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COLUMBIDAE - PIGEONS AND DOVES
Sixteen species in this global family reach Paraguay, all belonging to the subfamily Columbinae. Members of this subfamily are seed-eating forms. The earliest known fossil pigeons date back 30 million years, but the family is likely much older. Though the term "pigeon" and "dove" are widely understood they are of no taxonomic value. In general "pigeon" is used for large species and "dove" for smaller species, though in some cases the terms are interchangeable, and for simplicity the generic term "pigeon" is used throughout the rest of this account.
Columbids are morphologically very uniform and easily recognised even by non-specialists, with small rounded heads, short legs and well-developed pectoral muscles giving a barrel-chested appearance. Most Paraguayan species have mute colouration in greys and browns, often with metallic gloss on the neck and/or wings. Pigeon plumage is soft and dense and detaches easily. They have short, stubby bills, often with a fleshy cere and a horny tip, and the middle part of the bill is somewhat constricted. Nostrils are narrow and covered with a valve-like scale. Most species have bare orbital skin around the eye, often brightly-coloured. Legs are usually short and robust, though terrestrial forms tend to be longer-legged than arboreal species. The toes are well-separated and sturdy, capable of a firm grip. Seed-eating species have muscular gizzards and long narrow intestines and often ingest mineral substances. They drink by dipping the tip of the bill into water and sucking the liquid. Many species are sociable, at least when not breeding, and large flocks may have a significant effect on agriculture in some areas - leading some landowners to develop profitable hunting businesses in certain parts of the Chaco. As a family pigeons are adaptable and have colonised the vast majority of habitats on the planet, including those considered uninhabitable by many other bird families. Vocally however they are unimaginative with deep coos the norm and only slight variation between closely-related species.
Compared to other similar-sized birds pigeons are long-winged and with low wing-loading, resulting in direct, rapid flight. The flight muscles may be as much as 45% of body weight, proportionately more than twice as much as other bird groups. Another unique feature of the pigeons is their ability to produce a high-protein substance known as "crop-milk" to feed their young. This is produced in a bilobed crop that is attached to the oesophagus, with prolactin stimulating the thickening of the crop lining, and the cells sloughing off to form the "milk". Juveniles stimulate regurgitation by forcefully inserting the bill into the throat of the parent. This unique character trait has been cited as one of the reasons for the success and diversity of the group worldwide, which would otherwise seem surprising in light of the fact that they are edible, apparently of low intelligence and lacking in any real traits to defend themselves from predators. Perhaps a more likely explanation for their success however is their ability to reproduce rapidly and efficiently. Pigeons almost invariably lay a clutch of 2 white eggs in an untidy and often flimsy stick platform. Incubation is by both sexes, though females take the majority of the responsibility. No crypticity is necessary in egg-colour because the eggs are rarely left exposed. Chicks hatch with a sparse downy coat. Incubation and fledgling periods are short and chicks often make their first flights before plumage growth is complete. Their first moult (pre-basic) begins shortly after leaving the nest. This rapid breeding cycle means that adults may produce several successive clutches, often re-using old nests.
The characteristics of the eight Paraguayan genera are summarised below.
Patagioenas "Neotropical Pigeons" - Large size, short legs. Medium to long wings and square or round-ended tails. Strong fliers. Typically arboreal. No sexual dimorphism. Ecological equivalents of the Old World Columba.
Columba "Old World Pigeons" - Morphological characteristics similar to Patagioenas which was until recently incorporated within this genus. They differ in elements of display and physiology. Slight sexual dimorphism. The sole Paraguayan species is a commensal of man found worldwide in urban habitats.
Zenaida "Mourning Doves" - Small, brownish doves with iridescence on the neck, spots on the wing and white markings on the tail. Perch in trees but frequently forage on the ground. 14 retrices. No sexual dimorphism. Ecological equivalents of Old World Turtle Doves Streptopelia.
Columbina "Ground Doves" - Tiny to small semi-terrestrial doves. Compact and plump usually with a short tail (except C.picui). Iridescent spots on the wings. Slight sexual dimorphism. Emargination on 6th or 7th primary.
Claravis "Blue Ground Doves" - Medium-sized semi-terrestrial forest doves. Attenuated 1st primary. Notch like emargination on inner web of 8th primary. Great sexual dimorphism.
Scardafella "Scaly Doves" - Sometimes included with Columbina but distinctive on account of long tail and scaly plumage. No iridescent markings on wings or body. Emargination on 6th or 7th primary. No sexual dimorphism.
Leptotila "Neotropical Ground Doves" - Medium-sized with long legs and exposed tarsus. Semi-terrestrial walking swiftly. Medium-length tail with 12 retrices. Tip of outermost primary steeply attenuated. Underwing rufous and white-tipped tail. No sexual dimorphism.
Geotrygon "Quail Doves" - Dumpy, partridge-shaped, terrestrial forest doves with long legs and short tail. Distinctive facial markings and steep forehead. Dull colouration. Retiring behaviour, rarely emerging from cover. Slight sexual dimorphism.
Baptista LF, Trail PW, Horblit HM 1997 - Columbidae Handbook of the Birds of the World Volume 4 - Lynx Ediciones.
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Gibbs D, Barnes E, Cox J 2001 - Pigeons and Doves: A Guide to the Pigeons and Doves of the World - Pica Press.
Goodwin D 1970 - Pigeons and Doves of the World 2nd ed - British Museum of Natural History.