The role of predation risk in stopover habitat selection in migrating bramblings, Fringilla montifringilla

Migrating bramblings (Fringilla montifringilla) on migratory stopover in southern Sweden normally forage in summer rape (Brassica napus) stubble fields. However, in years with beech mast crops many finches switch to beech forests. Both predation rate and instantaneous energy-intake rate were lower in the beech forest than in the rape fields. The ratio of predation risk to energy-intake rate was only half as high in the beech forest. This ratio is proportional to the probability of predation over accumulated distance. By minimizing this ratio, migrating birds will maximize the probability of reaching their destination. Thus, bramblings seem to prefer avoiding predation to attaining maximum speed of migration. However, the importance of maximum migration speed cannot be ruled out. Energy-intake rate was very high, and the maximum speed of migration may be constrained by the birds' reaching a maximum limit of sustained metabolizable energy-intake rate in both habitats. [Behav Ecol 1990;1:102-106]