The combination of GPS, accelerometer and camera trap data allows to document the bearded vulture's nocturnal behaviour for the first time, providing new information about the ecology of one of our most iconic scavenger birds.
The differences between diurnal and nocturnal raptors are more than evident if we pay attention to various physical aspects, but also to their behaviour, starting with the obvious: diurnal raptors make their lives during the day and nocturnal raptors do so at night. This, which is mostly due to evolutionary adaptations that enable nocturnal raptors to see better in the dark, does not mean that both types of raptors cannot carry out part of their activity when in theory they are not supposed to do it.
The nocturnal activity of diurnal raptors is a topic that has attracted increasing attention of ornithologists over the last century, and in fact, it has been documented during migration or while hunting and feeding, or even to avoid potential competitors from their own trophic niche, in both natural –by moonlight– and artificial light conditions –because of, for example, the proximity of roads or urban areas–.
Attracted by the ecological and conservation implications derived from this interesting behaviour, especially in the case of scavenger birds owing to their requirements for flying, scientists from the Universidad de 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 Regional Government of Aragon and TRAGSATEC, have studied the nocturnal activity of the Bearded vulture (Gypaetus barbatus) in the Pyrenees, using a combination of accelerometer, global positioning system (GPS) and camera trap tracking data.
The effectiveness of the bearded vulture (Gypaetus barbatus) conservation plans greatly depends on knowing in depth the ecology and behaviour of the species (Photo: Pilar Oliva-Vidal).
Results showed that 55% of the monitored individuals performed nocturnal flights on at least 19 different nights, and that in 37% of these cases the moonlight intensity was lower than 20%. On the other hand, the bearded vulture only showed feeding activity in 8% of the feeding events analyzed, but always during the hour after dawn and the hour before dusk.
In most cases, nocturnal flights occurred around overnight roosting sites, reaching distances of between 0.7 and 6.1 km and speeds of up to 24.4 km/h. Curiously, unlike the juvenile individuals, all the adults studied (n = 6) performed nocturnal flights during the study period, lwhich may be due to a better knowledge of the territory and the confidence that their age provide them to fly at night.
This work has been possible thanks to a PhD grant (FPI-2016-077510) awarded to the Universidad de Lleida, to funding from the Spanish Ministry for the Ecological Transition and the Demographic Challenge, the Ministry of Economy and Competitiveness, the Ministry of Science and Innovation, the Regional Government of Aragon and the Regional Government of 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).
Everything seems to indicate that the nocturnal flights of bearded vultures are not related to foraging behaviour, but rather to disturbances –provoked by the presence of ungulates or the visit of small predators because of the food stored in nests and roosting sites– or adverse weather conditions that result in the sudden abandonment of overnight roosting sites, with the consequent risk that this entails for a diurnal species not adapted to fly at night.
The information available to date on the population status, distribution and reproductive parameters of the bearded vulture in Spain, which it has recently been published through a monograph edited by the IREC, shows how the progressive knowledge of the bearded vulture ecology has served to apply successful strategies for the conservation of the species. There is no doubt that the study of this unusual nocturnal behaviour, not documented to date, will provide valuable scientific material to further improve the conservation strategies of one of our most iconic scavenger birds.
The scientific publication of this research is available at:
- García-Jiménez, R., Martínez-González, J., Oliva-Vidal, P., Piqué, J., Sesé, J. A., Margalida, A. 2020. Nocturnal flights by Bearded Vultures Gypaetus barbatus detected for the first-time using GPS and accelerometer data. Bird Study (2020).