Flaco died from a combination of the ingestion of four different rodenticides and pigeon herpesvirus.
The pigeon herpesvirus was contracted from the consumption of pigeons, which Flaco had been preying on towards the end of his life. On its own, it did great harm to Flaco and would have been fatal eventually.
Of course, rodenticide is used abundantly in New York City, with no regard to the major damage it does up the food chain. It too did great damage and would have been fatal.
The damage to Flaco’s brain caused by both the herpesvirus and rodenticides were almost certainly the major factor for his flying into the building.
In addition to his brain, Flaco suffered from major inflammation in his spleen, bone marrow and other systems.
