Great question Dennis!
The history is reviewed in detail in the Foreward of Guy's edition by Stephen Havera from the Illinois Natural History Survey. Essentially, Francis H. Kortright's The Ducks, Geese, and Swans of North America was published in 1942. With permission and support from Glen Sanderson head of the Wildlife Research section of the Natural History Survey, his graduate intern Frank Bellrose revised and updated the classic in 1976, with subsequent reprints and revisions in 1978 and 1980 respectively. Frank continued to work on an additional revision until his death at age 88 in 2005. Discussion ensued about whether revision efforts should proceed, and Guy Baldassarre stepped forward to accept an invitation from Richard McCabe, retired Vice President of the Wildlife Management Institute, to assume the enormous task.
Guy was quoted, "It's been a beast to do, but loads of fun." He focused on expanding species accounts and new information from the previous 30 years, presenting in-depth biology of each species with new and improved color photos and range maps. He also added habitat, courtship displays, survival and recruitment, brood parasitism and molts and plumages sections. He wanted to make it bigger and bolder to satisfy the reader but fit within the original mission of Kortright, "to help in the conservation of of our wildlife."
I hope this answers your question.
Thanks for asking,
Mik