Survival rate and mortality of juvenile and immature eastern imperial eagles (Aquila heliaca) from Bulgaria studied by satellite telemetry

Abstract A long-living species like A. heliaca has a natal dispersal period lasting several years. This period is crucial for the survival and conservation of the eagles. In this study we present mortality factors and the survival rate of juvenile and immature A. heliaca from Bulgaria as established by satellite telemetry. A total of 20 juvenile A. heliaca were fitted with GPS/Argos transmitters in their nests in Bulgaria. Fourteen birds were tracked till their death and the bodies were found. Tracking allows the survival rate of juvenile and immature A. heliaca to be estimated for the first time. It is 59.1% for the first calendar year, 83.3% for the second calendar year and 80.0% for the third calendar year. The main mortality factor for juvenile and immature A. heliaca from the Bulgarian population is electrocution, which caused 59.0% of the mortality cases. Other threats identified are shooting, poisoning and collisions. Most of the fatalities of these tracked eagles occurred in Bulgaria (50%) and Turkey (43%). Thus, Turkey is a key country for conservation of the Bulgarian population ofA. heliaca during its dispersal period. Eagles from Bulgaria have been recorded dispersing further south, to Sudan and Saudi Arabia. Conservation efforts are needed both inside and outside Bulgaria in order to reduce mortality. International collaboration and the exchange of experiences should be part of any conservation strategy or plans focused on the eastern imperial eagle. Abstrakt U dlhožijúceho druhu A. heliaca trvá disperzia z miesta vyliahnutia niekolko rokov. Je to obdobie velmi dôležité pre prežitie a ochranu orlov. V tejto štúdii prezentujeme faktory mortality a prežívanie mladých a imaturných A. heliaca z Bulharska na základe štúdia satelitnou telemetriou. Celkom bolo v hniezdach v Bulharsku vysielackami GPS / Argos oznacených 20 mladých A. heliaca. Štrnást vtákov bolo sledovaných až do smrti vrátane nálezov kadáverov. Ide o prvé takéto štúdium prežívania mladých a imaturných jedincov A. heliaca. Prežívanie má hodnotu 59.1 % v prvom kalendárnom roku, 83.3 % v druhom a 80,0 % v tretom kalendárnom roku. Hlavným faktorom mortality sledovaných jedincov z bulharskej populácie je smrt v dôsledku zásahu elektrickým prúdom, ktorý spôsobil 59,0 % prípadov mortality. Dalšie identifikované hrozby sú zástrely, otravy a kolízie. Väcšina prípadov mortality sledovaných orlov nastala v Bulharsku (50%) a v Turecku (43%). Preto je Turecko klúcovou krajinou pre ochranu bulharskej populácie A. heliaca pocas jeho disperzie. Orly z Bulharska sa rozptylujú aj dalej na juh, do Sudánu a do Saudskej Arábie. Preto je potrebné ochranárske úsilie s cielom zníženia mortality tak vo vnútri ako aj mimo Bulharska. Medzinárodná spolupráca a výmena skúseností by preto mala byt súcastou každej stratégie ochrany a plánov zameraných na ochranu orla královského.