Lanius ludovicianus Linnaeus, 1766
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Basis for Listing
The loggerhead shrike is widely distributed throughout most of the continental United States and the southern part of the Prairie Provinces of Canada. Its range appears to be influenced by human-induced landscape changes. Because the species utilizes open habitat, it expanded its range northward in response to deforestation and the introduction of agriculture that occurred as the United States was settled. Since the 1940s, however, some areas have experienced population declines, partly as a result of tree encroachment on grasslands and increasingly intensive row-cropping practices.
The loggerhead shrike is a robin-sized bird with striking features, including a slate gray back, a broad, black mask through the eyes, a white patch on otherwise black wings, and white outer tail feathers. It is a summer resident of Minnesota and often confused with its slightly larger counterpart, the northern shrike (Lanius excubitor), which is only a winter visitor in the state. Loggerhead shrikes can be distinguished by their smaller size, smaller, less strongly hooked bill, and broader black facial mask, which extends above the bill in loggerhead shrikes, but not in northern shrikes. Also, the loggerhead shrike usually lacks faint barring on the breast, which is often present on northern shrikes. The shrike's unique behavior of impaling prey items on thorns and barbed wire is often a telltale sign of the bird's presence in an area.
Loggerhead shrikes live in areas of upland grasslands and sometimes in agricultural areas, where short grass vegetation and perching sites such as hedgerows, shrubs, and small trees are found. They occur in both native and non-native grasslands, including native prairie, pastures, old fields, shelterbelts, farmyards, and cemeteries.
Biology / Life History
Loggerhead shrikes are believed to be solitary migrants, moving short distances each day and sometimes staying in an area for several days to feed (Yosef 1996). They overwinter in the southern U.S. and Mexico, returning to Minnesota and the northern part of their range in March. Pairs defend territories of 2-25 ha (5-62 ac.). Nests are well hidden in trees or brush and are usually less than 2 m (6.6 ft.) above the ground. Females lay 3-7 eggs (Brooks and Temple 1990) and incubate them for approximately 16 days. While on the nest, the female is fed by the male. Once the eggs hatch, both parents participate equally in feeding the chicks until they fledge at about 16 days old. The young practice hunting and manipulating objects for several weeks, and are usually able to precisely impale prey at 2 months of age (Yosef 1996). Loggerhead shrikes use their sharply-hooked bill to subdue vertebrate prey by biting their neck and severing their cerebral vertebrae. Small items, such as grasshoppers or beetles, may be impaled or eaten whole, but larger items, including large invertebrates, amphibians, lizards, small snakes, mice, and small birds, are always impaled first or wedged into a forked branch, and then eaten. This is an adaptation that allows loggerhead shrikes to eat large prey without the benefit of strong talons and feet.
Conservation / Management
Habitat destruction is partly responsible for this species' decline, as loggerhead shrikes require relatively large areas of grassland habitat with scattered shrubs or small trees for nesting. Many of the sites currently used by this species in Minnesota are threatened by rural residential construction. Intensive farming practices often preclude shelterbelts and hedgerows, making the habitat unsuitable for loggerhead shrikes. Additionally, as predators, shrikes are vulnerable to environmental contamination via reduced food supply and ingestion of contaminated prey. In one study, the decrease in loggerhead shrike numbers corresponded to the treatment of grasshoppers with an insecticide (Yosef 1996).
Conservation Efforts in Minnesota
The short-term clustering of birds, the fact that only the males are known to be philopatric, and the shifting of territories between years make it difficult to monitor loggerhead shrike populations. For example, Brooks (1988) reported 32 nesting pairs and 37 nest attempts in 1986 and 19 pairs and 27 nest attempts in 1987, scattered across 12 counties. In the same search area, just 18 nesting attempts were documented in 1995 and 10 in 1996 (Eliason 1996) . Based on the number of occupied territories in 1986-1988, Brooks and Temple (1990) calculated an average re-occupancy rate of breeding territories of 47%. The Minnesota DNR's Nongame Wildlife Program funded a study to develop a standardized surveying protocol and management recommendations for the loggerhead shrike, but the frequency with which shrikes shifted territories made the results unreliable. Population numbers were so low and shrikes were so widely dispersed that none of the methods tested proved to be practical for tracking population changes (Eliason 1996) . A survey protocol specific to loggerhead shrikes is still needed and necessary for accurate population monitoring in Minnesota.
Brooks, B. L. 1988. The breeding distribution, population dynamics, and habitat availability and suitability of an Upper Midwest Loggerhead Shrike population. M. S. Thesis, University of Wisconsin, Madison, Wisconsin. 58 pp.
Brooks, B. L., and S. A. Temple. 1990. Dynamics of a Loggerhead Shrike population in Minnesota. Wilson Bulletin 102(3):441-450.
Eliason, B. 1996. Statewide survey and habitat protection for the loggerhead shrike in Minnesota. Final Report submitted to the Partners for Wildlife Program, U. S. Fish and Wildlife Service. 7 pp. +.
Peterjohn, B. G., and J. R. Sauer. 1995. Population trends of the Loggerhead Shrike from the North American breeding bird survey. Proceedings of the Western Foundation of Vertebrate Zoology 6:117-121.
Yosef, R. 1996. Loggerhead Shrike (Lanius ludovicianus). Number 231 in A. Poole and F. Gill, editors. The birds of North America. The Birds of North America, Inc., Philadelphia, Pennsylvania.