The Great Grey Shrike, Northern Grey Shrike, or Northern Shrike (Lanius excubitor) is a large songbird species in the shrike family (Laniidae). It forms a superspecies with its parapatric southern relatives, the Southern Grey Shrike (L. meridionalis), the Chinese Grey Shrike (L. sphenocerus) and the Loggerhead Shrike (L. ludovicianus). Within the Great Grey Shrike species itself, there are nine subspecies. Males and females are similar in plumage, pearly grey above with a black eye-mask and white underparts.
An adult Great Grey Shrike is a medium-sized passerine about as large as a big thrush, measuring from 22 to 26 cm (8.7 to 10 in) long. It typically weighs around 60 to 70 g (2.1 to 2.5 oz), although some subspecies are noticeably smaller or larger, and even in the nominate subspecies adult weights between 48 and 81 g (1.7 and 2.9 oz) are recorded. The wings are around 11.4 cm (4.5 in) and the tail around 10.9 cm (4.3 in) long in the nominate subspecies, its bill measures about 23 mm (0.9 in) from tip to skull, and the tarsometatarsus part of its “legs” (actually feet) is around 27.4 mm (1.08 in) long. Wingspan can range from 30 to 36 cm (12 to 14 in).
The general colour of the upperparts is pearl grey, tinged brownish towards the east of its Eurasian range. The cheeks and chin as well as a thin and often hard-to-see stripe above the eye are white, and a deep black mask extends from the beak through the eye to the ear coverts; the area immediately above the beak is grey. The scapulars (shoulder feathers) are white, and the wings are black with a white bar made up by the bases of the primary remiges, continuing slightly offset onto the bases of the secondary remiges in some regions. The tail is black, long, and pointed at the tip; the outer rectrices have white outer vanes. The underparts are white, slightly tinged with grey in most subspecies. In particular the breast is usually darker and sometimes browner than the rest of the light underside, and may appear as an indistinct band between the lighter belly and white throat. In the subspecies around the North Pacific in particular and in females elsewhere too, there may be faint brownish bars on the breast. The bill is large and hooked at the tip and coloured nearly black, but pale at the base of the under mandible (though the extent varies seasonally). The legs and feet are blackish.
Males and females are about the same size, and do not differ conspicuously in appearance except by direct comparison. In the female the underparts are greyer and are usually visibly barred greyish-brown, and the white wing and tail markings are characteristically less in extent (though this is rarely clearly visible except in flight). Fledged young birds are heavily tinged greyish-brown all over, with barring on the upperside and indistinct buffy-white markings. The tips of the tertiary remiges and the wing coverts are also buffy, with a black band in the latter. In the North American subspecies borealis, the fledglings are tinged quite brown indeed on upperside and wings, and have sharp and dark underside bars. In Eurasia, fledglings moult into a female-like plumage with the tertiary bars usually remaining in autumn. Across its range, the young acquire the adult plumage in their first spring.