Description
The Socorro Dove is a medium-sized, principally terrestrial dove with long legs for a Zenaida dove. It is 26.5–34 cm long and weighs 190 g on average. In overall color pattern, it agrees with its relatives. It is considered to be a stronger-colored insular representative of the Mourning Dove. The male is deep cinnamon on its head and underparts, with an ear streak like its relatives. The nape is blue-grey and the neck has an iridescent pink patch, most prominent after moult. The upperparts are rufous brown. Female and juvenile coloration is slightly duller. The most conspicuous differences from the Mourning Dove - darker coloration and more well-developed feet - were useful amid the dark lava rock and the shady forests of its island home, where native mammalian predators were absent but constant threats from Red-tailed Hawks and Great Frigatebirds were present. The advertising call begins with a disyllabic coo, followed by three single calls, and ends with another disyllabic coo: "Coo-oo, OO, OO, OO, Coo-oo". Each of these 5 elements takes a little less than one second.
The arid and fairly barren Clarión Island, some 400 km (250 mi) west of Socorro, has an endemic subspecies of the Mourning Dove, Zenaida macroura clarionensis. These birds are roughly intermediate in appearance between the Socorro Dove and the mainland Mourning Doves. It is highly likely that they represent a later colonization by Mourning Doves (rather than "proto-Mourning Dove" stock), which evolved its phenotype independently from but in parallel with the Socorro birds. This would mean that predation by Great Frigatebirds is significant enough to select towards a cryptic darkening of the plumage, as these are the only predators of Z. m. clarionensis. On a semidesert island such as Clarión, birds would be expected to evolve towards lighter plumage - to better withstand the heat and lack of reliable freshwater sources - in accordance with Gloger's Rule.
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