Of a Feather: The color of their raiment

COURTESY EUGENE BECKES
Earlier this week I surprised our local ruffed grouse. It burst out of a stand of white pine saplings, flew down the woods road and ducked back into the woods. As it braked and veered to the right, it spread its tail and I could see that it is a red phase bird. Or was it? Ruffed grouse are one of those species that has several different plumages.

Color phases or morphs are usually geographical. The northern flicker was once broken into two species, red- and yellow-shafted, because the western birds are red and the eastern yellow. But since many Midwestern birds are orange-shafted it became obvious that the variation was caused by incomplete dominance of a gene within one species.

In other species the geographical segregation is incomplete. One morph is much more common in one part of the range, but the other is not unknown. This is the case with the snow goose. The so-called “blue goose” is much more common in the western population — which is moreover considered a subspecies called the lesser snow goose — and rare in the east. Furthermore, a complete range of intermediate plumages exist between the pure blue and pure white forms.

A similar situation holds for the eastern screech owl. The rufous phase is more common in the southeast, while the gray phase is more abundant up north. Pairings of the two different phases are not unknown. A third “brown” phase is restricted to Florida. A pale gray (“washed out”) type is known in the north-central U.S.

Color phases are very common among raptor species, and most of them are geographical. The red-tailed hawk may take the cake in this category. While several buteo taxa have light, intermediate, and dark morphs , the red-tail is said to have seven different forms, most of them geographically defined, but with intergrades. William S. Clark’s field guide to hawks describes four “light morphs”: eastern, western, Fuertes’ and Krider’s. The eastern is found from the Great Plains eastward, the western from the Plains north of Oklahoma to Alaska, the Fuertes from Oklahoma to Arizona (Sibley calls this the “southwestern” morph), and the Krider’s is a rare variant on the northern Plains states among the eastern birds. The three dark morphs include the Harlan’s, which is found in central Alaska, and two variants in the western population called “rufous” and “dark,” which are not geographically segregated.

As among the raptors, color phases are frequent in gallinaceous birds. This is one reason it has been relatively easy to develop domestic breeds of wildly different plumages. The ring-necked pheasant displays a number of different plumages across its Asian range, as does the bobwhite across its North American distribution. The spruce grouse has a population from southern Alaska to central Alberta called the “Franklin’s grouse” that lacks the chestnut tips on the tail feathers and instead has white tips on the tail covert feathers.

Sibley’s field guide pictures only red and gray ruffed grouse phases. But the website of the Ruffed Grouse Society divides the species into gray, red, intermediate, brown, and split plumages. The site excerpts text from “A Grouse in the Hand, Tips for Examining, Aging & Sexing Ruffed Grouse” (2014) by S. DeStefano, R.L. Ruff and S.R. Craven. The gray and red phases have tails of uniform color, but the intermediate phase birds “have gray tails with a wash of light brown throughout.”

“The ‘brown’ birds, which are always males, have light brown tails and relatively distinct black and white transverse bars that stretch across most of the tail feathers. A hybrid color phase is the ‘split’ bird, which is always a female. Split phase birds are generally gray or intermediate with some or all of the tail feathers showing streaks of the chestnut of red birds.”

The plumage variations do not end there in ruffed grouse. Distinct from tail color, the color of the tail tips and the ruff on the neck are apparently controlled by a linked gene or genes. In the “vast majority” of birds these are both black. According to Stefano, Ruff, and Craven, “Approximately five percent have a tail band and ruff that are bronze or chocolate in color. Tail band and ruff coloration is independent of color phase.”

Why do color phases exist? Natural selection dictates that variations must be either beneficial or neutral to an individual. Color variants arise by mutation. In some taxa, like the raptors, waterfowl, and fowl, mutations seem to arise quite regularly. In other groups, mutations are apparently less common; all the birds look more or less the same. In my many years of birdwatching, I have never noticed, for example, a lot of variation among chipping sparrows.

That said, color variants are well documented in other sparrow species. The white-throated sparrow has a “tan” color phase. There is also a complete tangle of plumage variations, mostly geographical, among seaside and song sparrows. Juncos too are a quagmire of regional varieties that include, in addition to feather color, changes in eye color. The latter is also true of eastern towhees (really just a big sparrow), which has southern white-eyed and northern red-eyed forms with a clinal transition between the two.

So, while mutation produces the variation, it is natural selection that preserves or destroys it. This is why variants are geographically distinct. Stefano, Ruff and Craven write of the ruffed grouse, “Red birds are better camouflaged on a forest floor of predominantly oak leaves, and gray birds are less conspicuous on snow.” This, they say, is why red birds are more common in the south and gray in the north. This environmental effect can be quite local. They note that on the western slopes of the Cascades, which are wet, birds tend to be red tailed, while in the arid “rain shadow” on the eastern slopes, gray is more common.

Bill Chaisson has been a birdwatcher from the age of 10. He is a former managing editor of the Eagle Times and now lives and works in the town of Wilmot. Contact him at [email protected].