Guy Tudor, a self-taught ornithologist and wildlife illustrator whose detailed field guides helped shape the work of generations of naturalists, died on July 14 at Stony Brook Eastern Long Island hospital in Greenport, New York. He was 91. According to a close friend, Claudette F. Welch, pneumonia was the cause of his death.

Throughout a career spanning several decades, Tudor specialized in the birds of the Neotropics, focusing particularly on songbirds native to Central and South America. Long before digital databases like eBird became widely accessible, Tudor meticulously documented avian species through his watercolors and gouaches, which were noted for their precision and ability to capture the distinct characters and behaviors of a range of bird species.

Known for his distinctive illustrations of species such as the rufous-breasted leaftosser, lesser hornero, and the elusive spadebill—an often shy tyrant flycatcher—Tudor’s artistic talent was complemented by his deep knowledge of ornithology. His work earned him a MacArthur fellowship in 1990 in recognition of his skill in portraying the unique plumage, behavior, and motion of obscure species.

Tudor’s illustrations became central references in major bird guides, including “A Guide to the Birds of Colombia” (1986), “A Guide to the Birds of Venezuela” (1978), and the “Field Guide to the Songbirds of South America” (2009). He also collaborated with ornithologist Robert S. Ridgely to produce the multivolume “The Birds of South America,” published in 1989 and 1994, which covered nearly half of the region’s identified avian species.

Although his work commanded respect in scientific circles, Tudor’s approach targeted both professional ornithologists and dedicated amateur birders. Colleagues described him as a natural mentor who helped nurture the careers of many young scientists and wildlife artists despite his reputedly cantankerous demeanor.

Born on September 28, 1934, in New York City, Guy Adwill Tudor III was the son of Charles Tudor, a journalist and artist noted for his work with the Resettlement Administration during the Great Depression and for designing Life magazine’s iconic logo. Raised in Manhattan, Tudor attended Governor Dummer Academy, then completed studies at Princeton and Yale before serving in the U.S. Army.

Tudor’s personal life included two marriages, both ending with the deaths of his spouses, Elizabeth Linko and Michelle Le Marchant. A son from his first marriage died in infancy, and his brother Matthew survives him.

Beyond birds, Tudor’s interests extended to other winged creatures, particularly butterflies. He was a founding member and longtime president of the New York City Butterfly Club and helped establish the North American Butterfly Association, contributing to efforts that track and highlight declines in butterfly populations due to environmental threats including pesticides and climate change.

Peers recall Tudor not only as an accomplished artist and scientist but also as a passionate conservationist alarmed by the ongoing degradation of natural habitats. His friend John A. Gwynne Jr., who worked with him on several field guides, noted that while Tudor was sometimes seen as a curmudgeon, his edge stemmed from deep concern for the natural world’s fragility and the encroachment of human impact on wild places.