ARTICLES ON HAWAIIAN AND PACIFIC BIRDS, BIRDWATCHING AND WILDLIFE

Arctic Warbler (Phylloscopus borealis) at Kilauea Point NWR, Kaua'i - The first record for Hawaii.

After having my suspicions aroused by the call, when I saw the bird I was in no doubt that the bird was clearly an Old World Warbler. The combination of coloration, behavior, call and plumage details enabled me to rule out the introduced Japanese Bush Warbler (Cettia diphone), the only resident Old World Warbler in the main Hawaiian Islands. I identified the bird as a probable Arctic Warbler (Phylloscopus borealis) whilst watching the bird, but was aware that there are numerous Asian Warblers that are similar to Arctic and all are as unlikely to occur in Hawaii as the next! If accepted, this would be the first vagrant passerine ever in historical times to have occurred in the main Hawaiian Islands and the only modern day record of a vagrant Warbler in the whole archipelago, as such this is one of the most important sightings ever to be recorded in Hawaii. Unfortunately I had very little useful information available at the time but subsequent research and information from other birders in Hawaii helped in ruling out most other species. There are however a few features which do not completely fit with Arctic Warbler and so it may be best left as simply Phylloscopus species. Unfortunately a couple of key features, which would have proved the identification beyond doubt were not noticed (or were not present). The following descriptions and drawings describe and illustrate the "Kilauea Warbler", Arctic Warbler and the most likely other species which could have been involved and describes how they can be distinguished from one another and how in all probability the Kilauea Warbler was in fact an Arctic.

The "Kilauea Warbler"

The bird was fairly small, although a little larger than a Japanese Whiteeye, the only bird nearby for comparison. Its behaviour and movements were typical of the Phylloscopus Warblers, being active and restless. The bird appeared to be in fresh plumage as it was clean and bright with no worn feathers noted. Underparts: The Underparts were white to off-white, perhaps slighty grayer on the flanks and breast sides. Upperparts: The upperparts were a pale olive-green. The wings were much as the upper body and had a thin whitish wing bar running across the closed wing. Tail: The tail was also olive-green but perhaps a little darker than the body and was square-ended. Head: The head was olive-green with paler cheeks and lower face, pale supercilium which was slightly wider at the rear than at the front and a dark eyestripe, although this was not as obvious as I recall on Arctics I have seen in Europe. The face appeared quite "clean and open" which is not usually a feature of Arctic Warbler, but more consistent with Greenish Warbler (Phylloscopus trochiloides). Although I do not recall if the supercilium continued right to the upper mandible, it seems highly likely that it didn't for two reasons. Firstly, I noted that the supercilium was wider behind the eye than in front - probably indicating that it stopped short of the bill or was very indistinct here, and secondly, the width of supercilium in Greenish Warbler is much more even for its entire length, right up to the bill and would have been rather prominent (as it is in some of the other species described below) and therefore more noticeable. Bare Parts: The bird had a dark eye and a typical Phylloscopus insectivorous, mainly pale bill. The size of the bill, although not directly comparable at the time, appeared heavier than one might expect for Greenish, Green (Phylloscopus nitidus) or Yellow-browed Warblers (Phylloscopus inornatus) (perhaps indicating Arctic). The legs were pale, fleshy-straw in color.
Call: The call reminded me at first of Dusky Warbler (Phylloscopus fuscatus) but on listening to sound recordings of this species and Arctic and Greenish Warblers it appears closer to the call of Arctic. However, the call made by the Kilauea bird does not fit exactly with the call of Arctic, being slightly harsher than that species. (But is closer to this species than anything else listened to on tape or heard first-hand including Japanese Bush Warbler (Cettia diphone), which has a call somewhat reminiscent of Dusky). Calls of the other species dealt with here were not heard.

Arctic Warbler (Phylloscopus borealis)

This species differs from Greenish and Two-barred Warblers (Phylloscopus plumbeitarsus) in several rather subtle features. It is slightly larger and bulkier and has a slightly larger bill that is often heavier looking and usually has a darker tip to the lower mandible. The eyestripe extends right to the bill-base and the supercilium does not quite reach it. The ear coverts are usually fairly well mottled. The legs are usually much paler than Greenish, especially towards and on the toes. The underparts are often duller or grayer than Greenish (which in my experience, especially in spring, appear much cleaner and brighter) and can often appear faintly streaked. Arctic can be distinguished from Eastern Crowned by its plain olive-green crown, lack of the yellow undertail coverts and its paler legs. The call note of Arctic is transcribed as dzip, dzrt or zic.

Photo Link: www.sennen-cove.com/ images/arctic2.jpg

Sound Link: http://midopika.cool.ne.jp/songs_e/mebosomushi.html

Greenish Warbler (Phylloscopus trochloides)

Differs from Arctic Warbler in being slightly smaller with a slightly smaller and lighter looking bill, which usually has a completely pinkish lower mandible. The supercilium extends right to the bill base and has a less prominent eyestripe before the eye. The ear coverts tend to be plainer than on Arctic. The legs and feet are usually duller, although pale-legged birds have been recorded. When in fresh plumage the wing bar is often longer and broader on the greater coverts. The call of Greenish is a sparrow-like ch'wee or ts'iwi.

Photo Link: www.lincsbirdclub.co.uk/image_3/ Greenish_web_10_9_02.jpg

Two-barred Warbler or Two-barred Greenish Warbler (Phylloscopus plumbeitarsus)

This is an eastern subspecies of Greenish (although subsequent changes in taxonomy may upgrade this and the following species to full specific status) and is in all respects very similar to Greenish. This species differs in having two wing-bars in fresh plumage and at this time can resemble a Yellow-browed Warbler but is larger and does not possess the white edges to the tertials. The call is similar to Greenish and is a tri-syllabic chireewee or chir'ee'wee.

Photo Link: http://home8.swipnet.se/~w-85702/image/ostlundsang.gif

Green Warbler (Phylloscopus nitidus)

Again very similar to Greenish Warbler but shows bright yellow on some of the underparts, especially the throat. Eastern- crowned Warbler (Phylloscopus coronatus). This species is again very similar to Arctic Warbler but shows a darker crown with a quite distinct median stripe, brighter yellowy-green upperparts (especially on the fringes of feathers on the wing), whiter
unmarked ear coverts, whiter underparts and pale, but distinct, yellow undertail-coverts. The bill usually shows an all pale lower mandible, as in Greenish. The call is transcribed as a harsh zweet, similar to, although apparently quieter than in Arctic Warbler.

Photo Link: www.fuglesiden.com/ Ostsanger5.jpg

Pale-legged Leaf Warbler (Phylloscopus tenellipes)

This is best distinguished by its dark grayish crown, which contrasts with the mantle and supercilium as well as an olive-brown rump and uppertail-coverts. The legs and feet are pale as in Arctic. The species usually shows two wing-bars, although one is much shorter and could probably be lost when in worn plumage. The call is a distinctive high-pitched tib or tip, very unlike the call of Arctic Warbler.

Photo Link: http://www1.ocn.ne.jp/~banding/kyou8.jpg

Sound Link: http://midopika.cool.ne.jp/songs_e/ezomushi.html

Large-billed Leaf Warbler (Phylloscopus magnirostris)

Larger and heavier than Greenish, more like Arctic. Has a much longer bill which has pale restricted to the base of the lower mandible. The supercilium reaches right to the base of the lower mandible.The legs and feet are darker than on Arctic. It appears that this species could easily be confused with Arctic Warbler in a brief view (on paper at least) but it has a distinctive tit-like call: duu-ti or dir-tee, quite unlike the call of the bird at Kilauea.

Photo Link: http://www.indiabirds.com/obc/Content/ImagePage.asp?Bird_ID=1799&Bird_Family_ID=162

Japanese Bush-Warbler (Cettia diphone)

Larger, longer and heavier than Arctic Warbler. Upperparts are green-grey-brown, depending on age and plumage wear and the underparts vary from off-white to buffy, again depending on age and time of year. The tail is fairly long and round-ended. The face is plain except for a pale supercilium. This is the only (introduced) resident Old World Warbler present in the Main Hawaiian Islands, and is very common on Kaua'i although seldom recorded at Kilauea Point. The call and song are also very distinctive, and both unlike Arctic Warbler.

Photo Link: http://www.indiabirds.com/obc/Content/ImagePage.asp?Bird_ID=1852&Bird_Family_ID=162

Sound Link: http://midopika.cool.ne.jp/songs_e/uguisu.html

Although most of the distinguishing features are very subtle each species has characteristics which enable separation and identification and can be used to eliminate them from the identification of the bird at Kilauea Point. Pale-legged Leaf Warbler can be eliminated by call alone, although the gray crown and brownish rump also rule this species out. Eastern Crowned Warbler would have shown a median crown stripe and yellow undertail coverts, although the plain ear-coverts of this species fitted quite well with the Kilauea bird. Large-billed Warbler has a noticeably longer bill, supercilium extending to the bill, two wing bars and darker legs, but shares the mottled ear coverts of Arctic, however it has a very distinctive call. Two-barred and Green Warblers can be excluded by call as well as plumage features such as the wing bars and lack of yellow in the underparts of the Kilauea bird. Greenish Warbler can also be excluded on call and leg color, although features such as the plain ear-coverts are consistent with both Greenish and the Kilauea bird.

Behaviour

In this case it is unlikely that the behavior of the Kilauea bird would help in its identification. Some of the species described have a preference for canopy feeding (eg. Eastern Crowned Warbler) whilst others prefer feeding near or on the ground (eg. Pale- legged Leaf Warbler), however a vagrant Warbler with little choice in habitat is likely to exhibit little in the way of normal feeding behavior and is likely to be found in any habitat, especially upon first arrival.

Distribution

Arctic Warbler breeds right across the Northern Palearctic, China, Japan and Alaska and winters in South East Asia, the Philippines and NW Australia. Birds have been recorded as vagrants on the West Coast of North America, as far south as California. The distribution of this species and its proven ability to migrate long distances also support this as the identity of the Kilauea bird. Greenish Warbler breeds across the Northern Palearctic and into Asia, where Two-barred and Green Warblers replace it. All three species winter south of the breeding grounds and Two-barred winters in South East Asia. Two-barred is the most likely of the three "Greenish" Warblers to reach Hawaii. Pale-legged Leaf Warbler breeds in the Eastern Palearctic, Japan and China and winters in certain areas of South East Asia. Eastern Crowned Warbler has a similar distribution to Pale-legged Leaf Warbler. Large-billed Leaf Warbler breeds in India and southwest China and winters in southern India and Sri Lanka, and is unlikely to be encountered in the extreme east. Japanese Bush-Warbler is found naturally in Japan but has become a widespread introduction in the Main Hawaiian Islands since the 1930s and is now found on Kaua'i, O'ahu, Maui, Moloka'i and Hawai'i.

Origin

Obviously the origin of this bird is completely unknown and there are several possible explanations for its occurrence/possible origin. One of course is that it flew all the way from Asia and Kilauea Point, as the Northern-most point of the main Hawaiian Islands would be an ideal landfall. However this is a very long flight unless assisted by strong winds or storms, none of which had occurred around this time. The second scenario is that it arrived sometime previously during adverse weather conditions and was simply re-orientating itself along the coast in time for spring migration and so moved to the northern most point it
could find. Thirdly the bird may have island-hopped down the North West Hawaiian Islands and ended up on Kauai by chance. This would involve many flights and it seems improbable that a bird this size would undertake a migration route like this. Lastly the bird could have hitched a ride on board a boat that was travelling from Asia to Hawaii or North America and departed the vessel when it saw land. It is well-known that many species of birds stop-off on or board ships far out at sea (or in docks) and stay on board until they sight land, often thousands of miles away from their natural habitat. I think it is much more gratifying and more appreciative of the bird if one believes that the bird managed to arrive here unaided - after all that's what the original endemic colonizers did!

Unfortunately as no photograph was obtained and as this would be the first ever record for Hawai'i of this species - not to mention the first passerine species to have been recorded naturally in the Main Islands since the original endemics arrived and evolved, it can only remain as a hypothetical addition to the Hawaiian list.

I would like to thank all those that helped with the identification and discussion of this bird particularly Reggie David and those on the Hawaii Birders network.

Kilauea Point & Moku'ae'ae Islet from the air. (Photo: © USGS)

References

ALSTROM, P; P.COLSTON and I. LEWINGTON. 1997. A Field Guide to the Rare Birds of Britain and Europe. London.

BAKER, K. 1997. Warblers of Europe, Asia and North Africa. Christopher Helm, London.

BEAMAN, M and S. MADGE. 1999. The Handbook of Bird Identification for Europe and the Western Palearctic. Christopher Helm, London.

JEYARAJASINGHAM, A. and A. PEARSON. 1999. A Field Guide to the Birds of West Malaysia and Singapore. Oxford University Press. Oxford.

LEADER, P.J. 1992. The Field Identification of Arctic, Eastern Crowned, Two-barred Greenish and Pale-legged Leaf Warbler in Hong Kong. Hong Kong Bird Report 1992. Hong Kong Birdwatching Society, Hong Kong.

PARMENTER, T. 1985. A guide to the Warblers of the Western Palearctic. CCG Canada.

ROBSON, C. 2000. A Field Guide to the Birds of South East Asia. New Holland . London.

SVENSSON, L. 1992. Identification Guide to European Passerines, 4th Edition. BTO. Norfolk, UK.

Old World Warblers ……??????


Christian Melgar, PO Box 1128, Kilauea, Kauai, Hawaii. 2000, revised 2003.

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