Montana Best Times: Big Sky Birding Column (November 2004)

Part 1 - Rock Doves, or Rock Pigeons: Changes in the Way We View Birds

Everyone knows what a pigeon is - even those that aren't into birds. It is one of the most common birds in urban areas of Montana. Most people growing up used to call these Rock Doves (Columba livia) "pigeons."

However, in 2003, the American Ornithologists' Union (AOU) changed the name from Rock Dove to Rock Pigeon to conform with English names of birds in Eurasia. So today you are actually half correct if you call these birds simply pigeons, but to impress your friends, the more technical English name from this point forward is Rock Pigeon.

The word "pigeon" is derived from Latin and basically means "squab or young dove." The French name for this bird is "Pigeon biset," and loosely translated means "a pigeon with two wing bars." The coloration of pigeons varies widely, with the most common variety being blue-gray in color with a white rump, two black wing bars on each wing, a broad black terminal band on the tail, and red or pink feet.

This description also closely approximates the original coloration of Rock Pigeons of wild origin, since all Rock Pigeons in North America are not endemic or native, but are instead an introduced species that has gone feral - escaping and surviving in the wild. However, they can come in colors ranging from dark gray to brown to even white. Male pigeons are slightly more colorful and larger than females.

The name for the Rock Pigeon in German-speaking countries is Felsetaube, whereas in Spanish-speaking countries the bird is commonly referred to as Paloma Bravia.

They are about three times the mass of an American Robin, weigh about 13 ounces and are approximately 11 inches in length. The descriptive word "Rock" refers not to its plumage coloration, but to the rock cliffs where Rock Pigeons have traditionally nested in the wild.

How did they get to North America?
Rock Pigeons were first introduced into eastern North America by colonists in the early 17th century, and can be best narrowed down to the dates 1603-1607. They were brought along in ships mainly as a source of fresh food and protein, and eventually became feral on the continent from these colonial source points. Today they can be found inhabiting a large section of North America encompassing all of the conterminous U.S., Mexico and Central America, the Greater Antilles, extending to the coastal areas of Newfoundland and southern portions of Canadian provinces bordering the United States and the west coast portions of Canada and Alaska.

The original range of the wild Rock Pigeon in Eurasia was much smaller than it is today and confined probably to the Middle East, western Asia and North Africa, but domestication changed everything. Grain farmers in the eastern Mediterranean reportedly domesticated it 5,000 to 10,000 years ago, making the Rock Pigeon one of the earliest known domesticated avian species in the world.

Characteristics of pigeons
The difference between a pigeon and a dove is basically size, with pigeons being larger than doves. Nearly all large columbids under the genus Columba are classified as pigeons, with the exception of the Stock Dove of Eurasia. Rock Pigeons can have two to three broods per year in the wild in Montana, with two eggs laid with each brood. At a maximum they can fledge four to six young per year.

They can nest in a variety of places, ranging from cliffs to barns, buildings and bridges. Their nest is made of sticks and is quite flimsy, I may add. Incubation of the white eggs is 16 to 19 days and is performed by both sexes, and results in asynchronous hatching, or young born of different sizes often one day apart. Fledgling typically takes 35 to 37 days.

Rock Pigeons have many unique morphological or physical form features. The nostrils on the bill are covered with a soft, raised skin-like feature that acts as a valve, which is called the opercula(operculum). The eyes are surrounded by bare skin that becomes very pronounced and colorful during breeding.

But the most interesting feature of all is that Rock Pigeons are notorious for producing what is called "crop-milk." During breeding season, inside the esophagus of the pigeon and just in front of the breastbone are two sac-like structures that connect to the esophagus, or what is known as a two-lobed crop. As young squabs are born they stimulate the parent to drop off these nutrient-rich cells resembling cottage cheese into the sac cavity or lumen, where they are stored as crop-milk. The adult touches the side of the bill of the one-to-three-day (rarely, up to nine-day) squab, which stimulates the adult to regurgitate crop-milk when the squab inserts its bill in the mouth of the mother's buccal cavity. Interesting enough, sometimes the adult can feed both young simultaneously.

Pigeons feed on three different forms of food: those that feed extensively on seeds (granivores), those that feed extensively on fruit (frugivores), and a combination of the two. Rock Pigeons, like Mourning Doves, are primarily granivorous, or granivores. These granivorous types have a thicker-walled gizzard, or muscular stomach,in addition to a smaller-sized intestine, which aids in digestion of seeds.

Rock Pigeons, like other columbids, have other noteworthy adaptations to counteract temperature changes and in their method of drinking water. Birds have no sweat glands like mammals, so how do they adjust to temperature changes? They possess a vascular plexus, which is a series of blood vessels surrounding particularly the sides of the neck that vacillate and keep the body cool through evaporation during extremely warm temperatures.

On a hot day you can observe pigeons inflating the feathers in the neck, allowing the heat to escape the body. During cold spells to conserve heat the feathers are ruffled throughout the body, making the bird look larger, and feathers are actually touching each other, thus maximizing the conservation of heat.

Another interesting feature of columbids is that they are one of the few bird groups that can drink water with their heads down. Most birds take a sip of water and lift their head to swallow it. This is not the case with columbids. They leave their heads down and suck water up into the body, thus allowing them additional time to survey the landscape for predators. The only exception to this in the pigeon family is the Thick-billed Pigeon of Samoa, which actually lifts its head to swallow water. This method of drinking water with the head down is quite unique to columbids.

Lastly, pigeon breeding behavior is fun to watch. Next time you drive in your vehicle and see a Rock Pigeon, try paying attention to their flight. You will notice pigeons flying with their wings uplifted, or what is called "V-shaped" flight. This is one of the outward signs of pigeon courtship, and if you are really lucky and close enough you can actually hear the wings coming together as they are lifted, causing a clapping sound. This is the aerial courtship display of the Rock Pigeon. On the ground the male pigeon makes a different courtship display called the "bow-coo" display, which consists of inflating the front of the neck or crop, raising the wings at the wrists, spreading the tail, and bowing to the female, delivering his "coo" sound.

Even though pigeons seem like a dime a dozen, they still are fun to watch.

Now that the reader has a better understanding of Rock Pigeon morphology, identification, behavior, and ecology, the next topic will be how to live with Rock Pigeons and, if space permits, a special feature on homing pigeons and pigeon navigation for the January issue of Montana Best Times.

Enjoy! And the Best of Big Sky Birding to you!