"Most people think of pigeons as rats of the sky, but in fact they're really incredibly diverse," says Michael Shapiro, an assistant professor of biology and senior author of the study published online Jan. 19 in the journal Current Biology.
More than 350 breeds of pigeons differ in color, color pattern, body size, beak size and shape, structure of the skeleton, posture, vocalizations, feather placement and flight behavior. With help from pigeon breeders worldwide, the researchers studied the genetic relationships and visible traits of 361 pigeons from 70 domestic breeds and two free-living populations, one from Salt Lake City and the other on Scotland's Isle of Skye.
"What we found through this study is that birds that are only distantly related to each other can have very similar traits, and others that are very closely related to each other can look quite different in terms of their traits," Shapiro says.
In some cases, birds of a feather don't stick together -- genetically: The old German owl pigeon and English trumpeter both have head feathers known as a head crest, yet the two pigeon breeds aren't closely related. Another case: English trumpeters have feathers on their feet instead of scales. So do English pouters. Yet they are not closely related.
A few more examples of traits not matching genetics: Pigeon breeds known as the African owl and Budapest short-faced tumbler both have very short beaks, but they are not closely related. The African owl and old German owl pigeon breeds both have short beaks and are closely related, yet the African owl pigeon has a plain head, while the German owl has a head crest. And the English pouter and Brunner pouter are closely related, yet the former has foot feathers and the latter does not.
In other findings from the study:
-- Free-living pigeons -- including the common city pigeons known as "rats of the sky" -- carry the DNA of escaped or lost racing pigeons. Feral rock pigeons living in Salt Lake City are substantially related to a breed known as racing homers. Feral and perhaps wild pigeons from Scotland "are similar to an old domestic breed called the Modena, which used to be a racing pigeon but now is exclusively a show pigeon," Shapiro says.
-- Genetic analysis bolsters the idea that most of these pigeons studied have roots in the Middle East, and some with more recent origins in India.
-- Since birds with similar traits may be only distantly related (with no shared ancestors), it means certain traits in pigeons were selected by breeders repeatedly.
"Pigeons are a remarkable example of how selection and heredity work," Shapiro says. "These breeds are all members of the same species, but look really different. This happened because pigeon fanciers over the ages favored particular traits. This happened in dogs, too. It also happens to animals and other living things in the wild, except the agents of selection and change are environmental factors rather than human preference."
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