Northern Shrike
| Scientific Name | Lanius borealis |
| Survival Strategy | Short-distance migrant, Medium-distance migrant |
| Arrival in Upper Midwest | Late October to late November |
| Departure | March |
| Destination | Subarctic boreal forest |
| Conservation Status | Least Concern |
Spring
In March, northern shrikes begin migrating to the north edge of the boreal forest (taiga). The female lays four to six eggs in a deep cup-shaped nest from May to June. The male feeds the female as she incubates the eggs for 17 to 18 days. The young are born naked and blind (altricial) and fledge in 19 to 20 days.
Summer
By July or August, hatch-year shrikes are independent and have dispersed away from their parent’s territories.
Fall
Northern Shrikes arrive in the Upper Midwest in late October through Late November and lay claim to their winter territory by singing. Like snowy owls and rough-legged hawks, they are an irruptive species whose numbers vary dramatically from year to year.
Winter
Northern shrikes spend the winter feeding on birds and small mammals. As winter draws to a close, shrikes begin migrating to their breeding grounds.
Behavior
Hunting
The hunting skills of the northern shrike are legendary. This predatory songbird will prey on small mammals and birds, such as doves and blue jays. Equipped with tomial teeth, a single sharp triangular wedge on both sides of its upper beak, and a matching notch on each side of the lower beak, the shrike will bite its next meal in the back of the neck and shake it until the spinal cord has snapped. Before it can eat, the shrike impales its prey on a thorn or barbed wire. As the carcass ages, the collagen in the muscle tissue breaks down, making the flesh more tender and easier to rip apart.
Physiology
Seasonal Acclimatization to the Cold
Like other birds that overwinter where harsh weather is likely, northern shrikes undergo a gradual change in metabolic processes known as seasonal acclimatization, which increases their ability to survive in sub-zero conditions.
The adjustments to colder temperatures must be gradual. If a northern shrike, captured in mid-summer on its breeding ground, were placed in a freezer at -20°C (-4°F), it would not survive long. And yet that shrike can thrive at the same temperature in its winter range after gradually acclimatizing to the environmental changes.
Through seasonal acclimatization, the metabolic rate of the northern shrike is 50% higher in the winter than in the summer. The warmth provided by the increase in metabolism comes at a heavy energy cost. Since shrikes do not carry extra fat as a fuel reserve, they must actively hunt for food or rely on cached prey spiked in a nearby tree.
Unlike mammals, birds have mitochondria in their red blood cells, which generate heat due to respiration. A recent study found that the mitochondria in the blood of birds acclimatized to winter conditions produce more heat in the winter than in the summer. While the blood of mammals removes heat from the cells like the cooling system in an automobile engine, the blood of birds is more like an in-floor radiant heating system.
Diet
While spending the summer on the northern edge of the subarctic boreal forest, the northern shrike feeds primarily on invertebrates, including spiders, bees, beetles, and grasshoppers.
Shrikes wintering in the Upper Midwest prey on mice, voles, and birds.
Lifespan and Mortality
Northern shrikes live for 4 to 6 years.
Predators
Predators of the northern shrike included the northern goshawk, peregrine falcon, merlin, and red fox.
Weather Hazards
Late spring snows can reduce the number of insects available, leading to the death of hatchlings from hypothermia or starvation.
Climate Vulnerability
A warmer climate will likely shift the range of the northern shrike north and out of the lower 48 states.
Never Stop Learning
First Nations: The Vuntut Gwitchin First Nation people of Old Crow, Yukon call the northern shrike “Tzi kwut go katshi lyi.”
Ambassador-at-large: The northern shrike can be found in Canada, China, Mongolia, Russia, and United States.
References
| 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 |
| Shrikes: Meet the Bird That Impales Prey on Spikes https://blog.nature.org/science/2020/01/27/shrikes-meet-the-bird-that-impales-prey-on-spikes/ |
| Paruk, James & Cooper, Sheldon & Mangan, Anna & Brady, Ryan & Tucker, Logan. (2015). Resting Metabolic Rates of Adult Northern Shrikes ( Lanius excubitor ) Wintering in Northern Wisconsin. The Wilson Journal of Ornithology. 127. 510-514. http://dx.doi.org/10.1676/14-061.1 |
| Lund University. “Bird blood is a heating system in winter.” ScienceDaily. ScienceDaily, 9 April 2021. < www.sciencedaily.com/releases/2021/04/210409104242.htm >. |
| Nord, A, Metcalfe, NB, Page, JL, Huxtable, A, McCafferty, DJ, Dawson, NJ. Avian red blood cell mitochondria produce more heat in winter than in autumn. The FASEB Journal. 2021; 35:e21490. https://doi.org/10.1096/fj.202100107R |
| How Climate Change Will Reshape the Range of the Northern Shrike https://www.audubon.org/field-guide/bird/northern-shrike |
| Irving, Laurence. “Naming of Birds as Part of the Intellectual Culture of Indians at Old Crow, Yukon Territory.” Arctic, vol. 11, no. 2, Arctic Institute of North America, 1958, pp. 117–22, https://doi.org/10.14430/arctic3738 |