By Michelle Z. Donahue
Residents of the southeastern United States might occasionally come across an oddity along a barbed-wire fence: a series of insects, mice or even small birds and lizards impaled on the barbs.
This is the work of the loggerhead shrike (Lanius ludovicianus), a bird about the size of a mocking bird, and identifiable by a stark black mask across its eyes. Some folks call it the “butcher bird” for its curious habit of killing prey with its sharp, hooked beak, then hanging its kills in thorny shrubs and on fences.
It’s a macabre sight that is rapidly disappearing. Populations of an eastern subspecies of the loggerhead shrike, L. l. migrans, once widespread from Ontario to Florida, have dropped alarmingly across many parts of its former range. Although the species as whole is declining less precipitously across the United States, it is part of a greater group of grassland bird species that are all following a steady drumbeat of decline.
To try and learn more about the reasons why, researchers and biologists at the Smithsonian’s Conservation Biology Institute (SCBI) in Front Royal, Va., have been working with a Canadian breeding program to help build populations of the threatened migrans subspecies. Their hope is that with a larger group of birds to study, they’ll be able to root out reasons why loggerhead shrikes—and perhaps other grassland-dependent species—are declining.
Warren Lynch, a biologist and the bird unit manager at SCBI, has been working with staff at the Toronto Zoo and Wildlife Preservation Canada to breed shrikes to be released back into the wild. SCBI wrapped up its first full year of breeding in 2014; in Canada, efforts have been underway since 1997, when only 18 breeding pairs were counted in the wild in Ontario.
“Ultimately we’d like to work towards releasing birds locally,” Lynch says. Virginia is the epicenter of the shrikes’ traditional range, and they would normally be a common sight in the Mid-Atlantic region.
The primary focus of the project is to build a stable population to study. The causes of the birds’ decline are likely due to a combination of factors such as habitat destruction and fragmentation, pesticides, harsh winters, falling prey to other predators, competition for food and territory by non-migratory shrikes.
“There’s been little work done, very little methodical scientific inquiry to investigate these potential causes of decline,” Lynch says.
Through the 1800s, shrike populations in the East exploded as new American settlers cleared the vast forests of the East for farming. Shrikes thrived with the addition of so much new pasture, bounded by dense, brushy hedgerows that were perfect for building nests.
But since the 1960s, and possibly even before, their numbers have dropped. Though some experts speculated that this was a normalization toward what their populations had been prior to the late 1800s, an analysis of 25 years of breeding-bird surveys showed shrikes were declining by 3 percent each year across the continent, with regional declines as high as 17 percent in some years. Acreage of actively grazed pastureland declined in proportion to the shrikes’ population during that time.
At SCBI, captive shrikes are paired according to a Canadian studbook to ensure genetic diversity. In April, after a winter of spending time next to each other in adjacent outdoor enclosures, most of the program’s birds immediately started courting and nest building—except for one couple that didn’t hit it off. They fought and had to be separated.
The enclosures are furnished with shrike-friendly items: a bristling hawthorn tree, a strand of barbed wire, all the crickets and mealworms they would want to stick on a stake, and even bunches of exotic animal hair to line their nests, collected from other animals being studied at SCBI. Researchers check nests with mirrors or ladders, count eggs and monitor the health of new nestlings.
At the end of the season, some individuals are swapped out for new captive birds from Canada to broaden the overall gene pools of each breeding effort. Eventually, researchers hope there will be enough birds to release into the local area to monitor their natural life cycles using tools including GPS satellite technology.
In the meantime, Lynch says, researchers are continuing to have conversations with farmers and local landholders on how to make their farms and properties suitable for the remaining local populations, such as tolerating some dense shrubbery around their pastures and croplands.
“We explain that these birds are helpful to them,” Lynch says. “They kill rodents and agricultural pests like grasshoppers and beetles that cause crop damage. Shrikes seem to prefer actively grazed pastures that aren’t perfectly groomed. It’s better to have hedgerows, overgrown fences and some scattered trees and bushes.”