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.

In response to declining population levels, the loggerhead shrike was placed on the National Audubon Society's Blue List in 1972. Federal breeding bird survey routes, which are run throughout the country, revealed a population decline of nearly 3% each year from 1966 to 1993 (Peterjohn and Sauer 1995). Additionally, annual survival rates of adult and juvenile loggerhead shrikes in the Upper Midwest are too low to maintain population stability (Brooks and Temple 1990). Once considered a common inhabitant of grassland habitats, the loggerhead shrike population in Minnesota has fallen sharply, and the species is currently very rare or absent throughout much of its former range. There are now only a few localities, primarily in western and east-central Minnesota, where the species is consistently reported each year. The loggerhead shrike was designated a threatened species in Minnesota in 1984, however, elevating its status to endangered is currently being considered.

  Description

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.

  Habitat

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).

The reproductive rate and success of the loggerhead shrike is high, so the overall population could increase if factors responsible for the species decline were identified and eliminated. Management efforts should focus on increasing and maintaining suitable grasslands and shelterbelts, brush along fence lines, and scattered trees and shrubs for nest and perch sites. Some loggerhead shrike habitat has become overgrown with trees, particularly red cedar. While red cedar is often an important nest tree for loggerhead shrikes, dry grassland slopes can become so covered by the dense growth of this tree that it becomes unsuitable shrike habitat. Management efforts to control the encroachment of red cedar would benefit this species, as well as many other grassland species. Habitat losses on loggerhead shrike overwintering grounds are likely a big factor in the species decline as well, especially as migrating shrikes from northern breeding areas increasingly encounter habitats already saturated by resident, non-migratory shrikes (Brooks 1988; Brooks and Temple 1990). Further research should focus on identifying where midwestern loggerhead shrikes overwinter and whether habitat management activities in those areas could help reduce population declines.

  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.

As of the 1990s, the densest population of shrikes in Minnesota occurred in Dakota County where territories were monitored annually and all reports during the nesting season were investigated. This Dakota County population as well as all known historical shrike locations in Goodhue County, Rice County, and the Anoka Sand Plain were surveyed in 2008 and 2009, but very few shrikes were detected. Loggerhead shrikes continue to be observed at widely scattered locations elsewhere in Minnesota each year, but few persistent populations are known. To educate landowners about loggerhead shrike identification and how to best maintain and enhance habitat for them, the Nongame Wildlife Program created a Landowners Guide for Maintaining and Encouraging Loggerhead Shrikes.

  References

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.