15. Chickadee Notes

Loggerhead Shrike in New Brunswick

Status

Loggerhead ShrikeThe Loggerhead Shrike, Lanius ludovicianus, has always been a very rare breeding bird in New Brunswick. Since the late 1960s the Loggerhead has declined greatly over most of its North American range. In New Brunswick it has not been known to breed since 1972, although individual birds are occasionally sighted. During the Maritimes Breeding Bird Atlas (1986-1990) only one shrike, undoubtedly a Loggerhead, was recorded in New Brunswick, near Centreville, Carlton County.

The Federal-Provincial Committee on the Status of Endangered Wildlife In Canada assigned Canadian populations of the Loggerhead Shrike threatened status in 1986. Continuing declines and habitat loss led, five years later, to designation of the eastern Canadian population as endangered.

The precise reasons for the decline of the Loggerhead Shrike are not clear, but loss of both breeding and wintering habitat has been implicated. The Loggerhead Shrike is essentially a bird of prairie grasslands. The clearing of forests for agriculture during the last century led to eastward expansion of the species' breeding range into Ontario, Quebec and the Maritimes. However, since the middle of this century the reversion of farmland to forest and the industrialization and urbanization of farmland have meant large losses in Loggerhead Shrike breeding habitat. The increased use of agricultural insecticides and herbicides may also be playing a role in the species decline.

Natural History

The Loggerhead Shrike is a medium-sized songbird with a heavy, hooked upper bill, a gray-white breast, a deep bluish-grey back, and black wings and tail. There is a very distinctive black face mask and the outer tail feathers are white. The Northern Shrike, Lanius excubitor, is a related species and is very similar in appearance. However, this latter species breeds far north of New Brunswick and is only encountered here on migration and during the winter months. The Loggerhead Shrike breeds across much of North America as far south as southern Mexico. Southern populations are sedentary but northern birds winter in the north-central United States southward.

The Loggerhead Shrike is an opportunistic predator, feeding on large-bodied insects such as grasshoppers, as well as on mice, small birds and snakes. Loggerheads perch alone, usually on treetops or telephone wires in open areas from which they have a wide view. They fly low, with alternate rapid fluttering and gliding. The species has earned the nickname "butcher bird" because it impales its prey on a thorn or a barbed wire fence, so that it might more easily be torn apart.

Loggerhead shrikes often nest and forage along roads, which has led to the suggestion that collisions with automobiles may be a major cause of shrike mortality. Predation on nestlings by domestic cats has also been identified as a problem, as has reproductive failure caused by exposure to agricultural pesticides.

Pastureland, old fields and natural grasslands are the most conspicuous aspects of Loggerhead Shrike breeding and wintering habitat. Loss of such habitat on the breeding range has been identified as a probable cause of decline in some areas although in other regions different factors appear to be at work. Generally, northern populations of this species have suffered the most precipitous declines, even where breeding habitat has been largely unaltered. In these cases it has been suggested that loss of habitat on the winter range may be the problem. Northern populations of the Loggerhead mix with resident southern Loggerheads in the winter, where these latter birds defend winter territories. If resident shrikes are limited by habitat availability, migrants may be forced to occupy marginal habitat, reducing their chances of survival through the winter.

There are only two nest records for New Brunswick with egg dates; May 25th and July 3rd, both with the typical clutch size of five. Both sexes participate in construction of the bulky nest, which is placed high in an isolated conifer or low in a thicket, small tree or bush, usually near pasture or grassland. The nest is well constructed of twigs, securely interwoven, and lined with fine rootlets, fibers and feathers. The four to six dark spotted and blotched grayish eggs are incubated largely by the female and hatch about 15 days after laying.

Newly hatched young are unfeathered, with bright orange skin and an apricot-yellow bill and feet. Both parents feed the nestlings, which will spend a little more than two weeks in the nest before their first flight. Over much of the breeding range the species is an early nester, with two and even three broods being raised. In New Brunswick, however, adults with young have been observed only in early and mid-August and it seems likely that the species would be single brooded here where it reaches its northern range limit.

Helping Out

There are several things we can do that may help the Loggerhead Shrike and which will benefit wildlife in this region generally. Hedgerows and vegetated windbreaks in rural areas are an important habitat for a surprising diversity of plants and animals, including shrikes, and should be maintained. Such areas may also be important corridors for the movement of certain species and help provide a mosaic of habitat types.

Pesticides and herbicides have led to reproductive failures and even mass mortality of several species of birds associated with agricultural habitats. We should limit, or better still eliminate, our use of such chemicals wherever possible. Several pesticides have been connected with reduced reproductive success in the Loggerhead Shrike.

Observations of single Loggerhead Shrikes in New Brunswick, or nesting pairs, should be documented, photographed if possible, and the information sent to the New Brunswick Museum where such information is stored. Nesting birds should, of course, never be disturbed.

Further Reading

Cadman, M.D. 1986. Status report on the Loggerhead Shrike, Lanius ludovicianus. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 17 pp.

Erskine, J.S. 1992. Atlas of breeding birds of the maritime provinces. Nimbus Publishing and the Nova Scotia Museum, Halifax, Nova Scotia. 270 pp.

Gawlik, D.E. and K.L. Bildstein. 1990. Reproductive success and nesting habitat of Loggerhead Shrikes in north-central South Carolina. Wilson Bulletin 102: 37-48.

Prescott, D.R.C., and D. M. Collister. 1993. Characteristics of Occupied and Unoccupied Loggerhead Shrike Territories in Southeastern Alberta. Journal of Wildlife Management 57: 346-352.

Robert, M. and P. Laporte 1991. History and current status of the Loggerhead Shrike in Quebec. Progress Notes No. 196, Canadian Wildlife Service, Ottawa.