Sunday, December 23, 2007

Butcher birds seek larder in Ohio

We find a Northern Shrike (Lanius excubitor) on Delaware Wildlife Area, Delaware County, central Ohio, and we comment on unusually frequent sightings in Ohio this winter.

A Northern Shrike (a.k.a. butcher bird), rare Ohio visitor, on the lookout for rodents and small birds, Delaware Wildlife Area, central Ohio.

See a beautiful closeup photo of a Northern Shrike at Michael McDowell's Birding and Digiscoping blog.

Northern Shrikes typically perch atop twigs reaching skyward from small trees and tall shrubs along shrubby edges and roadsides. They are rare visitors in Ohio; solitary sentinels keeping watch over our wintry old fields. During most years birders find very few Northern Shrikes in Ohio and these are usually found in counties near Ohio's northern coast along Lake Erie.

Typical Ohio winter shrike habitat mimics the vegetative structure of taiga openings: An elevated perch overlooks accessible thick turf and duff supporting abundant rodents. Note the shrike on uppermost branch of tree, at center.

Shrikes hunt from their perch, and they perch where they can see prey. During their southerly sojourns they find that they see well from roadside utility wires, too. Roadsides hold small mammals and birds starved for habitat and desiring roadside minerals or grit.

Their descriptive Latin name "Lanius excubitor" is translated "butcher watchman," a perfect description. Shrikes are skilled passerine predators with voracious appetites for small mammals and birds, especially during winter. Their large heads and muscular necks power their raptor-like hooked bills through the spine of their prey, sometimes leaving their prey alive but unable to muster a response.

A full belly will not tame this aggressive hunter. Like humans, shrikes kill more than they eat, collecting their prey like trophies on display in their thorny larder, in cold storage for a snowy day. Their larder might be found in a honeylocust tree festooned with branchy spines that serve nicely as meat hooks; and meat hooks they are: Shrikes impale mice, voles, shrews, and small birds, dead or alive, on thorns and spines, and even on barbed wire. Their larders serve them well during lean times such as when rodents remain hidden under crusted snow!

This is an exceptional winter for shrike sightings, and predictably so. Northern Shrikes are irruptive: Their southerly occurrences cycle with rodent populations in their northerly range where taiga meets tundra, and wherever the taiga canopy opens to let the Northern Lights cast their electric glow on grassy turf and undergrowth.

Rodents are scarce in the far north this winter. Speaking of food availability and owls in his winter forecast (September, 2007), Ron Pittaway of the Ontario Field Ornithologists predicted good movements of northern owls in response to plummeting rodent numbers. Ron didn't mention Northern Shrikes but I'm sure the same reasoning works for them.

"Small mammal populations were abundant this summer in northern Ontario, presumably increasing after the big seed/berry/fruit crops in 2006. However, crops this year are very poor in much of the north, partly caused by cold weather and snow in late spring that froze the buds and flowers of many plants. . . . The huge population of deer mice in central Ontario is declining rapidly now because of poor seed crops this summer, particularly sugar maple samaras, which they store for the winter."

Some of Ontario's Northern Shrikes have wandered as far south as central Ohio this year, I think. No doubt, there is slim pickings up north; the rodent cycle has bottomed-out. That's good news for Ohioans because we find it a little easier to see these northern wonders when they come to our back-forty. There have been at least 26 sightings reported to the Ohio Birds Listserv since October (several, at least, are repeats of the same birds).

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