Dr. Royer's personal research since 1986 has been focused principally on distribution and ecology of Great Plains and North American arctic butterflies. As Great Plains Coordinator for The Lepidopterists' Society Season Summary, he is responsible each year for gathering, editing, and publishing formal records of butterfly occurrences in the Great Plains states and central Canadian provinces through News of the Lepidopterists' Society. Over more than a decade, work on this project has involved field assistance from a number of North Dakota high school teachers and their students. His second edition of Butterflies of North Dakota, published by MSU in 2003, remains the only comprehensive guide to the state's butterflies. He has also contributed materially to several other books on butterflies and butterfly conservation.
Through cooperative agreements with the Northern Prairie Wildlife Research Center in Jamestown, North Dakota, Dr. Royer produced several site-specific butterfly monitoring guidebooks for use by federal land managers across the state. He has directed a number of projects involving rare and endangered butterfly species, most recent among them inventories in the Dakotas for the
U.S. Fish and Wildlife Service, the Grasslands Ecosystem Initiative of the Northern Prairie Wildlife Research Center, and the North Dakota Natural Heritage Program. Since 1988 he has also been studying speciation and habitat characteristics of several arctic and subarctic butterfly species that live beyond or near treeline in the the Yukon, Northwest Territories, and Nunavut.