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Many bird species have been successfully introduced beyond their natural range, some becoming more abundant in their new environment than in their country of origin. In this study, bird density was measured at 2 study areas comprising a total of 48 recreational parks in northern England and Canterbury, New Zealand, for 10 focal species (native to the former, introduced to the latter). Site characteristics and presence of other bird species were also recorded and investigated as potential explanatory factors for differences in density between the 2 study areas. Common redpoll, common starling, European greenfinch and house sparrow had significantly higher densities at the New Zealand sites. Analysis using generalised linear models revealed a negative relationship between common starling density and proportion cover of trees and shrubs, and a positive relationship between common redpoll, common starling and European greenfinch densities and site species richness. However, since there were no significant differences in site characteristics or site species richness between study areas, these relationships could not account for higher densities at the New Zealand sites. There was an apparent negative relationship between densities of common starling and house sparrow and foraging guild diversity, suggesting that interspecific competition may contribute to differences in density between study areas. The proportion of variation explained by the models was relatively low, suggesting that there may have been missing variables that influenced species density. More detailed study of a wider range of variables is required to investigate this further.