Who is Ken? In short, Ken is a national treasure. As a well-known birdwatcher, writer and environmentalist, Ken Kaufman devoted his life to observing birds, reading birds, writing articles about birds, and sharing the bird world with others.With all the bird’s-eye knowledge in his mind, he also served as the site editor Audubon Magazine. So, whenever we encounter a question about birds in the office, we ask Ken. Now you can too! If you have questions about birds or bird watching that Kenn would like to answer, please leave them in the comments on Facebook or send us an email. Maybe next month you will get the kind of thorough, thoughtful and even humorous response we have loved so much from Kenn for years. ——Editorial
Question: WWe saw a very dark red-tailed eagle during a field trip. Some people call it the dark stage, but another person calls it the dark metamorphosis.Which one is correct?
Ken Kaufman: No two birds look exactly the same. This fact can make bird watching more interesting and sometimes more frustrating. If every individual of a species matches all other individuals in the same species, it will be easier to identify them, but there are actually many variations.
Individual differences occur in each species. At first glance, every bird in the flock seems to be the same, but when you look closely, you will notice subtle differences. Study a flock of American robins in winter and you will discover how everything changes in them: reddish brown on the chest and gray on the back, yellow tones on the beak, number of stripes on the throat, shape around the eyes and on the corners of the tail White dot. Even a solid color bird, such as the American crow, will be different in shape and size if you hold and measure them. (But I don’t recommend this, so you may have to believe me.)
If we narrow down from the individual level, we can also see larger categories of variation. Many species show regional differences. These may be obvious: For example, in the north flicker, the eastern population has a bright yellow wing liner, while the western population has a salmon pink color.Black eyeballs that breed in different parts of North America Wearing a significantly different color patternUnlike the “slate” Juncos in the east, the “Oregon” Juncos in the northwest has brown and red hues, even though they are all part of the same species. Of course, in many birds, males and females look different.
Most species also show some differences between juvenile and adulthood, and in some age differences are extreme; herring gulls almost constantly change their appearance during the first four years of life, between the dark brown of the young bird and the gray-white feathers of the adult bird. There are many immature stages in between. There are also seasonal differences. For example, the male American goldfinch sheds its skin from a subtle light yellow in winter to a bright yellow in spring, and then returns to its light yellow in autumn. Even species that only molt once a year will gradually change. As the next moulting time approaches, the color begins to fade and the edges of the wing strips gradually wear.
But a completely different variation involves species with different color variants. In these cases, variants are not the result of geography, because different variants coexist. They are also not caused by age, gender or season. On the contrary, a large part of the adult members of the species wear a different color pattern from others, which is a permanent condition. Species with different color variants are called polymorphisms.
Some examples are amazing. For example, in snow geese, adults are white with black wingtips—or mostly dark blue-gray with white heads. Until 1973, Dark Form was considered a separate species called the “Blue Goose”. But the two forms are almost indistinguishable genetically. They mate with each other. A pair of “blue” snow geese may have some white offspring, or some black offspring. Although their appearance is different, they are just the color form of the same species.
Another example involves the Oriental Screech Owl. Most individuals are gray with complex black markings, but some are bright reddish brown with reduced markings. (Some are gray-brown in the middle.) In general, “red” birds make up about one-third of the population.
Then there is the seasonally suitable polymorphic bird, the wild turkey.As mentioned in one Audubon A story a few years agoApproximately 1 in every 100 turkeys is just an example of a “smoky” variant, where the usual reddish brown body color is replaced by a light smoky gray. Of course, the color of domestic turkeys may be different (as do many domestic birds), but in wild turkey populations, smog distortion occurs naturally.
For certain polymorphic species, there are the most common geographic trends in different forms. Among the snow geese, the blue variety is the most abundant in the central population that spends the winter near the Gulf Coast. Among the eastern screech owls, the red variant is most common in warm and humid climates-accounting for more than half of the population in parts of the south-and is rare in dry climates, such as near the western edge of the Great Plains.
Another example of geographic bias is the Red-Tailed Hawks. In the eastern United States and Canada, almost all red-tailed horses are pale variants, with white chests and black belly bands. But in the West, many appear in black or reddish-brown variants, and the lower body is very dark brown or warm reddish brown. (There are other Western variants, such as the dark “Harlan” subspecies of Alaska and the mysterious pale “Krider” redtail on the northern prairie, but discussing all of these will take up a whole column.) For whatever reason, North America Bird prey shows more variation in the West than in the East. Swainson’s Hawk and Ferruginous Hawk, found westward from the Great Plains, in addition to their typical patterns, there are quite common black variants. Broad-winged eagles, mainly eastern birds, almost never appear in dark forms–except at the northwestern edge of the breeding range in western Canada.
There are also fascinating geographic trends in places where some seabird color changes are found. Parasitic and pomarin predators build their nests on the Arctic tundra and spend the winter at sea. They appear in light and dark forms, with some intermediates. Among parasitic Jaegers, darker varieties are more common in the southern part of the breeding range, such as southern Alaska and central Canada, while pale birds dominate the Arctic highlands. On the other hand, at Pomarine Jaegers, this geographical trend has not been confirmed. Northern Fulmar, which breeds in high-latitude island communities, also has pale and dark variants. In the North Atlantic, except in the northernmost colonies, birds are almost all pale variants, and many of them are dark. In the North Pacific, the strange thing is that this pattern is reversed. The northernmost colonies are mostly pale and smoky, while the darker variants are concentrated further south. These different patterns of occurrence confuse scientists trying to explain why this polymorphism occurs.
You may have noticed that so far, I have mainly mentioned raptors and waterfowls. Only about 3.5% of the birds in the world are polymorphic, and few of them are songbirds. However, we do have a very common example in North America. Adult diphtheria sparrows come in two colors, with brown or white stripes on the head; the behavioral differences between these forms have been studied for many years, Provide endless surprises.
You may also notice that I was only talking about examples, but did not answer the original question: Is it correct to call these color forms phases or deformations? However, I have been hinting at the answers, calling them deformations. The term “phase” refers to things that change over time, such as the phases of the moon. An example of a bird is the little blue heron. In this species, juvenile feathers are white, and adult feathers are dark blue. Between them, when they partially molted, their mottled black-and-white pattern is often called the “calico stage.” This is a stage, and it is wrong to call it deformation-it is temporary, not permanent.
So, when someone tells me excitedly that they just saw the “red screech owl”, should I correct them? Do not. I know what they mean very well, and I am glad they even know that this owl has different color forms. If they ask me about terminology, I will explain that what they see is a transformation, not a stage. But unless they ask, I will only celebrate with them the excitement of seeing these interesting changes in nature.