Consistent differences among individual monarch butterflies (Danaus plexippus L.) in flight activity at low temperatures

Previous work suggested differences in allozyme frequencies between samples of monarch butterflies collected at different times of the day. This study examines the prediction that some individuals are active consistently earlier in the day than others. Four specific hypotheses were tested: (1) Individuals caught early on one day were more likely than those caught late to be caught early on subsequent days. This was true in some experiments. (2) Individuals caught early in the field were more likely than those caught late to fly early in outdoor flight cages. This was true when outdoor temperatures were low (between 10 and 20^oC) but not when they were above 20^oC. (3) Individuals caught early in the field were more likely to be able to fly at low body temperatures than those caught late. This was not true. (4) Individuals that flew early in outdoor flight cages were more likely to be able to fly at low body temperatures. This was not true. Overall we conclude, on the basis of field and flight cage experiments, that some individuals are active consistently earlier in the day than others. The lack of a relationship between field and temperature cabinet results indicates that this is not purely a result of differences in ability to fly at low body temperatures. The implications of these results are discussed.