A flock of geese in the San Francisco Bay Area were likely exposed to an anticoagulant rodenticide, according to findings released in February from a postmortem examination by the California Department of Fish and Wildlife’s Wildlife Health Lab, or WHL.

In fall 2020, approximately ten Canada Geese shot by hunters in Contra Costa County were found to have blue-colored fat.

The WHL conducted an examination on one of the carcasses and detected Diphacinone, an anticoagulant rodenticide, in the goose’s liver.

“Rodenticide baits like diphacinone often contain a dye which identifies the bait as a poison. We suspect the blue-colored fat was caused by ingestion of a diphacinone bait containing blue dye,” said CDFW Senior Environmental Scientist Krysta Rogers, an avian disease specialist.

Diphacinone is a first-generation anticoagulant rodenticide that typically requires multiple feedings to cause death. It is labeled for use for agriculture, landscape maintenance, and in and around homes and businesses. Canada geese often forage in flocks and readily feed on grasses, sedges and seeds including agricultural grains such as corn, alfalfa and oats.

CDFW encourages hunters to report any unusual findings in harvested wildlife and not to consume any part of an animal with blue fat or other abnormality. Incidents may be reported to the CDFW’s Wildlife Health Lab at This email address is being protected from spambots. You need JavaScript enabled to view it. or 916-358-2790.

Pesticide applicators are urged to use care when using rodenticides so as not to expose wildlife. Prior to application, it is important to ensure non-target wildlife are not using the area where the pesticide is to be applied.

For more information, please visit the rodenticides page on CDFW’s website. For questions about pesticide use and regulations, or to report misuse, please contact your County Agricultural Commissioner’s office.