Pie-grièche migratrice

Identification

The loggerhead shrike is a medium-sized passerine. "Loggerhead" refers to the relatively large size of the head as compared to the rest of the body. The wing and tail length are about 3.82 in (9.70 cm) and 3.87 in (9.83 cm) long, respectively. It weighs on average 1.8 oz (50 g), with a range of 1.6–2.1 oz (45–60 g) for a healthy adult shrike.<p>The adult plumage of the loggerhead shrike is grey above with a white to pale grey breast and black tarsi and feet. The bird possesses a black mask that extends across the eyes to its bill. The wings are black with a distinct white patch on the primaries. The tail is black edged with white and the irises are brown. The beak is short, black, and hooked, and contains a tomial tooth to help tear into prey. It is difficult to sex an adult loggerhead shrike in the field as they are sexually monochromatic. However, several studies have reported sexual dimorphism in plumage and size traits. Juveniles possess a paler gray plumage that is subtly vermiculated.<p>The loggerhead shrike can be distinguished from the northern shrike by its smaller size, darker grey plumage, and larger black face mask that covers the eye completely. It also has a shorter bill with less prominent hook. Their calls are similar.<p>Their vocal range is broad and varied, and has been described as harsh and jarring. The shrike's notes include squeaky whistles, shrill trills, and guttural warbles. The trills sung by males during breeding season vary in rhythm and pitch. When alarmed, a shrike will produce a "schgra-a-a" shriek while spreading out its tail feathers. A distinctive alarm call is often given when threats from above are detected. Nestlings will make "tcheek" and "tsp" sounds shortly after hatching. During courtship feedings, females may ask for food with "mak" begging notes; conversely, males emit "wuut" or "shack" sounds to offer food. The male emits a territorial, harsh shriek, while the female's song is pitched lower and softer than the male's. Generally, the male is far more vocal than the female.

Taxonomie

In 1760 the French zoologist Mathurin Jacques Brisson included a description of the loggerhead shrike in his Ornithologie based on a specimen collected in Louisiana in the United States. He used the French name La pie-griesche de la Louisiane and the Latin Lanius ludovicianus. Although Brisson coined Latin names, these do not usually conform to the binomial system and are not recognised by the International Commission on Zoological Nomenclature. When in 1766 the Swedish naturalist Carl Linnaeus updated his Systema Naturae for the twelfth edition, he added 240 species that had been previously described by Brisson. One of these was the loggerhead shrike. Linnaeus included a brief description, adopted the binomial name Lanius ludovicianus (identical to Brisson's Latin name) and cited Brisson's work. The specific name ludovic is Late Latin for "Louis" and the epithet "-ianus" is to describe something being of another or possessed by it. When translated, its scientific name means something alongside the lines of "Louis’ butcher". "Loggerhead," a similar word to "blockhead," refers to the unusually large head to body ratio of this bird.<p>There are seven recognized subspecies:<p>Miller, in 1931, suggested that the wing-chord-to-tail-length ratio was an important indicator for distinguishing between subspecies. Lanius ludovicianus migrans, found in eastern North America, can be distinguished from the western subspecies, L. l. excubitorides by wing length, tail length, and colour. L. l. migrans have a paler forehead than the top of the head.According to Mundy et al.’s 1997 study, there is a substantial genetic difference between the island subspecies L. l. mearnsi and the mainland subspecies L. l. gambeli due to a gene flow barrier between the two species.

Nom scientifique

Lanius ludovicianus

Autorité

Linnaeus, 1766

Ordre

Passériformes

Famille

Laniidés

Genre

Lanius

Répartition et habitat

Loggerhead shrikes were once widely distributed across southern Canada, the contiguous USA and Mexico. However, their populations have heavily declined since the 1960s. Four subspecies reside in southern coastal California: mearnsi, gambeli, grinnelli and anthonyi. L. l. mearnsi is only found on San Clemente Island in California, whereas L. l. gambeli breeds on the mainland and L. l. anthonyi breeds on the Channel Islands. L. l. excubitorides is found in central North America, whereas the non-migrating L. l. ludovicianus resides in southeastern North America. The distribution of L. l. migrans ranges from north to eastern North America; however, its range has been diminishing since the 1940s.<p>The bird requires an open habitat with an area to forage, elevated perches, and nesting sites. They are often found in open pastures or grasslands and appear to prefer red-cedar and hawthorn trees for nesting. The hawthorn's thorns and the cedar's pin-like needles protect and conceal the shrike from predators. It may also nest in fence-rows or hedge-rows near open pastures and requires elevated perches as lookout points for hunting. Open pastures and grasslands with shorter vegetation are preferred by loggerhead shrikes, as they increase the bird's hunting efficiency. Longer vegetation often requires more time and energy to be spent searching for prey, so these birds gravitate towards areas of shorter vegetation.

Migration

Migrateurs complets

Comportement

Mode de migration: Migrateurs complets.

Conservation

Tendance de la population: en déclin.

Tendance de la population

en déclin