As reported by M. Franchuk and A. Simon on the website of the Ukrainian Centre of Birds of Prey Research, monitoring of the Ukrainian population of the Greater Spotted Eagle (Clanga clanga) in the Rivne Nature Reserve has been ongoing for several years. Over time, the research has expanded to cover various aspects of breeding biology, including telemetry studies on migration, chick banding, genetic analysis of hybridization with the closely related Lesser Spotted Eagle (Clanga pomarina), trophic studies, and more.
As part of these efforts, a study on the breeding success of the Greater Spotted Eagle using camera traps was initiated. This work began in 2020, with camera traps being installed at Greater Spotted Eagle nests in mid-July during the chick banding process. The initial objective was to track the fledging success of the young birds. However, installing cameras late in the breeding season did not allow for an understanding of key aspects of nest ecology, such as breeding phenology, clutch size, and clutch survival. Thanks to technical support from the „Polesie – Wilderness Without Borders” project, 10 camera traps were successfully installed at Greater Spotted Eagle nests in 2021; however, due to technical issues, only a few were installed prior to the start of the breeding season, which meant a complete picture could not be obtained. The war in 2022 also posed an obstacle. In total, data regarding the end of the nesting period (July–August) and subsequent nest usage was documented for 10 greater spotted eagle nests between 2020 and 2022.
Fortunately, in the 2023 season, it was possible to install camera traps before the start of the breeding season — specifically, before the males arrived at the nests, which typically occurs in the second half of March. This approach was intended to minimize disturbance to the birds. The start of the 2023 season was marked by specific challenges: high water levels in the spring made some nests inaccessible, and there was a ban on entering border areas. Consequently, the authors focused primarily on the results from 2023, a year that allowed for a broader scope of observation covering the entire period and yielded interesting data.
A total of 13 camera traps were deployed across 10 nests; some nests were equipped with two traps to capture different angles and utilize combined camera settings (varying intervals, combinations of photos and video, and different shooting angles). Two of the traps were placed at lesser spotted eagle nests to facilitate a comparison of the nesting ecology of the two species. Bushwhacker Big Eye D3/D3R camera traps served as the standard equipment for the study (shooting mode for March–July: two 5 MB photos triggered by movement every 10 minutes; medium sensitivity). Cameras were positioned either above or to the side of the nest, depending on the configuration of the trees hosting the nests. A side-view angle of 30–45 degrees proved most effective (allowing for better tracking of food deliveries, reading of leg rings, etc.). In some cases, side-mounting was problematic and failed to capture the entire nest area; consequently, additional cameras from other manufacturers (e.g., Cuddeback G-5048) were deployed. To meet the project objectives — specifically ensuring battery life lasted until mid-July — images were captured during daylight hours, between 04:00 and 22:00. During a follow-up visit to the nest in July, memory cards and batteries were replaced, and camera settings were adjusted (capturing three 5 MB images every four minutes, with 24-hour operation). The cameras remained active from July through November.
The following data were obtained for each of the observed pairs.
Somyne Massif
Pair 1. Did not initiate nesting. The male visited the nest periodically, sometimes carrying nesting material. Additionally, the nest was visited by five other Clanga eagles; two of these bore color and metal rings. One was a fledgling from the 2021 brood at this same nest, while the other bore a metal ring from the Belarusian Bird Ringing Centre.
Pair 2. Breeding success and productivity: 50%. The female laid two eggs, both of which hatched. One chick subsequently died due to siblicide (specifically, it was killed by its sibling). This phenomenon is quite common and typical for this species. The second chick survived and successfully fledged, continuing to visit the nest until mid-September.
Pair 3. Breeding success and productivity: 50%. The situation mirrored that of the previous pair (Pair 2): the second chick died. The pair had two nests on the same forest island (spaced 300 m apart); one was used by the male only in early spring and was virtually unvisited thereafter. This pair has been known since 2012 and is a hybrid (Lesser Spotted Eagle male × Greater Spotted Eagle female). In 2023, the male changed mates; the new female was identified via a metal ring, which had also been fitted in Belarus. The second chick successfully fledged and continued to visit the nest until mid-September.
Chase Massif
Pair 4. Did not initiate nesting. The male periodically visited the nest and brought nesting material. The nest likely remained unoccupied due to the presence of two pairs of Northern Goshawks (Astur gentilis) nesting nearby. An attempt to locate an alternative nest — often found within a 1–2 km radius — was unsuccessful.
Perebrody Massif
Pair 5. Due to high water levels in the bog, no camera was installed in the spring. One chick appeared in July; it successfully fledged and continued to visit the nest until the end of September.
Pair 6. Breeding success and productivity: 50%. The female laid two eggs and two chicks hatched; one died due to weather conditions (cold and precipitation). The surviving chick successfully fledged and was observed at the nest site until early October.
Pair 7. This pair laid a single egg later than any of the other females — specifically, two weeks later (on May 12). The chick hatched on June 21 but, unfortunately, died three weeks later in July. The cause of death was likely an illness, as the chick was weak and had stopped eating for the two or three days preceding its death.
Consequently, out of the seven pairs of greater spotted eagles that occupied nests in the spring, five pairs (71.4%) attempted to breed. The average breeding success rate was 50%, with a productivity of 1.0 chick per breeding pair and 0.7 chicks per pair overall. These figures are quite high for the species, given that a rate of 30–50% is considered normal for population maintenance. It is known that, among greater spotted eagles, usually only one chick survives. There are numerous causes for the death of the second chick, including siblicide (specifically cainism), food shortages, predation, and disease. Thanks to the use of camera traps, the observers were able to determine the causes of chick mortality, assess breeding success and productivity, and gather a wealth of other information regarding nesting ecology.