Overview

Brief Summary

Lanius ludovicianus

A medium-sized (9 inches) shrike, the Loggerhead Shrike is most easily identified by its gray body, dark wings, and large hooked bill. Other field marks include a black tail with white edges, a black eye-stripe, and white “wrists” visible on the underside of the wings. This species may be separated from the Northern Shrike (Lanius excubitor) by the latter species’ faintly barred breast and from the Northern Mockingbird (Mimus polyglottos) by that species’ large white wing patches. Male and female Loggerhead Shrikes are similar to one another in all seasons. The Loggerhead Shrike breeds across the southern and southwestern United States as well as the Great Plains and locally in the Great Lakes region. Breeding populations also exist at higher elevations in northern and central Mexico. Northern Loggerhead Shrike populations are migratory, moving south in winter as far as Mexico. Loggerhead Shrikes inhabit a variety of open habitats, including grasslands, agricultural fields, and deserts. This species utilizes similar habitats in winter as in summer, especially those populations which are non-migratory. Loggerhead Shrikes eat a variety of small animals, including insects, small mammals, and birds. Loggerhead Shrikes are most easily observed perching in prominent areas, such as on bare branches, while watching for prey. This species impales its prey on thorns or barbed wire, and birdwatchers who stumble across one of these “larders” would likely find a Loggerhead Shrike nearby. This species is primarily active during the day.

Threat Status: Least concern

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Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: California, eastern Oregon, eastern Washington, and central Alberta eastward across southern Canada to southwestern New Brunswick and Nova Scotia, and south to southern Baja California, throughout Mexico to Oaxaca and Veracruz,the Gulf Coast, and southern Florida (AOU 1983). Recently has been disappearing from the northeastern portion of the breeding range. In the northeastern U.S., breeds in in western Maryland, extreme eastern West Virginia, and Virginia (perhaps several dozen pairs); extirpated elsewhere (Bartgis 1992, R. W. MacDonald pers. comm.). NON-BREEDING: central Washington, eastern Oregon, California, southern Nevada, northern Arizona, northern New Mexico, and (east of the Rockies) the southern half of breeding range south to the Gulf Coast, southern Florida, and Mexico (AOU 1983).

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Geographic Range

Prominent in many parts of central Canada, border states of Canada, and in the Greater Midwest of the United States. During its spring / summer migration, however, it can sometimes be seen as far south and west as California though in ever decreasing numbers. For example, its predicted range of migration to and from the state of Indiana is: Arrival from March 15 to 25, and Return from about November 1 to 15.

There are some exceptions to the Shrike's migration, such as its noted presence in the well-suited Florida environment. Thus, habitat and environment are more important in determining migratory patterns for this species than the standard geographic range, especially as suitable hunting grounds become increasingly scarce.

Biogeographic Regions: nearctic (Native )

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Geographic Range

Prominent in many parts of central Canada, border states of Canada, and in the Greater Midwest of the United States. During its spring / summer migration, however, it can sometimes be seen as far south and west as California though in ever decreasing numbers. For example, its predicted range of migration to and from the state of Indiana is: Arrival from March 15 to 25, and Return from about November 1 to 15.

There are some exceptions to the Shrike's migration, such as its noted presence in the well-suited Florida environment. Thus, habitat and environment are more important in determining migratory patterns for this species than the standard geographic range, especially as suitable hunting grounds become increasingly scarce.

Biogeographic Regions: nearctic (Native )

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Physical Description

Morphology

Physical Description

This shrike is a medium-sized passerine. As with many song birds, the Loggerhead Shrike has several different colors whose arrangement is considered important in attracting a mate (along with displayed hunting prowess). The shrike's greyish back and black wings are evident against its white breast and other body areas. Most prominent, however, is the Loggerhead's black mask which extends around the eyes and down into the forehead. This shrike also has a slightly hooked beak somewhat similar to that of a falcon's beak which is used for impaling its prey, though unlike many birds of prey lacks talong or claws.

It is eight to ten inches long and has a wing span of approximately 12 inches, making it about the size of an average robin.

The male and female of the species are similar in appearance.

Average mass: 46 g.

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Physical Description

This shrike is a medium-sized passerine. As with many song birds, the Loggerhead Shrike has several different colors whose arrangement is considered important in attracting a mate (along with displayed hunting prowess). The shrike's greyish back and black wings are evident against its white breast and other body areas. Most prominent, however, is the Loggerhead's black mask which extends around the eyes and down into the forehead. This shrike also has a slightly hooked beak somewhat similar to that of a falcon's beak which is used for impaling its prey, though unlike many birds of prey lacks talong or claws.

It is eight to ten inches long and has a wing span of approximately 12 inches, making it about the size of an average robin.

The male and female of the species are similar in appearance.

Average mass: 46 g.

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Size

Length: 23 cm

Weight: 47 grams

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Diagnostic Description

Differs from northern shrike (LANIUS EXCUBITOR) in having the base of the lower mandible black instead of pale, unbarred or barely barred underparts (adults), a shorter and less hooked bill, a darker head and back, and a more extensive black mask. Differs from the northern mockingbird (MIMUS POLYGLOTTOS) in having a black mask and a shorter, less curved bill.

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Ecology

Habitat

Comments: BREEDING: Open country with scattered trees and shrubs, savanna, desert scrub (southwestern U.S.), and, occasionally, open woodland; often perches on poles, wires or fenceposts (Tropical to Temperate zones) (AOU 1983). Suitable hunting perches are an important part of the habitat (Yosef and Grubb 1994).

For nesting, prefers shortgrass pastures in western Canada, Texas (Telfer 1992), and many other areas (Luukkonen 1987, Novak 1989, Gawlik and Bildstein 1990, Bartgis 1992). In Missouri, pasture land surrounded 67% of 60 nests (Kridelbaugh 1982). In New York, occupied nest sites were in pasture areas with less than 20% woody cover (Novak 1989). However, others have found no preference for short-grass areas (e.g., see Chavez-Ramirez et al. 1994). Historically, orchards seemingly were used with some frequency (see Novak 1989). In the upper Midwest, Brooks (1988) found that nestling growth rate, nesting success, and fledgling success were positively correlated with percentage of home range coverage in grassland. In Virginia, pairs nesting in active pastures produced twice as many young as did those in other habitats (Luukkonen 1987).

Nests in shrubs or small trees (deciduous or coniferous, e.g., in eastern North America, JUNIPERUS VIRGINIANA, CRATAEGUS sp., MACLURA POMIFERA, ROSA MULTIFLORA). In northern latitudes, nest sites include spruce and fir trees (Bent 1950, Brooks 1988). In some areas, vine-covered plants are preferred (Luukkonen 1987, Novak 1989). In Missouri, nests in multiflora rose were less successful than were those in trees, perhaps because the nests in roses were lower and poorly supported (Kridelbaugh 1982). In South Carolina, nests in JUNIPERUS fledged a larger number of young than did nests in other sites (5.0 young per successful nest vs. 4.0) (Gawlik and Bildstein 1990). Nests generally are 1.5-3 m above ground, in a crotch or on top of an old nest. In New York, nests were typically 1.5-2.5 m high in trees 4-5 m tall, and usually they were more than a meter back from the outside of the tree (Novak 1989). In Virginia, average nest height was 2.6 m in trees averaging 6.8 m tall; nest height was higher (mean 5.5 m) in second and third nesting attempts (Luukkonen 1987). Nests often in isolated woody plants but also commonly along fencelines or hedgerows (Brooks 1988, Luukkonen 1987), in an open area in a wooded area or in open country. Tends to nest in areas with several potential suitable nesting trees/shrubs (Brooks 1988).

Sometimes nests in the same site in successive years, but return rates generally are low; males are most likely to reoccupy previous breeding territories (Kridelbaugh 1982, Luukkonen 1987, Brooks 1988, Bartgis 1989, Haas and Sloane 1989). In Minnesota and Virginia, respectively, 50% and 30% of breeding territories were not occupied the following year; in Virginia, reoccupation was more frequent in active pasture than in pastures allowed to grow tall (Brooks 1988, Luukonen 1987). Causes of variation in rates of territory reoccupancy have been discussed but available evidence is inconclusive and may differ in different areas (cf. Brooks 1988, Luukkonen 1987, Novak 1989, Haas and Sloane 1989). For a particular pair during a single season, nesting attempts after the first one generally are close to the first site (mean 90 m in Virginia) (Luukkonen 1987). Both sexes are involved in nest site selection and nest construction (Kridelbaugh 1982).

NON-BREEDING: During periods of cold with snow cover, sometimes moves into woodlots (Byrd and Johnston 1991). In winter in Virginia, many move from pastures to shrub and open forest habitats during periods of cold, wet weather (Blumton et al. 1989).

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Habitat and Ecology

Systems
  • Terrestrial
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Except when nesting, both sexes of the species will prefer to spend most of their time in open places hiding in order to search for prey and surprise it. Thus, the Loggerhead will prefer a country field bordered with trees or replete with brush / thickets to almost any other.

Terrestrial Biomes: savanna or grassland

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Except when nesting, both sexes of the species will prefer to spend most of their time in open places hiding in order to search for prey and surprise it. Thus, the Loggerhead will prefer a country field bordered with trees or replete with brush / thickets to almost any other.

Terrestrial Biomes: savanna or grassland

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Withdraws southward from northern half of breeding range for winter. Banding returns indicate that birds from as far north as Alberta and Quebec winter from southern Kansas, Missouri, and Virginia south to Alabama, Louisiana, and Texas (Fruth 1988). Shrikes in Wisconsin begin moving south in August. In Oklahoma and Missouri, begins to arrive and set up breeding teritories in mid-February (Tyler 1992). Returns to nesting areas in New York in mid- to late April (Novak 1989). Shrikes breeding in the Virginias and Maryland frequently are resident, but there appears to be some southward movement. Shrikes that formerly bred in New England apparently followed a predominantly coastal migration route (Milburn 1981). Nonmigratory in much of California, especially in southern and central coastal regions (Matthews and Moseley 1990).

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Trophic Strategy

Comments: Feeds primarily on large insects (especially beetles and orthopterans), also other invertebrates, small birds, lizards, frogs, and rodents; sometimes scavenges (Fraser and Luukkonen 1986). Diet varies with season and location; in parts of the range, most of the food eaten in winter may be vertebrates, which comprise only a small part of the diet in California. In California, the summer diet comprises mainly insects (Terres 1980). Captures prey usually via a short flight from a perch; sometimes hovers kestrel-like or walks when foraging (Bent 1950, Luukkonen 1987). Sometimes impales food items on a plant thorn or on barbed wire (Fraser and Luukkonen 1986); such items may be eaten later or fed to young (Applegate 1977).

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Food Habits

Loggerhead shrikes are the only known predatory songbird. They prey on both vertebrate and invertebrate animals, but due to their lack of talons or claws they must impale their prey. Impaling is done with the slightly hooked beak, often against either a tree or into barbed wire. While its diet consists mostly of mice, it will also eat insects, small amphibians, and even small birds.

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Food Habits

Loggerhead shrikes are the only known predatory songbird. They prey on both vertebrate and invertebrate animals, but due to their lack of talons or claws they must impale their prey. Impaling is done with the slightly hooked beak, often against either a tree or into barbed wire. While its diet consists mostly of mice, it will also eat insects, small amphibians, and even small birds.

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Associations

Known prey organisms

Lanius ludovicianus preys on:
Auriparus flaviceps

This list may not be complete but is based on published studies.
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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

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Global Abundance

2500 to >1,000,000 individuals

Comments: See trend comments for information for particular states.

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General Ecology

Territorial throughout the year. Size of territory may be about 10-16 ha in semidesert. In Florida, territory size varied from about 0.7 ha to 18 ha (Yosef and Grubb 1994). In New York, successful nesting pairs foraged over an area of 5.7-9.3 ha; the smallest area of active pasture in the nesting territory was about 5.5 ha (Novak 1989). Miller (1931) reported nesting territories of 4.4 to 16 ha. Kridelbaugh (1982) reported an average territory size of 4.6 ha in Missouri, with territory size increasing significantly after fledging. In Minnesota during the nesting season, shrikes foraged up to a quarter mile away from the nest (Brooks 1988). In general, nesting territories are smaller in areas with a greater amount of good quality habitat (Kridelbaugh 1982). In Virginia, juveniles established 2 ha to 36 ha (mean 19 ha) fall and winter territories, although use of woody habitats in inclement weather significantly enlarged the home range (Blumton et al. 1989). In Virginia, winter home ranges averaged 52 ha (Blumton et al. 1989).

Breeding and winter territories may or may not be separate. Males and females defend separate territories during the nonbreeding season.

In Virginia, juveniles 10-13 weeks old moved an average of 5.5 km from parents' territory to fall territory; predation by hawks and owls accounted for most fall and winter mortality, with the heaviest mortality in January when temperatures were coldest (Blumton et al. 1989). Suspected nest and fledgling predators in the northeastern North America include black rat snake (ELAPHE OBSOLETA), blue jay (CYANOCITTA CRISTATA), sharp-shinned hawk (ACCIPITER STRIATUS), domestic cat, and house wren (TROGLODYTES AEDON) (Luukkonen 1987, Novak 1989).

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Life History and Behavior

Life Expectancy

Lifespan/Longevity

Average lifespan

Status: wild:
150 months.

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Lifespan/Longevity

Average lifespan

Status: wild:
150 months.

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Lifespan, longevity, and ageing

Maximum longevity: 12.5 years (wild)
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Reproduction

Male courtship behavior involves singing, flashing of white wing and tail markings, zigzagging flights and occasional chases of the female, and feeding of the female (Miller 1931, Bent 1950, Kridelbaugh 1982). Primarily monogamous, but polygny known (Yosef 1992, 1996). In Oklahoma, completed nests were found from mid-March through late June; nesting peaked in mid-April, with second nestings from late May to late June (Tyler 1992). In Missouri and Illinois, nesting peaked in late April, with a second peak in late May in Missouri (Tyler 1992). In Maryland, second nesting attempts occurred in June and July (Bartgis 1992). In Virginia, egg-laying extended from early April to mid-June (Byrd and Johnston 1991). Egg laying began in Colorado in early May. Egg dates for California and Florida are mainly February-July, March-June in Arizona and Texas. Single eggs are laid at intervals of one day. Clutch size usually averages 4-6. Incubation usually lasts 16-18 days (Lukkonen 1987, Tyler 1992), probably begins with the laying of the penultimate egg. Male feeds female during incubation. Young tended by both adults, fledge in about 17-20 days, independent in 36 days. Young generally stay concealed in foliage during the first few days out of the nest. About two weeks after leaving the nest, fledglings begins to capture food for themselves; they contunue to be fed by adults for about two more weeks (Luukkonen 1987, Novak 1989). By this time, adults and young begin foraging in areas away from the nesting territory (Novak 1989). In New York, family groups began to break up and disperse in August (Novak 1989). Renesting after nest failure is frequent in the Virginias and Maryland (Luukkonen 1987, Davidson 1988; Bartgis, pers. comm.), but second nesting attempts may be less common in the northern part of the range (Brooks and Temple 1986, Fruth 1988, Novak 1989). A third nesting attempt, usually unsuccessful, may follow an unsuccessful second nesting. Sometimes female leaves fledglings in care of male (Kridelbaugh 1982, Novak 1989); female may renest elsewhere with another male (Novak 1989, Haas and Sloane 1989).

Probability of survival from start of incubation to fledging ranged from 43% to 72% in several studies in different areas (see Tyler 1992). Nesting success tends to be fairly high (range was 50-74% in several studies in the eastern U.S.); generally at least 60% of nesting attempts fledge at least one young (Luukkonen 1987, Brooks 1988, Blumton et al. 1989, Novak 1989, Gawlik and Bildstein 1990, Bartgis 1992). Average number of young fledged per successful nest was 2.6, 3.5, 4.0, and 4.7 in Virginia, New York, Virginia, and South Carolina, respectively (Blumton et al. 1989, Novak 1989, Luukkonen 1987, and Gawlik and Bildstein 1990, respectively). Nest failure was attributed to cold wet weather and predation in New York (Novak 1989) and to predation, abandonment, and inadequate support of nests in Virginia (Luukkonen 1987). Nesting success tends to be better with dry, warm conditions than during cool, wet periods (Kridelbaugh 1982).

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During its April to July breeding season, the male Loggerhead will often kill prey it does not otherwise need in order to display its power. This will hopefully attract a female who seeks a dominant male who is capable of providing food for itself and the offspring.

As for the offspring themselves, nests for eggs are always built in trees, usually about 8 to 15 feet above the ground. The nests are cup-shaped, and house approximately four to seven dull white to light grey spotted eggs.

Average time to hatching: 11 days.

Average eggs per season: 5.

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During its April to July breeding season, the male Loggerhead will often kill prey it does not otherwise need in order to display its power. This will hopefully attract a female who seeks a dominant male who is capable of providing food for itself and the offspring.

As for the offspring themselves, nests for eggs are always built in trees, usually about 8 to 15 feet above the ground. The nests are cup-shaped, and house approximately four to seven dull white to light grey spotted eggs.

Average time to hatching: 11 days.

Average eggs per season: 5.

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Molecular Biology and Genetics

Molecular Biology

Barcode data: Lanius ludovicianus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 7 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNTNNNTACCGCCCTAAGTCTCCTTATTCGAGCAGAACTAGGACAACCTGGTGCTCTTCTAGGAGACGATCAAATCTACAATGTAATTGTTACAGCTCATGCTTTCGTAATAATTTTCTTCATAGTTATACCTATTATAATTGGAGGGTTTGGAAACTGATTAGTCCCACTAATAATCGGTGCCCCAGACATAGCATTCCCACGAATAAATAACATAAGTTTCTGACTTCTACCTCCATCATTTCTCCTCCTACTAGCCTCTTCAACAGTAGAAGCAGGAGCAGGAACAGGATGAACTGTGTACCCACCACTAGCCGGCAACCTAGCTCATGCCGGAGCCTCAGTCGACCTAGCCATCTTTTCACTACACCTGGCAGGTATCTCATCAATCCTAGGAGCAATCAACTTTATCACAACAGCAATTAACATAAAACCTCCTGCCCTATCACAATACCAAACCCCACTATTTGTATGATCAGTGTTAATTACCGCAGTGTTACTACTTCTTTCCCTACCAGTACTTGCCGCTGGAATCACTATACTCCTTACAGACCGTAACCTAAACACCACATTTTTCGACCCAGCAGGAGGAGGAGATCCAGTACTATATCAACATCTATTCTGATTCTTCGGCCACCCAGAAGTATACATCTTAATTCTG
-- end --

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Statistics of barcoding coverage: Lanius ludovicianus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 8
Specimens with Barcodes: 10
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: N3B - Vulnerable

United States

Rounded National Status Rank: N4 - Apparently Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Still widespread and common in some areas but has been declining throughout North America since the 1960s, and perhaps earlier. The decline is particularly severe in the northeastern and north-central regions. The species is now extirpated from most of the Northeast, and is nearly extirpated from Minnesota, Wisconsin, and Michigan. Part of the decline can be attributed to reforestation and loss of open habitat and thus represents a return to pre-settlement conditions when shrikes were probably absent from much of the heavily forested northern states. However, the decline has proceeded beyond what can be explained by habitat loss, as much suitable habitat remains unoccupied in most northern states. Further, decline has been recorded in all regions of the country, even those with much open habitat. Thus, the decline remains unexplained. Pesticides, loss of wintering habitat quality, and/or dependency on roadside habitat with high predation pressure have been suggested as possible causes. Of most urgent importance is research to unravel the cause of decline, and to identify critical habitat features.

Intrinsic Vulnerability: Not intrinsically vulnerable

Comments: Reproductive rates are potentially high; could expand current numbers and range if the factors responsible for decline could be eliminated (Yosef 1996).

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s

Justification
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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Overall, loggerhead shrikes have a large population size and a large range. One subspecies, the San Clemente loggerhead shrike (Lanius_ludovicianus_mearnsi) is listed as endangered by the U.S. Fish and Wildlife Service. Also, migrant loggerhead shrikes (Lanius_ludovicianus_migrans) are listed as endangered in the state of Michigan. Loggerhead shrikes are protected by the U.S. Migratory Bird Act.

IUCN Red List of Threatened Species: least concern

US Migratory Bird Act: protected

US Federal List: endangered; no special status

CITES: no special status

State of Michigan List: endangered

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Overall, loggerhead shrikes have a large population size and a large range. One subspecies, the San Clemente loggerhead shrike (Lanius ludovicianus mearnsi) is listed as endangered by the U.S. Fish and Wildlife Service. Also, migrant loggerhead shrikes (Lanius ludovicianus migrans) are listed as endangered in the state of Michigan. Loggerhead shrikes are protected by the U.S. Migratory Bird Act.

US Migratory Bird Act: protected

US Federal List: endangered; no special status

CITES: no special status

State of Michigan List: endangered

IUCN Red List of Threatened Species: least concern

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Global Short Term Trend: Decline of 10-50%

Comments: Breeding Bird Survey data for 1980-2000 indicate ongoing, significant declines, although the rates of these declines may be slowing down for some populations. Rangewide, the decline was 2.2% annually, or 53% for the 20 year period (Sauer et al. 2001). Regionally, the declines were 3% annually (46% overall) for the eastern region, 1.9% annually (32% overall) for the central region, and 1.6% annually (28% overall) for the west.

Even thought there is no evidence to suggest that the species has recovered to any great extent since 1980, it is still common enough in most of the southern portion of its range that most states in the region do not provide special protection or monitor populations.

Global Long Term Trend: Decline of 70-90%

Comments: Has declined significantly nearly rangewide (Robbins et al. 1986, Sauer et al. 2001). A slow decline began in the 1930s and continued until the late 1960s and 1970s when the decline accelerated. This pattern is well-documented in the literature for all but the Southern Great Plains and the West (Fruth 1988). North American Breeding Bird Survey (BBS) data for the period 1966-2000 indicate a 71% population decline rangewide (-3.6% annually), with regional declines of 78% in the east, 65% in the central region, and 75% in the western region. Since declines began before 1966, these are conservative figures for overall declines during the past century. Christmas Bird Count data for 1961-1978 documented a 22% decline in winter sightings nationwide (Morrison 1981). Declined in recent decades in western Canada (Telfer et al. 1989, Telfer 1992) and in eastern Canada (Cadman 1986, 1991).

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Population

Population Trend
Decreasing
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Threats

Degree of Threat: High

Comments: PESTICIDES: Since shrikes are high on the food chain, pesticides have been implicated as a potential cause of the decline (Fraser and Luukkonen 1986). DDE, a metabolite of DDT, has been detected in eggs from Illinois and Virginia (Anderson and Duzan 1978), but crushed eggs associated with eggshell thinning have not been reported. While there is evidence of some eggshell thinning in Illinois, there is no apparent eggshell thinning in California and Florida (Hands et al. 1989). The relatively high nesting and fledging success rate in the areas of marked decline indicate that pesticides have not reduced reproduction (Brooks 1988, Gawlik and Bildstein 1990, Kridelbaugh 1982, Luukkonen 1987, Novak 1989). Young exposed to dieldrin have been shown to attack and kill prey more slowly than unexposed birds (Busbee 1977). Wide-scale use of organochlorides was curtailed in the U.S. in the 1970s, yet the population decline continues. Blumton et al. (1989) reported that necropsies on six Virginia shrikes showed traces of pesticide contamination, but drew no conclusions on the relationship between contamination and mortality. Pesticides may pose a greater threat in reducing food availability; clutch and brood sizes declined after the introduction of organochlorines; and significant declines on the Canadian prairies corresponded with dieldrin treatment of grasshoppers, which make up 30-75% of the diet (Yosef 1996, Yosef 1994, C. Campbell in Cadman 1985).

FOOD AVAILABILITY: Pesticides may affect populations through reducing food availability (see comments under PESTICIDES above). In Virginia, Luukkonen (1987) reported several nests with malnourished nestlings and developmental variability within a brood, both evidence of limited food availability at some sites. However, on a broader scale, early breeding, brood reduction, and multiple broods should off-set any local problems from food shortages, at least for the nesting season (Luukkonen 1987). In the Midwest, excessive winter mortality may be an important cause of the decline; reduced food supplies may weaken shrikes and cause them to move into woodlots occupied by raptors (Byrd and Johnston 1991).

PREDATION: Predation is the leading cause of nest failure, but nest predation does not appear to constitute an important limiting factor (Bartgis 1992).

BREEDING HABITAT LOSS/DEGRADATION: Limited evidence from most of the Northeast suggests that lack of suitable breeding habitat limits abundance in this region. Habitat loss has been caused by farmland abandonment, development, and widespread changes in farming practices (Novak 1989). Although acreage in pasture has decreased dramatically since World War II in New York and Virginia, there apparently is a substantial amount of unoccupied habitat remaining in both states (Luukkonen 1987, Novak 1989). There also seems to be considerable unoccupied breeding habitat in Maryland and West Virginia (Bartgis, pers. comm.). At least on a local level in Virginia, habitat loss may be the primary problem (Ridd, pers. comm.). Luukkonen (1987) expressed concerns about the fragmenting of potential habitat into islands in the Ridge and Valley of Virginia. Occasional use of marginal habitat may be partially to blame for the decline in Virginia. In southern Idaho, nearly 70% of original sagebrush steppe has been destroyed by agriculture and other development (Woods 1994). In the north-central states, however, habitat loss may explain some of the decline, but not all of it. In Missouri, declining populations coincided with regions with the highest proportion of lands being converted from pasture to row crops (Kridelbaugh 1982). Several reports have concluded that much suitable habitat remains unoccupied in Michigan, Minnesota, and Wisconsin, although shrikes now are nearly absent from these states (Brooks and Temple 1990, Robbins 1991). However, Luukkonen (pers. comm.) questioned the availability of adequately sized pastures for habitat in Michigan. Threats in western Canada (Telfer et al. 1989) include habitat loss such as the conversion of unimproved pasture to cropland (Telfer 1992). In eastern Canada, declines probably have been due to loss of breeding habitat to changing agricultural practices, industrial development, residential development, and vegetation succession (Cadman 1986, 1991). Yosef and Grubb (1992) suggested that a human-caused reduction in the number of hunting perches is at least partially responsible for the decline.

WINTER HABITAT LOSS: Populations that winter along the Gulf Coast have lost much habitat, and remaining habitats are often impoverished by red fire-ants and associated pesticide-control procedures (Lymn and Temple 1991). Because of relatively high reproductive success in southern Minnesota, Brooks (1988) concluded that the 20% mean annual rate of decline in the population in the region was "probably due to factors on their nonbreeding range" to the south. Brooks (1988) further summarized concerns that the decline in Minnesota is possibly caused by decreases in winter habitat in the breeding birds' wintering range. She stated that "if resident (southern) shrike populations are being limited by habitat availability, migrant shrikes wintering in the same area are almost certainly being forced to occupy marginal habitats that are not being held by territorial residents." However, a banding study in Missouri indicated that the winter and summer populations in that state are completely separate (Kridelbaugh 1982). Conclusive evidence that factors during the nonbreeding season are limiting is not available (Yosef 1994).

COWBIRD PARASITISM/NEST PREDATION: A study documented cowbird nest parasitism in shrikes in Iowa, but the frequency was very low, only 3 out of 261 nests (DeGeus 1991). The same study found a high incidence of nest predation among shrikes nesting along roadsides (86% of all losses), and only 35% nesting success overall. Predation is apparently more intense in roadside and other linear habitats (DeGeus 1990). If shrikes are utilizing roadside habitat extensively throughout their range, high nest predation may be one explanation for their decline.

OTHER MORTALITY: Locally, mortality from vehicle collisions may be significant. A high incidence of automobile-caused mortality was noted by Miller (1931). Shrikes typically fly low to the ground, sometimes across roadways, and often feed on roads. Inexperienced juveniles have been observed following adults across highways and learning from adults to feed on highways (Hershberger 1989, Novak 1989). In many areas, hedgerows, barbed-wire fences, and other habitat features utilized by shrikes are concentrated along roadways. Fledglings and other juveniles are frequently killed by automobiles. Automobile collisions killed all three fledglings produced at an Ontario nest and four of seven young fledged over three years at a New York site (Novak 1989). Juveniles killed by vehicle collisions in the summer have also been observed in both Virginias (Bartgis 1989, Luukkonen 1987) and Maryland (Hershberger 1990). Blumton et al. (1989) reported that automobiles accounted for 29% of the observed fall and winter mortality among Virginia shrikes.

FIRE ANTS: In Florida, Yosef and Lohrer (1995) found no evidence of an effect of imported red fire-ants on territory size and prey capture rate, but cautioned that insecticides used to control red fire-ants are likely to be detrimental (see PESTICIDES and WINTER HABITAT LOSS).

DISTURBANCE: Shrikes are not particularly alarmed by proximity to human activity. Brooks (1988) noted that nests near buildings had a success rate similar to those farther away from buildings. In Virginia, a shrike continued to incubate a nest in a tree after the top was trimmed off (Luukkonen 1987), although a Maryland nest in a tree was abandoned after a multiflora rose concealing it was killed with herbicide (Dean, pers. comm.). Some shrikes have nested less than 3 m from a road, but were not flushed by passing vehicles (Bartgis 1989, Luukkonen 1987). Food shortages may occasionally limit nesting success.

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Management

Restoration Potential: Since reproductive success rates are relatively high for shrikes, there seems to be excellent potential for the species to significantly expand its existing population if the cause or causes of the decline can be identified and eliminated. Although there has been substantial loss of suitable habitat in the Northeast and perhaps elsewhere, there appears to be enough remaining unoccupied suitable habitat that existing areas can accommodate a larger population than that which currently exists. However, trends in habitat loss are likely to continue and may ultimately limit the possibility of any long-term expansion. Release of captive-bred individuals eventually may be a useful management tool (Bartgis 1992). See Cade (1992) for information on successful captive breeding.

Management Requirements: Until the cause of the decline can be determined, maintaining suitable nesting and wintering habitat in areas of regular shrike activity is worthwhile. Maintaining suitable nesting habitat in the Northeast will require keeping suitable landscape features in active pastures. Suitable nest tree criteria are described under Habitat. Kridelbaugh (1982) recommended discouraging multiflora rose (unsupported bushes, not those that climb up trees) in a breeding area since they provide poor nest support. Potential perch sites are also important. In Virginia, pastures with many potential perches had higher productivity (Luukkonen 1987). In New York, Novak (1989) reported tall isolated shrubs were typically present near nest sites at a density of three or more shrubs per hectare. Removal of fences, hedgerows, and woody vegetation eliminates potential perches and lowers habitat quality (Luukkonen 1987). Adding hunting perches can enhance habitat and can also increase the size of a local population (territory size may be decreased and thus more territories can be accommodated into a given area) (Yosef and Grubb 1994).

The timing of habitat selection could cause shrikes to select marginal habitat. For example, a hayfield selected in early spring could appear to be similar to an active pasture, but it would be quite different once vegetation begins to grow (Luukkonen 1987). However, in the states where shrikes are resident, birds have the opportunity to continually evaluate habitat. Changes in location, timing and intensity of grazing could still decrease the predictability of habitat suitability (Luukkonen 1987). Consequently, active grazing regimes should be maintained at the nest site, or if stock use is rotated between fields, there should be adjacent fields so that foraging activity will require minimal changes.

Herbaceous vegetation that is allowed to grow too tall or woody vegetation that becomes too dense eliminates the area as potential foraging habitat. Thorny shrubs, barbed-wire fences, and other objects suitable for impaling prey are also significant features of habitat that should be maintained. For specific sites in the Northeast where it is important to maintain a given shrike territory, landscape features that could attract activity to roadways, such as perches and potential nesting trees near highways, might be eliminated if similar features occur away from roadways. Such management could reduce mortality resulting from collisions with automobiles. However, for the northcentral states, Hands et al. (1989) recommended maintaining perches along a road since shrikes frequently use roadsides. If highway mortality at a site has severe impacts on local nesting success, speed bumps and traffic enforcement may be required. Chavez-Ramirez et al. (1994) cautioned that management practices developed in agricultural systems may not be appropriate in natural grasslands.

Hands et al. (1989) recommended restricting pesticide use in shrike habitat in order to avoid depressing the abundance of potential prey items. Also, for local situations where predation is identified as a problem, predator management may be necessary once nest and fledgling predators are identified (Hands et al. 1989).

Management Research Needs: Determining the cause(s) of the decline remains the major emphasis of most research activities. In the northeastern and north-central states, studies of reproductive success have not provided an answer. Studying the causes of mortality could prove valuable. For example, is automobile mortality highest for migratory birds because these birds encounter a greater number of areas with which they are unfamiliar? Is automobile caused mortality higher for inexperienced juveniles than for adults? Are BBS trends correlated with geographic trends in road density? Are predation rates always much higher along roads, and are shrikes tending to use roadside habitat more and more often? Though pesticides have not been linked to lowered reproductive success, additional studies of other potential pesticide impacts on shrikes should also be conducted.

Although the decline in potential breeding habitat acreage in the Northeast is well documented, the potential impact of habitat fragmentation remains to be addressed. One approach would involve comparing size and degree of isolation for blocks of suitable habitat among areas which have: a stable population; a declining population; or an extirpated population. Several researchers expressed concern that declines in winter habitat quality or quantity may be affecting migrant populations. Tracking foraging success and overall vigor of resident versus migrant birds in the winter may provide some answers (Bartgis 1992).

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Global Protection: Few to several (1-12) occurrences appropriately protected and managed

Comments: Protected in some national parks in the western states.

Needs: The most effective land protection for shrikes will probably require regional land use planning tools, such as zoning, special agricultural districts, and agricultural easements, that will help maintain large areas of suitable habitat. Sites with both regular summer and winter use should be priorities for protection in the Northeast. In many circumstances, acquisition may be unfeasible because of agricultural land values and the need to keep the land in production in order to maintain it as shrike habitat. Acquisition may also be of limited value until the cause of the decline can be determined. In New York, Maryland, and the Virginias, landowner contact programs will probably be more effective. These programs can appeal to a farm owner's sense of pride in the land while offering guidance to assure that key landscape features, such as suitable nest trees, are maintained. Because of the limited opportunities for habitat acquisition, existing federal facilities within primary shrike range, such as Antietam National Battlefield and the Leetown National Fisheries Center, should be encouraged to manage for shrike habitat when appropriate (Bartgis 1992).

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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Though not directly having much of an effect either negatively or positively, the fact that the Loggerhead is an endangered species with very specific hunting patterns means that any area in which a Loggerhead is found to reside is instantly zoned for its protection, even if it is a residential area. Such a zoning occured in 1993 in a suburb of Los Angeles.

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Economic Importance for Humans: Positive

May eat potentially harmful insects.

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Economic Importance for Humans: Negative

Though not directly having much of an effect either negatively or positively, the fact that the Loggerhead is an endangered species with very specific hunting patterns means that any area in which a Loggerhead is found to reside is instantly zoned for its protection, even if it is a residential area. Such a zoning occured in 1993 in a suburb of Los Angeles.

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Economic Importance for Humans: Positive

May eat potentially harmful insects.

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Risks

Stewardship Overview: In the north-central and northeastern U.S. and adjacent Canada, maintenance of suitable habitat away from roads, encouragement of farming practices that retain or establish hedgerows and permanent pastures, and minimization of pesticide use in shrike habitat may be beneficial.

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Wikipedia

Loggerhead shrike

The loggerhead shrike (Lanius ludovicianus) is a passerine bird. It is the only member of the shrike family endemic to North America; the related northern shrike (L. excubitor) occurs north of its range but also in the Palearctic.

Description[edit]

Loggerhead Shrike florida RWD6.jpg

The bird has a large hooked bill; the head and back are grey and the underparts white. The wings and tail are black, with white patches on the wings and white on the outer tail feather. The black face mask extends over the eye, unlike that of the similar but slightly larger northern shrike. "Loggerhead" refers to the relatively large size of the head as compared to the rest of the body.

Behavior[edit]

The bird breeds in semi-open areas in southern Ontario, Quebec and the Canadian prairie provinces, south to Mexico. It nests in dense trees and shrubs. The female lays 4 to 8 eggs in a bulky cup made of twigs and grass. There is an increase in average clutch size as latitude increases.

The shrike is a permanent resident in the southern part of the range; northern birds migrate farther south.

The bird waits on a perch with open lines of sight and swoops down to capture prey. Its food is large insects, small birds and lizards. Known in many parts as the "butcher bird," it impales its prey on thorns or barbed wire before eating it, because it does not have the talons of the larger birds of prey. The bird decorates its impaled victim with feathers and bills in order to attract a mate.[2] Loggerhead shrikes are perhaps the only known predators of eastern lubber grasshoppers {Romalea guttata) and will consume the head and abdomen of these very large insects, leaving behind the poisonous and foul-tasting thorax.[3]

The population of this species has declined in the northeastern parts of its range, possibly due to loss of suitable habitat and pesticide use.

Conservation status[edit]

The eastern loggerhead shrike (L.l. migrans) is critically endangered in Canada. (Although only one island subspecies is legally listed as endangered in the United States, the species is declining continentwide and no longer occurs in most of the northeastern U.S.)[4] 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 and then the young 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.[5] [6]

Subspecies[edit]

There are ten recognized subspecies of loggerhead shrike:[7]

References[edit]

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Names and Taxonomy

Taxonomy

Comments: Constitutes a superspecies with L. excubitor and L. sphenocercus (AOU 1998).

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