Great Grey Shrike

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 (3.1 mi) apart, while individual territories within each group may be as small as 20 ha (49 acres) but more typically are about twice that size. In less hospitable climes, territories may be more than 350 ha (1.4 sq mi). 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/km (about thirty per square mile) 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 (which typically is some small tree or shrubbery). 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 (if close by), or by imitating the crouching fluttering pose and calls given by fledglings begging for food (if sitting father apart). The submission gesture to prevent an imminent attack by a conspecific is pointing the beak straight up. Fledgelings moult part of their juvenile plumage before their first winter, and the rest in spring. Adults moult on their breeding grounds before going on migration, or before the depth of winter if they are resident. Sometimes adults also seem to moult some feathers before attempting to breed. As moult requires a considerable investment of energy, some significant evolutionary benefits to offset this are likely. Reducing feather wear and parasite load, moulting can make a bird more physically attractive and healthy, and may thus increase its chance of successful reproduction. The phenomenon is not well understood, however.

Generally, its breeding range is found in Eurasia and northern Africa. In the high mountains of the Altai-Tian Shan region, it ranges south perhaps as far as 42° northern latitude. Its northern limit is generally 70° northern latitude. It is only found as a vagrant in Iceland, the British Isles, the Mediterranean region (excluding the Iberian Peninsula and perhaps Romania but including Cyprus), and Korea. There do not appear to be breeding records from the entire Kamchatka Peninsula; in Switzerland, the present day Czech Republic and southern Germany small populations were found in the mid-20th century but have declined or even disappeared since then. Except for the subspecies bianchii which is largely all-year resident, and subspecies excubitor in the temperate European parts of its range with their mild maritime climate, the species is a short-distance migrant. The migrations are triggered by scarcity of food and therefore, according to prey population levels, the winter range might little extend south beyond the breeding range, or be entirely parapatric to it. The populations of the Central Asian mountains mostly migrate downslope rather than southwards. Females are more prone to migration than males; they do not appear to migrate, on average, longer or shorter distances than males, and consequently are the dominant sex in many parts of the winter range. Birds leave for winter quarters a more or less short time after breeding – July to October, with most birds staying to September – and return to nest mainly in March/April, but some only arrive in May. In recent decades, the number of birds remaining on the breeding grounds all year has been noted to increase e.g. in Fennoscandia, whereas for example borealis seems to be as rare a winter visitor in northern Ohio as it was a century ago. The preferred habitat is generally open grassland, perhaps with shrubs interspersed, and adjacent lookout points. These are normally trees – at forest edges in much of the habitat, but single trees or small stands at the taiga-tundra border. In steppe, it will utilize any isolated perch, be it fence posts, power lines or rocks. In general, some 5–15 perching sites per hectare habitat seem to be required. It avoids low grassland with no lookouts and nesting opportunities (trees or large shrubs), as well as dense forest with no hunting ground. Apart from grassland, the birds will utilize a variety of hunting habitats, including bogs, clearings or non-industrially farmed fields. Breeding birds appear to have different microhabitat desires, but little detail is known yet.

As remarked above, the great grey shrike has apparently become extinct as a breeding bird in Switzerland and the Czech Republic. Overall, its stocks seem to be declining in the European part of its range since the 1970s. In North America, the populations seem to have been stable by contrast, except in the east. The increase and decline seem to be reactions to changing land use, with an increase as the number of agricultural workers declined after World War II and land fell fallow, declining again when land consolidation (see e.g. Flurbereinigung) had seriously depleted the number of hedgerows and similar elevated growth formerly common amidst the agricultural landscape. For such a predatory bird, the indiscriminate use of pesticides (which will accumulate in adult carnivores and inhibit breeding success) around the 1960s probably had a detrimental influence on stocks too. Altogether, the great grey shrike is common and widespread and not considered a threatened species by the IUCN (though they still include L. meridionalis in L. excubitor). Wherever it occurs, its numbers are usually many hundreds or even thousands per country. Its stronghold is the region around Sweden, where at least almost 20,000, perhaps as many as 50,000 were believed to live in the late 20th century. However, in some countries it is not robustly established; in Estonia only a few hundred are found, with less than 200 in Belgium and some more or less than 100 in Latvia and Lithuania, respectively. The few dozen in the Netherlands and the 10 birds or so in Denmark might disappear because of a few years of adverse circumstances. By contrast, in Luxembourg plentiful high-quality habitat is found; though the number of great grey shrikes in this tiny country is necessarily limited, the average population density there is 25 times as high as in Lithuania.