About Apus pacificus (Latham, 1801)
The Pacific swift, Apus pacificus (Latham, 1801), measures 17–18 cm (6.7–7.1 in) in length, making it the largest species in the Apus swift genus. It has a wingspan of 43 to 54 cm (17 to 21 in). Females average 44.5 g (1.57 oz), which is slightly heavier than males that average 42.5 g (1.50 oz). Its general shape is similar to the common swift, but it has slightly longer wings, a more protruding head, a deeper tail fork, and a broader rump. Its upperparts are black, except for a white rump band and a somewhat greyer head. The underparts are black, though white feather fringes give the belly a scaly appearance when viewed clearly from below. The tail and upper wings are black, while the underwings are brown. The eyes are brown, and the small bill and very short legs are black. The sexes have identical plumage. Juveniles differ from adults only by pale fringes on their feathers, most noticeably on the wings. The southern subspecies, A. p. kurodae, has a narrower white rump patch than the nominate form: 15 mm (0.6 in) versus 20 mm (0.8 in), plus a grey throat and blacker underparts. Juveniles of migratory Apus swifts undergo a partial moult before migration, but keep their larger wing feathers. Moult is completed on the wintering grounds, where adults undergo a complete moult. This species is usually straightforward to identify. The white-rumped swift is similar to the Pacific swift, but its slender body and long, deeply forked tail make it look quite different from the more powerfully built Pacific swift. A common identification mistake can occur with a partially leucistic common swift that has a white rump. With careful observation, the Pacific swift can be distinguished by its deeper tail fork, longer wings, larger head, larger white throat patch, and patterned underparts. In parts of Southeast Asia, migrating Pacific swifts pass through the resident ranges of former subspecies, so clear views are required to confirm correct identification. The nominate subspecies, A. p. pacificus, breeds in eastern Asia from the Ob River northeast to Kamchatka, and east to the Kuril Islands, Sakhalin, and Japan. It is strongly migratory, and winters in southern Indonesia, Melanesia, and Australia, including Tasmania. It is a common migrant through coastal Malaysia, Sumatra, and Java, with vast numbers crossing the Strait of Malacca. Subspecies A. p. kurodae breeds from southeastern Tibet through eastern China to southern Japan, Taiwan, and Orchid Island. It is a relatively short-distance migrant, wintering in the Philippines, Malaysia, and northern Indonesia. As a powerful long-distance migrant, the nominate subspecies of Pacific swift has occurred as a vagrant far outside its normal range. Individual birds have been recorded in Brunei, the Maldives, New Zealand, and Macquarie Island, and there have been multiple records in the Seychelles. In the United States, this species is casual in the Pribilof and Aleutian Islands. A claimed 2010 sighting from the Yukon will be the first record for Canada and the North American mainland if it is ratified. In South America, there is a 1959 record from Colombia. As of 2013, there are 13 European records, from Denmark (two), Spain, Sweden (four), and the UK (seven). It is possible this number overstates the true count of visiting birds. All the listed countries had a sighting on different dates in the summer of 2013, which could all come from a single wandering bird. The four most recent English records in 2005, 2008, 2011, and 2013 all include sightings at Spurn, East Yorkshire, and may refer to the same returning individual. A mainly aerial species, this swift is not restricted to specific land habitats or climatic zones. It breeds from the Arctic to subtropical China, and from sea level to at least 3,000 m (9,800 ft) in Japan. It is often found around human settlements. It generally winters in lowlands, and in Australia it occurs in arid areas, as well as in towns and along the coast. Flocks of thousands may appear when there are hot strong winds. Pacific swifts often travel and feed alongside white-throated needletails. The Pacific swift probably sleeps in flight when it is not nesting, a behaviour confirmed to occur in the common swift and suspected in other Apus species, but there is an Australian record of these swifts roosting in a tree, and they are occasionally seen landing briefly on the ground or on vertical surfaces.
