People often ask how I could possible hope to locate a bird as rare as an Imperial Woodpecker in an area as vast as Mexico's Sierra Madre Occidental—that is, if there are any of them left at all. It's a fair question. Unless you're lucky enough to see one fly past close enough to make a positive identification or hear one calling or drumming, you could walk right past an Imperial Woodpecker as it clung to the other side of a tree trunk and never know it was there.
To help increase our odds, we used a custom-made device to mimic the unique double-knock drumming done by most Campephilus woodpeckers—which sounds like BAM-bam, with the second impact hitting only a fraction of a second after the first, sounding almost like an echo. Martjan Lammertink designed the device, which consists of a birdhouse-like wooden box lashed to a tree trunk to act as a resonator, and a striker, which resembles two lengths of broomstick, each about a yard long, with a pivot bolt in the center. To make the sound, you swing the striker in an arc, hitting the box hard with the first stick while the other one swings over the pivot bolt, hitting the box less than a second later, producing a near-perfect rendition of a Campephilus woodpecker double-knock.
Martjan tried out the double-knock box in Latin America and was able to draw responses from two species of Campephilus woodpeckers, the Pale-billed and Magellanic (which are relatives of the Ivory-billed and Imperial woodpeckers). To see this device in action, watch "Talking with a Pale-billed Woodpecker."
(Photo by Tim Gallagher)
Above, Martjan Lammertink uses a GPS unit to record the precise location of each double-knock session during our expedition in the Sierra Madre.