San Francisco State University
Department of Geography

Geography 316:  Biogeography

The Biogeography of the Loggerhead shrike (Lanius ludovicianus)

by Adam Ashton, student in Geography 316, Fall 2000

Loggerhead shrike
Bruun, Robbins, Singer, Zim 1983

Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Laniidae
Genus: Lanius
Species: Lanius ludovicianus
 

Description of Species:

The loggerhead shrike is a native North American perching bird that preys on insects, lizards and small birds (Alden 1998).  Although the bird eats similar food to hawks and falcons, it cannot kill its prey with talons, as Falconiformes birds do.  To compensate, the loggerhead shrike manipulates a heavy bill, its diagnostic trait, to stun and then impale its prey.

When seen from below, the loggerhead shrike can be mistaken easily for a mockingbird.  Both birds are grayish with large white spots on their primaries.  However, the loggerhead shrike is a little smaller than the mockingbird, the loggerhead shrike’s white spots are likewise smaller than the mockingbird’s and the loggerhead shrike’s bill is much thicker than the mockingbird’s (Alden 1998).  The loggerhead shrike is about 10 inches long and it has 10 primaries.

The loggerhead shrike has a black eyemask that extends from its bill to its neck.  The top of its head and its back are silvery gray.  Its throat is white.  Its underbelly is light gray.  The loggerhead shrike’s tail and wings are both black.  The loggerhead shrike’s call consists of repeated harsh phrases that sound like shack (Alden 1998).

Loggerhead shrike perching
Kaufman, 1996

Habitat:

Loggerhead shrikes prefer grasslands with low trees and shrubs.  They are mostly found in deserts, scrubland, savanna and some agricultural land (Cade & Woods 1997).  In California, loggerhead shrikes are known to live in sage scrub, cropland, non-native grassland, chaparral and riparian communities (Western Riverside County Multiple Species Habitat Conservation Plan 1999).  Generally, shrikes prefer to nest in trees that overlook grasslands (Cade & Woods 1996).  In agricultural areas, where scattered trees and shrubs are mostly absent, shrikes will nest along fencelines, where the only shrubs and trees in monocrop farms will be located.
 

Natural History:

Passeriformes is the dominant order of modern birds.  More than half of all modern bird species belong to the order.  The diagnostic trait of this order is a perching foot.  All Passeriformes birds have four non-webbed toes joined at the same level with the first toe (the hallux) directed backward.  This foot allows passerines to perch with their feet wrapped around branches (Encyclopedia Brittanica 2000).

All passerines have an unfeathered oil gland, no gap between the fourth and fifth primaries, altricial young and between nine and 10 primaries.  They first appeared in the fossil record about 40 million years ago (Encyclopedia Brittanica 2000).  Ornithologists have a difficult time classifying passerines into genera, species and subspecies because the order has radiated into so many niches.  Many seemingly related birds evolved from different ancestors in different places.

Laniidae, the shrike family, has about 100 members.  All of them share in hooked bills, large heads and sharp claws.  Laniidae has two subfamilies.  Laniinae, the subfamily to which the loggerhead shrike belongs, has about 30 species.  Laniinae shrikes are true shrikes.  Malacontinae, a subfamily of mostly African bush shrikes, has up to 70 members.  Bush shrikes often have brighter plumage and less hooked bills than true shrikes (Encyclopedia Brittanica 2000).  Only two shrikes, the loggerhead and northern shrike, inhabit North America.  These birds are not competitive.  The northern shrike tends to live in ranges north of loggerhead populations (Kaufman 1996).
Laniidae birds first appear in the fossil record about 7 million years ago.  At that time, passerines adapted to and radiated into new grasslands that formed as the planet underwent a cooling and drying period (Lynch & Proctor 1993).  Laniidae species still tend to prefer grassland habitats.
 

Loggerhead shrike on barbed wire.
Alden, 1998

Evolution:

Although paleontologists agree birds evolved from reptilian ancestors at some time between 150 to 200 million years ago in the Mesozoic Era, they continue to debate over two hypotheses that attempt to identify which kind of reptiles antecedes avian life.  According to one, proto-birds evolved from pseudosuchians (crocodile ancestors) more than 200 million years ago.  The other hypothesis says birds evolved as an offshoot from predatory theropod dinosaurs about 200 million years ago (Lynch & Proctor 1993).

 The pseudosuchian hypothesis suggests birds evolved in the early Triassic Period from a stock of unspecialized thecodont dinosaurs such as Euparkeria and Sphenosucus.  Proponents of this hypothesis point to similarities in the inner ear and in other skeletal structures between pseudosuchians, crocodiles, ancient birds and modern birds (Lynch & Proctor 1993).

 The theropod avian ancestral route indicates birds evolved from predatory coelurosarian dinosaurs in the early Jurassic Period.  This hypothesis centers on similarities between small coelurosarians like Compsognathus and Archaeopteryx, one of the first birds to appear in the fossil record (Lynch & Proctor 1993).

 The first fossil record evidence of Passeriformes, the order to which the Loggerhead Shrike belongs, occurs in a 40 million-year-old species related to modern titmice (Encyclopedia Brittanica).  The first shrikes occur about 7 million years ago in the Miocene Epoch.  Many modern bird families first appear at this time because of a climatic cooling and drying period that reduced forests but spread grasslands (Lynch & Proctor 1993).  Subsequently, birds had entirely new habitats into which they could radiate new species.
 

Distribution

The loggerhead shrike can be found throughout the United States except in northeastern states from New Jersey to New England.  Its range extends from southern Canada to northern Mexico (Western Riverside County Multiple Species Habitat Conservation Plan 1999).  Northern loggerhead shrike populations are migratory.  A Canadian study observed loggerhead shrike pairs in Texas during winter and in Alberta and Saskatchewan during spring and summer (Telfer 1992).  The densest breeding range for the loggerhead shrike occurs in the American south (Cade & Woods 1997).  It is most commonly found in semi-open territory such as deserts, agricultural land and grasslands.

Before European settlers came and began altering natural American habitats, the loggerhead shrike was a common bird all over the country.  Now, the bird is entirely absent from northeastern America.  Its northeastern range spread northward in the late 1800s as settlers turned forests into agricultural fields.  A corollary northern expansion occurred in the early 1900s as midwestern grasslands were likewise turned into croplands (Cade & Woods 1997).

Map of Distribution:

(Kaufman 1996)

Other interesting issues:

Loggerhead shrike populations have decreased steadily nationwide since 1900 and have experienced a documented decrease of about 5 percent annually since 1966 (Yosef & Lohrer 1995).  Reasons for this decline are poorly understood.

Habitat depletion is a likely culprit.  Telfer (1992) reported that loggerhead shrike populations that experienced large declines in numbers also lost 39 percent of pasture through conversion to cropland between 1946 and 1986.  Areas in which shrike populations decreased less lost only about 12 percent of pasture area to conversion to cropland.  The study concludes, “In both Canada and Texas, Loggerhead Shrike management requires preservation and enhancement of remaining grasslands” (Telfer 1992).

Habitat depletion also takes its toll on the daily habits of loggerhead shrikes. Loggerhead shrikes are perching birds that prefer to spend 80 percent of their days sitting; shrikes that live in suboptimal habitats will spend excessive amounts of time foraging (Western Riverside County Multiple Species Habitat Conservation Plan 1999).

Another source of concern for loggerhead shrike populations comes in the effects of nesting near roadsides and fencelines.  A 1993 Canadian Field Naturalist article reported that almost half of all observed loggerhead shrikes in southeastern Alberta were spotted with 200 meters of a roadside.  (Bjorge, Prescott 1996).  The productivity of shrike pairs that live near roadsides is half that of pairs that live in other habitats because of accidents with vehicles and because raptors have an easy time spotting prey (such as altricial loggerhead shrikes) along roadsides where cover vegetation is lined up parallel to the road (Yosef 94).  Likewise, loggerhead shrikes that nest along fencelines in monocrop agricultural communities suffer high predation because birds that eat shrikes simply hunt along fence corridors where they will find the most prey in the least space (Yosef 1994).

 Preservation of loggerhead shrike populations will require better identification of limiting factors and conservation of grassland communities.
 
 
 

Bibliography

Alden, Peter.  National Audubon Society Field Guide to California.  Knopf.  1998.  New York.

Bjorge, RR; Prescott, DC.  “Population estimate and habitat associations of the loggerhead shrike in Southeast Alberta.”  Canadian Field Naturalist, vol.110, no. 3,
September 1996.

Bruun, Bertel; Robbins, Chandler; Singer, Arthur; Zim, Herbert.  Birds of North America.  Goldenbooks.  1983.

Burton, KM.  “Use of barbed wire by Loggerhead Shrikes to manipulate nest materials.”  American Midland Naturalist, vol. 42, no. 1, July, 1999.

Cade, TJ; Woods, CP.  “Nesting habitats of the loggerhead shrike in sagebrush.”  Condor, vol. 98, no. 1, 1996.

Cade, TJ; Woods, CP.  “Changes in distribution and abundance of the loggerhead shrike.”  Conservation Biology, vol. 11, no. 1, February 1997.

Cully, JF; Michaels, HL.  “Landscape and fine scale habitat associations of the loggerhead shrike.”  Wilson Bulletin, vol. 110, no. 4, December 1998.

Encyclopedia Brittanica. http://brittanica.com/.  2000.

Kaufman, Ken.  Lives of North American Birds.  Houghton Mifflin.  1996. Boston.

Lohrer, FC; Yosef, R.  “Loggerhead shrikes, red fire ants and red herrings?”  Condor, vol. 97, no. 4, 1995.

Lynch, Patrick; Proctor, Noble.  Manual of Ornithology.  Yale University Press.  1993.  USA.

Telfer, ES.  “Study of shrike on breeding range in Alberta and Saskatchewan and on winter range in Texas.”  Canadian Field Naturalist, vol. 106, no. 3, 1992.

Tyler, JD.  “Nesting ecology of the Loggerhead Shrike in southwestern Oklahoma.”  Wilson Bulletin, vol. 104, no. 1, 1992.

Western Riverside County Multiple Species Habitat Conservation Plan.  UC Riverside.  1999.  http://ecoregion.ucr.edu/full.asp?sp_num=67

Yosef, R.  “The effects of fencelines on the reproductive success of loggerhead shrikes.”  Conservation Biology, vol. 8, no. 1, 1994.
 
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