Dispersal Movements and Hot Spot Areas of Juvenile Bonelli’s Eagles on the Island of Crete, Greece

Abstract

The Bonelli’s Eagle (Aquila fasciata) is the main avian predator in almost all the islands of the Greek archipelagos. The phase of its natal dispersal has never been studied in Greece, though it constitutes a crucial part of the species ecology and conservation. In an effort to investigate the movement patterns and settlement areas of young eagles, we tagged 30 fledglings on the island of Crete during 2019–2023 with GPS/GSM transmitters. Fledging date was set the first day with full satellite coverage and consecutive GPS fixes for individual birds while the initiation of the dispersal period was established when they performed consecutive long flights, overstaying away from their natal territory (>10 km). Mean fledgling date was calculated at May 27 (range = 20/5–8/6), whereas the dispersal period started on average on September 03 (range = 30/8–21/9), namely ca. 90–100 days after the abandonment of the nest. All juvenile birds wandered around over the entire island residing primarily in two distinct habitat types i.e. coastal cliffs and satellite islets around Crete and agricultural areas in the lowlands covered with olive groves and vineyards. Preliminary surveys show that the juvenile birds avoid active Bonelli’s Eagle territories and select rural areas near landfills, water reservoirs, fowl pens, and uninhabited islets, specializing on prey species that are readily available (i.e. gulls, corvids, rock pigeons, wild rabbits and poultry). This fact makes them particularly susceptible to human-induced mortality such as electrocution, drowning in open water tanks and poaching, which accounted for ca. 60% of the casualties of this age group. Overall, the study confirms that land use changes and human pressure are the major threats for the species on Crete, likewise in the rest of its distribution range in the Mediterranean.