Relationships between Abundances and Life Histories of British Birds

Attempts to explain the abundances of species in assemblages using the biology of the species concerned have primarily concentrated on species body size. Body size is considered to be an important determinant of abundance, because it is related to resource requirements via metabolism. 2. There are a number of problems with this approach, including the rather poor correlation of body size with abundance in many animal assemblages, and the failure to test whether species metabolism is actually a better predictor of abundance than is body size. In fact, there are many correlates of body size which could potentially be determining species abundance, but their effects have never been tested. 3. Here, we use correlation and phylogenetic methods to test what aspects of the life histories of British birds, if any, are related to their abundances. Specifically, we are interested in looking for better correlates of abundance than species body size; we test specific hypotheses linking species metabolic rates, birth and death rates, and life-history correlates of birth and death rates, with population abundance. 4. Most life-history traits examined correlate with abundance across species, and in many cases the correlations are stronger than that of bird body size with abundance. Traits associated with fast offspring production explain the most variation in bird abundances, independently of body size, whereas the relationship between body size and abundance is generally not significant once other traits are controlled for. Within avian taxa, no variables are consistently correlated with abundance. 5. We find little evidence of a role for death rate as a possible determinant of bird abundance, although birth rate may be important, acting through the speed, rather than the quantity, of offspring production. We find no evidence that metabolic rate is an important determinant of the abundances of British birds. 6. We tentatively suggest a hypothesis for why fast offspring development is related to the abundances of British birds.