Table - link
||Kevin J. Gaston & Tim M. Blackburn, How many birds are there? Biodiversity & Conservation, April 1997, Volume 6, Issue 4, pp 615–625 p.619 table 3
||See refs beneath table
||Abstract: "Here, [investigators] use a variety of methods to estimate the global number of individuals for a single taxon, birds."
||P.618 bottom paragraph: "Table 3 gives the same information as Table 2 [BNID 116943], but with estimates for the numbers of individual birds on continents. Averaging these estimates gives a mean of 1432 birds per square kilometre, which extrapolates to 1.95×10^11 individual birds. Summing the numbers of individuals and the extents of the two areas, [investigators] obtain an estimate of 1600 birds per square kilometre, yielding a global estimate of 2.18×10^11 individuals. Alternatively, assuming that the African figure is representative of tropical regions and the Nearctic estimate representative of temperate regions, multiplying up by the land areas of these regions (as calculated above) gives a value of 2.08×10^11 individual birds."