IDENTIFICATION

VOCALISATIONS

The typical call is a somewhat explosive ‘kyeeow’ that descends sharply in pitch. This is uttered when flushed, when moving between foraging sites (including at night) and on nocturnal migration.

DISTRIBUTION & HABITAT PREFERENCE

Usually found in dense vegetation along streams, rivers and estuaries, particularly mangroves. Most breeding season records are from coastal mangrove areas such as those fringing Deep Bay, Tolo Harbour and Lantau, but especially at Mai Po. There are very few summer records from inland sites. Striated Heron was recorded in 4.4% of 1km squares during the 1993-96 breeding bird survey, but this decreased to only 0.6% in the 2016-19 survey. The decline has occurred across HK, even in the core breeding area of Deep Bay.

The distribution of records in the non-breeding season is different, with most records coming from wooded areas such as Tai Po Kau and elsewhere in the Tai Mo Shan massif, Tai Lam, Sai Kung and on Lantau. Some records do occur on the coast at this time, but they are usually associated with adjacent woodland or shrubland. The Winter Atlas of 2001-05 recorded Striated Heron in 1.7% of 1km squares, which declined to 0.6% in the 2016-19 survey.

The difference in habitat occupancy summer and winter is presumed to relate to the occurrence of different subspecies, with B. s. amurensis present in winter and B. s. actophila in summer.

OCCURRENCE

Figure 1 illustrates the pattern of occurrence of Striated Heron. Spring passage is weak, with small numbers recorded until mid-April. The rise that occurs from the middle of April that peaks during the second half of May is due to the breeding population arriving and being more obvious. The peak count is 20 birds at Mai Po on 29 May 1988, which compares with no spring count higher than ten since 1999.

Birds present in July and August appear to be a post-breeding population, as monitoring of nocturnal migration at Pak Sha O during 2017-21 recorded passage only from mid-August to mid-November, and mainly in the first three weeks of October. The highest count at this time is 17 at Mai Po NR on 27 July 2007.

The winter population is stable from mid-November to early March. At most sites one or two birds are counted, with three at Shum Chung on 28 January 1997 being the highest.

In addition to the migratory populations, however, there is possibly a small resident population since what appear to be the same individuals have occasionally been recorded all year round at Tai Mei Tuk, Shuen Wan and Ho Chung.

Vaughan and Jones (1913) stated that Striated Heron was a summer visitor to the area. However, in the 1940s it was rare or even absent from HK, since Herklots (1941) considered it to be a species that ‘…may one day be recorded…’. In 1957 and 1958, however, breeding was noted in Deep Bay, and by the mid-1960s it was considered a summer visitor (Macfarlane and Macdonald 1966, Herklots 1967).

BREEDING

The earliest record of birds seen carrying nesting material is 14 April 1979. Nests with chicks have been recorded in the final week of June. Its preference for densely-vegetated and rather inaccessible nesting sites mean there are rather few observations of breeding behaviour. An estimated 15 pairs were present at Mai Po NR in summer 1994.

BEHAVIOUR, FORAGING & DIET

Usually seen in flight when flushed from dense cover or heard giving its explosive call. Only recorded predating small fish. Habitually forages nocturnally.

RANGE & SYSTEMATICS

Breeds in south America, sub-Saharan Africa, the Red Sea area, Indian Ocean islands, Indonesia to New Guinea and north and east Australia and from the Indian subcontinent through Indochina to China, southeast Siberia and Japan (Martínez-Vilalta et al. 2020). In China a summer visitor to areas south of a line from southern Tibet to the northeast; in winter occurs south of a line from Guizhou to Zhejiang, including Hainan (eBird, Liu and Chen 2020).

Polytypic, with more than 20 subspecies recognised, of which two are relevant to HK. B. s. amurensis breeds in southeast Siberia, northeast China and Japan, and is presumed to migrate through and/or winter here. B. s. actophila breeds from east China to north Vietnam and north Myanmar and is presumed to breed here.

CONSERVATION STATUS

IUCN: Least Concern. Population trend decreasing.