The night flights of the bearded vulture

    The combination of data from GPS, accelerometers and camera traps makes it possible to document for the first time the nocturnal behavior of the bearded vulture, providing new information on the ecology of one of our most emblematic scavenger birds.


    The differences between diurnal and nocturnal birds of prey are more than evident if we look at various physical aspects, but also in their behavior, starting with the obvious: diurnal raptors do their life during the day and nocturnal ones do it at night. This, which is mainly due to evolutionary adaptations that enable nocturnal raptors to see better in the absence of light, does not mean that both types of birds of prey cannot carry out part of their activity when in theory it is not their responsibility.

    The study of the activity of birds of prey "out of their hours" has attracted the interest of ornithologists for decades, and in fact, the nocturnal activity of diurnal raptors has been corroborated sporadically during migration or hunting events, and even to avoid potential competitors from their own trophic niche, normally in environments that are naturally well lit –by moonlight– or artificially lit –due, for example, to the proximity of roads or urban centers–.

    Attracted by the ecological and conservation implications derived from this curious behavior, especially in the case of scavenger birds due to their requirements to fly, scientists from the University of Lleida and the Research Group in Game Resources and Wildlife Management of the Instituto de Investigación en Recursos Cinegéticos (IREC – CSIC, UCLM, JCCM), together with technicians from the Government of Aragon and TRAGSATEC, have studied the nocturnal activity of the bearded vulture (Gypaetus barbatus) in the Pyrenees combining data from GPS, accelerometers and camera traps.

     

    The effectiveness of bearded vulture conservation plans (Gypaetus barbatus) depends to a large extent on knowing in depth the ecology and behavior of the species (Photo: Pilar Oliva-Vidal).

    The results show that 55% of the monitored individuals made night flights on at least 19 different nights, and that in 37% of these cases the lunar illumination was less than 20%. On the other hand, bearded vultures only showed feeding activity in 8% of the analyzed feeding events, but always during the hour after sunrise and the hour before sunset.

    In most cases, the flights occurred around the nocturnal roosts, reaching distances between 0,7 and 6.1 km and speeds of up to 24.4 km/h. Interestingly, unlike juvenile individuals, all the adults studied (n=6) made night flights during the study period, which may be due to a better knowledge of the territory and the confidence that their age gives them to make night trips.

    This work has been possible thanks to a pre-doctoral grant (FPI-2016-077510) awarded to the University of Lleida, funding from the Ministry for the Ecological Transition and the Demographic Challenge, the Ministry of Economy and Competitiveness, the Ministry of Science and Innovation, the Government of Aragon and the Generalitat de Catalunya, and the projects CGL2015-66966-C2-1-R2, RTI2018-099609-BC22 and ECOGYP-EFA-089/15 of the INTERREG VA Spain-France-Andorra Program (POCTEFA 2014 -2020).

    It seems that the reason for the bearded vulture's night flights is not to obtain food, but rather they may be motivated by the occurrence of disturbances –caused by the passage of ungulates or the visits of small predators to perches or nests in search of food scraps– or by sudden changes in weather conditions that cause the sudden abandonment of the perches during the night, with the consequent risk that this entails for a diurnal species not adapted to night flight.

    The information available to date on the population status, distribution and reproductive parameters of the bearded vulture in Spain, which has recently been published through a monograph edited by IREC, shows how the progressive knowledge of the ecology of the bearded vulture has served to apply successful strategies for the conservation of the species. There is no doubt that the study of this unusual nocturnal behavior, not documented to date, will provide valuable scientific material to further improve the conservation strategies of one of our most emblematic scavenger birds.

    The scientific publication of this research is available at: