Guy Tudor, a self-taught ornithologist and wildlife illustrator whose detailed field guides helped shape the study of neotropical birds, died July 14 at Stony Brook Eastern Long Island Hospital in Greenport, New York. He was 91. The cause of death was pneumonia, according to a close friend.

Tudor’s career spanned decades and was distinguished by his meticulous watercolors and gouaches portraying some of the world’s most obscure and colorful bird species. Before the widespread availability of digital databases, his work provided vital visual references for both amateur and professional birders. His field guides, including "A Guide to the Birds of Venezuela" (1978), "A Guide to the Birds of Colombia" (1986), and the multivolume "The Birds of South America" (1989, 1994), co-produced with ornithologist Robert S. Ridgely, remain landmark publications. These guides cover nearly 1,700 species prized by scientists and enthusiasts alike.

Tudor, born Guy Adwill Tudor III on September 28, 1934, in New York City, was raised in Manhattan’s Yorkville neighborhood. His father, Charles Tudor, an accomplished journalist and founding art director of Life magazine, influenced his early interest in illustration. Tudor attended Governor Dummer Academy (now The Governor’s Academy), Princeton University, and Yale before serving in the Army.

Though described as a self-professed curmudgeon, Tudor was also known as a dedicated mentor who helped launch the careers of many wildlife artists and researchers. His passion extended beyond birds to include butterflies; in 1984, he co-founded the New York City Butterfly Club and later played a key role in establishing the North American Butterfly Association, which monitors insect population declines linked to environmental threats.

Tudor’s expertise was not only artistic but behavioral, capturing unique traits and movements of species like the shy Spadebill flycatcher and the vibrantly plumed Keel-billed Toucan and Scarlet Macaw. His work was recognized with a MacArthur Fellowship in 1990, an acknowledgment of his ability to bring elusive tropical birds to life through art.

Despite a modest life centered in a small Queens apartment, Tudor’s reach was global. He traveled extensively, logging sightings in more than 50 countries. His brother Matthew recalled an incident in Venezuela where Tudor’s intense birdwatching antics attracted the attention of local military forces.

Colleagues noted Tudor’s deep concern about environmental degradation. Bird illustrator John A. Gwynne Jr. highlighted Tudor’s alarm over habitat loss and species decline, quoting Tudor’s metaphor that “infidels have invaded my church” in reference to threats facing the natural world.

Tudor was married twice, to Elizabeth Linko and Michelle Le Marchant, both of whom predeceased him. A son from his first marriage died in infancy. He is survived by his brother, Matthew Tudor.