The new taxonomy of the "Isabelline Shrike" Lanius isabellinus complex - with notes on racial identification

By Brian J Small

Photos by Paul Gale (Paul's website)

"Isabelline (or Red-tailed) Shrike" Lanius isabellinus has been treated in the past as conspecific with Red-backed Shrike L collurio (e.g. Vaurie, 1959) or with both Red-backed and Brown Shrike L cristatus (e.g. Dement’ev and Gladkov, 1954). Until recently, it has generally been treated as a separate species comprising four sub-species: two, phoenicuroides and speculigerus breeding in central Asia and migrating southwest, wintering in Arabia and NE Africa; two, isabellinus and tsaidamensis, breed in North China and are shorter distance migrants, wintering in Pakistan and NW India west to Iran.

David Pearson had for a while suspected that the "type" specimen of Isabelline Shrike L isabellinus isabellinus, through which the species was first described (collected in western Arabia and described by Hemprich and Ehrenberg 1833), was in fact of the race speculigerus. Following an investigation, with the type specimen being located by Gerhard Nikolaus at the Berlin Museum, Pearson was able to confirm that the plumage of the type specimen was indeed that of speculigerus, freshly moulted and like the birds that over-winter in the Sudan Nile valley. Therefore, following the rule of precedence involved in taxonomic names, what was previously known as L isabellinus speculigerus is now to be known as the nominate form L isabellinus isabellinus, and a new name found for the previously known "isabellinus."

Pearson has recently published in the Bulletin of the B.O.C. (2000, 120), a review of this specimen and consequently the taxonomy of the "Isabelline Shrike" complex (Pearson, 2000). The results of his investigation are:

• The form previously known as speculigerus Taczanowski 1874, which breeds in Mongolia, should be known as L i isabellinus (speculigerus now becomes synonymous with isabellinus).

• The form breeding from Iran and Afghanistan to southern Kazakhstan, remains as L i phoenicuroides Schalow 1875.

• The form previously known as isabellinus, which breeds in the Tarim basin of NW China, is re-named L i arenarius Blyth 1846.

• The other form that breeds in the Tsaidam depression in N China remains as L i tsaidamensis, although in truth this form is said to be non-valid, with birds from that area being more reminiscent of isabellinus and not arenarius, (Tim Worfolk, pers. com.).

The paper by Pearson (2000) also outlines the various morphological differences between the races in adult plumage and studies the moult pattern. It is apparent that isabellinus and phoenicuroides are structurally and physiologically closely related, have similar moult patterns, breed later and have longer migrations than the eastern races, and as one might expect show a longer wing, second primary and primary projection (six or seven clear primary tips visible, opposed to five, sometimes six on arenarius). Pearson states that in general their moult strategy differs in that they have a complete moult on arrival on the wintering grounds (some may have moulted inner primaries on the breeding areas or migration routes), finishing between January and March (this affects both adults and immatures). There is, however, considerable variability amongst all races.

In comparison, the Chinese race arenarius, has slightly shorter wings, second primary (equal to or shorter than the sixth) and primary projection. It also has a different moult strategy, in which the adults usually have a complete moult starting in late summer and usually completing before migration.

The decision of the Dutch committee for systematics (CSNA) to "split" the "isabelline" shrike complex into three species was published in 1998 (Sangster et al, 1998), and was based on the grounds of "qualitative differences in morphology and analyses of their contact zone" and "vocalizations" (Sangster 1998). They name them as follows: L isabellinus (formerly speculigerus), Daurian Shrike, L phoenicuroides, Turkestan Shrike; L arenarius (formerly isabellinus) and tsaidamensis, Chinese Shrike.

The result of these changes is to generate a determination to understand and clarify the differentiating morphological characters for the new (sub-) species. An important identification paper by Tim Worfolk has been published in Dutch Birding, in which identification features for birds of both sexes and all ages are discussed. The CSNA are currently reviewing the situation for the Netherlands, although the number of records is small. So what is the situation in the UK? It is clear from past decisions that a review is needed here (take for example the "isabelline" shrike at Portland in September 1985 aged as first-winter, but it showed no barring on the under-parts, pale primary patch and apparent moult contrast in the greater coverts, features more indicative of a female phoenicuroides). Recent records are coming under closer scrutiny in an attempt to identify them to race: the female in Cambridgeshire, UK, is generally thought to be Daurian Shrike L (i) isabellinus on account of its plumage features.

Within the context of Western Europe what are the features to look for? What follows is a brief (and probably over-simplified) summary of the key aspects of structure and plumage to look for when attempting to identify the various forms of "isabelline" shrike. It is unlikely that arenarius will occur in the west, being a short distance migrant so I will deal with it in less detail.

Daurian Shrike L (i) isabellinus
In appearance isabellinus is said to be intermediate between phoenicuroides and arenarius, but, although morphologically and structurally close to phoenicuroides, it has distinct plumage features of its own.

Adults. Above, generally uniform isabelline-grey (from the crown to upper back and including the scapulars); below, pale creamy buff, with a richer orange tone (males) or yellow-buff (females), often from the chin to the ventral region – the overall appearance is more uniform, with less contrast between the upper- and under-parts than phoenicuriodes. The supercilium is quite subdued to the point of being absent, and creamy. On males the mask is black, running from the forehead across the lores to the ear coverts; on females the lores tend be paler, with a small amount of brown-black in front of the eye and on the ear coverts, and there may be pale barring in the malar region, breast and flanks. The rump and tail is bright rufous, although the rump is usually subtly paler than the upper tail. On males there is a small cream-white or whitish patch at the base of the primaries, visible as a small speculum, but on females this is absent or very subdued. The bill of adults is variably black or pale with a darker tip.

Turkestan Shrike L (i) phoenicuroides

Adults. Above, males have a rufous crown, nape and hind-neck blending with a fairly dark sandy or tan-brown mantle, scapulars and back, a prominent and contrasting white supercilium above a black mask extending from the forehead, across the lores to the ear-coverts, and a prominent white speculum. Below they are much paler than isabellinus, usually white or, at the most, pale cream-buff or pinkish on the breast and flanks – some may have some colour on the centre of the throat. There is therefore a greater contrast between the upper- and under-parts than isabellinus. The rump and tail are rich rufous, with the rump usually richer in colour than isabellinus. Paler males, with a sandy isabelline-grey crown and upper-parts occur within phoenicuroides, "typically in lowland areas" (Pearson 2000), and these are quite similar to isabellinus, but may differ in paler under-parts and more clear-cut supercilium.

Females differ markedly from males in being duller above, with only a faint rufous-tan crown, brown mask – restricted or absent on lores, a less distinct or even absent primary patch and fine barring on the malar area, breast and flanks. The barring is usually darker than on isabellinus, more the tone of the upper-parts.

In most respects phoenicuroides is darker and more richly coloured above than isabellinus, with a rufous or rufous-tinged crown, white speculum, richer rufous rump, and paler under-parts.

Immatures. Juveniles or first-winters are the real challenge, with, in comparison to adults fewer features to ‘go on’, so I have left this until last to discuss. Of most importance is the overall appearance, which tends to echo that of adults: on isabellinus there is less contrast between the upper- and under-parts; on phoenicuroides there tends to be more.

First-winter isabellinus is uniformly warm buff, created by a paler gingery mantle and crown, yellowish or creamy buff wash to the whole under-parts, barred finely on the malar region, breast and breast-sides – this barring tending to be very light in tone and orangey. The general lack of contrast is further added to by the paler centres to the wing coverts and tertials, which may bleach by late October to be almost uniform cream.

With colours echoing the adults, phoenicuroides is generally darker above, with a slightly more rufous-toned crown and greyer mantle. The centres to the greater coverts tend to be darker, contrasting more with the pale edges. Pale, whitish under-parts may be washed buff or pinkish on the breast and flanks, and marked with quite strong barring, typically darker than on isabellinus. (See the first-winter in Kent in Birding World 6:10 p386, which shows richly coloured upper-parts and crown, a fairly strong wash on the flanks with dark barring).

Having said all this, there is an overlap of features between isabellinus and phoenicuroides, meaning that some may not be identifiable in the field.

Chinese Shrike L (i) arenarius and L (i) tsaidamensis
The palest form and, being a short distance migrant, the least likely to arrive in Western Europe. I will describe the features briefly below.

Adults. Above, pale isabelline- or sandy grey. Mask more restricted in front of eye and browner than isabellinus and phoenicuroides, and bordered above by a pale cream, indistinct supercilium. Wing coverts paler than other races (lacking dark centres), forming a more uniform area on wing – reminiscent of Isabelline Wheatear as is the contrasting black alula. The edges to the secondaries and primaries are also pale whitish cream– indeed the remiges are paler and browner than isabellinus and phoenicuroides, and the primary bases are marked with a small white or whitish speculum. Below, tinged pale pinkish buff (perhaps more strongly coloured than phoenicuroides, but not as strongly as isabellinus). Rump and tail, pale rufous, sometimes lightly barred. Females are similar, but have a paler brown mask and rarely show a primary patch, as well as very weak barring on the under-parts.

Immatures. First-winter arenarius is similar to the female, but shows slightly stronger barring on the under-parts.

British Records
In attempting to make an assessment of British records, I have looked at some "isabelline" shrikes from the past few years, trying to find helpful photographs or descriptions in the available literature. In reality it may prove an impossible task to be able to separate all past records to race. One problem in working from photos is the colour cast and the other is people’s perception of colour, which in trying to judge subtle distinctions is clearly going to hinder the racial separation.

Examine the photograph of the female trapped on Fair Isle in Birding World 7:vol 8, p305. This shows a really quite dull and dark bird almost lacking any rufous tone at all – I suspect it has a cyan colour cast. In trying to allow for this it may be possible that this bird is a female phoenicuroides, with earth-brown upper-parts, a (for a female) fairly prominent supercilium and white under-parts. Also of interest, the speculum is very white, the forehead and crown is mottled/barred white and the upper-tail coverts are also barred.

Other observations from looking at photographs of first-winter "isabelline" Shrike, are the number in which the tertials seem very worn and bleached, and the number that don’t show the classic sub-terminal markings on the greater coverts, being generally paler; a number show quite a prominent pale or whitish wing bar; most show quite a strong peach wash on the rear flanks and cream on the rest of the under-parts. Variability is enormous and, quoting (loosely) from a recent British Birds, it would be a brave person indeed who claimed to be able to assign to race first-winter "isabelline" shrikes. It will also be a very observant one.

However, this scan through a number of images of "isabelline" shrikes in Birding World would suggest that the majority of first-winters are isabellinus, Daurian Shrike. In the photographs most appear uniform in colouration, with quite a strong wash to the under-parts and rufous, not dark, barring. The wing coverts and tertials also tend to be more concolorous with the upper-parts.

Being a longer distance migrant than phoenicuroides, it may well be expected that isabellinus is more frequent, but it is also apparent that both have been seen, so keep your eyes peeled and next time you find an "isabelline" shrike, take careful note of the overall tone and colour of the bird, the contrasts in the coverts and tertials, the colour and strength of the barring, and if possible photograph it. You may well than have a chance of identifying it as either Daurian or Turkestan Shrike

Acknowledgements

Many thanks to Tim Worfolk and David Pearson for their help and advice and to Paul Gale for allowing us to reproduce his excellent photos to illustrate this article.

Brian Small
November 2000