Dr Nial Moores, National Director, Birds Korea, January 25th 2025.
Shrikes can be among the easiest species to identify (adult males in breeding plumage, for example), or can be among the most difficult, due to a combination of seasonally different plumages and bare parts’ coloration, sexual dimorphism, highly complex and varied moult strategies, taxonomic uncertainties and hybridization. This post aims to introduce some of the features used to identify the Republic of Korea’s first Red-tailed Shrike Lanius phoenicuroides.
On December 22nd 2024, Ms Lee Yunha, a Middle School student, noticed an odd-looking shrike at a popular birding spot in Gimpo, Gyeonggi Province. On January 11th 2025 several birders visited the site, including Birds Korea member Dr Sung Soyoung (whose photos are used here) and Dr Park Jong-Gil, the lead ornithologist with the Korean National Parks. The shrike was still present, and showed extremely well.
I was sent multiple excellent images and opinions on this shrike; and also saw other images posted online over the next few days, all taken in strong winter sunshine with excellent cameras, as more and more birders visited the site. Thanks to the kindness of several Birds Koreans I was then able to visit the site and see the shrike on January 22nd (exactly a month after the first observation), when a combination of dense yellow dust and hazy, flat sunshine provided interesting conditions for assessing plumage tones.
The “Gimpo shrike” is obviously a member of the closely-related “super species” (Svensson 1992) group comprising Brown Shrike Lanius cristatus (a locally common migrant through the ROK and very local breeder, with records typically spanning late April to early October, and no adequately documented mid-winter records on the mainland); Red-backed Shrike L. collurio (fewer than ten Korean records and none in winter); Isabelline Shrike L. isabelllinus (two previous Korean records, on August 25th 2022 in Seosan and in December 2023 in the Saemangeum reclamation area); and Red-tailed Shrike L. phoenicuroides (a species sometimes known as Turkestan Shrike, previously unrecorded in Korea, with no records on eBird in eastern China, on the Korean Peninsula or in Japan).
Changes over recent decades in the taxonomic treatment of these species reveal the difficulty of the ID challenge. Svensson (1992) did not recognize the split of Red-tailed from Isabelline while Panov et al. (2011) in Pyle et al. (2015) consider that Red-backed and Turkestan may be one biological species, based on their extensive hybridization.
Immediate impressions from images suggests that the Gimpo shrike superficially looks like a Brown Shrike, with fairly dark brown and in some lights grey-brown upperparts, a slightly brighter tail and crown, and a rather contrasting head pattern, with an obvious supercilium and dark ear coverts.
The bird can quickly be aged too as a First-winter, because of e.g., the small dark subterminal bars on the retained juvenile greater coverts and the small black markings near the tip of the tail. Although First-winters are the most challenging age group to identify, vermiculations (wavy bars) shown most prominently by juveniles and First-winters, and again generally by females in mid-winter, can be helpful in narrowing the identification process somewhat (Worfolk 2000).
In January, the Gimpo shrike has obvious vermiculations on the flanks and uppertail coverts and rump. Although moults are extremely complicated in these species, the extent of these markings would be very unusual in Isabelline (which usually shows almost none by mid-winter) and probably of Red-backed, which might be expected to show more such markings on the upperparts, including e.g., on the crown.
Based simply on these vermiculations, the three most likely identifications for the Gimpo bird therefore become Brown Shrike or Red-tailed Shrike or a hybrid.
Looking more closely, the bird’s structure confirms the bird is not a “pure” Brown Shrike. In field conditions especially, the bill invariably looks long and slender (while in some images, the bill looked rather heavier); the head looks quite small; the legs look quite long; and the tail is obviously shorter than might be expected in Brown, though longer than would be expected in a Red-backed. These are all structural impressions expected in Red-tailed or Isabelline, and help to give the bird a very different feel in field conditions to a Brown Shrike.
In addition, in both images and in the field, the tertials look obviously shorter than in Brown, revealing a medium-length primary projection with six or so primary tips visible – quickly ruling out most “pure” Red-backed Shrike (which typically show 7 or 8) and the vast majority of Brown Shrike (which often shown only 5, though can rarely show 6 or even 7 – perhaps due to hybrid influence?).
Visible in images too, the all-important primary formulae (the relative length of each primary) shown by the bird in flight is also a very good match for Red-tailed Shrike. This according to a comparison with Svensson (1992) and expert analysis of images by Dr Park Jong-Gil. In addition, the lack of white though with some paling at the primary bases seems to be good for a female Red-tailed Shrike in her first winter of life.
Therefore, even before looking in any detail at plumage tones, the most likely contender for this shrike is Red-tailed Shrike.
Worfolk (2000) list several plumage features that can be used to identify First-winter Red-tailed Shrike, while also advising that, “It should not be thought that every bird can be identified. While many first-winter isabelline shrikes clearly show features of either phoenicuroides or isabellinus, a significant percentage (probably more than 10%) appears to be intermediate. These may indeed be of mixed parentage or it may be that one or both taxa are more variable than their adult plumage would suggest” (Worfolk 2000).
Features in support of identification of Red-tailed would include “earth-brown to pale sandy-grey upperside contrasting with the predominantly whitish underside” and as First-winters resemble females in many features, “a slightly warmer tone to the crown” and, “a rufous rump contrasting with the more drab mantle” (Worfolk 2000).
Plumage tones in First-winter shrikes can be remarkably difficult to assess well from images, due to e.g., differences in light conditions and even camera gear (see Pyle et al. 2015). In most images (e.g. in Figs 1 & 2), the Gimpo shrike looks brown above and lightly buff-washed below, with an obviously warmer crown and rump and contrastingly paler underparts (i.e., as expected in Red-tailed Shrike). In field conditions and in some images taken on January 22nd (e.g. Figs 11 & 14) , the bird looked much brighter above, especially on the crown, and in head-on views with flat light, the underparts showed buff flanks and off-white underparts – much too pale for Isabelline.
The bird therefore matches Red-tailed Shrike well.
Can a hybrid origin be sufficiently excluded so that Red-tailed Shrike can be added to the national list?
Probably the most detailed analysis of hybrid shrikes in the literature can be found in Pyle et al (2015). This paper sets out in often painstaking detail the process of identifying a shrike from this same “super-species” group which was found in Mendocino in California.
The Mendocino shrike was found in March and remained into April, during which time moult of key feather tracts progressed rapidly, allowing the initial suspicions of hybrid origin to be more or less confirmed. The most reasonable identification was Red-backed x Red-tailed (called Turkestan in the paper). This meant that the Mendocino shrike holds “the distinction of being the only individual bird to represent two species new to North America.” (Pyle et al. 2015). Initially, the most obvious anomalies were a combination of grey wash on the crown and nape (initially meaning the bird was identified as a lucionensis Brown Shrike) but warm brown upperparts; some hint of darkening in the central tail feathers; and a structure that did not fit at all well with Brown Shrike.
Some images of the Gimpo shrike suggested a greyish wash on the nape and also darker edges to some of the tail feathers, as shown in an image taken on January 22nd.
Field views removed those suspicions. The greyish wash on the nape “rippled” with the angle, sometimes looking to cover the mantle, and at other angles disappearing entirely. In addition, the suspected darker edges to some of the tail feathers suggested in some images also disappeared as the angle changed. For now, any “contrast” in the tail looks simply to be the result of a combination of shadow and less wear than shown by more exposed parts of the same feather.
In a similar way too while the tail looks quite dull in most images, in the field, the underside glows orange when catching the light – another very strong feature in support of identification as Red-tailed Shrike. The underparts also look really quite pale (buff on the flanks and off-white on the belly), and even the vermiculations look much finer and more delicate grey-brown (spider’s web-like) than suggested by images. All these features fit Red-tailed Shrike well.
Another initial concern about this bird related to several small dark markings on the tail, shared by juveniles of all the shrikes in this “super-species” group. Although largely worn away, in high resolution images they show as a narrow “V”, set off by a rather broad wedge of white, especially on t6 on the right side of the bird. Typically, Brown has the least extensive black and the least contrast on t6; and Red-backed the most. Svensson (1992) depicts two variants in the latter species – one broad with a narrow point and a wedge of white, and the other much narrower and more curved, with a white edge of even width. The only illustration of Isabelline / Red-tailed in Svensson (1992) shows a fairly broad black band, with a broad tip, and no obvious white wedge. Are these troubling tail markings better for Red-backed than for Red-tailed? And if combined with other anomalous features, are they enough to suggest hybrid influence?
Fortunately, Pyle et al. (2015) includes images of specimens of all four species. Although the pale border in t6 of the Gimpo bird is a little more extensive than expected, perhaps matching Red-backed Shrike more closely, the dark markings themselves match a specimen of Red-tailed Shrike very well (Figure 14, page 23).
The coloration of ear coverts is perhaps the only potential anomaly that remains to be addressed. In most images and often in the field, the ear coverts looked very dark brown, occasionally showing chestnut at certain angles. They therefore match Red-tailed Shrike. In field conditions, however, there were also times when the ear coverts looked almost concolorous with the crown, and these impressions were supported by some of the images taken at the same time (e.g., Figure 14). Worfolk (2000) states that, “The ear-coverts appear to be never as rufous as is typical in” Red-backed Shrike. Rather than list this as an anomalous feature, in the absence of any contradictory information, it might be wiser to amend Worfolk’s text to something closer to “never look consistently, at multiple angles, as rufous as is typical in Red-backed Shrike” .
There are plans to catch the bird and to take DNA to confirm the identification. This would resolve this identification even further. Another less stressful way (both for the bird and for the banders!) might simply be to wait for the bird to moult, so that other plumage features become better; or perhaps to sample droppings.
Either way, unless strongly contradicted by DNA analysis, there is no longer any compelling reason to doubt the identity of the Gimpo shrike as a Red-tailed Shrike, as also stated in lit. on January 18th by Grahame Wallbridge and Brian Small after reviewing some of the images.
We will therefore add Red-tailed Shrike in our next revision to the Birds Korea Checklist (which we are actively undertaking…). And as an eBird reviewer, I will approve records of the Gimpo shrike on eBird as Red-tailed Shrike. I will also try to return to see this sometimes subtly beautiful and at other times dazzling shrike in March or early April!
In the meantime, I would like to finish this post by congratulating Ms Lee Yunha warmly for becoming the youngest birder ever to find a national first in Korea! Wonderful!
(Finally, as always, please let us know if there are any mistakes or misrepresentations in this post so that we can correct them: thank you).
Acknowledgements
My sincere thanks go especially to Dr Sung Soyoung for permission to use his wonderful images; to Dr Park Jong-gil for his initial ID and expert comments; to Dr Shim Kyu-Sik for his encouragement and persuasion to travel up to Gimpo to see this bird; and to Dr Bernhard Seliger and Dr Choi Hyun-Ah for permitting me to join their regular survey in Gimpo, which included the area with the shrike, and for sharing of images. Many thanks too to Grahame Wallbridge for his emails, and for relaying his and Brian Small’s expert opinion on the identification.
Further Reading:
References
Pyle, P., Keiffer, R. J., Dunn, J. L. & Moores, N. 2015. The Mendocino Shrike: Red-backed Shrike (Lanius collurio) x Turkestan Shrike (L. phoenicuroides) hybrid. North American Birds. Vol, 69 (2015). Number 1, pages 4-35.
Svensson, L. 1992. Identification Guide to European Passerines. Fourth Revised and Enlarged edition. Stockholm, 2014.
Worfolk, T. 2000. Identification of red-backed, isabelline and brown shrikes. Dutch Birding 22: 323-362, 2000