White-headed Stilt identification can be tricky. Christian Perez has sifted through the different expert opinions on the differences and similarities between the Black-winged Stilt and White-headed Stilt and how to tell them apart in in the field. He presents his findings here to guide WBCP members in making IDs and correctly reporting stilts.
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Differentiating Between Black-winged Stilt and White-headed Stilt
by Christian Perez

New Splits in the WBCP 2013 Checklist

One of the new species in the WBCP Checklist of Birds of the Philippines 2013 is the White-headed Stilt (WHS), which was split from the Black-winged Stilt (BWS). When endemic or resident species are split, the split is usually described by the geographical range of the new species, which can therefore be identified based on location. This is not the case for migrant species. Birders need a description of the two (or more) species resulting from a split in order to identify them in the field. In this article I will try to give practical advice on the identification on the Back-winged Stilt Himantopus himantopus and White-headed Stilt Himantopus leucocephalus. Subsequent articles are planned to cover other similar cases such as the Arctic/Kamchatka Leaf/Japanese Leaf Warbler and the Himalayan/Oriental Cuckoo. This is not a scientific paper. It is a compilation of information I have gathered from available sources to give practical advice to WBCP members for the preparation of trip reports.

Range

Kennedy does not split the WHS from the BWS but recognizes the two subspecies. It describes the bird as “uncommon”, indicates the range to be “Central and southern Eurasia … to Australia”, and lists only nine islands in the Philippines. It says “himantopus known to migrate from the north. The race leucocephalus may migrate from the south or may breed.” It adds “recorded every month except July”. In A Field Guide to the Waterbirds of Asia (B. Bhushan et al., Tokyo, 1993), the two species are split and the WHS is called Australian Stilt. The distribution of the BWS is “breeds from Central Asia to South and continental South-East Asia; northern breeders migrate south.” The distribution of the WHS is “Australasian species resident in Borneo, the Philippines and Java.”

In a letter to the editors entitled “What is the status of White-headed Stilt Himantopus (himantopus) leucocephalus in the Oriental region?” published in BirdingASIA issue number 17 of June 2012, David Bakewell states: “BirdLife International (2012) shows White-headed Stilt as resident in Australia, New Zealand, Java, southern Sumatra, Sulawesi and east Kalimantan, and non-breeding visitors in New Guinea and Maluku, Timor and the islands west to Bali (West Nusa Tenggara), southern Kalimantan, Brunei, the East Malaysian states of Sabah and Sarawak, the Philippine islands of Mindanao, Negros and Luzon, and Sri Lanka. […] Arne Jensen (in litt.) reports that he has seen fewer than five White-headed types among thousands of stilts on Luzon, and that stilt numbers increase during the northern winter season, suggesting that the bulk are Black-winged. A photograph of a bird at a nest on 12 August 1999 in Zamboanga, Mindanao (reportedly the first breeding record of a stilt in the Philippines), appears to show a Black-winged rather than White-headed. However, White-headed Stilt is regularly observed on Palawan (Rob Hutchinson in litt.).”

What can be concluded from a review of the above sources is that both species can be present anywhere in the Philippines almost throughout the year (except perhaps July for BWS). Although BWS are more likely to be seen in northern Philippines and WHS in southern Philippines, the conclusion is that the location of the observation cannot be used for species identification in the Philippines.

Black Hind Neck

Kennedy says that “races differ by presence leucocephalus or absence himantopus of back hind neck in adult”. Robson (Birds of South-East Asia, 2010) describe male breeding BWS “Head/neck typically all white. Can have some variable grey or black on head/hindneck” and the adult WHS “like breeding male BWS, but long black ‘mane’”. Bhushan describes adult BWS: “crown to hindneck varies in amount of dusky-black” and adult BWS: “white crown; a ridge of raised black feathers runs down whole length of hindneck”. Based on these “traditional” sources, it would seem that it should be easy to separate adult male WHS by the black hind neck. However, it is not that simple and Malaysia-based expert David Bakewell in his blog entitled “Black-winged Stilt” shows that BWS can sometimes exhibit features of the WHS:

http://digdeep1962.wordpress.com/waders-month-by-month/stilts-avocets-black-winged-stilt/

This is a quote from Bakewell’s letter to BirdingASIA: “Amongst these winter influxes have been several birds showing plumage characteristics associated with White-headed Stilt. Birds with a full, well-developed black nuchal mane and pure white head are relatively rare, and have always occurred singly in flocks of more typically plumaged Black-winged Stilts. However, birds with poorly marked dark nuchal manes are not uncommon; perhaps 5% show this feature, some of which have pure white heads, while others have variable amounts of black on the crown and ear coverts. Some birds appear to have a white head at a distance but, on close inspection, have some darker markings on the crown or ear-coverts. The birds showing White-headed Stilt plumage characters which I have observed in Malaysia have not been distinguishable vocally from Black-winged Stilts. This, and the fact that they occur at times of year typical for northern hemisphere migrants, has led me to conclude that these birds are variant-plumaged Black-winged Stilts, rather than White-headed.”

From the same letter: “A cursory survey of photographs on the internet reveals that the extent and pattern of black on the nape and head of Black-winged Stilts occurring in Asia is far more variable than most literature suggests. Danny Rogers (in litt.) has suggested that black feathering on the hindneck might be some kind of ancestral plumage character that is occasionally expressed in stilts, and might therefore be part of the normal variation in Black-winged—even in the case of birds which look virtually identical to White-headed. Another possibility is that it is the result of hybridisation in areas where the two taxa have now met. In view of the apparent expansion in the breeding ranges of both taxa, hybridisation may be increasing. Whatever the case, I suggest that there is sufficient evidence for the existence of Black-winged Stilts showing White-headed Stilt plumage characteristics for extra-limital sightings of apparent White-headed Stilts to be treated with great caution, particularly if such birds occur singly and in the company of Black-winged Stilts during the northern winter. Special attention should be given to the extent of the nuchal mane, and whether the rest of the head is in fact pure white, with no darker flecking or shading.”

This is all rather confusing, but it can be safely concluded from the review of those sources that the presence/absence and thickness of a black hind neck cannot be used alone as diagnostic to separate the two species.

Calls

It seems that the best way to separate WHS from BWS is through the calls. The BWS’s voice is described as “sharp nasal kek and yelping ke-yak; monotonous high kik-kik-kik in alarm” by Robson and “loud keek and kee-it; also continuous kikikikiki” by Bushan. The WHS voice is described as “feeble, puppy-like yap-yap-yap (incessant when agitated); plaintive mournful piping” by Robson and “like BWS but softer and more nasal” by Bhushan.

Recording of the calls of BWS and WHS can be found in xeno-canto:

http://www.xeno-canto.org/species/Himantopus-himantopus?pg=1

http://www.xeno-canto.org/species/Himantopus-leucocephalus

Here are typical BWS calls recorded in Europe (taken from the xeno-canto link):

And here is a typical WHS call recorded in Australia (also taken from the xeno-canto link):

It is important to become familiar with the calls in order to identify the species. It would be recommended to record the calls in the field for later confirmation. Fortunately the Stilts are usually quite noisy and easy to record. Even a simple video of a smartphone would do.

It is important to become familiar with the calls in order to identify the species. It would be recommended to record the calls in the field for later confirmation. Fortunately the Stilts are usually quite noisy and easy to record. Even a simple video of a smartphone would do.

[youtube=http://youtu.be/1q8aBg7y4PU]

Video of a White-headed Stilt in Malalag, Davao del Sur. The call can be heard in the first second of the video and is clearly that of a White-headed Stilt. Video by Tonji Ramos.

Size

Kennedy does not separate the size of the two subspecies and measures the bird at 355 mm. Robson measures the BWS at 37.5 cm and the WHS at 35 cm, and Bhushan the BWS at 32 cm and the WHS at 37 cm. This is the opposite of Robson and is most probably an error in view of the latest data available.

I quote from Bakewell’s letter in BirdingASIA: “Comparison of measurements reveals that Black-winged has a wing length about 6–9% longer than White-headed, the bill is about the same length in both taxa, and the tarsus is about 9% longer in Black-winged (Cramp 1993, Marchant & Higgins 1993). Given the slightly smaller size overall of White-headed, these differences may not be big enough always to be diagnostic, but the difference in tarsus length may be noticeable in the field where the two are close enough for comparison.”

In theory, the proportion of the length of the tarsus to the thigh or the proportion of the length of the bill to the size of the head could be used as diagnostic. However there is no scientific publication on the subject and identification based on proportion is not recommended.

If two adult individuals of each species are seen side by side at the same distance, angle and posture, they can in theory be separated by size. However, this situation in unusual and in general the species should not be identified on size alone. The size may only be used in some cases as a confirmation when species have been separated on call.

Conclusions

In conclusion, it is very difficult if not impossible to separate BWS from WHS based on physical features alone. The identification at species level should be based on calls. The presence of the thick black hind neck, the size and the location can be used as supporting circumstances only. In all other cases, it is recommended to just report “Stilt sp.”

Birds in a flock should be identified individually, and the identification of a few birds in a flock should not be generalized to the whole flock. Examples of typical reports would therefore be “Stilt sp. 45”;  “BWS 1, Stilt sp. 75”;  “WHS 3, Stilt sp. 280”;  or “BWS 4, WHS 2, Stilts sp. 160”.

These recommendations should be followed by WBCP members when preparing trip reports. The recommendations have been reviewed by Records Committee members and reflect the views of the Records Committee.