Use And Selection Of Roost Sites By Eurasian Griffon Vultures Gyps Fulvus In Bulgaria

Capsule Roosting behaviour during the pre-breeding season is an important part of the Eurasian Griffon Vulture Gyps fulvus life cycle. We demonstrate the importance of roost site selection and its relation to the breeding distribution of the Griffon Vulture. Aims To quantify the distribution, population size, age structure and roosting site selection of the Eurasian Griffon Vulture in the Eastern Rhodopes, Bulgaria during the pre-breeding season. Methods We used correlation analysis and generalized linear mixed models to examine the relationship between the vultures use of roost sites and their distribution in relation to topographic variables. We additionally used GPS telemetry data from 25 birds to study and compare the use of roosting cliffs. Results During the 14-year survey period the number of roosting Eurasian Griffon Vultures gradually increased from 25 birds in 2005 to 201 in 2018. We recorded 16 cliffs used by 124 +/- 51 (sd) vultures for roosting. The number of non-adult vultures increased by 25% and reached 41% of all the recorded birds in the last year of the survey. We found that the number of breeding pairs correlated positively with the number of roosting vultures (r( )= 0.85) and that roosting cliff selection was determined by cliff length and height, distance to the nearest feeding site, and whether the cliff was used for breeding. Conclusions Cliffs regularly used by vultures in the pre-breeding season, were afterwards used for breeding. Thus, cliffs used in the pre-breeding season for roosting could be used as an index for the breeding distribution of the species, and should be protected to sustain the species in and out of the breeding season.