Australian Field Ornithology 2018, 35, 129–131 http://dx.doi.org/10.20938/afo35129131 Mayr’s Swiftlet Aerodramus orientalis: A reinterpretation Michael Tarburton School of Science and Technology, Pacific Adventist University, Private Mail Bag, Boroko, Papua New Guinea. Email: [email protected] Abstract. Mayr’s Swiftlet Aerodramus orientalis was described from two specimens, one each from the islands of Guadalcanal and New Ireland, 880 km apart and with many other islands between. Both had blue gloss on the dorsal surface and a pale rump and, although one had naked tarsi, the other had feathered tarsi. It is here shown that these features are found on some Uniform Swiftlets A. vanikorensis, with which there is considerable size overlap, and so it is more consistent to subsume Mayr’s Swiftlet into the Uniform Swiftlet. The first specimen of Mayr’s Swiftlet (now Aerodramus orientalis) was collected from Guadalcanal, Solomon Islands, by R. H. Beck in 1927. Upon examination, Mayr (1935) assigned it to Collocalia lowi as a new subspecies, orientalis. It was reported to be similar to C. lowi whiteheadi but darker and with a pale rump. The wing-length was said to be 132 mm and the tarsus to have a few feathers. A second specimen was collected from the Lelet Plateau on New Ireland by Salomonsen (1962). This was said to be similar to the Bare-legged Swiftlet C. (now = Aerodramus) nuditarsus (even having a naked tarsus) except that it had a grey band on the rump, and a much stronger bluish gloss on the upperparts. He named it C. whiteheadi leletensis. Later, Mayr (1945) included both leletensis and orientalis as subspecies of Whitehead’s Swiftlet Collocalia whiteheadi. However, Somadikarta (1967) considered C. orientalis to be a separate species because it alone had a pale rump, a fourth toe, and a thinly feathered tarsus, separating it from the Three-toed C. papuensis, Bare- legged and Whitehead’s Swiftlets. Somadikarta then went one step further to place letensis and orientalis together as subspecies of orientalis because they alone have the pale-grey rump. Currently, these swiftlets are all placed in the genus Aerodramus (Brooke 1972). Subsequently, Ripley (1983) described a swiftlet skin Figure 1. Dorsal surface of a live Uniform Swiftlet collected by Bruce Beehler and Don Hadden at 1200 m Aerodramus vanikorensis from Mount Diamond, Papua above sea-level (asl) 15 km south-south-west of Arawa, New Guinea. Photo: Michael Tarburton Bougainville, as C. whiteheadi. To this classification, Ripley also placed the two skins leletensis and orientalis that are discussed above. He believed that Somadikarta (1967) feature be used to separate Mayr’s Swiftlet from the was not justified in separating them from whiteheadi as others? I was able to catch and examine eight Uniform their larger measurements and paler rump united them Swiftlets just south of Lelet village, inland from Dalom with the Philippine birds. village in New Ireland, and all had naked tarsi. On the other It appears that in dealing with these three specimens of hand, some Uniform Swiftlets that I caught in New Guinea Mayr’s Swiftlet it has been ignored that numerous Uniform had naked tarsi but some had tarsal feathering. In addition, Swiftlets Aerodramus vanikorensis from New Ireland, New because these feathers moult, this feature cannot always Guinea and other locations have a pale rump and throat, be used to identify a species. Ripley (1983) did not state and so leletensis is probably referrable to A. vanikorensis. whether the Bougainville specimen had feathers on its Mayr (1936) cited another example of A. vanikorensis from tarsi. Whereas Somadikarta (1994) found tarsal feathering Palau, Caroline Islands, with a pale rump though not as in northern Marquesan Swiftlets A. ocistus ocistus but not pale as in the White-rumped Swiftlet A. spodiopygius. So in southern Marquesan Swiftlets A. o. gilliardi, Cibois et al. this feature cannot be used to separate Mayr’s from the (2018) found naked and feathered tarsi in skins and live Uniform Swiftlet. birds in the field for both northern and southern birds. The second feature of Mayr’s Swiftlet was whether the The third feature used to differentiate Mayr’s from the tarsus had feathers or not. The single original specimen Uniform Swiftlet was that both subspecies of Mayr’s of leletensis had a naked tarsus, but the single specimen Swiftlet, A. o. leletensis and A. o. orientalis are said to of orientalis had some feathers there. So how could that have a varying degree of blue gloss on their upper surface. 130 Australian Field Ornithology M. Tarburton Mayr (1945), in contrast, described the dorsal surface of the Bougainville bird’s wing (130 mm) was intermediate the Uniform Swiftlet as black with a faint greenish gloss. between leletensis (134 mm) and orientalis (127 mm). The bird from Bougainville described by Ripley (1983) is However, Mayr (1935) gave the wing-length of orientalis said to be browner than A. o. leletensis and A. o. orientalis, as 132 mm and, because the two outer primaries were still with gloss not being mentioned. in moult, the wing-length would actually be >132 mm. For Whether there is a green or blue or even no gloss (just a a large sample size, making this distinction would probably dull brown) in the Apodidae is often not a permanent feature be meaningless, but we have only three specimens (Collins 1968; Koon & Cranbrook 2002), and so it is unwise assigned to this species. to use the presence or absence of dorsal gloss to separate The Bougainville bird was collected at an altitude of species or subspecies. Dorsal gloss occurs in many of 1200 m asl (Ripley 1983). Uniform Swiftlets collected at the Apodidae, as was first pointed out (for Chimney Swift 900 m asl from the Lelet Plateau in New Ireland and at Chaetura pelagica) by Sutton in 1928 (Sutton 1928). Then, 1250 m asl in south-eastern New Guinea showed a in 1948, Sutton and Phelps found it to be true of Vaux’s significant increase in size compared with birds collected Swift C. vauxi as well (Sutton & Phelps 1948). Ferguson- nearby but below 100 m asl from both sites (Salomonsen Lees (1960) found it true for the White-throated Needletail 1983, 1985). This altitudinal variation, shown in Table Hirundapus caudacutus. In 1968, Collins (1968) pointed 1, applies to other swiftlet species as well (Salomonsen out that Chapman’s Swift Chaetura chapmani specimens in 1985), and as all Whitehead’s Swiftlet specimens were fresh plumage exhibit a distinct greenish iridescence to the collected from two mountains (Oberholser 1906), this feathers of the darker areas. Collins (1968) reiterated that would help to explain their large size. this is purely a structural gloss. With the natural wear of the feathers, it changes from greenish to a bluish-purple gloss Comparing all the measurements available (Table 2), and eventually to a dull, completely lustreless, black-brown we can see that there is significant overlap between the shortly before the annual moult. This sequence of gloss wing-length of the three groups, signifying that size cannot colour changes contrasts with that described by Chantler & be used to differentiate A. orientalis as a distinct species. Driessens (2000), who mistakenly suggested (in describing I am confident that the overlap would be greater if the the Cave Swiftlet Collocalia linchi) that a fresh blue gloss wing-lengths for the high-altitude Uniform Swiftlets in my changes to greenish. Figure 1 shows the dorsal surface large sample were known. However, they are not known. of a Uniform Swiftlet from New Guinea, and it is clear that None of the previous authors have used the birds’ weight the new primary feathers and wing-coverts exhibit a green to indicate size but, when the weights are known, birds gloss, whereas the old ninth and tenth primaries are dull collected above 200 m asl weighed on average 12.3 g brown. This bird also displays the slightly pale rump found (n = 17) and those collected below 200 m asl weighed in some populations of the Uniform Swiftlet. 10.0 g (n = 90). The fourth feature used by Ripley (1983) to separate We do not have any mitochondrial sequencing for the these three swiftlets (A. leletensis, A. orientalis and the species discussed here, but it is interesting to note that both Bougainville specimen of A. whiteheadi) as A. whiteheadi Rheindt et al. (2014) and Cibois et al. (2018) have found was their being larger than the Uniform Swiftlet. He close links between both the Tahiti Swiftlet A. leucophaeus judged size on the basis of wing-length and said that and Marquesan Swiftlet, in eastern Polynesia, and the Table 1. Variation in wing-length (range and average) of the Uniform Swiftlet Aerodramus vanikorensis at different altitudes (Salomonsen 1985). Location Range (mm) Average (mm) Altitude (m asl) Sample size South-eastern New Guinea 113–117 115.5 <100 ‘a series’ 118–123 120.0 1250 ‘a series’ New Ireland 113–124 117.7 <100 67 117–125 122.3 900 3 Table 2. Wing-length (mm) of Mayr’s Swiftlet Aerodramus orientalis compared with that of the two Aerodramus species with which it might be merged. Data from live birds and museum skins; A = adults, J = juveniles, M = moulting birds; n = sample size. ‘Species’ A A + J + M n Range Average Range Average Mayr’s A. orientalis 130–133 132 127–134 130.3 3 Whitehead’s A. whiteheadi 128–140 135 123–140 129 10 Uniform A. vanikorensis 101–130 117.6 397 Mayr’s Swiftlet: Reinterpretation 131 Uniform Swiftlet in Melanesia, with >4000 km between Mayr, E. (1935).