Control of crows in almonds by broadcast distress calls

The American crow (Corvus brachyrhynchos) is the primary avian pest in almond orchards of California, causing significant financial loss to growers. Although few good strategies are available for controlling birds in agricultural areas, preliminary work in small blocks has demonstrated the potential success of broadcast distress calls for reducing damage caused by crows. Based on these findings, our objective was to evaluate the effect of crow alarm/distress calls on damage levels in large commercial almond orchards. We recorded calls of crow chicks in the nest and obtained calls from dying adult crows, common ravens (Corvus corax), and ring-billed gulls (Larus delawarensis) from other sources. These calls were broadcast to crow flocks to select the ones eliciting the most favorable response. An electronic circuit was designed to broadcast four crow distress calls in the field on a rotational basis. Tests were conducted in paired orchards from three regions in the central valley of California over two growing seasons (2002-2003). In the first year, damage was surveyed without treatment. In the second year, damage was surveyed with one orchard in each pair treated using distress calls. In two of the three regions, we found significant differences in damage distribution between years at both untreated and treated sites. In the other region, the crow population and resulting damage were too low to show a difference. Pooling regions and separating the effect of time from treatment, we demonstrated a significant effect of distress call treatment. The savings due to broadcast call treatment were estimated to be $12 and $25 per ha in the two regions that had significant damage. Finally, a protocol is recommended for treating commercial almond orchards with crow distress calls.