Tropical birds take small risks

The life history of tropical birds differs from that of their temperate counterparts by late start of reproduction, small clutch sizes, and high rates of adult survival. Thus, tropical species should have greater residual reproductive value than temperate species. Therefore, tropical birds can be predicted to take smaller risks than closely related temperate birds in order not to jeopardize their prospects of survival, which is the single most important component of fitness, and which is greater in tropical than in temperate species. We estimated flight distances as a measure of risk-taking behavior of common species of birds for populations living in tropical areas in China (mainly Hainan) and in temperate Europe (mainly Denmark and France), predicting that flight distances should be longer in tropical than in temperate populations, and that the difference in flight distance between these 2 environments should be positively correlated with the difference in clutch size. Mean flight distance was more than twice as large in tropical compared with temperate populations for 25 pairs of taxa. The difference in flight distance between tropical and temperate taxa decreased with the difference in clutch size between the 2 environments. These findings are consistent with the hypothesis that tropical birds take smaller risks than closely related temperate taxa to minimize the risk of early death due to predation.