Characteristics and Sexual Functions of Sky-dancing Displays in a Semi-colonial Raptor, the Montagu’s Harrier (circus Pygargus)

-Raptors perform spectacular aerial displays but our understanding of their complexity and functions is still limited. We describe the characteristics of Montagu ́s Harrier (Circus pygargus) sky-dancing displays and evaluate possible sexual functions. Sky-dancing was performed by both sexes, but much more frequently by males. Although occurring throughout the breeding season and into the post-fledging period, frequency of sky-dancing displays by males was much higher during the pre-laying period (from 3 wk before laying, when pair formation is occurring, until just after laying onsetQUERY: OK? THE PERIOD SHOULD BE DESCRIBED AS “FROM... UNTIL....”. IT WAS UNCLEAR AS WRITTEN). Pre-laying display frequency by males and females increased with colony size and vole abundance. A Principal Component Analysis on display characteristics (height, speed, number of loops, twists, undulations and calls) identified three main axes (PC1-3). PC1correlated with all parameters, identifying displays that started at higher altitude, descended at higher speeds, with higher frequencies of twists, undulations, loops and displaying calls. PC2 opposed high and fast displays with low complexity (in term of twist and undulation frequency) to displays that were slower, started from lower altitude, but were more complex. PC3 contrasted displays with loops to others with undulations. PC1 scores differed between sexes, with males having more intense displays (greater PC1 scores) than females. Male displays were more intense in larger colonies and when voles were more abundant, but less intense when wind speed increased, or when males displayed while carrying prey. Variation in PC2 and PC3 scores in males was mostly explained by wind conditions: displays started from higher and were faster when there was no wind, and aerial displays tended to have more loops instead of undulations in more windy conditions. Our results support the hypothesis that Montagu ́s Harrier sky-dancing displays performed during the pre-laying period, particularly the most elaborate ones, are costly to produce and may thus potentially honestly advertise individual