Contrasting phenotypic correlations in food provision of male Tengmalm's owls (Aegolius funereus) in a temporally heterogenous environment

Abstract

We examined the food provision rate of male Tengmalm's owls,Aegolius funereus, during one 3 year vole cycle consisting of consecutive low, increase and peake vole years. The data were collected in the midnestling period when males provisioned the whole family. In the low vole year, males with a low loading index (g/cm2) of flying area fed their offspring more often than did males with a high loading index, whereas in the peak vole year the opposite trend was evident. Similar relationships were found in the food mass provisioned to the nest. In the increase vole year, male body size had no effect on feeding efficiency. In the peak vole year, when large voles are abundant, heavy males preyed on larger voles than were generally available in their territories, indicating that largeness may increase strike power in hunting attempts. In the low vole year, when breeding is costly due to food scarcity and extensive hunting area, small males are more economical fliers and efficient hunters than large males. The contrasting trends in correlations between male size and feeding efficiency in years of vole abundance versus scarcity suggest that no fixed phenotype may most efficiently cope with variable food supply.