Frederick II, the Holy Roman Emperor born on this day in 1194, is remembered for fighting with the Pope so much he was excommunicated, for promoting literature and science in Sicily and for his fascination with birds.

De arte venandi cum avibus, or On the Art of Hunting With Birds is now considered to be “the first book devoted entirely to ornithology,” writes author Janice M. Hughes. The Holy Roman Emperor, a keen falconer, drew on thirty years’ experience working with birds of prey and included observations about natural behaviors and feeding habits as well as falconry.

“Frederick’s interest in bird migration was substantial,” Hughes writes. “His book includes discussions of the types of birds that migrate and where to find them, why they migrate, where they go and when, even where they stop along the way. In general he attributed birds’ seasonal movements to oncoming inclement weather and resulting shortages of food, but he was careful to note that differing tolerances of these conditions led to varying migratory strategies. For example, hardier species often traveled shorter distances, and species with particular food preferences might have to migrate farther in order to find them in abundance.”

Falconry became popular in Europe during the Middle Ages, starting around 500 A.D., writes PBS. “It was the sport of royalty for centuries, with the possession of falcons and other birds of prey considered a status symbol.” Frederick II, who the Richard III Society calls “the greatest falconry enthusiast of all time,” definitely had an influence on falconry. But his book, and the attitude it takes to birds, also marked the beginning of the scientific study of the winged creatures for their own sake–that is, the beginning of modern ornithology.

Frederick II was an odd figure: His nickname was “Stupor Mundi” or “Wonder of the World” because he was gifted in many areas, writes Brown University. His skepticism and focus on removing Italy from papal control, making it instead part of the more secular Holy Roman Empire, marked him as a modern leader. The orderly approach he took to studying birds–developing, through observation, rules and principles of avian behavior specific to individual species–was likewise modern.

The falconer was influenced by Aristotle’s system of classification as articulated in his text On Animals. In that text, as Frederick II wrote, the Greek philosopher divided birds into three categories: waterfowl, land birds and “neutral birds” that spend time both in the water and on land–like the duck. The emperor further divided birds within these categories as well as into categories relating to what they ate and whether they attacked other animals, as raptors do. This approach to birds drew on Aristotle’s thought but took the idea of classification farther. These ideas would be picked up during the Renaissance and beyond.