Cooperative Fish and Wildlife Research Units Program: Montana Cooperative Wildlife Research Unit
Education, Research and Technical Assistance for Managing Our Natural Resources

Life history theory predicts a trade-off between annual adult survival and fecundity. Globally, clutch size shows a latitudinal gradient among birds, with south-temperate species laying smaller clutches than north-temperate species, but larger clutches than tropical species. Tropical birds often have higher adult survival than north-temperate birds associated with their smaller clutches. However, the prediction that tropical birds should also have higher adult survival than south-temperate birds because of smaller clutch sizes remains largely untested. We measured clutch size and annual adult survival for 17 south-temperate African species to test two main predictions. First, we found strong support for a predicted trade-off between adult survival and clutch size among the south temperate species, consistent with life-history theory. Second, we compared our clutch size and survival estimates with published estimates for congeneric tropical African species to test the prediction of larger clutch size and lower adult survival among south-temperate than related tropical species. We found that south-temperate species laid larger clutches, as predicted, but had higher, rather than lower, adult survival than related tropical species. The latter result may be an artefact of different approaches to measuring survival, but the results suggest that adult survival is generally high in the south temperate region.