Anthraquinone repellent to reduce take of non-target birds from zinc phosphide rodenticide applications

We evaluated anthraquinone as an avian repellent to reduce take of non-target birds from zinc phosphide rodenticide applications. We observed zero mortalities and no overt signs of zinc phosphide toxicosis among 20 Canada geese (Branta canadensis), 24 horned larks (Eremophila alpestris), and 47 ring-necked pheasants (Phasianus colchicus) offered baits treated with 1% or 2% anthraquinone and 2% zinc phosphide (target concentrations; wt/wt) during laboratory performance experiments. Thus, anthraquinone successfully prevented consumption of 2% zinc phosphide baits among non-target birds in captivity. We observed 10% mortality among black-tailed prairie dogs (i.e., target rodent; Cynomys ludovicianus) offered oats treated with 1% anthraquinone and 2% zinc phosphide, and 30% mortality among black-tailed prairie dogs offered oats treated with 2% anthraquinone and 2% zinc phosphide. Upon completion of our experiments, chemical analyses indicated that actual concentrations were 1.66% and 1.45% zinc phosphide among oats treated with1% anthraquinone + 2% zinc phosphide, and 2% anthraquinone + 2% zinc phosphide, respectively. We observed 24-37% repellency during a concentration-response test with black-tailed prairie dogs offered corn seeds treated with 0.5-4% anthraquinone (target concentrations; wt/wt). Thus, anthraquinone may affect consumption of repellent-treated rodenticide baits for black-tailed prairie dogs. Supplemental performance testing and field efficacy studies (e.g., 0.25-0.5% anthraquinone and 2% zinc phosphide, actual concentrations; wt/wt) are necessary for further development of an efficacious, bird-repellent rodenticide bait.