CANTERBURY, U.K.--When bird ecologists want to get seabirds to settle down in a promising nesting site, they lure them by broadcasting recorded calls. This works for birds that flock together, but no one knew if the same trick would succeed with territorial songbirds--which normally sing to keep fellows off their territory, not call them closer. Now the method has proved its mettle for an endangered songbird, the black-capped vireo in central Texas.
Except for nesting pairs, black-capped vireos tend to avoid each other, belting out their songs to demarcate their territory. Nevertheless, Michael Ward and Scott Schlossberg, both ecologists at the University of Illinois, Urbana-Champaign, suspected that young vireos might be attracted to the songs of their elders, in order to learn how to choose a nesting area. They tested their theory by playing recorded calls at suitable nesting sites near Fort Hood, north of Austin, Texas. The faux-chirping took place in spring as the birds were returning from overwintering in Mexico.
In the first year of the study the pair attracted 73 vireos to settle at five experimental sites, Ward said here 17 July at the annual meeting of the Society for Conservation Biology. No vireos settled at two silent sites. Moreover, birds who were looking for a nesting site for the first time were particularly attracted by the recordings. And they liked what they found: This year, Ward said, almost all birds from one test site returned, even though the call boxes had been removed. Previously, the U.S. Army had unsuccessfully tried for 12 years to establish black-capped vireos on the base.
The effectiveness of the method in this new context impresses Ken Norris, a bird ecologist at the University of Reading, U.K. He says it could be used for other migrating birds and might be especially helpful for speeding up the settlement of areas set aside for conservation--a process that often takes years.