Distribution

In his classic work Crows of the World, Derek Goodwin notes that "the amount of adaptive radiation and consequent differentiation found within the Corvidae surpasses that within many Passerine families." With the exception of Antarctica and some remote archipelagos of the Pacific, there is at least one corvid species for most parts of Earth.

In south and Southeast Asia, where Corvids may have originated, arboreal species proliferate. These include the primitive monotype crested jay and black magpie (Platysmurus leucopterus) of the Malay Peninsula and Southeast Asian islands, as well as the "tropical" magpies. This group of 18 colorful species consists of the blue Urocissa and green Cissa magpies, Dendrocitta treepies, racket-tailed treepies Crypsirina, and ratchet-tailed treepies Temnurus. The Pica genus of pied magpies has three species, widely distributed throughout the Northern Hemisphere, but geographically distinct.

On the central Asian desert scrub and steppe, stretching from Iran and Turkmenistan in the west to Tibet and Mongolia in the east, live the Podoces and Pseudopodoces ground-jays. Higher altitudes are occupied by the alpine chough (Pyrrho-corax graculus). Both the alpine and the lower-altitude red-billed chough (Pyrrhocorax pyrrhocorax) range through central and southern Europe.

The mountainous, coniferous forests of the Old World contain the Nucifraga nutcrackers, a genus of three species. The six Garrulus and Perisoreus jays occupy a wider variety of forest habitats in the Old World, including deciduous, mixed, and coniferous woodland. The Clark's nutcracker (Nucifraga columbiana) and gray jay (Perisoreus canadensis) are the only members of these genera to colonize the forests of North America.

The New World jays (36 species) are unique to the Americas, found in most forest and scrub south of the Canadian boreal forest. They are all bluish in color, with the exception of the brown jay (Cyanocorax morio). The crested Cyanocitta genus is found in woodland, parks, and gardens throughout North America; the Steller's jay (Cyanocitta stelleri) replacing the blue jay in the west and south. The crestless Cyanocola genus of southern United States, Mexico, and Central America includes the three species of scrub-jay. The largest genus in the Americas, Cyanocorax, consists of 16 similar species, which range through the forests of Central and South America, with northeast Argentina their southernmost limit.

The mostly blackish Corvus genus is the biggest (48 species) and most wide ranging of all genera. It is the only genus found in Africa south of the Sahara, and the only one represented in Australia, where there are five species. The distribution of the most widespread Australian species, the Australian raven (Corvus coronoides) in the east, south, and southwest of Australia corresponds with that of sheep. The majority of island endemics belong in this genus. Most are in the islands of the Pacific and Southeast Asia. Oddly, although no corvids other than jays are found in South America, five Corvus species have colonized the West Indies.

Wide-ranging Corvus species include the northern raven (Corvus corax), which has colonized much open country of the Northern Hemisphere, and the pied crow (Corvus alius), which adapts well to human habitation and is Africa's most widespread corvid, found in the southern half of the continent. Coexistence with human settlement has enabled other crows to flourish. The American crow (Corvus brachyrhynchos) in North America and the carrion crow (Corvus corone) of Europe and Asia are found in both rural and urban areas. In the twenty-first century, the house crow (Corvus splendens) may prove to be the most successful colonist of all. The native Indian subcontinent population is flourishing, but the bird's readiness to board ships heading for other parts of the world has enabled it colonize and thrive in Malaysia, the Middle East, and Africa. In the South African city of Durban alone, the population reached 12,000 birds just 12 years after the first sighting.

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