From: Birds of the Soviet Union: Vol VI by G. P. Dementev & N. A. Gladkov (1954)
Siberian Red-Tailed Shrike or Butcher-Bird
Lanius cristatus Linnaeus
In 1954 when this book was published the four subspecies of Brown Shrike were still all considered subspecies of a superspecies which included The Red-backed Shrike (L. collurio collurio & L. collurio kobylini) and the Isabelline Shrike (L. isabellinus isabellinus, L. isabellinus phoenicuroides, L. isabellinus speculigerus, and L. isabellinus tsaidamensis).
The accounts of the four subspecies of Brown Shrike are as follows:
Subspecies and differentiation characters: Various subspecies differing in proportions (relative length of remiges and rectrices, length of tip of wing), coloration, range of color changes, and sizes (particularly length of wing and width of rectrices), as well as in biology -- voice, breeding peculiarities, seasonal movements, food relationships, and biotopic sites.
The first proposal to unite all red-backed shrikes into one species was advanced by Stresemann (1927). Controversy however still invested the question of the relationship of the red-tailed butcher-bird proper of the east Asian group L. c. cristatus -- confusus -- supercilious -- lucionensis. A number of authors (Shtegman, Hartert and Steinbacher) inclined to the view that this should be distinguished as species from the red-tailed butcher-bird [Meaning, I take it, to distinguish L. cristatus from the L. collurio-L. isabellinus complex. - C.M.]. Supporting this are the constant morphological differences (proportions of length of extreme and middle rectrices, while the tail is more graduated in the cristatus groups; rectrices of these birds narrow); a stronger bill of L. c. cristatus; peculiarities of sexual dimorphism (conspicuous in L. c. collurio, extremely faint in L. c. cristatus), biological characters (song "primitive" in L. c. cristatus, which in addition rarely imitates other birds; details of reproductive cycles), and finally, differences in location of areas of migration and winter quarters.
However, the occurrence in Middle Asia of butcher-birds of the group L. c. isabellinus -- speculigerus -- tsaidamensis essentially levels these differences. Thus the author of the latest monograph on shrikes, Olivier (1944), isolates the subspecies mentioned above as species, and divides the entire group of butcher-birds into the three species L. collurio (collurio, kobylini), L. isabellinus (isabellinus, speculigerus, tsaidamensis) and finally L. cristatus (cristatus, confusus, superciliosus, lucionensis).
Since the isabellinus group is morphologically and biologically intermediate between the other two groups. it would be more cautious today to combine all forms of butcher-birds into a single polytypic species. No proofs of a joint isolated habitation of the two forms of these species groups in breeding ranges are available. except for the occurrence or hybrid populations, which, however, supports the points of view advanced. A notable exception is the fact that L. c. collurio and L. c. cristatus here jointly distributed in the eastern parts of West and central Siberia -- in Altai, Salair, even in spurs of the Kuznetsk Alatai at Tomsk (but even here hybrids are occasionally encountered; Johansen, 1944).