White-rumped Swiftlet Aerodramus spodiopygius Scientific name definitions

10–11·5 cm; male 6–7·5 g, female 6–8·5 g (leucopygius). A small to medium-sized swiftlet with a deep tail-fork; highly polytypic. Rump pale throughout, but degree of paleness varies geographically. Most races are much paler below than A. vanikorensis, practically pure white in the case of leucopygius, although throat is often rather dark; races townsendi, desolatus and epiensis are sooty below. Degree of tarsal feathering is variable both within and especially among races: heavily feathered in epiensis and ingens, but unfeathered or only lightly feathered in most other races; in ingens, dark brown face shows greater contrast with pale underparts. Species capable of echolocation.

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Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Occurs over wide range of island habitats, from lowlands to highlands, on New Britain to 1890 m and on Bougainville to 1600 m. On Santa Isabel occurs above 700 m over montane forest.

Resident. Vagrant to New Zealand.

Race assimilis of Fiji compared with A. terraereginae chilla­goensis of Australia: present species takes smaller prey in smaller boluses, containing more individuals; 32 boluses of present species contained 167 species of invertebrate, whereas 32 boluses of A. terraereginae contained 303 species, averaging 10 species more per bolus than in present species. Can be encountered foraging in large groups, alone or with sympatric congeners. Forages over a range of elevations.

Main vocalization is a continuously repeated rhythmic phrase, “twee-twee-chew-chew”or “twee-twee-chrrrr”. This results in a pleasant-sounding twittering, sometimes interspersed by drawn-out reeling notes. Also a repeated dry “chi-chi-chi”. Known to use echolocation by continuously emitting clicking notes within its nesting caves.

Season on Vanuatu Oct–Feb; active colony reported on Lou I (S of Manus in Admiralty Is), Mar; on Fiji first eggs laid Sept–Oct, most chicks fledging Jan, but replacement clutches extend season into Feb, sometimes Mar. Colonial. Nests in caves , including sea-caves, or similar situations, including man-made structures, but also below overhanging rocks in gulleys or under fallen trees; mainland sites are used, as well as island ones. ­Substantial self-supporting, bracket-shaped nest with shallow central depression, consisting of fine vegetable matter; on Fiji lichens, liverworts, filmy ferns and mosses predominate, though grasses used extensively at 1 site, agglutinated with firm saliva and attached to cave walls; nests sometimes cylinder-shaped where birds add to them each time they breed. On Fiji nests of assimilis typically closely bunched, though sometimes 1–2 m apart and exceptionally 70 m, often attached not to wall but to other nests; measure 50 × 50 × 21 mm, mean volume index 52·5 cm³. Clutch of 1 or 2 white eggs, though mean of 57 clutches 1·98; laying interval 3–5 days, mean 4; incubation period 22–25 days, shared by both parents who also brood at night; lost clutches and even lost broods typically replaced within 9–14 days; evidence suggests that sometimes more than 1 female lays eggs in same nest. Second chick hatches within 1·5 days of first; nestling period 45–46 days; daily feeding rate 2·8 visits. Average breeding success 53%, with 1·1 young fledged per breeding effort.

Not globally threatened. Fairly common to abundant over much of range; 8 colonies in Fiji contained over 1400 nests in 1975 and 1976. Commonest swiftlet in W New Britain. However, decline noted in some parts of range, e.g. by 1960’s epiensis occurred, uncommonly, only on Malo I and W coastal Espíritu Santo I in Vanuatu. Local and uncommon on Santa Isabel, Solomon Is.