Individual study: Broadcasting of crow distress calls as a non-lethal deterrent significantly reduces almond losses to American crow Corvus brachyrhynchos in orchards in California, USA
Houk A., Delwiche M., Gorenzel P. & Salmon T. (2002) Electronic repeller and field protocol for control of crows in almonds in California. 130 Proceedings-Vertebrate Pest Conference, 21, 130-135.
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Reduce conflict by deterring birds from taking crops using bird scarers
A controlled, paired study in central California, USA (Houk et al. 2002), found that two of three almond orchards with crow distress calls broadcast had reduced damage from American crows Corvus brachyrhynchos in 2003, compared to 2002, when broadcasts were not used. Damage reduced from 6.0 kg/ha to 1.1 kg/ha, and 18.2 kg/ha to 4.8 kg/ha. There was no change in three paired sites without broadcasts. Orchards were 16-30 ha in area and monitored in June-August. Broadcasting units were deployed at onset of crow damage until almond harvest (1 unit/1.6 ha; hung in trees at 1-2 m) throughout the orchard, moved to a new tree every two weeks, switched to a different call every 3-4 days, broadcast dawn to dusk, each 25 seconds long with approximately 12 min between calls.