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WILSON BULLETIN Tuesday Apr 04 2006 01:54 PM Allen Press • DTPro System

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THE WILSON BULLETIN • Vol. 118, No. 2, June 2006

The Wilson Journal of Ornithology 118(2):254–256, 2006

Reverse Mounting and Copulation Behavior in Polyandrous Bearded Vulture (Gypaetus barbatus) Trios Joan Bertran1 and Antoni Margalida1,2 ABSTRACT.—We present the first report of reverse mounting in the Bearded Vulture (Gypaetus barbatus). The reverse mounting, which occurred in the Pyrenees of northeastern Spain, took place between the female and the alpha male in a polyandrous trio. The function of reverse mountings is discussed in relation to the previously reported high frequency of male-male mountings in this raptor species. Received 25 April 2005, accepted 17 January 2006.

Reverse mounting, in which the female mounts the male, has been described in a number of bird species (see James 1983, Nuechterlein and Storer 1989). This behavior has been rarely documented in raptors, however, except for a few isolated cases in species such as American Kestrel (Falco sparverius; Bowman and Curley 1986) and Egyptian Vulture (Neophron percnopterus; Dona´zar 1993). We describe a case of reverse mounting in 1 Bearded Vulture Study and Protection Group, Apdo. 43, E-25520 El Pont de Suert (Lleida) Spain. 2 Corresponding author; e-mail: [email protected]

a polyandrous trio of Bearded Vultures (Gypaetus barbatus). Bearded Vultures are territorial and socially monogamous (Hiraldo et al. 1979); however, in the Pyrenees (in both Spain and France), where the species’ largest European population occurs, polyandrous coalitions are relatively common (Heredia and Dona´zar 1990). The birds in this population maintained 104 breeding territories (R. Heredia and M. Razin pers. comm.), 18 of which were occupied by polyandrous trios. Before egg-laying, Bearded Vultures in the Pyrenees engage in their copulations for an average of 67 days (range 5 50–90; Bertran and Margalida 1999), during which male-male mountings in trios occasionally occur (Bertran and Margalida 2003). Between 2004 and 2005, we monitored a polyandrous trio of Bearded Vultures in the central Pre-Pyrenees mountains in Catalonia, northeastern Spain, during their courtship period (200 hr of observation). We sexed and identified the individuals by observing their copulatory activities and specific plumage pat-


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TABLE 1. Number of male-female, male-male, and reverse mounting copulation attempts observed in monogamous pairs (n 5 8) and polyandrous trios (n 5 5) of Bearded Vultures in the Pyrenees, northeastern Spain, 2004–2005.

Pairs Trios

Male-Female

Male-Male

Female-Male

Source

189 356

— 39

0 1

Bertran and Margalida (1999) This study

terns. On 30 October 2004 at 12:19 UTC11 (84 days before egg-laying), the female mounted the alpha male after she had been mounted unsuccessfully by the beta male. Following the female’s mount, the alpha male drove the beta male off the perching site. The duration of the reverse mounting (8 sec) was similar to that of behaviorally successful male-female copulations recorded in other polyandrous groups (mean 5 10.49 sec 6 1.30 SD, range 5 8–14, n 5 37; Bertran and Margalida 2004). Previously, researchers have studied reverse mounting in the context of pair formation, degree of sexual motivation, or reversal of sexual dominance (Nuechterlein and Storer 1989, Bowen et al. 1991, Ortega-Ruano and Graves 1991). Due to their physical and behavioral characteristics, it has been suggested that female Bearded Vultures can dominate males (see Negro et al. 1999); in the Cattle Egret (Bubulcus ibis), reverse mounting has been associated with establishing dominance (Fujioka and Yamagishi 1981). However, if reverse mounting were of adaptive value (e.g., to maintain female dominance or to strengthen heterosexual couplings), it likely would be more common. On the other hand, sexual interactions outside the context of fertilization appear to be relatively common in polyandrous trios (Table 1), and reverse mounting might simply be a side effect of male-male mountings. That is, the function of reverse mounting may be to regulate socio-sexual tensions—similar to the function of male-male mountings (Bertran and Margalida 2003, see also Heg and van Treuren 1990, Cockburn 2004). Further research is needed to determine whether reverse mounting is the result of confrontational situations or helps to regulate them. ACKNOWLEDGMENTS We thank A. Bonada, X. Macia`, P. Romero, and E. Vega for their help during fieldwork, and D. Heg and

two anonymous referees for their comments. This study was supported by Departament de Medi Ambient i Habitatge de la Generalitat de Catalunya and Ministerio de Medio Ambiente.

LITERATURE CITED BERTRAN, J. AND A. MARGALIDA. 1999. Copulatory behavior of the Bearded Vulture. Condor 101:161– 164. BERTRAN, J. AND A. MARGALIDA. 2003. Male-male copulations in polyandrous Bearded Vultures (Gypaetus barbatus): an unusual mating system in raptors. Journal of Avian Biology 34:334–338. BERTRAN, J. AND A. MARGALIDA. 2004. Do females control matings in polyandrous Bearded Vulture (Gypaetus barbatus) trios? Ethology, Ecology and Evolution 16:181–186. BOWEN, B. S., R. R. KOFORD, AND S. L. VEHRENCAMP. 1991. Seasonal pattern of reverse mounting in the Groove-Billed Ani (Crotophaga sulcirostris). Condor 93:159–163. BOWMAN, R. AND E. M. CURLEY. 1986. Reverse mounting in the American Kestrel. Wilson Bulletin 98: 472–473. COCKBURN, A. 2004. Mating systems and sexual conflict. Pages 81–191 in Ecology and evolution of cooperative breeding in birds (W. D. Koenig and J. L. Dickinson, Eds.). Cambridge University Press, Cambridge, United Kingdom. DONA´ZAR, J. A. 1993. Los buitres ibe´ricos: biologıá y conservacioń. J. M. Reyero (Ed.), Madrid, Spain. FUJIOKA, M. AND S. YAMAGISHI. 1981. Extramarital and pair copulations in the Cattle Egret. Auk 98:134– 144. HEG, D. AND R. VAN TREUREN. 1998. Female-female cooperation in polygynous Oystercatchers. Nature 391:687–691. HEREDIA, R. AND J. A. DONA´ZAR. 1990. High frequency of polyandrous trios in an endangered population of Lammergeiers Gypaetus barbatus in northern Spain. Biological Conservation 53:163–171. HIRALDO, F., M. DELIBES, AND J. CALDERON. 1979. El Quebrantahuesos Gypaetus barbatus (L.). Monografıás, no. 22, Instituto para la Conservacioń de la Naturaleza, Madrid, Spain. JAMES, P. C. 1983. Reverse mounting in the Northwestern Crow. Journal of Field Ornithology 54: 418–419. NEGRO, J. J., A. MARGALIDA, F. HIRALDO, AND R. HEREDIA. 1999. The function of the cosmetic colour-


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ation of Bearded Vultures: when art imitates life. Animal Behaviour 58:F14–F17. NUECHTERLEIN, G. L. AND R. W. STORER. 1989. Reverse mounting in grebes. Condor 91:341–346.

ORTEGA-RUANO, J. AND J. A. GRAVES. 1991. Reverse mounting during the courtship of the European Shag Phalacrocorax aristotelis. Condor 93:859– 863.