Date: 11/1/17 1:14 am From: Dan Gleason <dan-gleason...> Subject: [obol] Gull color and ID
I agree with Mike that there may always be some gulls that you are unable to identify. There is simply too much variability of plumage. We all know that immature gulls can often be more challenging to ID, but it’s not as simple as a matter of age.
Although somewhat rare in most birds, a few kinds of birds have feathers containing a significant amount of pigments known as porphyrins. Owl feathers have many of these pigments and so do gulls in some parts of their plumage. Unlike melanin (typically dark pigments), or carotenoids (bright red, yellow, orange from plants) porphyrins are light-sensitive and fade when exposed to the ultraviolet light of full sunlight. This means that appearances can change without a molt. The gray-brown streaks we see on the head of a Ring-billed Gull in winter, for example, gradually fade away to white without the need of a molt. Immature gulls have plumages that often contain more porphyrins than adults. As these pigments gradually fade in the light, the bird will look somewhat different as time goes on. The amount of streaking may be different in two individuals of the same species and age due to some difference in the amount of fading that has taken place. This can add to our confusion when attemp ting to sort out kinds of gulls in a mixed flock of birds. So no two birds may look exactly alike or like any field guide illustration. Certainly, with practice, and help from experts, you can learn the basic patterns and other features that help you identify many species of gulls, but there can always be a few individuals that just don’t fit and may leave you guessing.
Porphyrins are an interesting group of pigments. Owls have many porphyrins in their feathers, but since most are nocturnal and well-concealed during the day, little fading occurs. Predominately day-hunting owls have fewer porphyrins. When exposed to strong UV light, many owl feathers will fluoresce a bright pink. Brown streaks on juvenile Osprey or White-tailed Kites are porphyrins that fade over time leaving white feathers by fall. Porphyrins are responsible for the bright green and violets found is some African Turacos. These species are mostly arboreal and live in dense forests where UV light is scarce allowing the colors to remain stable.Some porphyrins are far less stable then others. Some species of Bustards have pinkish-colored phorphyrin in the down feathers that is very light-sensitive. If the body feathers are pulled aside to expose this down, it apparently fades in 12-15 minutes, the least stable color found in any birds. Apparently, the males most fit for breeding have t he brightest pink, which fades as the season progresses. Since sperm production also decreases over the breeding season, bright pink signals being ready for first mating with the highest sperm count and the greatest chance of fertilizing the females egg.
Dan Gleason Owner, Wild Birds Unlimited of Eugene Ornithology Instructor, University of Oregon <dan-gleason...>
> On Oct 31, 2017, at 6:07 PM, Mike Patterson <celata...> wrote: > > Now that I am able to actually look at the Infamous Gull Chart (thank > you Treesa), I will officially weigh in… > > First, the blasphemy: Gull ID is not nearly as important as some folks > might want us all to believe. Depending on where one is standing at a > particular instant in time, the majority of gulls one would be looking > at will be one of maybe three or four species (plus or minus hybrids). > In a census, we shoot for 95%. Most of us don't need to be able to identify every possible gull. Missing the Slaty-backed Gull DOES NOT > MATTER. Most folks interested in seeing a Slaty-backed or Black-headed > Gull would do better waiting for someone else to find it, given that the > alternative is sorting through gulls for hours on end over years and years. > > There will always be gulls in a group that we cannot identify, no matter > how many gulls we’ve looked at over the years. The pretense that we can > identify every gull is just that, pretense. The real Zen in gull ID is > recognizing, first, that we cannot satisfactorily place a name tag on > every gull and, second, it does not matter whether we place a name tag > on every gull. What matters in birding is the answer to the question: > are we having fun, yet? > > So, the gull chart – It IS useful, though the point made by Mr. Irons > about the importance of wing-tips is well taken. There is method in > starting with adults, in part because they are usually better > illustrated and easier to sort than juveniles. Because structure holds > from adults to juveniles, if one can get comfortable with adults, the > step into the more complex sub-adult morass can be more easily taken. > > The chart could use some qualifiers, the most important being: how do we > know we are looking at an adult? I’m also not sure about the efficacy > of including some of the rarer species. This chart is (presumably) for > initiates, not “experts”. Including gull species with low frequency of > occurrence might be unnecessarily confusing to a novice. > > This chart is intended to be a tool. Like all tools for identification, > it has its limitations and like all guides, is incomplete. It > represents a piece of the larger puzzle. It is not a solution. It will > not replace all our other field guides. It will not replace field work. > > But I never turn down a new tool when offered, especially if it’s free. > > -- > Mike Patterson > Astoria, OR > That question... > http://www.surfbirds.com/community-blogs/northcoastdiaries/?p=3294 > POST: Send your post to <obol...> > JOIN OR QUIT: http://www.freelists.org/list/obol > OBOL archives: www.freelists.org/archive/obol > Contact moderator: <obol-moderators...> >