1.75" for event likely held in Buffalo judging by the graphics centered by text "N.Y. State Shoot 1899/Audubon Club." This rare button reflects the fact that in its early years, club members actually shot birds to study them rather than merely counting species. This is the earliest button we've seen with the word "Audubon" and it pre-dates New York State's Audubon Plumage law which was not passed until 1910 as well as the federal Migratory Bird Treaty Act passed in 1918. Has W&H backpaper. Exc. and displays Mint. Rare.