Inconsistencies among secondary sources of chukar partridge (Alectoris chukar) introductions to the United States

An important source of information concerning the fates of intentionally introduced exotic bird species has been collections of historical data that sometimes include species released, numbers released, locations of release, and establishment success. These data have been used to assess potential predictors of establishment success such as propagule pressure, site-level factors, and species characteristics. In order to better understand the limitations of such historical compilations, we compared data for the Chukar (Alectoris chukar) introductions to the USA from two often used compilations and from other sources associated with Chukar introduction programs. We found the major compilations of Long (1981) and Lever (1987) are inconsistent and likely to be incomplete, and inaccurate, in terms of the taxa introduced, the numbers introduced, and the fates of these introductions. Propagule pressure analyses have often assumed that every bird in every release must be summed to represent the propagule pressure necessary for establishment. We found, however, that large numbers of birds were released into states and counties with already established populations. Additionally, in numerous states very large numbers of Chukars were unsuccessfully released. We conclude that site-level factors were more important influences of establishment success than propagule pressure was.