Loggerhead shrike
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The loggerhead shrike (Lanius ludovicianus) is a passerine bird in the family Laniidae. It is the only member of the shrike family endemic to North America; the related northern shrike (L. borealis) occurs north of its range, however it is also found in Siberia. It is nicknamed the butcherbird after its carnivorous tendencies, as it consumes prey such as insects, amphibians, lizards, small mammals and small birds, and some prey end up displayed and stored at a site, for example in a tree.<ref name="craig1978">Template:Cite journal</ref> Due to its small size and weak talons, this predatory bird relies on impaling its prey upon thorns or barbed wire for facilitated consumption.<ref name="smith1973">Template:Cite journal</ref> The numbers of loggerhead shrike have significantly decreased in recent years, especially in Midwestern, New England and Mid-Atlantic areas.<ref>Template:Cite journal</ref>
TaxonomyEdit
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.<ref name=brisson>Template:Cite book The two stars (**) at the start of the section indicates that Brisson based his description on the examination of a specimen.</ref> 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.<ref name=allen>Template:Cite journal</ref> 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.<ref name=allen/> 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.<ref>Template:Cite book</ref> 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".<ref name=hbwkey>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> "Loggerhead," a similar word to "blockhead," refers to the unusually large head to body ratio of this bird.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
There are seven recognized subspecies:<ref name=ioc>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- L. l. excubitorides Swainson, 1832 – central Canada, central and west USA
- L. l. migrans Palmer, W, 1898 – east North America
- L. l. ludovicianus Linnaeus, 1766 – coastal southeast USA
- L. l. anthonyi Mearns, 1898 – Channel Islands (off south California, southwest USA)
- L. l. mearnsi Ridgway, 1903 – San Clemente Island (off south California, southwest USA)
- L. l. grinnelli Oberholser, 1919 – extreme south California and north Baja California (northwest Mexico)
- L. l. mexicanus Brehm, CL, 1854 – west and central Mexico, south Baja California (northwest Mexico)
Miller, in 1931, suggested that the wing-chord-to-tail-length ratio was an important indicator for distinguishing between subspecies.<ref name="miller1931"/> 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.<ref name="chabot1994"/> 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.<ref name="mundy1997">Template:Cite journal</ref>
DescriptionEdit
The loggerhead shrike is a medium-sized passerine.<ref name="chapman1904">Template:Cite book</ref> "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 Template:Cvt and Template:Cvt long, respectively.<ref name= "chapman1904"/> It weighs on average Template:Cvt, with a range of Template:Cvt for a healthy adult shrike.<ref>Template:Cite journal</ref>
- Measurement ranges<ref>{{#invoke
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- Length: Template:Cvt
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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.<ref name="chabot1994">Template:Cite book</ref> The beak is short, black, and hooked, and contains a tomial tooth to help tear into prey.<ref name="miller1931">Template:Cite journal</ref> It is difficult to sex an adult loggerhead shrike in the field as they are sexually monochromatic.<ref name="sustaita2014">Template:Cite journal</ref> However, several studies have reported sexual dimorphism in plumage and size traits.<ref name="miller1931" /><ref name="sustaita2014" /><ref name="collister1996">Template:Cite journal</ref> Juveniles possess a paler gray plumage that is subtly vermiculated.<ref name="natgeo">Template:Cite book</ref>
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.<ref name=natgeo/>
VocalizationEdit
Their vocal range is broad and varied, and has been described as harsh and jarring.<ref>Template:Cite journal</ref> The shrike's notes include squeaky whistles, shrill trills, and guttural warbles.<ref name="chapman1904"/> 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.<ref name="soendjoto1995">Template:Cite book</ref> During courtship feedings, females may ask for food with "mak" begging notes; conversely, males emit "wuut" or "shack" sounds to offer food.<ref>Template:Cite journal</ref> 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.<ref name="chabot1994"/><ref name="soendjoto1995"/>
Distribution and habitatEdit
Loggerhead shrikes were once widely distributed across southern Canada, the contiguous USA and Mexico.<ref name="miller1931" /> However, their populations have heavily declined since the 1960s.<ref name="collister1996" /> Four subspecies reside in southern coastal California: mearnsi, gambeli, grinnelli and anthonyi.<ref>Patten M, Campbell K. 2008. Typological thinking and the conservation of subspecies: the case of the San Clemente Island loggerhead shrike. Diversity and Distributions. 6(4): 177–188.</ref> 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.<ref name="mundy1997" /> L. l. excubitorides is found in central North America, whereas the non-migrating L. l. ludovicianus resides in southeastern North America.<ref name="collister1996" /> The distribution of L. l. migrans ranges from north to eastern North America; however, its range has been diminishing since the 1940s.<ref name="chabot1994" />
The bird requires an open habitat with an area to forage, elevated perches, and nesting sites.<ref name="brooks1990" /> They are often found in open pastures or grasslands and appear to prefer red-cedar and hawthorn trees for nesting.<ref name="chabot2001">Template:Cite journal</ref> The hawthorn's thorns and the cedar's pin-like needles protect and conceal the shrike from predators.<ref>Gawlick D, Bildstein K. 1990. Reproductive success and nesting habitat of Loggerhead Shrikes in north-central South Carolina. Wilson Bulletin. 102(1): 37–48.</ref> It may also nest in fence-rows or hedge-rows near open pastures and requires elevated perches as lookout points for hunting.<ref name="brooks1990">Brooks B, Temple S. 1990. Habitat availability and suitability for loggerhead shrikes in the upper midwest. The American Midland Naturalist. 123(1): 75–83.</ref><ref name="chabot2001" /> 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.<ref>Template:Cite journal</ref>
BehaviorEdit
DietEdit
Loggerhead shrikes have been repeatedly observed killing prey larger than themselves by spearing the neck or head of the animal and twisting. The speed at which this occurs causes a whiplash injury to the animal. The neck strength of the shrikes compensates, making their talon weakness inconsequential.<ref>Template:Cite news</ref>
Although loggerhead shrikes are passerines, they are a predatory species that hunt during the day. They primarily eat insects, but also consume arachnids, reptiles, amphibians, rodents, bats and small birds.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> They have even eaten venomous snakes such as the water adder. The size of prey ranges from Template:Cvt insects to Template:Cvt mice or reptiles.<ref name= "craig1978"/>
They are not true birds of prey, as they lack the large, strong talons used to catch and kill prey.<ref name="smith1973"/> Instead, they are sit-and-wait hunters that stalk prey by hawking and diving from elevated perches. By scanning their vicinity from a perch instead of flying, the shrike does not exhaust its energy during the search. Preferred perches are approximately Template:Cvt off the ground, and are usually outer branches of trees or telephone wires.<ref name="craig1978"/><ref>Template:Cite journal</ref> In winter, prey availability is low due to the shrike's preference for insects and poikilothermic prey; during this time, shrikes may be energetically stressed and underweight.<ref name="craig1978"/> Insects are consumed in mid-flight, but vertebrates usually require more handling time and therefore more energy.<ref name="smith1973"/> Due to the shrike's small size in proportion to the size of its prey, it must rely on specialized adaptations to facilitate its hunting. The powerful, hooked beak of the loggerhead shrike allows it to sever the neck of a small vertebrate. Larger prey are subjected to impaling, in which they are pushed down into a sharp projection, such as a thorn or barbed wire. The bird can then tear off flesh by using the projection as an anchor.<ref name="smith1973"/> The shrike may also use the thorn to fasten and store its food to return to at a later time.<ref name= "craig1978"/>
The motion of impalement appears to be instinctive, as parent shrikes do not demonstrate the behavior to their nestlings. However, a young shrike must experience impaling prey upon an actual projection during a critical developmental period; otherwise, it will not learn to use the instinctive impaling action upon an actual projection.<ref>Template:Cite journal</ref> Kleptoparasitism has also been observed in nature, in which the shrike chased down another bird and stole its recently-caught prey.<ref>Template:Cite journal</ref>
ReproductionEdit
Loggerhead shrikes are monogamous birds. However, males are known to begin second nesting attempts with a second female before his first clutch has fledged. They begin breeding during their first spring.<ref name="chabot1994"/> During this time, the male performs a courtship ritual that occurs in flight. He dances erratically in the air, flying rapidly up and down and occasionally chasing the female. He presents himself to his potential mate by fanning out his tail and fluttering his wings.<ref name="smith1973"/><ref name="miller1931"/><ref>Template:Cite book</ref> Females may respond to the fluttering display with begging notes, similar to those of juveniles begging for food; this encourages the male to feed her.<ref name="smith1973"/>
The bird breeds in semi-open areas in southern Ontario, Quebec, and the Canadian prairie provinces, south to Mexico. It nests in isolated or small clusters of dense trees and shrubs from near ground level to over 4m in height. There is an increase in average clutch size as latitude increases. Shrikes begin incubation after laying the second to last egg, resulting in asynchronous hatching. Incubation, on average, lasts 16 days. The female lays 4 to 8 eggs in a bulky cup made of twigs and grass. Once hatched, nestlings are fed by both the male and female parent. Average fledging period is about 19 days. Young may then remain nearby and dependent on adults for 3 to 4 weeks. After that, they begin to forage independently. Oftentimes, nestlings do not survive long past hatching. In the case of dead nestlings, adult shrikes may eat or discard their bodies or else feed them to their remaining young.<ref>Template:Cite journal</ref> The oldest recorded age of a loggerhead shrike was 12 years and 6 months.<ref>Template:Cite book</ref>
Conservation statusEdit
Loggerhead shrike populations have been decreasing in North America since the 1960s. Reasons behind the decline remain unclear, although suggestions include habitat loss, pesticide contamination, and human disturbance.<ref name="collister1996"/> The eastern loggerhead shrike (L. l. migrans) is critically endangered in Canada, with fewer than 35 known breeding pairs in Canada.<ref>Template:Cite book</ref> The San Clemente Island shrike, L. l. mearnsi, is critically endangered, with a population as low as 5–10 individuals during 1983–1988.<ref name="mundy1997"/> Although only this island subspecies is legally listed as endangered in the United States, the species is declining continent-wide and no longer occurs in most of the northeastern U.S.; it is extirpated from every state in New England, as well as New Brunswick and Nova Scotia.<ref name=NS/><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A captive population was established at the Toronto Zoo and McGill University in 1997. In 2001, an experimental field breeding and release program managed by Wildlife Preservation Canada was established. "Field breeding" refers to moving captive pairs from their wintering cages at the Toronto Zoo and McGill to large enclosures within shrike habitat in Ontario where the pairs nest and raise their young. The young then are released to the wild when they'd naturally disperse from their parents. Since 2004, over 90 young have been released annually and between 2% and 6.5% of young released have successfully migrated and returned to breed in the subsequent year.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
ReferencesEdit
External linksEdit
Template:Sister project Template:Sister project
- The Ontongeny of Cricket and Mouse Killing in the Loggerhead Shrike
- The Effects of Dieldren on the Behavior of Young Loggerhead Shrikes
- Loggerhead Shrike Species Account – Cornell Lab of Ornithology
- Loggerhead Shrike – Lanius ludovicianus – USGS Patuxent Bird Identification InfoCenter
- Template:Usurped (for Mexico) with Range Map at bird-stamps.org
- Template:InternetBirdCollection
- Recording of its call
- Template:VIREO
- Template:IUCN Map