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Rather small, dark grey-brown swift, wit h grey chin and throat difficult to see. Except in late autumn and early winter, Plain Swift restricted to Madeira and Canary Islands, which it shares with migrant Swift and breeding and migrant Pallid Swift. Overlap of 3 similar Apus swifts creates severe test in field identification, though this passable given lengthy comparison in good light and at close range.
Breeds in 2 small groups of subtropical mountainous oceanic islands, in which it forms counterpart to Cape Verde Swift. In Canary Islands breeds at higher altitude than congeners, in caves and crevices in walls of higher barrancos or ravines, foraging above pinewoods and skimming over Retama bushes in full bloom which attract insects. Usually at above 300 m; a high flier, mounting to become a mere speck in the sky or even beyond visual range. In Madeira, also frequents higher peaks and gullies or ribeiras in summer, nesting in deep clefts of rocks, but commonly nesting and roosting in some sea-cliffs, and even breeding on solitary rock in sea.
Apus unicolor breeds only in Europe, with its entire global breeding range confined to Madeira and the Canary Islands. The current size of the population on Madeira is unknown, but the total breeding population is small (possibly as few as 2,500 pairs), and was probably stable between 1970-1990. Although trend data were not available during 1990-2000, there was no evidence to suggest that the species declined. Nevertheless, its population size renders it susceptible to the risks affecting small populations and is labeled rare.
It is endemic to Macaronesia in the Madeira and Canary archipelagos. Found throughout the island of Madeira all year round, although the population is smaller in winter. Has also been seen in Morocco in winter
This species has an estimated global Extent of Occurrence of 20,000-50,000 kmē. It has a large global population, including an estimated 5,000-20,000 individuals in Europe (BirdLife International in prep.). Global population trends have not been quantified, but populations appear to be stable so the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]
This species nests in small colonies, laying two eggs at a time. Two sets of eggs are frequently laid each year.
Largely migratory. Present all year on Madeira, numbers considerably reduced in winter though still quite common. Further south, on Canary Islands, largely migratory though winter status not clear: odd birds present at any time, but, at least occasionally, flocks occur in late December. Migratory birds depart September to mid-October and return January-March to mid-October. Winter quarters of emigrants unknown, but presumably in Africa; for winter occurrence in Morocco.