Capricious taxonomic history of Isabelline

n The Status of in Britain and Ireland (1971), the BOU Records I Committee mentioned five records of birds of the so-called 'isabellinus' or eastern group of races of the Red-backed Shrike collurio. These are the same birds which in The 'British Birds'List of Birds of the Western Palearctic

continued...

[Brit. , 72:573-578, December 1979] 573 574 Taxonomic history oflsabellim Shrike (1978) are called Lanius isabellinus. Earlier, these birds had been included by the BOU Taxonomic Sub-committee (Ibis 98: 167) in Lanius cristatus, which combines all Red-backed, Isabelline and Brown of and palearctic in one species, as was also advocated by Stresemann (1927), Dementiev (in Dementiev & Gladkov 1954), Por- tenko (1960) and Voous (1960). Authors who have advocated splitting these shrikes up into three species—Red-backed L. collurio, Isabelline L. isabellinus and Brown L. cristatus—include Olivier (1944), Johansen (1952), Stresemann & Stresemann (1971, 1972), Mauersberger (1971) and Voous (1977). Classic authors, such as Hartert (1907), Hartert & Steinbacher (1933), Stegmann (1930) and Vaurie (1959), combined the Red-backed and Isabelline Shrikes in one species (L, collurio) and kept the (L. cristatus) apart, in spite of the fact that Isabelline and Brown Shrikes look much more alike than do Red-backed and Isabelline. Clearly, the recognition of species in this group creates great difficulties. Stresemann, who wrote the most sensible accounts of these birds, changed his view: first, he combined them all in one species (1927) and, secondly, divided them up into three (Stresemann & Stresemann 1971). I shall try to explain what has led me to follow Stresemann's example by changing my mind, to recognise three species in my List of Recent Holarctic Bird Species (1977), instead of one, as in my Atlas ofEuropean Birds (1960). The basic data refer to plumage, reproduction, migration and moult. At the root of the problem stand the geographical distribution of the various forms and the history of their geographical isolation.

Plumage Three groups can be distinguished: (1) Red-backed or 'collurio' group (races spicuous rufous rump and tail, and white collurio, pallidifrons, kobylini), in which adults patch at base of primaries. show conspicuous sexual differences: males (3) Brown or 'cristatus' group (races cristatus, have grey head, rufous back and dark brown conjusus, superciliosus, luciontnsis), in which tail, whereas females are brown above, and both sexes resemble 'isabellinus' group to a creamy-white below with a variable amount considerable degree, but differ by being of cross-barring. darker, browner, often with some shade of (2) Isabelline, Red-tailed or 'isabellinus' rufous above, having tail yellowish- or group (races phoenicuroides, isabellinus, buffish-brown, and showing no visible white speculigems, tsaidamensis), in which the sexes patch in the wing. are the same: pale greyish-buff, with con-

Geography Roughly speaking, the dark 'collurio'group inhabits Europe, including Asia Minor, northern Iran and western Siberia; the desert-coloured 'isabellinus' occupies south-central Asia, as far east in Transbaicalia as the border river Argun at 120°E; and the 'cristatus' group is from eastern and east-central Asia, reaching almost as far west as the river Ob at about 82°E. All groups meet in central Asia, notably in the southern Altai (fig. 1). Although no special study has been made, the differentiation of these groups seems to have taken place as eastern, central and western isolates during some time of the glacial periods. Taxonomic history of Isabelline Shrike 575

Fig. 1. Distribution of three species of shrike Lanius: Red-backed Shrike L. collurio, Isabelline Shrike L. isabellinus and Brown Shrike L. cristalus. (After Mauersberger 1971)

Reproduction Where the 'collurio'and 'isabellinus'groups meet, widespread hybridisation has been reported, but data are contradictory on whether there is one or more zones of secondary intergradation, or whether there is still any selected mating. Of the contact between the 'collurio' and 'cristatus' groups in central Siberia, there now seems to be reason to believe, after reports to the contrary, that only two intermediate specimens ('hybrids') are known, collected near Tomsk on the river Ob (Mauersberger 1971). Still, in eastern Kazakhstan, hybridisation of all these shrikes seems to occur and, in the Tarbagatai, Johansen (1952) even speaks of a 'heilloses Durcheinander von Mischformen' (disastrous mixture of hybrids), involving mainly phoeni- curoides X speculigerus X pallidifrons. Throughout, the 'cristatus' group is found in woodland, whereas 'isabellinus' occurs in desert scrub; but apparently this describes the main vegetational differences of the inhabited areas rather than the habitat preferences of the birds. No other ecological or behavioural data have been reported that could inhibit the forming of mixed pairs, other than the time of arrival in spring, when late arrivals {cristatus) might find early ones (isabellinus) already paired.

Migration Most of these shrikes are long-distance migrants which winter in the tropics. The 'collurio'-group shrikes winter in eastern, central and southern Africa and cover the longest distances (9,000-11,000 km). They enter Africa exclusively from the northeast. For those breeding in west and central Europe, this involves a remarkably 'hooked' migration route, which in autumn is first due east, then changes to south and southwest. Birds in the 'cristatus' group winter mainly in south and southeastern Asia, each of the four races having a distinct main wintering area. Their routes may also have 'hooked' patterns, as the Siberian birds have to travel eastwards first, 576 Taxonomic history ofhabelline Shrike

235 & 236. Isabelline Shrikes Lanius isabel- linus. Left, Pakistan, March 1977; above, .Afghanistan, March 1972 (Ekko C. Smith)

then change to south or southeast. Shrikes in the 'isabellinus'group winter in south and southwestern Asia and northeast Africa. The main wintering areas of some races are unknown, but their migration routes are not so long as those of the others.

Moult There are widely varying moult patterns in this group, which seem to be primarily correlated with the migration behaviour (Stresemann & Strese- mann 1971, 1972). As a rule, there is a tendency for the long-distance migrants to postpone the post-nuptial moult of flight and tail feathers until after safe arrival in their winter quarters, or to undergo a double moult annually. Both ways are unusual among palearctic migrant songbirds. Within the 'coIlurio' group, flight and tail feathers are renewed only in the winter quarters. Shrikes in the 'cristatus' group renew their flight and tail feathers twice annually: post-nuptial, on the breeding grounds, and pre- nuptial, in the wintering area (Med- way 1970), though moult may be tem­ porarily arrested when long-distance migration has started. Within the 'isabellinus' group, flight and tail feathers are renewed in a post-nuptial moult on the breeding grounds, and the tail feathers again in the wintering area. In this group, however, there is much variation, and not all of the sub­ species wintering in Asia follow the general pattern.

237. Isabelline Shrike Lanius isabellinus phoeni- curoides, Afghanistan, August 1970 (Stuart L. Pimm) Taxonomic history ofhabelline Shrike 577

238. Isabcllinc Shrike Lantus isabellmus Isabel- linus, Afghanistan, August 1970 (Stuart L. Pimm)

Interpretation Originally, authors have been influenced mainly by reproductive behaviour. On account of undeniable hybridisation, if not downright intergradation, several hybrid specimens (or perhaps populations) have even been given their own 'subspecific' names. One of these is 'karelini' (Bogdanov) for intermediates between kobylini of the 'collurio' group and phoenkuroides of the 'isabellinus' group. As a consequence, recent authors have decided to lump the species, with or without cristatus. As the differences in moult pattern and migration routes gradually became clear, more and more authors were inclined to consider these as important characters of great survival value, evolved after long isolation; hence, as specific evolutionary attainments, of as much importance as reproduction behaviour. This may be true or not, depending on how mutable migration and moult patterns can be, and they seem to me to be very changeable. To this may be added the consideration that the detailed maps by Mauersberger (1971) show large regions in central and northern Mongolia where Isabelline and Brown Shrikes occur alongside each other without apparent interbreeding, and this may also be true of Isabelline and Red- backed Shrikes in Transcaspia. It should not be forgotten, though, that these regions are among the least covered by ornithological research in the whole Palearctic. One thing is certain, however: all these groups have acquired many distinct characteristics, testifying a long and efficient isola­ tion. Apparently, they have started lines of development of their own, which is why I have followed Stresemann & Stresemann (1971, 1972) in recognising three incipient species, or rather semi-species, Lanius cristatus, L. isabellinus and L. collurio, constituting one complicated, marginal superspecies, collectively to be known as Lanius cristatus (this name has page-priority over L. collurio, both of Linnaeus 1758). These shrikes then represent that kind of border-line case in which the formal splitting as species is more likely to stimulate research of the numerous interesting problems involved than the otherwise more logical combination into one 578 Taxonomic history qflsabelline Shrike species would ever do. This treatment more or less gives the specific status within the group the benefit of the doubt: it is certainly not considered to be a final answer. The combination of the 'collurio' and 'isabellinus' groups into one species, opposed to the 'cristatus' group, recently also advocated by Wolters (1978), is another, no less unlikely solution and might eventually prove to do more and appropriate justice to the facts than either the splitting into three or the amalgamation into one species. At all events, the Isabelline Shrikes recorded in Britain have to be referred to one or other of the races of Lanius isabellinus, most probably L. i. phoenicuroides, or else one of the intermediate types originating from one of the nearest westernmost breeding ranges.

References BRITISH ORNITHOLOGISTS' UNION. 1971. The Status of Birds in Britain and Ireland. London. DF.MENTIEV, G. P., & GLADKOV, N. A. 1954. The Birds of the Soviet Union, vol. 6. Moscow. [In Russian] HARTERT. K. 1907. Die Vogel der Palaearktischen Fauna, vol. 4. Berlin. & S'l'EINBACHER, F. 1933. Die Vogel der Palaearktischen Fauna, vol. 3. Berlin. JOHANSEN, H. 1952. Die Vogeliauna Westsibiriens. II.7. Urn. 92: 145-204. MAIERSBERGER, G. 1971. In STRESKMANN, E., PORTENKO, L. A., & MAUERSBEROER,G.Atlas der Verbreitung Palaearktischer Vogel. vol. 3. Berlin. MEDWAY, LORD. 1970. A ringing study of the migrating Brown Shrike in west Malaysia. Ibis 112:184-198. OLIVIER, G. 1944 Monographie des Pies-Grieches du Genre Lanius. Rouen. PORTENKO, L. A. 1960. [Birds of the USSR], vol. 4. Moscow & Leningrad. [In Russian] STEGMANN, B. 1930. L'ber die Formen der palaearktischen Rotrucken- und Rotschwanz- Wiirger und deren taxonomischen Wert. Orn. Monatsber. 38: 106-118. STRESEMANN, E. 1927. Die Wanderungen der Rotschwanz-Wiirger (Formenkreis Lanius cristatus). J. Orn. 75: 68-85. & S'l'RESEMANX, V. 1971. Die postnuptiale und die praenuptiale Vollmauser der asiatischen Wurger Lanius tigrinus und L. cristatus.}. Orn. 112: 373-395. 1972. Uber die Mauser in der Gruppe Lanius isabellinus. J. Orn. 113: 60-75. VAL'RIE, C. 1959. The Birds of the Palearctic Fauna. Passeriformes. London. VOOL'S, K. H. 1960. Atlas of European Birds. Edinburgh & London. — 1977. List of recent Holarctic bird species. . Ibis 117: 381. WOLTERS, H. 1978. Die Vogelarten derErde. vol. 3. Hamburg. Professor Dr K. H. Voous, V. D. Duyn van Maasdamlaan 28, Huizen-NH, Netherlands