Background: Antibodies from alternative immune hosts provide insights into novel mechanisms of antibody diversity in restricted germ-line repertoires. Results: The high-resolution crystal structures of the first two chicken single chain antibodies (scFv) with prototypical binding sites are described. Conclusion: Chickens exhibit unique canonical classes in the CDRL1. Significance: Aves employ distinct mechanisms to generate diversity resulting in unique binding-site topologies. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.