University of Twente Student Theses


Modelling foraging distribution of Griffon Vultures (Gyps fulvus) on the island of Crete, Greece

McIntyre, Alexis Louise (2010) Modelling foraging distribution of Griffon Vultures (Gyps fulvus) on the island of Crete, Greece.

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Abstract:The Griffon Vulture is an opportunistic scavenging raptor. It has a range which includes areas in Europe, Asia, North Africa and the Middle East. The European population is estimated to contain 20000 breeding pairs. Within Europe, the range is mainly distributed about the Mediterranean, and the majority of the European population is located in Spain. Whilst once widespread in Greece, the range has now been much reduced and the population in Eastern Europe can be considered to be endangered, regardless of the large Spanish population. Crete now contains the largest and most important population in Greece with 70 - 80% of the population. Crete has the biggest viable population in the Eastern Mediterranean. In Crete the population may be more closely tied to pastoralism than in other parts of Europe, possibly leaving it vulnerable to future changes in land use. Investigation into the relationship between Griffon Vultures and their food sources is required to gain a further understanding of the possible impact future changes may have. The food available to Griffon Vultures on Crete was initially determined using livestock census data and information from livestock owners. Modelling of the species distribution using telemetry data was then implemented under different scenarios, and the contribution of food availability to the Griffon foraging distribution was investigated. The models were implemented with 19 environmental variables, both natural and anthropogenic. Eight scenarios were modelled, being combinations of adults and juveniles, summer and winter, and with and without available food. The contribution of food resources to the foraging distribution of the Griffon Vulture modelling was performed using MAXENT, a maximum entropy model. Food availability is significantly greater above 600m, however the food availability does not contribute more than 10% to the Griffon Vulture foraging distribution models. There is a significant difference in the Griffon Vulture foraging distance in summer versus the foraging distribution in winter. There not a significant difference between the foraging distributions of adults and juveniles. Finally, food availability is significant in modelling Griffon foraging distributions. The environmental variables which contributed the most to the models were cloud cover, annual precipitation and the distance to colonies. Keywords: Gyps fulvus, species distribution modelling, Maxent, food availability.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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