Saturday, March 7, 2015

Xanthochromic Evening Grosbeak in Northern Maine?

Back in January, Brenda Ketch sent me some pictures of an unusual Evening Grosbeak that had appeared in her yard at Madawaska Lake here in Aroostook County.  The bird was clearly a male grosbeak with bright yellow body plumage and big conical bill, however it was unusually colored with a bright yellow head and neck and whitish wings.  The bird looked like a hefty canary.

Obviously this bird had a pigment problem.  Unlike leucistic birds which are missing pigment and appear light or white plumaged, Brenda's grosbeak appeared to have yellow where it should be dark or black.  

I did some reading and found there are a couple papers reporting this pigmentation condition in Evening Grosbeaks.  Xanthochromic is the term used to describe a bird that has yellow pigmented plumage where it should be some other color.  It seems to occur most commonly in red or pink-plumaged birds.   Records exist of yellow Northern Cardinals, yellow breasted Rose-breasted Grosbeaks and orangey-yellow House Finches.  A cool local example of a rare pigmentation form!  Case closed..or so I thought...

Brenda's bird kept visiting her feeder well into February and she got a bunch of great photos of the bird with its normal flock mates.  Eventually the bird moved on.

This morning I was watching the finch horde that has been hitting my feeders this winter and I was quite surprised to see a lemon yellow bird in the Evening Grosbeak flock.  Of course I scrambled to get some pictures of it.  It looked very similar to grosbeak that Brenda had photographed.  

I compared the photos that Brenda has sent and sure enough, this bird had all the same marks as the Madawaska Lake bird!  Spots on the back of the head, near the eye, and on the breast were identical. Very cool that a bird seen over 12 miles away ended up here!  I made a collage to illustrate the at this was the same individual.
Comparison of Madawaska Lake and Woodland grosbeak (click to enlarge)

As I watched the bird in my yard and compared it to Brenda's photos, I noticed something that I hadn't previously:  This bird didn't just have yellow feathers replacing black the wings and tail parts of feathers that should have normally been black were white.  It appears that the black wasn't necessarily replaced by yellow (as xanthochromism is defined)...but perhaps it was that the black was just missing in spots and the underlying pigmention (color that was obscured by the dark melanin pigment) was now visible.

Looking at normally pigmented male Evening Grosbeaks, it is clear that there is an underlying yellow pigmentation to all the head, neck and belly feathers.  These same feathers are suffused with dark (melanic) pigmentation but the yellow shows through, to varying degrees.  The underlying pigment (yellow) is concealed by the dark pigment.   The wings and tail feathers of a normal male Evening Grosbeak are primarily black with only the inner wing feathers (tertials) being white.  Without melanin it would be expected that these would be white as was the case with our bird.

So is this really Xanthochromism?

I went back to the literature and found that a few authorities don't agree that Evening Grosbeaks like ours are xanthochromic but rather use a term non-melanic schizochroic for cases where dark pigment is missing in places and revealing normally concealed pigmentation in the feathers.  This sounds like what we have here.

I haven't seen the bird again today. but it  was a great distraction in the depths of a northern Maine winter!

Thursday, January 29, 2015

Short-toed Doves

Paul Cyr sent me another great photo of a local bird last week: A Mourning Dove.

The bird was an attractive specimen with tan and gray-blue feathers melding into a subtle, pleasing plumage.  The dove's sky blue eye ring was sublime. Its bright pink feet were...FROZEN!!!

I'm not 100% sure (and I hope I'm wrong) but the dove sure looked like its feet were so stiff they could not grab the branch on which the bird was balancing.  For sure, the bird was missing some toe tips- in particular the outer portions of the longer central toes. It appeared this bird had frozen and damaged its outer digits while perched on a tree branch on a frigid northern night.  I felt bad for the dove, but thought the bird's condition was probably not a surprise considering the regular subzero temperatures that northern Maine has experienced recently.  I thought of a dove roosting on a could cover most of its feet with its fathers but that one, longer, central toe as it wrapped around the branch, was sure to be exposed.

I have a pretty good supply of overwintering doves here in my yard and I thought I'd check them out to see whether any of these showed similar injuries.  There were plenty feeding right out the window and I was able to get good looks at nearly all of their feet.

Out of 17 doves, NONE had a full set of toes!  This amazed me.  All the doves I observed were missing, at the minimum, the tips of at least one of the two central toes (as Paul's bird showed).  Many others were missing 3 four and five toe tips.  Several had lost their toes nearly back to the joints and were hobbling on stubs.  Some that weren't yet missing toes had shriveled and dark toe tips that were soon to be lost.  Yet here they were, shuffling along on the ground under my feeders, picking up seed and presumably doing all right.

I was quite shocked that so many of these birds were injured.  I did some investigation of the literature to find out whether this was unusual.  In bird banding papers primarily, I found that it is fairly common, in the north, to find Mourning Doves with missing toes. Apparently these birds, being relative newcomers to the northern climes have not adapted well to the cold.  Here in northern Maine, Mourning Doves have really just become common winterers in the past 30 years.  A short time.

Its tough to tell if the damage these birds are experiencing is a recent phenomena or something that happened over a long time.  I suspect much of this toe loss has happened in the past couple of very cold months.  (January is on track to be one of the colder on record here.)

Odds are that there are at least a few first-year birds in my little flock and the fact that I found no doves with intact feet would indicate these are injuries that occurred since summer.

I'll be watching their feet a little more closely the rest of this winter.