American ornithologist who used DNA to measure genetic similarities among different species of birds. In 1972 Ahlquist and Charles Silbey found that DNA hybridization applied to the classifications of birds. After studying over 1,700 species, they published Phylogeny and Classification of Birds, in which they introduced a revised taxonomy of the world's birds and discussed their evolutionary relationships. Ahlquist and Sibley received the Daniel Giraud Elliott Medal from the National Academy of Science in 1988 for their work.