I want to share an interesting bird photos from my last trip to Fulton-Rockport, Texas, US; July31-August 1. Three light brown/beige Black Skimmers. All females. I already have a confirmation from one of the best expert (if not the best), Hein van Grouw (thank you for his help), that it is safe to assume that this aberration is indeed caused by the mutation Brown.
I will start with a short description and a few points that are throwing me off .
Female #1- this skimmer is almost complete light brown (where should be brown-black) and light beige (lower parts – neck, chest, belly, flanks, underwings, etc that normally are white) with a few dark spots on her head (top - the coldest part of the body) and back. Note: Photos taken at harsh light can be misleading as the neck/belly area can be easy blown and produce highlights that do not show real color of these parts or they can look much lighter not showing true shade of the light beige (I am only posting photos taken in nice, soft light showing the true colors). The only hints of white are very small area on forehead right above the bill and near the gape. Tail feathers whitish with partially brown shaft and with dark vane areas on both sides of shafts widest toward the feather base. Whitish pattern on flight feathers matching this of normal colored skimmers. Legs orange-yellow (maybe somebody can describe this colors better?). Bird is molting. All rectrices worn (old). Secondaries, inner primaries, greater primary covers new; outer primaries, most or all secondary covers worn. There is some molt going on belly/flanks, head (the dark spots seem to be fresh unbleached feathers) and neck.
Note: I am not sure about inner most coverts - also feathers with a qualitative reduction of eumelanin are very sensitive to sunlight and can bleach very quickly so to see the original color I will have to find a freshly molted bird.
Female #2. Second bird is darker, more dark spots on head, back and upper covers but neck and lower body even lighter beige then first bird. Rectrices have less dark areas, shafts lighter. Legs are also orange-yellow. Also molting. New: inner primaries, most greater primary coverts, most secondaries, most median secondary coverts, a few outer lesser secondary coverts. Worn: rectrices, outer primaries, most lesser secondary coverts, a few inner median secondary coverts, some worn shown on a few innermost secondaries (tetrials).
These two skimmers (#1 and #2) were only seen once together on one of the roosting spots but not very close to each other. As they were keeping moving along the shore I was losing them and could not relocate lighter one (#1) at the end of the last day.
Female #3. I had only a few seconds to observe this one (could not relocate it at all), pattern on her head was slightly different from other two, colors were more similar to the female #2 and she also showed a lot of worn feathers.
All three aberrant females are showing only a slight differences in molting stage between each other but their molt stage is quite different compare to most of other skimmers (juveniles and adults) at this moment.
There are a few things that threw me off, e.g. color of normally colorless (white) feathers that are showing light brown/beige pigment so not only dark color was diluted (brown-black to light brown and beige) but also normally colorless (white) feathers have pigment. Only one known color aberration mutation in birds is recessively sex-linked (the ‘brown’ mutation) and males showing ‘brown’ are extremely rare. As we know bird sex chromosome system for determination of the gender is different from one in humans (birds: ZW are females and ZZ are males). It seems that Fulton-Rockport skimmer population has some of these recessive genes and it will be normal to see color aberrations occurs mostly in females. A brown male will have to come from a ‘brown’ mother and either ‘brown’ father or one carrying the ‘brown’ gene. I am quite interested to collect photographs of these birds in fresh plumage and see what will show up in the future generations. The fact that there are at least 3 aberrant skimmers in this area now (I found in just 2 days) suggests that there is a possibility of at least a few more.
I could not find any info/photos of ‘Brown’ or any similar skimmer color aberration neither in published material or on the web. I will appreciate any help in locating info about any published data and/or photo posted on the web, if there is any.
As this forum has members with knowledge about molting I would like to hear their opinion about the age suggestion of presented birds. At the first moment when I saw the first aberrant female I thought that this is a juvenile (based mostly on a bill shape but seen from far distance) but after a moment and after collecting many photos of other aberrant females my guess is a second year subadults. Why? First, as described above a lot of feathers are worn heavily including some of the flight feathers, and some are fresh. This year juvenile should have (like all others I observed at the same time) still fresh and even flight feathers. From what I found so far it takes a juvenile skimmer over 1.5 year to start molting the outer primaries (done during the second winter). All 3 aberrant birds have outer primaries worn and inner ones relatively fresh (compare to outer ones). Also a behavior issue: not even once any of these 3 females were taking begging postures and juvenile displays around adults. All juvenile skimmers present at that time were ’acting as juveniles’ very often - with female #1 I spent several hours total time and not even a hint of juvenile behavior. So if anybody who has experience with skimmers’ molt and wants to share her/his knowledge I will appreciate this a lot.
Thanks in advance for any info or help.