Potential risk to ring-necked pheasants from application of toxic bait for blackbird control in South Dakota

Blackbird (Icterinae) damage to sunflowers in the northern Great Plains can be locally severe. One approach to alleviating depredation pressure is to reduce blackbird populations through application of brown rice bait treated with the avicide DRC-1339. Because such baiting can potentially affect nontarget species, we conducted pen and field trials to evaluate the potential risk from avicide baiting to ring-necked pheasants (Phasianus colchicus). Although most female pheasants in pen tests preferred cracked corn and sorghum, 2 of 12 birds preferred brown rice. In 4-day trials within a 0.2-ha flight pen, pheasant consumption of brown rice from bait swaths simulating field bait applications was not affected by the presence of an alternate bait swath of cracked corn. Pen trials to evaluate possible avoidance responses following a sublethal dose of DRC-1339 showed that 2 of 7 birds shifted from their previously preferred feeding sites following exposure to the avicide. During March and April 1995, we recorded pheasant numbers in 6 pairs of 0.8-ha plots in corn stubble fields that were either baited with brown rice or were designated as reference plots. Overall, use of test plots was low, but at the most heavily used sites, pheasants visited reference plots more than baited plots (P = 0.004). We conclude that (1) pheasants will eat brown rice treated with DRC-1339; and (2) although chances of exposure to an acute lethal dose can be reduced by increasing the dilution, harmful repeated doses could be obtained because avoidance of feeding sites, following sublethal exposure, cannot be assumed.