Yet another potential Stejneger’s Stonechat from Finland

By Magnus Hellström

“…during the examination Kari and Jarmo discovered that the bird showed a distinct and rather large dark marking in one of the birds’ uppertail-coverts. The marking was blackish and extended from the shaft out on the inner vane of the feather, perfectly matching the ‘class 2B markings’…” 

 

On October 4, Finlands second stejnegeri-candidate for the autumn was found at Kristiinankaupunki (the first one can be seen in a blogpost from Martin here). The bird was trapped by Kari Korhonen and Jarmo Pirhonen and was identified as a 1cy male. The width of bill at the proximal edge of the nostrils was measured to 4.5 mm which, according to Svensson (1992), place this bird outside the range of stejnegeri (4.7–5.7 mm, compared to 4.0–4.9 mm in maurus). However, during the examination Kari and Jarmo discovered that the bird showed a distinct and rather large dark marking in one of the birds’ uppertail-coverts. The marking was blackish and extended from the shaft out on the inner vane of the feather, perfectly matching the ‘class 2B markings’ shown and discussed in Hellström & Norevik (2014).

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Note the marked uppertail-covert. Photo: Jarmo Pirhonen

Similar markings are found on c. 40% of the 1cy male stejnegeri that passes through Beidaihe, E China, during the autumn migration, while such bold markings are, to present knowledge, not known to occur within maurus. The dark marking was found in one single uppertail-covert feather only, but such sparse/irregular distribution of the markings is regularly seen also in the E Chinese birds.

A feather was collected, and subsequent genetic analysis will show whether or not this bird qualify as a stejnegeri (as suggested by the overall appearance and the pattern of the uppertail-covert) or as maurus (as suggested by the width of the bill). As always, analysis of mitochondrial DNA will only give the genetic history of the mother, but both taxa are commonly distributed over huge areas in N Asia and there are some indications pointing to that hybridization may be less common than earlier believed. True or not, the likelihood of a purebred bird should exceed that of a hybrid by far.

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Ageing the bird: The primary coverts show a typical first-winter pattern with pale buffish edges, typically widening to a broader (and slightly diffusely set off) tip. In a folded wing, the broad pale tips almost blur into each other, hiding most of the darker parts of the feathers. In adult (2cy+) birds, the pale edges are typically whitish, narrower, more sharply set of against the black feather centre, and does not widen towards the tip. This character is applicable in most autumn individuals, but a few birds (especially females) may be harder to assess. Since this young bird have conducted a partial moult there are also moult contrasts to be found in the plumage. However, these contrasts are often hard to detect in photos, like here. Photo: Jarmo Pirhonen

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Sexing the bird: Rather straight forward, since black underwing-coverts are shown by males only. Photo: Jarmo Pirhonen

Another bird:

Another good looking bird was trapped at Haparanda-Sandskär Bird Observatory in the far north Baltic Sea, Sweden, a week ago. This bird, also a 1cy male, shows a similarly dark, but even more sturated, plumage. No dark markings in the uppertail-coverts were seen, and no measurement of the bill is available, but the overall impression suggest this one as a stejnegeri as well.

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1cy male, Haparanda-Sandskär, Sweden, 2015-09-27, ringed and photographed by Magnus Karlefors & Ulf Öhman.

References: 

Svensson, L. 1992. Identification guide to European passerines. 4:th edition. Stockholm.

Hellström, M. & Norevik, G. 2014. The uppertail-covert pattern of ‘Stejneger’s Stonechat’. British Birds. 107:692-700.

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