ARTICLES ON HAWAIIAN BIRDS AND BIRDWATCHING AND OTHER PACIFIC WILDLIFE

Unusual plumaged Hawaiian Stilt in Kona during Spring 2002

Overview

Kim Uyehara of Ducks Unlimited noticed an odd-plumaged Stilt at the Cyanotech facility in Kona, Hawai'i during early February and reported the odd-looking bird to Robert Pyle at the Bishop Museum, O'ahu. She reported that the bird had a white forehead, face and crown and was quite unlike the usual Hawaiian Stilts. Scott Waddington, a biologist at Cyanotech was contacted and the three excellent photographs reproduced here were obtained by him.

Although Cyanotech is a closed private facility Scott Waddington was able to allow access for a few local birders to enter the site to try to observe the Stilt. The bird was not totally faithful to the facility and was sometimes found at other local sites in the area, such as the Kona Sewage Treatment Plant (STP).

Although rather unlikely as a vagrant to Hawai'i, Pied Stilt could conceivably occur and so discussion turned to this possibility, although it seemed more likely that the bird was some sort of variant Hawaiian Stilt. Research revealed that Stilt plumage variations can be complex, especially the hybrid birds of New Zealand and all birds need to be examined in some depth.

Dan Lindsay and Jason Rogers visited the Cyanotech facility on 16th March but could not locate the bird there and so decided to check other likely sites in the area. The bird was found by them at the STP, just a short distance away and were able to observe the bird fairly easily, although not at close range, and compiled the following description:

"The bird may be undergoing a molt, as there now appears to be a smudge of gray on the crown, and a grayish line from the back of the head to the eyes, neither of which shows up in Scott's pictures. It is in company with a female Hawaiian Stilt and they are apparently a mated pair. Their constant proximity gave us the chance to compare proportions pretty accurately.

Neither the bill nor the tibia on the white-headed bird appear to be longer than those of his mate. In flight, neither Jason nor I could see any difference in wing length when the pair flew. We heard him call, and he sounds just like a Hawaiian Stilt as far as we could tell. He appeared to be a little slimmer than his mate, but not very much, and that might be because she is pregnant - I don't know if that matters in birds or not.

In sum, we could not find anything in the bird's appearance or voice, other than the white head, to support the idea that it is a Pied Stilt".

Distribution and Status of Hawaiian, Pied, Black-necked and Black-winged Stilts

Stilt taxonomy is an issue of much debate with some authorities recognizing only one Stilt species, whilst others recognize two or three species and some split all the different forms into separate species. The taxonomy of Stilts is not dealt with here but the following lists each forms/species distribution.

Black-winged Stilt (Himantopus himantopus) - Eurasia, India, Sri Lanka and Africa.

Black-necked Stilt (Himantopus mexicanus) - North America and north South America and the Galapagos.

Black-necked Stilt (Himantopus mexicanus melanurus) - Peru and Brazil southwards to central Chile and Argentina.

Hawaiian Stilt (Himantopus mexicanus knudseni) - Hawaiian Islands. Rare and endangered.

Pied Stilt (Himantopus leucocephalus) - Australia, New Guinea and New Zealand.

Black Stilt (Himantopus novaezelandiae) - New Zealand. Critically endangered with few pure pairs left breeding.

Hayman et al. state that knudseni and mexicanus are closely related; mexicanus and melanurus intergrade in Peru; and leucocephalus and novaezelandiae hybridize in New Zealand.

Species Descriptions

It became clear after researching Stilt plumages that several books actually show hybrid-type Pied Stilts which are labelled as Pied Stilt. In Hayman et al. (1987) the illustrations of pure Pied Stilt illustrate birds with white mantles, a feature not shown by other Stilts in the Pacific region (but shown by some Eurasian birds). Further illustrations however of hybrid Pied x Black Stilt in New Zealand show birds with varying amounts of black on the mantle, from fully black to partly black. As the amount of black in the mantle increases often so does the amount of black shown on the breast and belly. The tarsi length also decreases with increasing black in the plumage. There are exceptions to this however, and the photograph shown below of a "Pied" Stilt in New Zealand appears to show a bird with a fair amount of black on the mantle but no black on the underparts. In Pratt et al. (1987) Pied Stilt is illustrated as a possible future vagrant to the Tropical Pacific region and the individual shown has a fully black mantle. From recent evidence it would appear that this bird would in fact have to have been a hybrid. All other books with illustrations or photographs that were consulted show Pied Stilts with pure white mantles and sharp edges to the black feathering, not smudgy as in the Kona bird.

The following written descriptions deal only with the head and mantles of Stilts, as these are the areas that differed in the Kona bird. The following tables deal with all parts of the plumage.

"Kona Stilt" - Forehead, crown and face white. Rear neck and nape black. Mantle black. Sides of neck white with black limited to very rear (note Hawaiian Stilt usually shows increased black on face and neck than other forms).

Hawaiian Stilt (H. m. knudseni) - Forehead white. Crown, nape and face black with small white spot above eye. Rear neck and mantle black. Neck sides usually show increased amounts of black.

Pied Stilt (H. h. leucocephalus) - Forehead, crown and face white. Nape and rear neck black. Mantle white.

Hybrid Pied Stilt x Black Stilt (H. h. leucocephalus x H. h. novaezelandiae) - Varying amounts of black on the forehead, crown, nape, rear neck and mantle. Some birds show only black on the rear neck whilst some show black over the entire body except for a small smudge of white on the belly or undertail.

Black-necked Stilt (H. m. mexicanus) - Much as Hawaiian Stilt but with reduced amount of black on the lower face and neck sides. Also often shows a larger white spot above the eye.

Black-necked Stilt (H. m. melanurus) - Forehead, crown and nape white. Face white but with black area extending rear from eye to rear neck and joining black of neck. Rear neck black. Mantle white.

Stilt plumage variations from Hayman et al. (1987).

	Eurasian & African	Australasian	North & Central American	Hawaiian	South American
	himantopus	leucocephalus	mexicanus	knudseni	melanurus
Adult
Centre & rear of crown	White or Blackish	White	Black	Black	White
Lower ear coverts	White	White	Black	Black	Black
Upper hindneck	White or mostly White	Black	Black	Black	Black
Base of hindneck	White	White	Black	Black	White
Mantle colour of female	Brown	Blackish-Brown	Brown	Blackish-Brown	Brown
Juvenile
Centre & rear of crown	Dark Grey	Dark Grey	Dark Grey-Brown	Dark Grey-Brown	Mid-Grey
Upper hindneck	Pale Grey	Pale Grey	Dark Brown	Blackish-Brown	Blackish
Base of hindneck	Pale Grey	Pale Grey	Blackish-Brown	Blackish-Brown	Mid-Grey
Mantle colour	Brown	Dark Brown	Dark Brown	Brown	Brown

According to Hayman et al. (1987) the following measurements apply.

	Eurasian & African	Australasian	North & Central American	Hawaiian	South American
	himantopus	leucocephalus	mexicanus	knudseni	melanurus
Average Size (mm)
Wing	236	228	220	233	237
Bill	63	61	64	76	63
Legs from feathers (exposed tibia & tarsus)	176 (S. Africa) 202 (Palearctic)	157 (New Zealand) 180 (Australia)	180	204	181

Conclusion

Danny Rogers, an Australian birder and ornithologist who participated in the writing and researching of the Stilt plumage accounts in The Handbook of Australia, New Zealand and Antarctic Birds (HANZAB) kindly provided the following comments:

"Deepal Warakagoda in Sri Lanka has documented some unusual stilts in Sri Lanka very carefully indeed, and I got the opportunity to see some of those photographs. Some of them were basically indistinguishable from Australian birds, but there
was a lot of variation. There was even one bird that looked astonishingly like mexicanus. Deepal's view, which I found very persuasive, was that there is simply some variation in nominate himantopus which has been overlooked in the past, and neither of us is convinced that there is adequate proof of Australian birds having reached Sri Lanka. My hunch is that there is some
kind of atavistic memory in the plumages of subcontinental Stilts which is occasionally expressed. I wonder if the same kind of thing might be happening in Hawaii? Somehow I don't think Australian stilts are taking over the world (but admittedly, they did take over NZ) - if anything, they are declining within Australia.

I don't think it is an Australian bird - in our birds, the black of the hindneck is always separated from the black of back and scapulars by a broad white band across the upper mantle. Admittedly there can be a bit of grey grunging in the mantle of juveniles and birds in first basic, but such birds don't have a black hindneck and look very different to the apparently adult bird in your photos. I've never seen an Australian bird matching the appearance of your bird. Nor do I think there is much chance of the bird being a hybrid between leucocephalus and NZ Black Stilt. Some such hybrids do have a black hindneck marking running straight onto the mantle and back, but in such individuals there is also usually a black band across the foreneck, or at least a substantial trace of it at the sides of the neck. In addition, they normally look noticeably shorter-legged than pure leucocephalus, not like your leggy bird. While I can't be sure about the identity of your bird, I'd be inclined to think it is a peculiar knudseni, or possibly a peculiar mexicanus".

The concensus of opinion amongst birders in Hawai'i (and elsewhere) favoured that the bird was just an oddly-plumaged knudseni Hawaiian Stilt. However the appearance of this individual and the debate and research that resulted from it has helped to make birders in Hawai'i more aware of the vagaries of Stilt plumage, as well as increasing their understanding of other Stilt forms in the Pacific and other areas of the World.

Footnote: During April 2002 the bird's plumage started to moult and the head was described as darkening up. The bird was reported to no longer have the white head it exhibited to begin with, instead there was a black smudginess on the neck which outlined the extent of black seen in typical Hawaiian Stilts. Also there was a black smudge running from the nape through the eye.

Below right: Hawaiian Stilts Himantopus (mexicanus) knudseni, Cyanotech, Kona, Hawai'i, Spring 2002 © by Scott Waddington.

The right bird is a typical adult knudseni Hawaiian Stilt, showing the extensive dark plumage around the head, neck and nape usually associated with this form. The left hand bird shows black confined to the rear neck, nape and mantle (as well as back and wings) and resemble the Pied Stilt (H. leucocephalus), however the bare parts (bill and legs) are typical knudseni and observers reported that the call was indistinguishable from the other Hawaiian Stilts at the site.

Below right: Hawaiian Stilt Himantopus (mexicanus) knudseni, with unusual head pattern, Cyanotech, Kona, Hawai'i, Spring 2002 © by Scott Waddington.

In this photograph the bird can be seen to have very limited black on the rear neck and neck sides. In life the slightly smudgy area behind the eye was said to be more noticeable than in this photograph, and this along with the poorly defined leading edge to the black on the nape (not a clear-cut edge) points towards the bird exhibiting part-albinism, rather than showing "true" Pied Stilt plumage traits.

Below right: Pied Stilt Himantopus leucocephalus, location unknown, New Zealand, date unknown © by Geoff Moon.

In this photograph the bird shows the typical "bulging" neck feathers of Pied Stilt, particularly at the rear crown. The legs and bill are slightly shorter than in Hawaiian Stilt, which often gives Pied Stilt a more dumpy looking gait. The black feathering on the neck and nape are separated from the black back and wings by a white mantle, although on this bird this area is broken with some black feathering, presumably this is indicative of some hybridization. Hybrid Pied and Black Stilts in New Zealand occur frequently, but these birds usually show a completely black mantle. Hybrids also usually show increased black on the underparts and breast in relation to increasing amounts of black on the mantle. However it may be that this is a hybrid at the extreme pale end of the spectrum, showing some white in the mantle but none on the underparts.

Below right: Hawaiian Stilt Himantopus (mexicanus) knudseni, Kaua'i, January 2001 © by Christian Melgar.

This second-year bird is a typical Hawaiian Stilt exhibiting the dark head plumage, however it shows slightly more limited black on the neck sides than adults and slightly paler legs.

Hawaiian Stilts have the longest bill and leg measurements for any Stilt species/ sub-species and the birds can often appear quite "gangly" and "leggy". Hawaiian Stilts also show the most black in the plumage, especially on the neck sides and nape/mantle. There is a strong case for splitting knudseni as a separate species on the basis of distribution, plumage details, calls, measurements and behavioural differences.

Hawaiian Stilt Himantopus (mexicanus) knudseni, with unusual head pattern,

Cyanotech, Kona, Hawai'i, Spring 2002 © by Scott Waddington.

Thanks to all those on the Hawai'i Birders Chatlist and special thanks to the following for supplying references, descriptions and information about Pied and Black-necked Stilts: Danny Rogers, Kim Uyehara, Scott Waddington, Peter Donaldson, Dan Lindsay, Jason Rogers and Doug Pratt.

References:

FLEGG, J. and S. MADGE. 1994. Photographic Field Guide: Birds of Australia. New Holland, U.K.

HAYMAN, P., J. MARCHANT, and T. PRATER. 1987. Shorebirds: An identification guide to the waders of the world. Helm, London.

MOON, G. 2001. New Zealand: Land of Birds. New Holland, Aukland.

PRATT, H.D. , BRUNER, P.L. and BERRETT, D.G. et al. 1987. A Fieldguide to the Birds of Hawai'i and the Tropical Pacific. Princeton.

ROSAIR, D. and D. COTTRIDGE. 1995. Photographic Guide to the Waders of the World. Hamlyn, U.K.

SIMPSON, K. and N. DAY. 1989. Field Guide to the Birds of Australia. Helm, U.K.

WATTS, D. 1999. Field Guide to Tasmanian Birds. New Holland.

Christian Melgar. Worthing, West Sussex, UK. 2002.

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