Northern Shrike Life History

Habitat

Northern Shrikes nest in open areas within the boreal forest (taiga) and especially at its northern edge, where the forest gradually blends with the tundra. These are areas where trees are stunted and scattered, leaving openings in the landscape. In Alaska and northern Canada, they often nest in dense cover provided by white or black spruce, mountain alder, feltleaf willow (and other dwarf willows), or quaking aspen (and other poplars). Openings in the forest landscape can be created by wetlands (creeks, rivers, lakes, bogs), recent fires, or logging, for instance. Northern Shrikes avoid open tundra that lacks bushes, and they also avoid dense forest. During migration and in winter, they use similar partly open landscapes with brushy cover, including clearcuts, recent burns, forest edges around wetlands, sagebrush plains, shelterbelts, hedgerows, overgrown pastures, and other areas that feature a mosaic of thickets.

Food

Northern Shrikes eat insects and small vertebrates. They do not eat fruit or other plant matter. During the few warm months of summer, they eat insects and other arthropods (including spiders); during most of the year, they eat songbirds (including fledglings), small mammals, and occasionally lizards. To capture prey, Northern Shrikes employ an impressive variety of tactics. Like kestrels, they often perch prominently and scan the area for signs of prey. Once they spot prey, they may fly to chase an insect or small bird in flight, capturing the prey with the feet or the bill. For songbird prey, they sometimes drive the bird to the ground to complete the kill, especially when killing birds heavier than themselves, such as American Robins. To capture small mammals, these shrikes make swift, direct flights to the ground or sometimes hover briefly over the spot before dropping down quickly. Although shrikes do not have talons as raptors do, their feet are strong and can be used for seizing birds in flight. They use the notched bill to kill prey. Once prey is dead, they may store it by impaling it on a thorn or wedging it in a branch fork. Northern Shrikes also hunt from concealed perches, waiting for songbirds such as warblers or sparrows to come close, then ambushing them in treetops or in dense cover (as Sharp-shinned Hawks do) or driving them to the ground. They may hunt by hopping through bushes, attempting to flush birds that are roosting in dense cover, and they use their white wing patch much as a Northern Mockingbird does, flicking open the wings to startle insects into moving. They sometimes feed on the ground, searching for insects and mammals while hopping through uneven terrain or brush. Prey include caterpillars, grasshoppers, ants, wasps, bees, flies, beetles, and many species of bird and small mammal, especially mice, shrews, voles, and lemmings. Before eating bees or wasps, shrikes usually remove the stinger, and for most large insects, they remove wings and larger legs and often soften the animal by manipulating it in the bill or beating it against a perch before consuming. Occasionally, wintering Northern Shrikes feed from carrion such as roadkilled animals or even dead livestock.

Nesting

Nest Placement

Males sing from potential nest sites and may indicate preferred sites to females by placing nest material. Nests are set in shrubs or trees, usually in a fork on a branch near the trunk about 8 feet (rarely up to 35 feet) above ground. Sometimes uses old hawk, jay, or magpie nests.

Nest Description

Females select the nest site and do most of the construction; males help by bringing material. Nest is a large, deep cup of twigs filled with ptarmigan feathers, animal hair, and other insulating material such as dried moss. It is lined with grasses and sedges, and finished with a layer of feathers and hair. Nests measure on average 11.8 inches across and 7.9 inches tall, with interior cup 4.3 inches across and 4.9 inches deep—very deep for a bird this size.

Nesting Facts

Behavior

Both male and female Northern Shrikes sing, especially in late winter and early spring. They arrive in breeding areas at the same time and begin nesting almost immediately. Males initially court females using what look like menacing displays, chasing and cornering them, sometimes snapping or opening the bill as they face the females. A receptive female may indicate interest by giving a specific call, crouching, and fluttering her wings like a fledgling begging for food. Once partnered, some pairs sing in duet or even perform a flight display, with the male ahead of the female flying on quivering wings. The two then spiral high into the air before dropping back to a perch. Males display their hunting prowess by caching prey items around the nesting territory. Females depend on males for most of their food through the nesting cycle, and so later courtship revolves largely around the male’s feeding of the female. Females may scold (with special calls) or even threaten (with displays) males that do not provide meals quickly enough. When females signal displeasure, males crouch and flutter the wings and tail, sing with head pointed skyward, or simply depart to continue hunting. Males sometimes perform similar displays when presenting food or just afterward. Females alone perform incubation duties, and males feed them at the nest. Both adults feed and care for the young. Once the young fledge, the pair may separate, each adult taking part of the brood to feed and care for. In some cases, fledglings remain together long after leaving the nest and may even begin migration together.

Throughout the year, Northern Shrikes are territorial, and they are aggressive against others of their species and against many birds, including many that are neither competitors nor potential prey: they attack birds as large as ducks and grouse. When nesting they defend a large area around the nest (about 7 acres), but their hunting territory may exceed 360 acres, a very large territory for a songbird.

Conservation

Population trends of Northern Shrike are not known. Partners in Flight estimates a global breeding population of 180,000 and rates the species an 11 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Although the boreal forest is remote, suitable nesting areas may be lost permanently or temporarily to oil and gas extraction activities, mining, hydroelectric projects, timber harvest, forest fires, or habitat alteration resulting from climate change. On the wintering grounds, modern agricultural practices and other land uses that eliminate brushy areas and hedgerows (and reduce rodent populations) may reduce availability of suitable wintering territories.

Credits

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Paruk, J. D., T. J. Cade, E. C. Atkinson, P. Pyle, and M. A. Patten (2020). Northern Shrike (Lanius borealis), version 1.0. In Birds of the World (S. M. Billerman, editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.norshr4.01

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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