Nial Moores, Birds Korea, November 2024
Following very robust northwesterly winds in late October 2024 no fewer than 5-10 presumed hybrid Silver-throated Bushtit Aegithalos glaucogularis 검은턱오목눈이 x Lengthy-tailed Tit Aegithalos caudatus 오목눈이were noticed on Baengnyeong Island, Incheon (Republic of Korea). These hybrids have been in amongst 50-60 caudatus and magnus Lengthy-tailed Tits seen on two completely different dates contained in rapidly-moving flocks. Each species sound related; lots of the people weren’t seen effectively; a few of these which have been seen effectively have been very “apparent” hybrids with nominate caudatus; and some have been extra doubtless hybrids with magnus Lengthy-tailed Tit (or maybe have been second or third technology?), and may effectively have been misidentified as “pure” Silver-throated if there have been no good photographs.
Because of a number of contributing birders, most particularly Kai Pflug in Shanghai, Terry Townshend in Beijing and Kim Eojin right here in Korea, the next put up goals to assist with the identification and documentation of Silver-throated Bushtits, hybrid Silver-throated Bushtits x caudatus and magnus Lengthy-tailed Tits, and intergrade magnus and caudatus Lengthy-tailed Tits.
Regardless of an overlap in vocalisations and large variation within the plumage of Lengthy-tailed Tit throughout its Eurasian vary, the Silver-throated Bushtit was break up from the marginally bigger Lengthy-tailed Tit following publications in 2008 and 2010 (per Gill et al. 2024), and is discovered often solely in PR China. The species is presently a real rarity within the Republic of Korea (ROK).
There are two subspecies of Silver-throats: vinaceus of central and North-east China, and the extra southerly-distributed nominate glaucogularis of “East central China” (Gill et al 2024), presumably kind of confined to Jiangsu, Hubei, Anhui and Zhejiang Provinces.
Adults of each subspecies are gray above (missing any pink), with very broad black lateral crown stripes and black foreheads and a darkish throat patch tipped paler, giving the species their scientific and English (“silver-throated”) and Korean (“black-throated”) names. In accordance with Geldard et al. (2020), the extra northern-distributed vinaceus, differs from the nominate subspecies “in having aspect of head and throat barely paler, underparts additionally barely paler, breast much less intensely washed buff, however typically marked by gorget of marginally darker and browner streaks, tail longer.” In accordance with on-line photographs, e.g. right here, the dark-headed juveniles of each subspecies are additionally extensively gray on the upperparts they usually additionally present way more intense reddish-pink on the breast than any juvenile Lengthy-tailed Tit in East Asia.
The primary Korean report of Silver-throated Bushtit was of two on Socheong Island in March 2022 discovered by the Migratory Chicken Analysis Centre employees. The second and third data have been of two and 4 people respectively which I discovered on close by Baengnyeong Island in Could and November the identical 12 months (although see beneath).
Each instances, the Silver-throated Bushtits on Baengnyeong Island have been in a big combined flock of magnus and caudatus Lengthy-tailed Tits, with a number of juveniles current in Could (each subspecies breed on the island).
The plumages of the Could Baengnyeong Silver-throated Bushtits have been very worn and whereas sharing all of the widely-expected options of the species, one or each confirmed a close to break within the black on the brow. Based mostly on photographs within the on-line Macaulay library, and as urged above and by Terry Townshend (in lit. Nov. 2024), a slim break within the black brow band appears to be a function proven (pretty) typically by birds in and round Beijing. Together with their long-tailed look, it subsequently appears affordable to determine the birds on Baengnyeong as belonging to subspecies vinaceus, as presently listed within the 2022 Birds Korea Guidelines.
In half-hour or so of observations on Could thirtieth 2022 , the Silver-throateds have been typically adopted by juvenile Lengthy-tailed Tits which have been begging meals. The Silver-throated Bushtits weren’t seen to feed these juveniles, however they did appear to reply to them, generally whereas carrying meals and will have been feeding them when out of view. Cooperative feeding, wherein adults feed younger from different broods, is understood in Lengthy-tailed Tit (Harrap 2020), complicated any inferences on breeding. Had been the Silver-throated Bushtits on Baengnyeong concerned in feeding the younger offspring from pairs of Lengthy-tailed Tits, or may one or each of them have been the precise dad and mom?
Determine 15 exhibits that one of many begging juveniles has a reasonably robust pink wash throughout the breast – whereas no less than another juveniles didn’t. Juvenile Lengthy-tailed Tit and Silver-throated Bushtits each begin feathered life largely dark-headed, with the grownup head sample rising over time. Nevertheless, juvenile Silver-throated Bushtits present in depth gray on the upperparts (like no less than some hybrids: see Figures 1, 2 and 28), whereas juvenile Lengthy-tailed Tits, like adults are dark-naped and backed, however with contrastingly paler scapulars. As well as, Silver-throateds, look extremely contrasting beneath, with intense red-toned saturation on the breast, whereas juvenile Lengthy-tailed Tits in East Asia are white-breasted (although a couple of photographs of juvenile Lengthy-tailed Tits within the Macaulay library from Korea and Japan do present a reasonably or very restricted pink wash). The pink flush throughout the entire breast proven by the chook in Determine 15, mixed with the darkish brow bar, makes it tempting to think about that this juvenile is perhaps from a hybrid pairing. Sadly, I did not take any photographs of the upperparts of this juvenile.
In contrast to Silver-throated Bushtit, Lengthy-tailed Tits are widespread and regionally quite a few within the ROK, and have a really vast distribution from Japan to western Europe.
There are two or a lot much less doubtless three sub-species of Lengthy-tailed Tit within the ROK: (1) The super-gorgeous and sometimes irruptive white-headed caudatus which breeds on Baengnyeong Island northward, and fewer steadily elsewhere near the inside border, and could be way more widespread in winter (being recorded no less than as far south as e.g., Heuksan Island in Shinan County); (2) The nonetheless cute and darkish head-striped magnus (both a part of the widely-distributed europeaus group or of the Far East Asian trivirgatus group: see Harrap 2020), discovered generally all through the mainland, which I additionally recorded as soon as within the DPRK, in Rason within the far northeast; and (3) trivirgatus on Jeju Island, in response to some authorities, e.g.. Harrap (2020). Gill et al. (2024) nonetheless, extra logically, confine trivirgatus to “c Japan”; and as such this taxon, presently included on the Birds Korea guidelines with a query mark, might be eliminated.
Additionally in northeast Asia, although unrecorded in Korea and never but recognised as a subspecies by both Harrap (2020) or Gill et al. (2024), is the japonicus subspecies of Hokkaido and the Kuriles, recognized by way of detailed evaluation by Lukyanchuk et al. (2017).
Plumage variations between the extra southerly-distributed magnus and the extra northerly-distributed caudatus Lengthy-tailed Tit in subject circumstances are apparent, with magnus having a slim darkish line throughout the lores, which broadens considerably above and behind the attention, persevering with unbroken as black lateral crown stripes in the direction of the extensively black nape and upperparts. Many additionally present a damaged, irregular, weak blackish band throughout the breast. As well as, the pink on the flanks and undertail coverts tends to be paler and fewer placing than in caudatus in Korea; and lots of seem to point out moderately narrower white outer edges to the tertials.
Close to the Korean inside border, magnus and caudatus sometimes pair up collectively to breed, together with on Baengnyeong Island, and out of juvenile plumage these intergrades can simply be recognized as a result of they present significantly lowered darkish within the lateral crown stripes, starting from barely light to nearly absent, maybe invariably exhibiting extra clearly to the rear of the stripe. Such birds can flip up nearly anyplace throughout winter irruptions, suggesting that these two taxa most likely breed collectively fairly often to the north of the ROK as effectively.
Simply accessible literature means that hybridisation between Silver-throated Bushtit and Lengthy-tailed Tit is uncommon or uncommon. For instance, Geldard et al. (2020) assert that there have been “no studies of standard intergradation or hybridization in northeastern China” the place ranges marginally overlap, though “Obvious ‘intergrades’ have been recorded as migrants in coastal Hebei, however the origin and standing of those are unknown’. By extension, hybrids appear extremely unlikely in Korea, a whole lot of km distant from the mapped zone of overlap of the 2 species – whereas being inside 180km of the common vary of Silver-throated in Shandong. Nevertheless, a documented hybrid pairing in Beijing in 2024 and the inflow of apparent hybrids on Baengyeong seen in October 2024 places an finish to such pondering: hybrids could be present in Korea. Such birds additionally assist with the event of standards for figuring out hybrids, which might be helpful for eBirders (though this hybrid mixture couldn’t be entered on eBird in October 2024, Marshall Iliff mailed in November to say that it’s going to quickly be added).
Principal hybrid options to search for seem to incorporate: very vast breaks within the brow band; black on the nape; lack of gray within the uppertail; and pink tones on the scapulars. A number of of the birds posted within the Macaulay library as Silver-throated Bushtit may subsequently be hybrids, together with birds in Beijing from no less than 2018 and Shandong in 2017. As well as, no less than one of many 4 Silver-throated Bushtit on Baengnyeong in November 2022 (and the one one to be correctly digiscoped) can now be confidently re-identified as a hybrid Lengthy-tailed Tit x Silver-throated Bushtit, with one dad or mum almost definitely a magnus: Figures 27-28). The place did this hybrid originate? May this have fledged on Baengnyeong in Could or through the summer season? Or did this chook arrive from the DPRK or PR China?
In 2024, following very robust northwesterly winds, a number of hybrids have been seen at Dumujin within the northwest of Baengnyeong Island on October twenty fourth, 2-3 of which have been documented in video and nonetheless images by Kim Eojin ; and no less than two extra have been seen within the southwest at Junghwadong on October twenty sixth on my own and Subhojit Chakladar, in a big flock of 30+ Lengthy-tailed Tits. No Lengthy-tailed Tits, Silver-throated Bushtits or hybrids have been seen within the following 5 days of subject work – suggesting that the birds had moved on – however to the place?
Based mostly on the vary maps on eBird (Figures 3 & 18) and climate circumstances previous to their commentary, it appears possible that the hybrids and the carrying flocks they have been with originated from Liaoning Province in PR China, the closest mapped location with a number of data of each Lengthy-tailed Tit and Silver-throated Bushtit (or if not, from the adjoining mainland Hwanghaenam within the DPRK, the place there aren’t any eBirders but…).
In abstract, in case you see an out-of vary Silver-throated Bushtit in Korea or in China, it’s value ruling-out (or ruling-in!) a hybrid origin as a part of the ID. Hybrids could be with both nominate or with darkish head-striped Lengthy-tailed Tit. Hybrids with nominates must be instantly apparent. In magnus-type hybrids, first examine:
- The black brow band. A small break within the centre of the band doesn’t appear to be proof of hybrid origin, however a large break is;
- Black on the nape;
- Any pink or white on the scapulars.
Thanks once more particularly to Kai Pflug in Shanghai (and to Andy Lee for contacting him on my behalf), Terry Townshend in Beijing and Kim Eojin for offering their extremely instructional photographs particularly for this put up; and to Subhojit Chakladar for sharing his picture for an earlier put up on Baengnyeong.
As at all times, everybody’s suggestions can be a lot appreciated.
References
Geldard, R. P., S. Harrap, and A. J. Spencer (2020). Silver-throated Tit (Aegithalos glaucogularis), model 2.0. In Birds of the World (S. M. Billerman and B. Ok. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.lottit5.02
Gill F, D Donsker & P Rasmussen (Eds). 2024. IOC World Chicken Listing (v14.2). doi : 10.14344/IOC.ML.14.1.
Harrap, S. (2020). Lengthy-tailed Tit (Aegithalos caudatus), model 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.lottit1.01
Lukyanchuk, O. A., Mariva, I. M. & Ya.A. Redkin. 2017. Geographical Variability of Morphological and Acoustic Indicators of the North Populations of the Lengthy Tailed Tit Aegithalos caudatus (Passeriformes, Aegithalidae) Biology Bulletin, 2017, Vol. 44, No. 9, pp. 1023–1031. © Pleiades Publishing, Inc., 2017. ISSN 1062-3590
