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Seasonal dynamics in the exploitation of natural carcasses and supplementary feeding stations by a top avian scavenger

Abstract

Supplementing vulture populations with carcasses disposed at feeding stations is a common management and conservation practice worldwide. However, there is a lack of knowledge on the dependence of large vultures on the supplementary feeding stations (SFS) in areas with high abundance of natural food. We tagged 11 Griffon Vultures (Gyps fulvus, Hablizl 1783) with GSM/GPS transmitters in the Eastern Rhodopes, Bulgaria and studied the seasonal dynamic of feedings at SFS and at occasional carcasses found in the field. We used combination of remote sensing and field inspections to identify the vulture feeding events. Our results show that most of the feeding events occurred at occasional carcasses found in the wild (77.4%), whereas only 22.6% were at SFS, but high seasonal variation was observed. Vulture’s reliance on feeding stations was lowest in summer (19.82 ± 7.8%) and highest in winter when 56.5 ± 16.1% of the feedings were at the SFS. Griffon Vultures travelled longer daily distances in days feeding in the wild compared to days when they were not feeding or were visiting SFS. Our study indicates that in habitats with high abundance of natural food (free-range livestock and game), vultures tend to actively forage and use feeding stations as supplemental sources of food, mostly during long periods of adverse weather or in winter when foraging conditions are worse and natural food is less abundant.

Zusammenfassung

Saisonale Dynamik bei der Nutzung natürlicher Kadaver und zusätzlicher Futterstellen durch eine aasfressende Vogelart

Eine ergänzende Versorgung von Geierpopulationen mit Kadavern, die an Futterstellen ausgelegt werden, ist weltweit ein typisches Management- und Naturschutzverfahren. Jedoch ist noch unbekannt, inwieweit große Geierarten auf diese zusätzlichen Futterstellen (engl. supplementary feeding stations, SFS) in Gebieten mit hohem natürlichen Nahrungsangebot angewiesen sind. Wir markierten elf Gänsegeier (Gyps fulvus, Hablizl 1783) mit GSM/GPS-Sendern in den östlichen Rhodopen, Bulgarien, und untersuchten die saisonale Dynamik der Fütterungen an SFS sowie an gelegentlich im Feld gefundenen Kadavern. Wir verwendeten eine Kombination aus Fernerkundung und Feldbegehungen, um die Fressereignisse der Geier zu erfassen. Unsere Ergebnisse zeigen, dass die meisten Fressereignisse an gelegentlich in der freien Natur gefundenen Kadavern stattfanden (77.4 %), während nur 22.6 % an SFS erfolgten, wobei jedoch starke saisonale Schwankungen beobachtet wurden. Die Abhängigkeit der Geier von den SFS war im Sommer mit 19.8 ± 7,8 % am geringsten und im Winter am höchsten, wo 56.5 ± 16.1 % der Fressereignisse an den SFS stattfanden. Gänsegeier legten an Tagen, an denen sie in der freien Natur gefressen haben, längere Tagesstrecken und weniger Direktflüge zurück als an Tagen, an denen sie gar nicht fraßen oder SFS aufsuchten. Unsere Studie lässt darauf schließen, dass Geier in Habitaten mit einem hohen natürlichen Nahrungsangebot (freilaufendes Vieh und Wild) dazu tendieren, aktiv auf Nahrungssuche zu gehen und SFS als ergänzende Nahrungsquelle zu nutzen, vor allem während langer Schlechtwetterperioden oder im Winter, wenn die Nahrungssuchbedingungen schlechter werden und das natürliche Nahrungsangebot abnimmt.

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Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Code availability

Not applicable.

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Acknowledgements

This research was financed by the National program "Young scientists and Postdoctoral candidates" funded by the Bulgarian Ministry of Education and Science. The fieldwork and data collection were conducted in the frame of the LIFE project “Conservation of Black and Griffon Vultures in the cross-border Rhodope Mountains” (LIFE14 NAT/NL/000901) funded by the European Union and supported by Rewilding Europe, Segre Foundation and WWF-Greece. We would like to express our gratitude to Hristo Hristov, Desislava Kostadinova, Vera Alekseeva, Stefan Avramov and Connor Panter for assisting in the fieldwork and to the Management body of Dadia-Soufli-Lefkimi Forest National Park, Marin Kurtev and Georgi Sheremetev for providing data on the number of supplementary feedings conducted at the SFS in the Eastern Rhodopes. We are grateful to Dimitar Demerdzhiev and two anonymous reviewers for providing helpful comments on preliminary versions of the paper and to Lavrentis Sidiropoulos for assisting in the statistical analyses.

Funding

This study was financed by the National program "Young scientists and Postdoctoral candidates" funded by the Bulgarian Ministry of Education and Science. The fieldwork and data collection were conducted in the frame of the LIFE project “Conservation of Black and Griffon Vultures in the cross-border Rhodope Mountains” (LIFE14 NAT/NL/000901) funded by the European Union and supported by Rewilding Europe, Segre Foundation and WWF-Greece.

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Correspondence to Volen Arkumarev.

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The trapping and tagging of Griffon Vultures were permitted by the Ministry of Environment and Waters of the Republic of Bulgaria (Permission No 675/14.04.2016, 710/25.05.2017).

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Communicated by O. Krüger.

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Arkumarev, V., Dobrev, D., Stamenov, A. et al. Seasonal dynamics in the exploitation of natural carcasses and supplementary feeding stations by a top avian scavenger. J Ornithol 162, 723–735 (2021). https://doi.org/10.1007/s10336-021-01865-1

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Keywords

  • Gyps fulvus
  • Remote sensing
  • GPS tracking
  • Accelerometer
  • Foraging
  • Movement ecology