Intermediate Egret Ardea intermedia 中白鷺
Category I. Common on passage but scarce at other times of year mainly in freshwater wetland areas. Appears to have increased in numbers over past 60 years.
IDENTIFICATION
Apr. 2017, Michelle and Peter Wong.
65-72 cm. All white egret intermediate in size and structure between Little and Great Egret, though resembles latter in general character; differs from both by more rounded crown and thus more obvious angle between forehead and bill. Legs and feet dark all year. Bill has variable dusky tip in non-breeding season but is all dark in breeding plumage, when it lacks head plumes but has extensive breast and back plumes (this plumage is rarely seen in HK).
Oct. 2017, Michelle and Peter Wong
Compared to Great Egret, the gape does not extend behind eye and, viewed from the rear, the thicker neck is not as long as the body. Bill usually obviously shorter, though beware young Great Egrets lacking fully grown bill.
VOCALISATIONS
Generally silent. Has a harsh alarm call when flushed that is similar to Little Egret but slightly higher-pitched.
Also, a somewhat nasal, buzzing call very different from other ardeids in HK.
DISTRIBUTION & HABITAT PREFERENCE
Intermediate Egrets favour freshwater marshy areas where loose aggregations are recorded. However, it also occurs in small numbers in the higher parts of intertidal areas or along freshwater streams that feed into estuarine waters. It also occurs, usually singly, in commercial fish ponds, where it is generally associated with areas of emergent vegetation.
Most records are from the Deep Bay area, but also recorded elsewhere where there is suitable freshwater habitat, in particular Long Valley, Kam Tin and Pui O. The much wider spread of records this century compared to last is probably a good indicator of the increase in observer activity and familiarity with the species.
OCCURRENCE
Recorded all year, mainly in the migration seasons. Numbers are highest in autumn, with main passage occurring from the second week of September to the third week of November (Figure 1). Highest numbers are recorded earlier in this period, with the highest being 107 on 15 September 2017. The period from the last week of November to mid-February sees lower numbers present, with the highest winter count being 20. The first spring migrants appear to arrive in the third week of February, certainly by the second week of March, and main spring passage occurs until the third week of May. The highest spring count is 79 on 9 April 2013. Birds on diurnal migration have been seen over southern waters from 23 April to 7 May and on 18 October.
The lowest numbers occur in summer, when one to ten birds are generally recorded, though there are occasionally notable counts, the highest being 47 on 15 June 2005. Although recorded throughout the summer, there are no observations that indicate breeding has been attempted.
Earlier authors considered Intermediate Egret to be rather rare. Swinhoe (1861) appears to have recorded this species in the markets at Guangzhou. Herklots (1953) had no records but considered it to be possibly a migrant, while Dove and Goodhart (1955) provide a second-hand report of one on 20 September 1953, which they stated was the first HK record. Subsequently, Macfarlane and Macdonald (1966) stated that Intermediate Egret was a vagrant to HK.
Chalmers (1986) stated that the main period of occurrence was from 22 September to 21 April (with only one summer record), that all but two records were from the Deep Bay area and the highest count was 17. Between 1985 and 1998 most records occurred from September to May, with greatest numbers in spring from mid-March to late April, and in autumn from late September to the third week of October; the highest count was 44.
The increase in records and numbers over the past 60 years no doubt reflects greater familiarity with the species, better reporting and, in the most recent period, an increase in the availability of freshwater marsh in managed wetlands in the Deep Bay area. However, it also seems likely to be the result of a genuine increase in numbers. The exception is in winter when the peak count has increased only slightly.
BEHAVIOUR, FORAGING & DIET
Forages singly or in rather loose groups scattered across a foraging site, birds moving slowly and purposefully as they search for prey. Recorded prey items are fish, mudskippers and Reeve’s Smooth Skink Scincella reevesii.
Unobtrusive and often in small numbers, Intermediate Egrets may be overlooked amongst Great Egrets. Diurnal migrants are occasionally seen over southern waters, often in the company of other egrets.
RANGE & SYSTEMATICS
Occurs from sub-Saharan Africa to the Indian subcontinent east to Japan and south through southeast Asia to Indonesia and Australasia; northern populations are migratory whilst some others are nomadic (del Hoyo et al. 2020). In China a summer visitor to areas south of a line from Yunnan to Liaoning but present all year in southern coastal provinces including Hainan and Taiwan (Liu and Chen 2020).
Of the three subspecies recognised, the nominate occurs from India to Japan and south to southeast Asia, including HK; A. i. plumifera occurs from east Indonesia to Australia, while A. i. brachyrhyncha occurs in Africa.
CONSERVATION STATUS
IUCN: Least Concern. Population trend decreasing.
Figure 1.
Chalmers, M. L. (1986). Annotated Checklist of the Birds of Hong Kong. Hong Kong Bird Watching Society, Hong Kong.
Dove, R. S. and H. J . Goodhart (1955). Field observations from the Colony of Hong Kong. Ibis 97: 311-340.
Herklots, G. A. C. (1953). Hong Kong Birds. South China Morning Post, Hong Kong.
del Hoyo, J., A. Martínez-Vilalta, A. Motis, N. Collar, and G. M. Kirwan (2020). Intermediate Egret (Ardea intermedia), version 1.0. In Birds of the World (S. M. Billerman, B. K. Keeney, P. G. Rodewald, and T. S. Schulenberg, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.integr.01
Liu, Y. and Y. H. Chen (eds) (2020). The CNG Field Guide to the Birds of China (in Chinese). Hunan Science and Technology Publication House, Changsha.
Macfarlane, A. M. and A. D. Macdonald, revised by Caunter, J. R. L. and A. M. Macfarlane (1966). An Annotated Check-list of the Birds of Hong Kong. Hong Kong Bird Watching Society, Hong Kong.
Swinhoe, R. (1861). Notes on the ornithology of Hong Kong, Macao and Canton, made during the latter end of February, March, April and the beginning of May 1860. Ibis 1861: 23-57.
