A manual digit found in Aves that is the most preaxial position and is morphologically similar to digit 1 in the standard tetrapod configuration and develops from embryonic digit 2, with contributions from embryonic digit 1. [ https://github.com/obophenotype/uberon/issues/247 http://www.ncbi.nlm.nih.gov/pubmed/10220427 https://github.com/obophenotype/uberon/issues/264 ]