RELATIONSHIPS BETWEEN ABUNDANCES AND LIFE-HISTORIES OF BRITISH BIRDS

1. Attempts to explain the abundances of species in assemblages using the biology of the species concerned have primarily concentrated on sp ecies body size. Body size is considered to be an important determinan t of abundance, because it is related to resource requirements via met abolism. 2. There are a number of problems with this approach, includi ng the rather poor correlation of body size with abundance in many ani mal 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 dete rmining species abundance, but their effects have never been tested. 3 . Here, we use correlation and phylogenetic methods to test what aspec ts of the life histories of British birds, if any, are related to thei r abundances. Specifically, we are interested in looking for better co rrelates of abundance than species body size; we test specific hypothe ses linking species metabolic rates, birth and death rates, and life-h istory 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 p roduction explain the most variation in bird abundances, independently of body size, whereas the relationship between body size and abundanc e is generally not significant once other traits are controlled for. W ithin avian taxa, no variables are consistently correlated with abunda nce. 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 produ ction. We find no evidence that metabolic rate is an important determi nant of the abundances of British birds. 6. We tentatively suggest a h ypothesis for why fast offspring development is related to the abundan ces of British birds.