IDENTIFICATION

VOCALISATIONS

Moderately high-pitched often extended excited trilling, especially when in foraging flocks.

DISTRIBUTION & HABITAT PREFERENCE

The resident population mainly occurs in urban Kowloon and towns in the New Territories, with only small numbers on HK and the Outlying Islands. Birds range widely when foraging, however. Migrant flocks mainly occur over rural areas, with the largest numbers found over fish ponds in the northwest New Territories.

OCCURRENCE

The 2019 breeding survey by the HKBWS Swift and Swallow Research Group (Wong in prep.) found 2,032 active nests in the territory. Although this is an increase over the 866 nests found in a similar survey in 2008 (Anon 2009), the 2019 survey was far more comprehensive, covering 164 sites c.f. 52 sites in 2008.

Most of these (1,859 active nests) were in urban areas of the New Territories, with the greatest number in Sha Tin followed by the North and Yuen Long districts. Small numbers were also noted in Kowloon and on HK Island and the Outlying Islands.

Of the sites surveyed, nest density was highest at the Chinese University of HK, where a total of 183 nests was observed on the library building. However, this marked a steep decline from the 455 nests recorded on the same building in 2015, apparently due to disturbance by a breeding pair of Crested Mynas Acridotheres cristatellus (Wong 2021).

There is evidence of a more general decline in the numbers of House Swifts breeding in the territory. Wong (op. cit.) noted that a nesting survey in three towns in the NT showed a decline from 1,324 nests in 1991 to 310 nests in 2008. Breeding surveys also revealed a distributional decline from 39.2% of squares in 1993-96 to 12.1% of squares in 2016-2019.

House Swift also occurs as a spring passage migrant (largely mid-January to mid-April) in variable numbers, mainly to the Deep Bay area. The highest count before 1999 was 3,000 on 18 March 1985, 30 March 1991 and 26 February 1993, all at Mai Po. Numbers in recent years are much reduced with annual peak counts all under 1,000 – sometimes considerably fewer – apart from an exceptional 4,000 at San Tin on 12 February 2015 (Figure 1). The reason for this decline is unclear. Welch et al. (2016) suggested it may be due to a change in the frequency and timing of suitable weather conditions, changes in local fishpond management or changes to habitats outside HK.

The House Swift appears to have colonised in the 1950s. Swinhoe (1861) found it resident further east along the coast at Xiamen but recorded a small party on only one date in HK. There were no further reports until the spring or summer of 1941 (Herklots 1953). Subsequently, Humphreys (1959) considered that breeding was first proven on HK Island in 1953 and in the New Territories from 1955. Walker (1958) gave totals of 14 breeding pairs in Kowloon and the New Territories and also considered the species a common passage migrant from 23 January to 31 May and 6 September to 8 October.

BREEDING

Nest sites are found mainly in the towns of the New Territories and in urban Kowloon. These are built communally under the eaves of buildings in untidy, overlapping clusters. They are constructed of vegetable matter and feathers, and sometimes include detritus such as polythene and paper; these materials are cemented together with the birds’ saliva. Not all nests are re-used from season to season. Of the total of 3,282 nests found in 2019, 2,032 (62%) were in active use.

House Swifts sometimes build their nests on top of inactive Barn Swallow Hirundo rustica nests and occasionally also appropriate active nests of this species (Wong 1991, 1994). During 14-22 May 2020, three House Swifts were observed occupying an active swallow nest at Palm Springs Commercial Centre. The young swallows were close to fledging and the attending parents were alarming though still feeding their young.  This behaviour happened over several days before the swifts departed. Later in the month, a nearby inactive swallow nest was taken over by House Swifts, which transformed the open mud-cup of the swallow nest into a closed chamber with a feather-lined entrance hole (D. J. Stanton pers. obs.).

The nesting season is between April and September. Unfledged chicks have been recorded up to 10 September, which suggests some pairs are double- or perhaps even triple-brooded. Birds may be present at colony sites throughout the year as the nests are used as roosting sites outside the breeding season.

BEHAVIOUR, FORAGING & DIET

The House Swift is an opportunistic aerial feeder preying almost exclusively on insects. Residents forage in groups above urban areas, fish ponds, open areas, hillsides and mountain tops, sometimes at considerable height when their presence is only revealed by their calls. Migrants are recorded most often over fish ponds, particularly in overcast conditions when they may fly low over the water, sometimes in their hundreds, feeding on swarms of chironomids.

The dietary composition of resident House Swifts in HK was analysed by DNA barcoding using faecal samples (Chung et al. 2021). Ten different orders and 44 families from three different classes of Arthropoda were identified in the collected faecal samples. Hymenoptera, Hemiptera and Diptera were the most prevalent groups of prey found in the samples.

Within the Hymenoptera, food sources recorded were bees (Apidae), wasps (Braconidae, Chalcididae, Eulophidae, Ichneumonidae, and Platygastridae), and ants (Formicidae). In the Hemiptera group, aphids (Aphididae), leafhoppers (Cicadellidae), planthoppers (Delphacidae), plant bugs (Miridae), and seed bugs (Rhyparochromidae) were detected, with seed bugs and plant bugs occurring most frequently. Within Diptera, mosquitoes (Culicidae) were the most common food source, followed by house flies (Muscidae) and tachinid flies (Tachinidae).

Differences in the dietary composition of House Swifts during the breeding (April to September) and non-breeding (October to March) seasons were also found. Hymenoptera, particularly ants (Formicidae), were predominant in the diet during the breeding season, whereas Diptera and Hemiptera were predominant during the non-breeding season.

RANGE & SYSTEMATICS

House Swift occurs in the Oriental region. Four subspecies are recognised, one of which, A. n. nipalensis, is found in HK. It was previously considered conspecific with Little Swift A. affinis.

A. n. nipalensis breeds from Nepal east to southeast China, and south through Assam and southeast Asia; this race is also considered resident in Japan. In China it occurs in the southern half of the country (Liu and Chen 2020). It is regarded as mainly resident in its range, but HK records indicate northerly movement through southern China in spring. A. n. kuntzi is resident in Taiwan. A. n. subfurcatus and A. n. furcatus are resident from the Malay Peninsula, Borneo and the Philippines south to Sumatra, Java and Bali (Chantler & Boesman 2020).

CONSERVATION STATUS

IUCN: Least Concern. Population trend increasing.