Wild Neighbors: In the Shrike Zone: Losing the Loggerhead?

By Joe Eaton
Wednesday April 01, 2009 - 09:43:00 PM
Loggerhead shrikes have learned how to use barbed wire
Kevin Cole
Loggerhead shrikes have learned how to use barbed wire

I miss shrikes. The loggerhead shrike, the local representative of this anomalous family of killer songbirds, used to be easier to see in the East Bay. This winter it was noteworthy when a single bird showed up at the Berkeley Meadow. We can still reliably find them in rural areas like the Altamont Hills, but they’ve become less common along the coast. 

Students of North American birds rely on two main indicators of abundance: the spring Breeding Bird Survey and the Audubon Christmas Count. By both measures, loggerhead shrike numbers in the Bay Area have been trending down for about the last 40 years. That also holds for most areas of the state, although some desert populations appear stable. The California Department of Fish and Game lists the mainland shrike population as a “species of special concern.” Two endemic subspecies in the Channel Islands are in even worse shape. 

The phenomenon is nationwide. Loggerheads no longer nest in New England, are rare in Pennsylvania, and have declined drastically in Quebec. Several Midwestern states have listed the species as endangered or threatened.  

I first encountered loggerhead shrikes when I was living in southwest Georgia, near a patch of longleaf pinewoods. They were hard to miss: mocker-sized birds boldly patterned in black, gray, and white, with bandit’s masks across their eyes. Someone has suggested that the shrike was what Mississippi-born sportscaster Red Barber had in mind when said a player was sitting in the catbird seat. That’s possible, but I’ve never heard anyone in the South call a shrike a catbird. Texans used to refer to them as “French mockingbirds.” Mostly, though, they were called butcherbirds, and with good reason. 

Shrikes, which are relatives of crows and jays, are stuck with mismatching equipment: they have the raptorial beaks of falcons—and dispatch their prey the same way, with a bite to the base of the head—and the feet of robins. Larger creatures are difficult to hold down. To that end, they’ve evolved the habit of impaling their prey on thorns or sharp twigs. Barbed wire, of course, was a godsend. 

The shrikes—there must have been a pair—lived near a wire fence, and on slow summer days I would go out and check their line. The catch, as I recall, was mostly insects: dragonflies, big fat cicadas, the gaudy but klutzy grasshoppers called lubbers, or Georgia thumpers. But there was the occasional field mouse or fence lizard, and once a green snake. With all that, I never actually got to see a shrike make its kill or stake out its prey. 

Shrikes’ affinity for fencelines may be one reason for their decline. One Texas study found a disproportionate number of road-killed shrikes, and vehicle collisions accounted for 29 percent of winter mortality in a Virginia sample. The birds fly low, with a distinctive undulating motion, at about the right height to collide with oncoming traffic. Nests along roadsides may also be more accessible to feral cats and other predators. 

More than that seems to be going on, though. Changes in land use have had a major impact on shrikes. Ironically, these birds may have benefited at first when the eastern forests were replaced by a mixed landscape of small farms, pastureland, woodlots, and hedgerows. But the rise of the megafarm left no room for them. In California, shrike-friendly habitats like oak savanna and coastal sage have given way to orchards, vineyards, and housing. Shrikes, which winter from California south to Chiapas, may be affected by changes in wintering areas as well, but the dynamics are unclear.  

Predatory birds, even smaller ones like shrikes, eat relatively high on the food chain, so pesticide effects have been implicated. But the evidence is less than conclusive. One California study found no difference in eggshell thickness before and after DDT was banned. In Illinois, however, thinner eggs had higher concentrations of the DDT breakdown product DDE. Overall, the loggerhead shrike’s decline coincided with the use of organochlorine pesticides beginning in the 1940s. Dieldrin exposure has been shown to delay the development of hunting behavior in young shrikes. Beyond direct effects on the birds, insecticides may also have reduced the prey base available to feed nestlings. 

For reasons that remain unclear, loggerhead shrikes seem particularly vulnerable just after fledging. A researcher in Indiana found that 46 percent of young shrikes died within a week of leaving the nest, and there’s comparable data from Alberta and Virginia.  

This is beginning to look like one of those Murder on the Orient Express situations: too many suspects, no smoking guns. 

Until causation becomes clearer, it’s going to be hard to recommend conservation measures. Let’s hope the economic crunch has left a pot of money somewhere for shrike research.