IDENTIFICATION

19-20 cm. Sexes alike. A large, long-winged, blue-glossed dark-brown swift with pale grey saddle, ill-defined dusky throat, dark forehead and a white horseshoe on the rear flanks and undertail coverts. The tail is square-cut and has short protruding spines at the tip, but these are usually only visible at close range. Although said to appear shorter-bodied and slimmer than White-throated Needletail (Brazil 2018), distant birds are very difficult to separate in the field. At closer range, the head and throat pattern are distinctive.

VOCALISATIONS

There are no reports of birds vocalising in HK. However, Chantler and Driessens (1995) describe it as a ‘soft, rippling trill’.

DISTRIBUTION & HABITAT PREFERENCE

Silver-backed Needletails forage over fish ponds, marshes, agricultural land, grassy hills, forests and woodland. They occur at widespread sites, including the Deep Bay area, the eastern and central New Territories (particularly Tai Lam County Park), HK and outlying islands, most regularly at Po Toi.

OCCURRENCE

The first record of Silver-backed Needletail in HK was of four at Nim Wan on 31 March 1985. Until the late 1990s it was reported annually, most frequently in spring, often during periods of inclement weather and occasionally in summer. Almost 90% of records occurred between the end of March and the middle of April (Figure 1), with a peak in the first week of April. Most reports referred to flocks of up to 20, occasionally 50, and on six occasions 100 or more. Highest counts were 150 at Mai Po on 7 April 1992 and at Kam Tin on 2 April 1995.

Since 1999 the peak passage period has extended from the third week of March to the first week of April (Figure 1), although there was an unusual early movement of at least 146 birds in mid-March 2017 (70 at Tai Po Kau on 17 March and 76 at Shek Kong catchwater on 18 March); these are the highest figures since 1995. The total number of individuals recorded per annum from 1999 to 2020 varied from zero to low double-digit counts (no more than 33 in 17 of the years). The three best years were 2004, 2009 and 2017 with minimum totals of 93, 92 and 146 individuals respectively (Figure 2).

As with White-throated Needletail, there has been a substantial decline in records since the 1990s, although it is still almost annual in reduced numbers (Figure 2). The reason for the decline is unknown.

Silver-backed Needletail tends to pass through earlier than White-throated, but there is considerable overlap. Extreme spring dates are 2 March and 11 May. In summer, it was recorded on four occasions in four years from 8 June to 21 July 1989 to 1995.

There have been just two autumn records: a moulting adult was found dead at KFBG on 8 October 1992, and one was seen at Po Toi on 29 September 2009.

BEHAVIOUR, FORAGING AND DIET

Tends to move through quickly on passage but may remain in an area if feeding conditions are favourable. Thus, a flock of up to 76 birds remained at Shek Kong catchwater during 16-23 March 2017. Feeds on flying insects over fish ponds and forested hills.

RANGE & SYSTEMATICS

Monotypic, breeds in central Nepal, northeast India, north Myanmar, south China (east Guangxi and Hainan) and Taiwan; it winters in Thailand, the Malay Peninsula, Sumatra, and west Java. It is possible that birds passing through HK are going to Taiwan as that is the only location north of here where it is known to breed (Chantler and Driessens 1995).

CONSERVATION STATUS

IUCN: Least Concern. Population trend stable.