Monitoring of Griffon Vultures

The survey of the Griffon Vulture population in Bulgaria has been conducted since 1988. It focuses on the following goals:

  • Establishing the number of individual birds
  • Establishing all breeding pairs
  • Identifying new nesting sites
  • Establishing the age structure of the population
  • Establishing the nesting and reproductive success of the colonies


Two methods of surveying are applied:


Night roosts monitoring


The monitoring takes place in November – December, and the census is carried out within a single day. All cliffs that have been identified as resting and breeding sites of the vultures are visited. Every cliff face is monitored by one team from a minimum distance of 300 metres (1000 ft). The teams use telescopes with magnification 20 – 60 x and binoculars (10x50) for the count. The meteorological conditions are noted down on the hour. The number of vultures roosting on the cliff is monitored constantly with checks performed every 15 minutes. The direction of flight of birds that take off is recorded. The age structure of the birds is determined by dividing them in several categories. Apart from the number and age of the vultures, the number of tagged individuals and their distinctive features – if present – are also noted. During the monitoring of vultures the number and age of other raptors and corvids sharing the cliffs for resting or roosting is noted. The census starts at 2 p. m. and ends 30 minutes after sunset; thus it spans over the whole period of daylight.


Monitoring of supplementary feeding. Observations of the feeding platforms are conducted at least once monthly throughout the period of the monitoring. For this purpose a 20 – 60 x telescope and 10x50 binoculars are used; the team takes position at a point 500 m away from the platform. The meteorological conditions are noted down on the hour. The number of feeding vultures is monitored constantly, keeping track of the age structure registered during the night roosts monitoring, and noting down any tagged individuals. The data gathered is filled in in a standardized form for monitoring of supplementary feeding. Extensive information about the species of the carrion, its weight and origin, as well as its medical record is also noted down.