Variation in peak swarm size (A) and the total number of couples per swarm (B) over time in each of the three zones. The box of each box whisker plot extends from the first to the third quartiles (the interquartile range, IQR), the whiskers extend to extreme observations up to 1.5 times the IQR, beyond which observations are marked by squares. The median and the mean are marked by line and a dot. The color of the dot indicates the zone. Sample size per date ranged between 7 and 10 swarms. Insets: Variation in swarm size (A) and the total number of couples per swarm (B) among marker types.