Edward Ayer (1841-1927) has been the principal benefactor of the Library. Instrumental in the founding of the Museum, and serving as its first President, Ayer gave great attention to the Library from the moment it was organized. In 1894 he presented to the Library his private ornithology collection of 400 carefully chosen volumes and his collection of ichthyological works. In the same year he purchased the 600 volume collection ornithologist Charles Barney Cory (1857-1921). In 1921, Ayer donated over 1600 volumes from the ichthyological and angling collection formed by publisher Robert Clarke of Cincinnati.
All these collections are distinguished by their rich retrospective coverage of these fields, which is an essential resource for ongoing biological systematics. These collections are also marked by the beauty of their scientific illustrations, the majority of which are hand-colored engravings and, from the mid-nineteenth century on, hand-colored or color-printed lithographs. Ayer continued to develop these collections through his own acquisitions and through an endowed fund for book acquisitions by the Library in these areas. The continuous development of the Ayer Ornithology Library during Ayer's lifetime was driven by his desire that it should be among the foremost collections of its kind. His success in achieving this goal became evident in the year before his death when the Museum published John Todd Zimmer's Catalogue of the Edward E. Ayer Ornithological Library (Chicago, 1926). This classic of ornithological bibliography clearly confirmed the Ayer Collection as one of the finest in the world. After Ayer's death, his endowments for the library were combined into the Library Fund, whose earnings have provided the core support for book acquisitions for the ensuing seven decades.