The taxonomy and systematics of the Brown Shrike and its relatives are rather complex. For a long time the Red-backed (L. collurio), Isabelline (L. isabellinus) and Brown Shrike (L. cristatus) were regarded as part of a large super-species. This was the case, for instance, in 1954 when Dementev and Gladkov published their Birds of the Soviet Union, although even in 1944 Oliver had already proposed dividing them into three species. In 1977 & 1979 the Dutch ornithologist K. H. Voous published studies that argued for them to be regarded as separate species, which they have been subsequently.
One basis of a variety of evidence the current thinking is that within this 'superpecies', the Red-backed and Isabelline Shrikes are more closely related, while the Brown Shrike is a slightly more distant relative. Although there are large areas where the range of Isabelline and Brown Shrikes overlap, there are very few recorded hybrids between these species. Thus one can consider them as sympatric species (i.e maintaining reproductive isolation even in the face of geographical overlap).
In contrast, the ranges of Isabelline and Red-backed Shrikes almost do not overlap at all, yet there are a large number of recorded hybrids from the small areas of overlap of their range.
Their systematic status is further complicated by the fact that there are two subspecies of the Red-backed Shrike, L. collurio collurio & L. collurio kobylini; four subspecies of the Isabelline Shrike, L. isabellinus isabellinus, L. isabellinus phoenicuroides, L. isabellinus speculigerus, and L. isabellinus tsaidamensis; and four subspecies of the Brown Shrike, L. c. cristatus, L. c. confusus, L. c. superciliosus, & L. c. lucionesis. For a more detailed description of the range of all these subspecies and taxonomic notes on them consult Dementev and Gladkov's Birds of the Soviet Union.
Adapted (below) is a range map that shows (roughly) the breeding territory of the ten subspecies of these three Shrikes. Note that, in general the subspecies of Red-backed Shrike winter in southern and eastern Africa; the subspecies of Isabelline Shrike winter in eastern Africa, Arabia and India & Pakistan; while the subspecies of Brown Shrike winter from eastern India across south-east Asia through Malaysia and Indonesia.
For a detailed description of the range of the subspecies of the Brown Shrike Lanius cristatus I reproduce here some notes from Charles Vaurie's Birds of the Palearctic Fauna (1959).
Range: Western Siberia from the Irtysh and Altai eastward to Anadyland, Kamchatka, and Japan, south to northern Mongolia, Manchuria, Korea, and China. Winters in India, southeastern China, Indo Chinese countries, and Indo Malaya, including Philippines, to the Lesser Sundas, Celebes, and Moluccas.
Bushes or trees along the edges of coniferous or mixed deciduous and coniferous forest or in its clearings, as well as on forested steppes, in thickets along streams or on the edges of swamps.
Lanius cristatus cristatus
Range: From the eastern parts of western Siberia (middle Irtysh and Tomsk) and Russian Altai eastward, north to Turukhansk, Olenek River, to the lower Lena, the delta of the Kolyma, Anadyrland and Kamchatka, south to central Altai and perhaps the Gobian Altai, to northern Mongolia (Uriankhailand, Tannu Ola Range, and Khangai eastward to Kentei), southwestern Transbaicalia and southern foothills of the Stanovoi Range; grades into L. c. confusus in southeastern Transbaicalia in the region of Chita, and, perhaps, in northwestern Manchuria and upper course of the Zeya River in Amurland. Migrates through Mongolia, Manchuria, and throughout China to winter in southeastern China, Indo Chinese countries south through the Malay Peninsula to Sumatra, Anamba Islands and Borneo, and India west to the Punjab, south to Ceylon, and Andamans.
Lanius cristatus confusus
Similar to nominate L. c. cristatus but paler above, paler rufous on crown, grayer on the back, and with a wider white frontal band.
Range: Amur and Ussuri Basins and northern and central Manchuria, in Amur- land north to about the middle Zeya River (see nominate cristatus for intermediate populations), said to intergrade with lucionensis on the border of southern Ussuriland and Korea. Migrates through Manchuria and Korea and probably eastern China to winter in the lower Malay Peninsula.
Lanius cristatus superciliosus
Distinctly more rufous and darker above than nominate L. c. cristatus, crown and rump much redder, with a very narrow black band at the base of the bill and with the white frontal band wider, bill longer and more attenuated.
Range: Sakhalin and Hokkaido south to south central Honshu. Migrates through Japan and eastern China to winter from southern Yunnan, southern Kwangsi and southern Kwangtung (probably), to Hainan, Indochina, southern Malay Peninsula, Anambas, and Greater and Lesser Sundas eastward to Flores and Sumba.
Lanius cristatus lucionesis
Much grayer above than the preceding races, not rufous except on the rump and upper tail coverts, black band at the base of the bill wider or better indicated than in superciliosus and forecrown not pure white, very pale gray grading into pale ashy on the top of the crown; bill similar to that of superciliosus or very slightly larger.
Range: Korea southward through northern and eastern China to the Yangtze Valley (Shanghai and Hankow), inland to southern Shensi (Tsinling Range) and Red Basin of Szechwan penetrating a little way into southeastern Sikang, also Kwangtung and probably other regions of southeastern China. Migrates through southeastern Manchuria, northern China and southeastern China (where it winters occasionally) and Formosa to winter chiefly in the Philippines south to the Talaud Islands and northern Borneo, occasionally to Celebes and the Moluccas, also Indochina to northern Slam and southern Burma, Malay Peninsula and Sumatra, and commonly in the Nicobars and Andamans, has straggled to southern India (Travancore) and Ceylon.