To minimize hazards to birds, do not apply zinc phosphide bait to bare ground, areas without vegetation, or in piles. is in one section. The question, if a vole dies from the poison, and is eaten by magpies, or other critters, are they affected?
Gallatin County Montana
Sorry for the late response, I was traveling for the holiday without my usual computer resources. This is not my area of expertise, but generally speaking poisoned carcasses of animals large and small can pose a threat to scavengers (birds and mammals). I am unfamiliar with zinc phosphide; however, this fact sheet says it has a lower risk of secondary poisoning (http://npic.orst.edu/factsheets/archive/znptech.html). I would be glad to but you in touch with our pesticide expert Cecil Tharp (http://animalrange.montana.edu/directory/faculty/1588736/cecil-tharp).