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.