I saw my first Pacific Swift in Copenhagen, Denmark, in June 2010 just a few weeks before moving to China. Since then I have seen many more in north-east China – it is a common migrant through Beijing in spring and autumn. Last year, a thorough assessment of four Pacific Swift subspecies by Paul Leader (Leader, P J. 2011. Taxonomy of the Pacific Swift Apus pacificus Latham, 1802, complex. Bulletin of the British Ornithologists’ Club 131: 81-93) found that they may deserve species status. This is an extract from an article in Birdwatch magazine by David Callahan in June 2011:
“Four subspecies of Pacific Swift are generally recognised, and the species as it is known traditionally has a wide breeding distribution throughout the eastern Palearctic. It is a long distance migrant, wintering south to Indonesia and Australasia.
Leader (2011) measured and assessed the plumage of 146 specimens of Pacific Swift from four different museums across Eurasia, as befits a species with pan-Palearctic records. The four forms were found to differ in wing and tail measurements, as well as the size and shape of their distinctive white rump patch, white throat patch, pale underpart fringes and the colour of the underwing coverts.
The new prospective species are as follows:
Pacific Swift Apus pacificus: cleaner white throat patch, a slightly longer tail fork and tail length, and the broadest rump patch by a margin; breeds from Siberia through to Japan, winters from Indonesia south and east to Tasmania (incorporating the subspecies A p pacificus and A p kurodae – other subspecies were found to be invalid).
Sàlim Ali’s Swift A salimali: five to 10 mm longer tail but with similar wing length to A pacificus, throat patch forming a thin white strip half the width of the other three forms, thinnest at the bill end, and very little white to the underpart feathers; breeds at high altitude on the east Tibetan Plateau and west Sichuan, China, but its winter range is unknown.
Blyth’s Swift A leuconyx: the smallest of the four forms, with the rump patch consistently narrow, brown-tinged crown and nape contrasting with the glossy black mantle, broad white thoat patch with black shaft streaks extending onto the upper breast, hardly any pale underpart fringing; mid- to high-altitude breeder across the Himalayan part of the Indian subcontinent into Bhutan and Nepal.
Cook’s Swift A cooki: shallowest tail fork, first primary the longest (the other three have P2 as the longest), narrow white rump patch with dark, club-shaped shaft streaking, overall black upper- and underpart-coloration (brownish tinge in the other three), broad well-defined fringes to the underpart feathers, throat patch off-white with broad black shaft streaks, black contrasting underwing coverts, and green iridescence to upperparts with some white fringed scapulars; restricted range in limestone caves in northern south-east Asia, and a short distance migrant to then south.”
During my recent trip to Jiuzhaigou, I enjoyed watching a flock of “Fork-tailed” Swifts wheeling around the mountain tops at around 3,000m altitude. A (poor quality) image of one of them is below.
Compare this image with a couple of Pacific Swifts taken at Laotieshan in May 2011:
To my eyes at least the bird from Jiuzhaigou appears longer tailed and with a narrower white patch on the rump. I don’t have access to the article by Paul Leader so I am not sure on precise range but I think there is a good chance this is a Salim Ali’s Swift. Comments welcome!