Bonelli’s Eagle - Golden Eagle: results of a breeding year

Another year of monitoring the breeding success of Bonelli’s Eagle, in the framework of LIFE Bonelli eastMed Program, has finally come to an end, with great results from our teams. Thanks to information from telemetry data and other sources, which is collected daily, we are able to shed even more light on the study of the Aegean's apex predator that continues to surprise us with its habitat and dietary preferences.

Foraging area on an Aegean island near a breeding territory of the Bonelli’s Eagle. © Archive NHMC/Aspasia Anagnostopoulou

The members of the program’s field team were divided once again this year, between the regions of Crete, Dodecanese, Cyclades, NE Aegean, Attica, the Peloponnese and Evia, in order to monitor the Bonelli’s Eagles’ annual breeding success  for the year 2023.

Members of the program’s field team while monitoring breeding territories of Bonelli’s Eagles. © Archive NHMC/Aspasia Anagnostopoulou 

Annual Monitoring of Bonelli’s Eagle population

The LIFE Bonelli eastMed team started their field trips between February and March. The team visited well-known territories of Bonelli’s Eagles in Crete, Karpathos, Sharia, Andros, Tinos and Naxos, where they managed to locate active breeding pairs either in the phase of incubation or in the phase of displaying courtship and mating.

Members of the program’s field team while monitoring breeding territories of Bonelli’s Eagles. © Archive NHMC/Aspasia Anagnostopoulou 

Of special focus during this year’s monitoring of the species’ breeding success, were the islands of the Dodecanese. Using the inflatable speedboat ‘TITHYS’ of the University of Crete - Natural History Museum of Crete (NHMC), members of the Program's field team travelled to the islands of Antitilos, Tilos, Nisyros and Kalymnos, Lipsi (Lipsi Archipelagos), Karpathos and Sharia, where they managed to locate and record both known and previously unknown territories of the species -either active or historical (i.e. territories that historically were occupied by the species but nowadays seem to have disappeared or were never re-colonised).

Pair of adult Bonelli’s Eagles in nesting position. © Archive NHMC/Aspasia Anagnostopoulou

Monitoring and search for breeding territories of Bonelli's eagle in the Dodecanese.© Archive NHMC / Aspasia Anagnostopoulou

This trip was followed by a second one to the island of Rhodes where, for the first time this year, a comprehensive monitoring of the species was attempted on the island. The same effort was later extended to other islands in the Cyclades Island complex, including Sikinos, Serifos and Folegandros. Last but not least, the annual monitoring of the established breeding territory of the species in Ikaria was repeated again this year (NE Aegean).

Monitoring and identification of active nesting sites. © Archive nhmc / Aspasia Anagnostopoulou

The growth of Bonelli’s Eagle nestlings, only a few weeks after birth, is carefully monitored by members of the program’s field team. © Archive NHMC / Kostis Damianakis, Aspasia Anagnostopoulou

Ringing and tagging of young Bonelli’s Eagles with a satellite transmitter

Ringing and tagging of young Bonelli’s Eagles with a satellite transmitter

As it happens every year, during the last phase of the monitoring of the annual breeding success of Bonelli’s Eagle pairs in the Aegean Sea, Crete, Attica and Evia, the field teams of the project set out on tagging and ringing missions in order to tag the fledglings that managed to survive with satellite transmitters and to collect morphometrics.  

Due to the inaccessible nature of Bonelli’s Eagle breeding sites, usually located on steep cliffs and slopes above the sea or in canyons, this procedure was only rendered possible again this year thanks to the valuable assistance of professional and/or volunteer climbers who helped us not only to approach and capture the young Bonelli’s Eagles but also to gather food materials from the nests that will be further used for the dietary analyses conducted within the framework of the Program.

Ringed and radio-tagged Bonelli's eagle chicks during their return to the nest by the climber. © Archive NHMC / Savvas Paragamian

Taking morphometric measurements of a Bonelli's eagle chick. © Archive NHMC / Savvas Paragamian

Collection of food material found in an active Bonelli's eagle nest for the analysis and recording of the species' dietary preferences. © Archive NHMC / Savvas Paragamian

Skull of a small mammal found in an active nest of Bonelli's Eagles. © Archive NHMC / Savvas Paragamian

Professional climbers as they approach the species' nesting sites. © Archive NHMC / Aspasia Anagnostopoulou, Kostis Damianakis

A parent Bonelli’s Eagle flying above an active nest as climbers approach the site. The whole procedure is carried out in a relatively short time in order to minimize disturbance to the species but with all safety measures for both climbers and chicks!  

Breeding success of year 2023

Breeding success in 2023

In total, during the 2023 breeding season, the breeding success of the species was monitored in sixteen (16) breeding territories of Crete, fourteen (14) breeding territories of the Dodecanese, five (5) of the Cyclades, one (1) of Ikaria, one (1) of Attica and one (1) of Evia. Six (6) young Bonelli’s Eagles were ringed on the island of Crete, eight (8) in the Dodecanese and six (6) in the Cyclades Island complexes, two (2) in Ikaria, two (2) in the region of Attica, six (6) in Peloponnese and one (1) in Evia. In aggregate, 2023 was a fruitful year for our teams, since this year in Greece we had  25 ringed and tagged young Bonelli’s Eagles.

Data collected this year will continue to provide valuable input for several studies and analyses conducted in the framework of the LIFE Bonelli eastMed Program. These include studies on the dispersal and habitat preferences of young Bonelli’s Eagles (telemetry data), studies on the sustainability of the species, as well as morphometric, genetic and dietary studies; in addition, the data will be useful for studies on the species’ main threats and causes of mortality.

Young Bonelli's Eagles in their nest with part of a dead Silver Gull that the parents have brought to feed their chicks. © Archive NHMC / Savvas Paragamian

The Golden Eagle is the main competitor of Bonelli’s Eagle

Golden Eagle: Bonelli’s Eagle main competitor

In the framework of the Program, studies and fieldwork are also carried out focusing on one of the species' main competitors: the Golden Eagle. In the framework of the Project, the annual monitoring of the Golden Eagle’s breeding success in established breeding territories of the species on the island of Crete was also carried out this year. These activities resulted in the ringing of a total of five (5) young Golden Eagles in territories of Central and Eastern Crete.

It is worth noting that, for the first time this year, two (2) Golden Eagle fledglings from the same nest were simultaneously ringed, an occasion not often recorded due to the phenomenon of "Cainism". Cainism occurs due to lack of food leading one of the two newly born chicks to kill and then proceed to consume its sibling.

Ringing a young Golden Eagle in Crete. © Archive NHMC / Aspasia Anagnostopoulou

Returning two ringed and radio-tagged Golden Eagle chicks to their nest. © Archive nhmc / Savvas Paragamian

Telemetry data collected from young Golden Eagles is considered equally valuable with data from Bonelli’s Eagles. Even though the Golden Eagle faces similar threats to the Bonelli’s Eagle and its presence in an ecosystem is an indicator of high ecosystem quality, there is no similar study or any dedidated program for the protection of this apex predator in Greece.

At the same time, Golden Eagles appear to be now occupying, in some cases, historic territories of the Bonelli's Eagles. Hence, further studies on the Golden Eagle, through the LIFE Bonelli eastMed program, will provide us with new data and knowledge on the species, which requires similar protection as the Bonelli’s Eagle.

Professional climbers approaching a Golden Eagle's nesting site. © Archive NHMC / Aspasia Anagnostopoulou

Telemetry data

Telemetry data

So far, telemetry data from satellite transmitters, placed on both young Bonelli’s and Golden Eagles during the 2023 breeding season, show that the young birds of both species have already started their first flights around their nesting sites. Some of them fly more timidly and some more vigorously, while others have already moved several hundred kilometres away from their breeding territories, having covered great distances in search of feeding and dispersal areas.

Telemetry data from transmitters placed this year (2023) on young Bonelli's eagles born on Aegean islands | Ornitela / 24.07.2023

Data already collected and all the data that continue to be collected during the 2023 breeding year, will be incorporated into the larger body of information that has been gathered since the start of the Program (2019),  with the aim of publishing aggregated data and results for the Bonelli’s Eagle in the following year (2024), as the Program will be heading towards its completion.

Ringed and radio-tagged young Bonelli's eagles that have just returned to their nest on an Aegean island. © Archive NHMC / Savvas Paragamian

FIELD TEAM MEMBERS (in alphabetical order):

Aspasia Anagnostopoulou

Aris Vouros

Kostis Damianakis

Tasos Dimalexis

Aggelos Evaggelidis

Afroditi Kardamaki

Eli Navarrete

Manolis Papadimitrakis

Anastasia Perodaskalaki

Nikos Tsiopelas

Dimitra Christidi

Stavros Xirouchakis

PROFESSIONAL & VOLUNTEER CLIMBERS

Grigoris Anastasopoulos

Alexis Grapsas

Markos Digenis

Vaggelis Kastanias

Thanasis Karageorgiou

Konstantinos Marmatzakos

Myrto Miliou

Ippokratis Palapanoglou

Savvas Paragamian