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1 June 2013 Characteristics and Sexual Functions of Sky-Dancing Displays in a Semi-Colonial Raptor, the Montagu'S Harrier (Circus pygargus)
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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, sky-dancing displays by males were more frequent during the pre-laying period (from 3 wk before laying, when pair formation is occurring, until just after laying onset). Pre-laying display frequency by males and females increased with colony size and vole abundance. A principle component analysis on display characteristics (height, speed, number of loops, twists, undulations, and calls) identified three main axes (PC1-3). PC1 correlated 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 terms 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 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 quality. Additionally, our observations were consistent with the hypothesis that these displays have both intra- and intersexual functions.

Las rapaces ejecutan espectaculares despliegues aéreos, pero nuestro entendimiento de su complejidad y funciones es todavía limitado. Describimos las características de los despliegues del baile aéreo y evaluamos sus posibles funciones sexuales. El baile aéreo fue realizado por ambos sexos, pero con mayor frecuencia por los machos. Aunque ocurren durante toda la estación reproductiva y en el periodo pos-volantón, los despliegues del baile aéreo por parte del macho fueron más frecuentes durante el periodo pre-puesta de huevos (desde tres semanas anteriores a la puesta, cuando la formación de parejas ocurre, hasta justo después de la puesta). La frecuencia del despliegue pre-puesta de machos y hembras aumentó con el tamaño de la colonia y la abundancia de topillos. Un análisis de componentes principales de las características del despliegue (altura, velocidad, número de vueltas, giros, ondulaciones y llamados) identificó tres ejes principales (CP1-3). El CP1 se correlacionó con todos los parámetros, identificando despliegues que comenzaron a una mayor altitud, descendieron a velocidades mayores, con mayor frecuencia de giros, ondulaciones, vueltas y llamados de despliegue. El CP2 enfrentó despliegues altos, veloces y de menor complejidad (en términos de frecuencia de giros y ondulaciones) con despliegues más lentos, que comenzaron a una altitud menor, pero que fueron más complejos. El CP3 contrastó los despliegues con vueltas contra otros despliegues con ondulaciones. Los puntajes del CP1 difirieron entre sexos, con los machos realizando despliegues más intensos (puntajes del CP1 mayores) que las hembras. Los despliegues de los machos resultaron más intensos en las colonias de mayor tamaño y cuando los ratones de c

The Raptor Research Foundation, Inc.
Beatriz Arroyo, François Mougeot, and Vincent Bretagnolle "Characteristics and Sexual Functions of Sky-Dancing Displays in a Semi-Colonial Raptor, the Montagu'S Harrier (Circus pygargus)," Journal of Raptor Research 47(2), (1 June 2013).
Received: 24 July 2012; Accepted: 1 January 2013; Published: 1 June 2013

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