The IOC Pakistan checklist is a subset of species from the complete IOC world list, based largely on the distribution and status data provided by Avibase and Birds of South Asia1. This provides an alternative with more up to date taxonomy than the OBC Pakistan list.
1 Rasmussen, P.C. & Anderton, J.C. 2005. Birds of South Asia. The Ripley Guide. Vols 1 and 2. Smithsonian Institution and Lynx Edicions, Washington D.C. and Barcelona.