3 literature references for Falco columbarius richardsoni Ridgeway, 1871:

Author:
Year: 1996
Title:
Source: database, NODC Taxonomic Code
Author: Dickinson, Edward C., ed.
Year: 2003
Title:
Source: The Howard and Moore Complete Checklist of the Birds of the World, 3rd edition
Author:
Year: 2005
Title:
Source: website, Howard & Moore [...] Corrigenda 3.1f