Rats vs rats
Arnold Trachtenberg (Fri, 03 Sep 2004 14:10:49 PDT)

* Effects on other organisms: Zinc phosphide is also toxic to
non-target mammals when ingested directly [8]. Nearly 60 studies
have been conducted on the toxicity of this rodenticide to wild
animals. Secondary toxicity to mammalian predators (animals eating
other animals that had been exposed to the compound) from zinc
phosphide is rather low, primarily because the compound does not
significantly accumulate in the muscles of target species [8].
Some of the toxic effects to predators have been due to the
ingestion of zinc phosphide that was in the digestive tract of the
target organism. Studies on secondary organisms have focused on
coyotes, fox, mink, weasels, and birds of prey. Under field
conditions, most of the toxic effects to non-target wildlife are
due to direct exposures resulting from misuse or misapplication of
this rodenticide [8].

From

http://extoxnet.orst.edu/pips/zincphos.htm

Arnold