aged based on the amount of striping on their wing coverts. HY (hatch year) and SY (second year) birds retain the duller, less patterned set of feathers they grew the year they were born. Only ASY (after second year) birds replace these covert feathers.

Looking at the unusual jay’s coverts, the secondary coverts were strongly striped and the primary coverts and alula were faintly striped. This suggests that this was at least an ASY (after second year) bird, but not especially old. As a general rule, Blue Jays become more thoroughly patterned with each year’s molt.

The spread wing collection represented a good mix of mature and immature birds. Since the wings had tags, many had their approximate age noted which made age identification easier and more reliable. The wings with white patterning on the secondaries showed no trends in terms of maturity, so this phenomenon is not correlated with or caused by age.

My Conclusion

So, what do we know now? This Blue Jay was a young adult with highly exaggerated, asymmetrical white patterning and an overall pale color. Whether this phenomenon should be attributed to leucism or individual variation depends on your interpretation of what range of patterns and asymmetry can be considered “normal” in Blue Jays.

I should note that without the extensive Blue Jay collection at the Delaware Museum of Natural History, I would have had no clue that individual variation could be a possibility. I had never seen anything like those white patterns on a Blue Jay, based only my small sample size, I neglected to think that the phenomenon could be anything other than an aberration. Even though museum collections with hundreds of individuals per species might seem excessive at first, they prove their worth in times like these where a large sample size helps determine whether a phenomenon is unusual vs. aberrant.

Update (5/18/2020): For a more detailed look at the factors that can lead to the expression of white feathers, read this great post.

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