Field characters of Isabelline and Brown Shrikes

Field characters of Isabelline and Brown Shrikes
A. R. Dean
British Birds 1982. 75(9): 395-406.

Summary: Although the Isabelline Lanius isabellinus and Red-backed Shrikes L. collurio are very closely related, and intergrading and hybridization have been reported, typical individuals of each species can nevertheless be identified in the field. A white primary patch is a consistent feature only on adult male Isabelline Shrikes of certain races, but there are other specific characters.

Aging is an important preliminary to identification, since in first-winter plumage the effectively unbarred mantle of the Isabelline Shrike is in itself a useful feature. On adults and first-winter birds, distinctly rufous tail, uppertail-coverts and lower rump contrasting with a pallid gray-brown to sandy mantle, and virtually unmarked body plumage, are good indicators of Isabelline Shrike, though some darker females of the race L. i. phoenicuroidies have less distinct body plumage. Such birds require care, as a small percentage of male Red-backed shrikes have atypically rufous tails. Immature Red-backed Shrikes not infrequently display a significant rufous component to both tail and lower rump; since juveniles Isabellines may have visibly barred mantles, the overlap of characters between July and early September may be considerable.

Subsidiary characters of the Isabelline Shrike include the lack of discrete white margins to the tail and, especially in immatures and L. i. isabellinus, a pellucid pink-tinged base to the bill.

The Brown Shrike L. c. cristatus is more problematical. Compared with the Isabelline shrike, birds of the nominate form display rather russet upperparts and basically concolorous mantle and rump, while the tail is russet-brown or ochraceous rather than rufous. The underparts frequently display an extensive russet flush. Certain eastern races, however, are rather grayer above and have a visibly rufous-tinged rump. There is normally no visible white primary patch, though on a few individuals a trace of white remains unconcealed by the coverts. Immatures are visibly barred, though generally less extensively than the Red-backed