The form and function of ascending flights in Colias butterflies

1. Pairs of butterflies are often seen in high, spiraling interactions called ascending flights. Interactions of this type and related male-female interactions are studied with a special effort made to document their temporal structure, context, and function for butterflies in the Colias eurytheme-C. philodice species complex. 2. Ascending flights occur only between males and mated females (not necessarily of the same species) and do not end in copulation. Typically, they begin with a level-flight phase followed by a female-initiated ascending phase that ends as much as 20 m above the ground when the pair separates an average of 17 s after initial contact. 3. Observations on the duration and form of male-female interactions that did not result in ascending flights suggest that many males depart before the female initiates an ascending flight. 4. Analyses of interactions between males and tethered females demonstrate that with ascending flights, females are able to curtail male courtship attempts and minimize time spent detained from other activities. The relationship between the structure and function of ascending flights and the variability in male courtship persistence is discussed.