Great grey shrike

Appearance

An adult great grey shrike is a medium-sized passerine about as large as a big thrush, measuring from 22 to 26 cm long. It typically weighs around 60 to 70 g, although some subspecies are noticeably smaller or larger, and even in the nominate subspecies adult weights between 48 and 81 g are recorded.

The wings are around 11.4 cm and the tail around 10.9 cm long in the nominate subspecies, its bill measures about 23 mm from tip to skull, and the tarsometatarsus part of its "legs" is around 27.4 mm long. Wingspan can range from 30 to 36 cm.

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 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. 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.

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.

Naming

The scientific name of the great grey shrike literally means "sentinel butcher": Lanius is the Latin term for a butcher, while excubitor is Latin for a watchman or sentinel. This refers to the birds' two most conspicuous behaviours – storing food animals by impaling them on thorns, and using exposed tree-tops or poles to watch the surrounding area for possible prey.

Distribution

The great grey shrike occurs throughout most temperate and subarctic regions of the Northern Hemisphere. Generally, its breeding range is limited to areas north of 50° northern latitude in Eurasia, and north of 55° northern latitude in North America.

Status

Altogether, the great grey shrike is common and widespread and not considered a threatened species by the IUCN. Wherever it occurs, its numbers are usually many hundreds or even thousands per country.

Behavior

This species is territorial, but likes to breed in dispersed groups of a good half-dozen adults. It is not known to what extent the birds in such groups are related. In the temperate parts of its range, groups are perhaps 5 km apart, while individual territories within each group may be as small as 20 ha but more typically are about twice that size.

Throughout the breeding season, in prime habitat, territories are held by mated pairs and single males looking for a partner. In less productive habitat, "floaters" hold territories more ephemerally. This leads to shifts in population density between regions, as "floaters" move between groups of territorial birds in search of a bountiful unclaimed territory to settle down and/or a partner to mate with.

On the wintering grounds, pairs separate to account for the lower amount of food available at that time, but if both members migrate they tend to have their wintering grounds not far apart. As it seems, once an individual great grey shrike has found a wintering territory it likes, it will return there subsequently and perhaps even try to defend it against competitors just like a summer territory.

Throughout the year, the birds regularly but briefly move through a range up to three times larger than their territory; this is tolerated by territory owners in winter more easily than in summer, and the parts of Europe where all-year residents and winter visitors co-occur typically have population densities around eight birds/km2 and occasionally more in winter.

Before and after the nesting season, groups of breeding birds will sometimes initiate gatherings; these seem to occur at the boundary of the group's combined range or in the unclaimed land separating it from neighbouring groups.

The initiation signal is a conspicuous display flight given by a bird surveying its territory: it spirals tens of meters/yards high into the air, usually briefly does a fluttering hover at the top of the spiral, and then glides down. Group neighbours will respond by performing the same type of flight, and eventually about half the group's members will depart to the meeting location where they will spend several tens of minutes – sometimes more than an hour – chattering, calling, duetting, and excitedly moving about the meeting site.

In winter, birds will often assemble in small groups and roost together, particularly to keep warm during the night; this is apparently not initiated with a specific assembly display however.

The flight of the great grey shrike is undulating and rather heavy, but its dash is straight and determined. It is, as noted above, also capable of hovering flights, which last briefly but may be repeated time after time because of the birds' considerable stamina.

It will usually stay low above the ground in flight, approaching perches from below and landing in an upward swoop. In social interactions, birds signal an aggressive stance by a bold upright posture, fanning and then flicking the tail and eventually the wings also as the bird gets more excited.

It signals its readiness to strike at an intruder by shifting to a horizontal pose and fluffing its feathers, raising them into a small crest along the top of the head. Birds appease conspecifics by head-turns away from them, or by imitating the crouching fluttering pose and calls given by fledglings begging for food. The submission gesture to prevent an imminent attack by a conspecific is pointing the beak straight up.

Reproduction

Great grey shrikes breed during the summer, typically once per year. In exceptionally good conditions, they raise two broods a year, and if the first clutch is destroyed before hatching they are usually able to produce a second one.

Their monogamous pair bond is strong during the breeding season and loosens over winter; birds often choose a different mate than the year before. To seek out potential mates, males will venture outside their breeding territories. If a female thus encountered finds a male to her liking, she will visit to see whether they get along well and inspect the nesting sites he can offer.

The courtship period is generally longer than in the southern grey shrike, usually starting about March and lasting to April/May. At first, the female rebuffs the male, only allowing him to feed her. Males give increasingly vocal displays and show off the white markings of the wings in flight and of the tail by fanning it and turning away from the female. He also occasionally turns to sit at a right angle to her.

Eventually, the female will join in the male's displays, and the songs will become duets. To feed females and to show off their hunting prowess, males will make their food caches in conspicuous places during this time. When presenting nesting sites, males give the variety of calls described above and jerk their head and fanned tail.

Copulation is typically initiated by the male bringing an attractive prey item to the female. With both giving begging calls, they approach until they are side by side. The male then raises and swings his body left and right a few times, and passes the prey to the female, followed by the actual copulation.

A full clutch of eggs can be produced by a female in about 10–15 days.

Nests are built in April or May more than 1 m above ground in trees. This height varies according to habitat, but while nests have been found almost 40 m up, most are 2–16 m above ground.

The actual nesting site is chosen by the male; the courtship visits of the female are mainly to form and strengthen the pair bond. Also, though the partners build the nest together, the male collects most of the nesting material.

The cup nest is quite sizable, measuring 20–28 cm in outer diameter. Its body is constructed of coarse vegetable material – mainly large twigs and chunks of moss, though bits of fabric and rubbish may be added. The interior cup is 8–12 cm in diameter and 10–15 c deep; it is lined with fine twigs and roots, lichen, hair and feathers. Building a nest from scratch takes a pair one to two weeks, but if nests of the previous year in good locations remain usable, they are repaired rather than discarded.

Laying usually takes place in May. The clutch numbers three to nine eggs, typically around seven, with North American clutches tending to be larger on average than European ones. If a second clutch is produced in one breeding season, it is smaller than the first one.

The eggs have a white background colour, usually with a grey hue and sometimes with a blue one; they are patterned with blotches of yellowish- to reddish-brown and purplish-grey, often denser around the blunt end. They measure around 26 mm in length and 19.5 mm in width.

Incubation takes around 16 days but may be closer to three weeks for large clutches; it is generally done only by the female. While the male may briefly take over incubating, his task during this time is to provide food.

Food

The great grey shrike eats small vertebrates and large invertebrates. To hunt, this bird perches on the topmost branch of a tree, telegraph pole or similar elevated spot in a characteristic upright stance some meters/yards above ground.

Alternatively, it may scan the grassland below from flight, essentially staying in one place during prolonged bouts of mainly hovering flight that may last up to 20 minutes. The keen eye of the watchful "sentinel" misses nothing that moves. It will drop down in a light glide for terrestrial prey or swoop hawk-like on a flying insect.

Small birds are sometimes caught in flight too, usually by approaching them from below and behind and seizing their feet with the beak. If no prey ventures out in the open, great grey shrikes will rummage through the undergrowth or sit near hiding places and flash their white wing and tail markings to scare small animals into coming out. As noted above, it will sometimes mimic songbirds to entice them to come within striking distance.