Nest Predation and Avian Life-History Evolution in Europe Versus North America: A Possible Role of Humans?

Life-history theory predicts that decreased mortality in early life can favor increased fecundity and reduced iteroparity. Similar to other causes of environmental variation, modification of the environment by humans potentially can change age-specific mortality and, hence, affect life-history evolution. Forests were removed throughout western Europe long ago, and nest predation (early mortality) is reduced in human-settled environments there, whereas nest predation is generally increased in areas settled by humans in North America. We controlled statistically for effects of body size and phylogeny and compared songbirds (Passeriformes) of Europe to those of North America and found that nest predation was lower in Europe. Associated with this decrease in early mortality in Europe, fecundity was increased and iteroparity was reduced via decreased adult survival rates, as predicted by theory. Moreover, continental differences were greater for species that were more vulnerable to nest predation (open-nesting species) than for species that used safer nest sites (hole-nesting species). These results suggest that nest predation can be an important influence on avian life-history evolution but that evolutionary constraints of nest predation may have been reduced in European systems because of large-scale modification of the environment.