Difficulties Identifying Three-Toed Swiftlets Aerodramus Papuensis in New Guinea

Australian Field Ornithology 2018, 35, 126–128 http://dx.doi.org/10.20938/afo35126128

Difficulties identifying Three-toed SwiftletsAerodramus papuensis in New Guinea

Michael Tarburton

School of Science and Technology, Pacific Adventist University, Private Mail Bag, Boroko. Papua New Guinea. Email: [email protected]

Abstract. This note shows that a pale throat is not a reliable means to distinguish the Three-toed Swiftlet Aerodramus papuensis from three other New Guinea swiftlets (Uniform A. vanikorensis, Bare-legged A. nuditarsus and Mountain Swiftlets A. hirundinaceus). It also gives weights and measurements for a much larger sample of the four species than previously known, and for the first time describes the calls and roosting times of theThree-toed Swiftlet.

In the hand, the Three-toed Swiftlet Aerodramus papuensis on 12–18 June 2000 and 27–29 July 2005, I observed is easy to identify because it is the only swiftlet that has Three-toed Swiftlets feeding outside the cave-entrance, three toes. Identifying it in the field is another matter. It over Mt Palawap, and noticed that sometimes (but not has been claimed that “most distinctively, it has a silvery- always) the throat appeared to be paler than the chest and grey throat that contrasts with the remainder of the sooty- stomach. By following and closely scrutinising one bird at grey underparts” (Chantler & Driessens 1995, p. 136). a time, I realised that the appearance of the throat varied This same feature has been used by other authors as from being the same colour as the chest and stomach to well (Salomonsen 1983; Beehler et al. 1986; Gregory being lighter than the chest, depending on the angle of the 2017). Pratt & Beehler (2014) in their second edition of the bird’s axis to the light source and the observer. I checked Birds of New Guinea deleted the statement that the pale this with some of the birds that we subsequently caught throat can be used in the field to distinguish the species inside the cave. The two accompanying photographs (as suggested in their earlier edition: Beehler et al. 1986), (Figure 1) show that the same individual can have a in response to my sending them photographs to show throat either lighter in colour or uniform with the chest. its deceptiveness. In-the-field and in-the-hand evidence It is unfortunate that the flash went off for one of these both show that the pale throat is not a reliable means to photographs but not the other. However, the difference was distinguish this species from the Uniform A. vanikorensis, real in natural light, and it is not a result of one photograph Bare-legged A. nuditarsus and Mountain Swiftlets A. having natural light and one having electronic light. This hirundinaceus. Beehler et al. (1986), Pratt & Beehler finding makes the identification of this species in the field a (2014) and Gregory (2017) indicated that its smaller size little more difficult. can be used to separate it from the Bare-legged Swiftlet, Because published measurements of this species and that Uniform and Mountain Swiftlets are both smaller are few (n = 23) and because I have considerably more than the Three-toed Swiftlet. Chantler & Driessens (1995) measurements from both museum skins and live birds, suggested that the Three-toed and Bare-legged Swiftlets these are recorded here. The museum skins are 17 birds are similar in size. from Wengomanga, (~–7.300, 146.21666) and eight from On two visits to Losapi Cave, Papua New Guinea (PNG), Hamo Aseki near Menyamya (–7.11123, 145.99434) (both

a b Table 1. Standard measurements of the Three-toed Swiftlet: weight (g) and other measurements (mm); n = number of birds.

Morphological feature Average Minimum Maximum n

Weight 19.5 15.4 25.4 107 Wing (flattened) 135 120 142 101 Outer rectrix 54 47 60 89 Inner rectrix 46.6 40 52 77 Tail 44 1 Wing span 314.4 306 324 8 Length 124.9 116 131 14 Tarsus 11.9 9.2 14.2 32 Middle toe 6.6 5.2 8.4 32 Claw 4.9 3.7 6.2 32 Figure 1. A Three-toed Swiftlet showing variable colour of Culmen 8.8 5.6 10 32 throat compared with chest, photographs (a) with flash Exposed culmen 5.0 4.0 5.7 32 and (b) without flash. Photo: Michael Tarburton Three-toed Swiftlet identification 127

in Morobe Province, PNG) (all these skins are in the Australian National Wildlife Collection, Canberra, ACT), four birds from Losapi Cave (skins in the PNG Museum), one bird from Luplupwiatem Cave (Western Province, PNG), one from Manjim on the Ganz River (~–5.520426, 144.452450) and one from Mt Orata (~–6.04315, 144.607) in the Kubor Mountains (Western Highlands Province, PNG) (all these skins are in the Australian Museum, Sydney). I also have measurements from 68 live birds caught at Losapi Cave and 11 live birds caught at Luleve Cave near Losapi Cave (–6.649167, 145.161389, at 1362 m above sea-level in Chimbu Province) 7 km west of Herowana, Eastern Province, PNG. These total 111 birds, and the measurements taken from them are given in Table 1. Figure 2. Three-toed Swiftlet showing some feathers on Does the larger sample still support the size differences the tarsus. Photo: Michael Tarburton given in the literature? Tables 2 and 3 enable us to determine this. The Three-toed Swiftlet averages only divide, and only south of that divide in the east (based on 1 mm shorter in wing-length and is 2.5 g lighter than the a dubious record discovered by Somadikarta (1975) and Bare-legged Swiftlet. With the huge overlap in the ranges thought to be close to Port Moresby). This distribution of these measurements, however, this distinction could not was also accepted by Salomonsen (1983), Beehler et al. be made in the hand, let alone in the field. Is the Three- (1986) and Chantler & Driessens (1995). The locations of toed Swiftlet larger than Uniform and Mountain Swiftlets? the birds in the present paper confirm that the distribution There is significant difference in their weights, so weight of the Three-toed Swiftlet does extend south of the central could be used to distinguish birds in the hand, but there is ranges in PNG, but not just in the east. overlap in the range of wing-lengths so this measure could not separate all individuals of the species in the hand or in Another feature that helped Somadikarta (1967) the field. distinguish the Three-toed Swiftlet from the Bare-legged It was when Somadikarta (1967) realised that the Three- Swiftlet was that the former had a densely feathered toed Swiftlet subspecies of Whitehead’s Swiftlet Collocalia tarsus. All 90 Three-toed Swiftlets that I examined for this whiteheadi (now Aerodramus whiteheadi) had only three character had a feathered tarsus, even though some of the toes that this was designated a full species. Somadikarta individuals were moulting at the time. The tarsi of some (1967) also defined the distribution of the Three-toed had only sparse feathering, but none was naked. Figure 2 Swiftlet as being in New Guinea north of the central shows this feature.

Table 2. Wing-lengths (mm) for similar Aerodramus swiftlet species in Papua New Guinea: mean ± standard error and confidence intervals of 95% and 99% per z-score, minimum and maximum Significance is given by comparing the z-score with that of the nearest mean, and therefore will also be significant to the other two means);n = number of birds; S = significance (* = significant, ns = not significant).

Species Mean Minimum Maximum n Mean 95% 99% S

Three-toed A. papuensis 135 ± 0.03 0.06 0.08 * 120 142 101 Bare-legged A. nuditarsus 136 ± 1.11 2.18 2.86 ns 131 142 10 Mountain A. hirundinaceus 120 ± 0.7 1.4 1.8 * 109 137 81 Uniform A. vanikorensis 117.5 ± 0.28 0.53 0.70 * 101 130 389

Table 3. Weights (g) for similar Aerodramus swiftlet species in Papua New Guinea: mean ± standard error and confidence intervals of 95% and 99% per z-score, minimum and maximum. Significance is given by comparing the z-score with that of the nearest mean, and therefore will also be significant to the other two means); n = number of birds; S = significance (* = significant, ns = not significant).

Species Mean Minimum Maximum n Mean 95% 99% S Three-toed A. papuensis 19.5 ± 0.2 0.4 0.5 * 15.4 25.4 107 Bare-legged A. nuditarsus 22 ± 0.2 0.4 0.5 * 21.5 23 8 Mountain A. hirundinaceus 9.5 ± 0.1 0.2 0.3 * 7.5 11.4 52 Uniform A. vanikorensis 10.3 ± 0.15 0.29 0.39 * 5.4 14 120 128 Australian Field Ornithology M. Tarburton

Gregory (2017, p. 82) noted for the Three-toed Swiftlet, Acknowledgements a presumed resident in New Guinea: “echolocation I thank Cliff Frith for his help with editing the manuscript as well as abilities are uncertain, vocalisation undescribed and some an anonymous referee for helpful input. nocturnal or crepuscular activities possible”. Beehler & Pratt (2014) said that this species echolocates with clicking calls but agreed that there is no information on its flight call. References My visits to Losapi and Lulevi Caves were in June 2000 Beehler, B.M., Pratt, T.K. & Zimmerman, D.A. (1986). Birds of and July 2005, the middle of the non-breeding season, New Guinea. Princeton University Press, Princeton, New thus indicating that Three-toed Swiftlets roost throughout Jersey, USA. the year in their breeding caves. On some evenings, Chantler, P. & Driessens, G. (1995). Swifts: A Guide to the Swifts they returned to roost just after sunset, but sometimes and Treeswifts of the World. Pica Press, Sussex, UK. Gregory, P. (2017). Birds of New Guinea, Including Bismarck many were returning well after midnight and were using Archipelago and Bougainville.Lynx Edicions, Barcelona, Spain. echolocation to fly to the second large chamber where they Pratt, T.K. & Beehler, B.M. (2014). Birds of New Guinea. 2nd edn. slept. On 13 June 2000, the first bird returned at 1917 h, Princeton University Press, Princeton, New Jersey, USA. but on 18 June a few returned before midnight, then 89 Salomonsen, F. (1983). Revision of the Melanesian swiftlets entered between 0100 and 0300 h, suggesting that they (Apodes, Aves) and their conspecific forms in the Indo-Australian had been feeding a long way from the cave. On 27 July and Polynesian regions. Kongelige Danske Videnskabernes 2005, 154 entered the cave before midnight, and the next Selskab Biologiske Skrifter 23, 1–112. day one entered early in the afternoon, so they do not Somadikarta, S. (1967). A recharacterization of Collocalia papuensis Rand, the Three toed Swiftlet. Proceedings of the have the regularity that I have observed in White-rumped United States National Museum 3629, 1–8. A. spodiopygius and Australian Swiftlets A. terraereginae. Somadikarta, S. (1975). An unrecorded specimen of Collocalia On 31 July 2005, 158 Three-toed Swiftlets were counted papuensis Rand. Bulletin of the British Ornithologists’ Club 95, leaving the cave, indicating that 154 was close to the total 41–45. population for Losapi Cave. As well as the echolocatory call used inside the cave, I recorded two other calls used while the birds were feeding over Mt Palawap, 3 km from Received 28 April 2018, accepted 29 July 2018, the cave. One I characterised as chitty chew chew and the published online 14 November 2018 other, given during fast pursuits, as ditdee de deer.