The current publication gives a detailed assessment of the results from a population reinforcement of a European ground squirrel's (
) colony in south-eastern Bulgaria. The reinforcement was planned ...and implemented along with multidisciplinary research of the adaptation process (including radiotelemetry, parasitological study and assessment of the stress in the animals) and regular monitoring (yearly burrow counting). Although the donor and recipient populations were genetically similar, morphometrical data indicated variations in the body size probably due to the difference in population densities in the two sites. The monitoring revealed that the burrows were aggregated and there was a positive correlation in the spatial distribution of the ground squirrels' burrow holes and the colonies of Harting's vole (
) - another social ground-digging rodent that co-inhabits the study area. The first results showed successful reinforcement according to the three classical evaluation criteria: the individuals survived the translocation process, they successfully reproduced and an initial population growth was observed, based on the burrow entrances' count - from 36 in 2017 to 280 in 2020. In 2021, however, a considerable decline in the abundance of the population was recorded - 58.5% decline in the burrow number and 36% decline in the colony area. A decrease was also observed in the abundance of the Harting's voles' colonies. A review of all the collected information suggests it is unlikely that the decrease is due to helminth parasites, translocation stress or other behaviour issues. The most probable explanation is the bad weather conditions - unusually high rainfalls combined with relatively high temperatures in January 2021. In conclusion, we strongly emphasise the need for detailed and long-term monitoring after conservation translocation and careful evaluation of all the influencing factors before, during and after such actions.
Assessing whether conservation management actions are effective requires a good understanding of the demographic parameters that contribute to the population growth rate. Among the key demographic ...parameters influencing a population, immigration is one of the most difficult to measure empirically but may mask or accentuate the effects of conservation measures. We use an integrated population model to assess whether a population increase of a large raptor species can be explained by high fecundity and survival resulting from local conservation measures, or whether immigration may have contributed to population growth. We monitored the Eastern Imperial Eagle (Aquila heliaca) population in Bulgaria from 1998 to 2014, and tracked juveniles using satellite transmitters to estimate survival probability over the first three years of life. We used intensive territory monitoring of breeding birds to estimate survival probabilities and fecundity of birds older than 3 years. The Imperial Eagle population in Bulgaria increased by about 11 % per year between 1998 and 2014 (λ = 1.111, 95 % credible interval 1.076–1.156). While local conservation measures have succeeded in reducing nest loss and the mortality of adults (adult survival = 0.924; 0.887–0.955), high mortality of juveniles during their first year of life resulted in only 12 % of fledglings surviving to adult age. Based on these survival probabilities and the estimated fecundity of breeding pairs in Bulgaria (1.063; 0.932–1.203), some immigration may have contributed to the population growth in Bulgaria. Because the integrated population model accounts for all the uncertainty associated with disparate data sources, the estimated immigration rate was too imprecise (0.143–2.862 young birds per breeding pair) to quantify the relative importance of immigration. Future conservation measures for Imperial Eagles need to focus on improving the survival of juvenile birds, particularly the reduction of electrocution risk in Eastern Europe and the Middle East.
Around fifteen thousand fieldworkers annually count breeding birds using standardized protocols in 28 European countries. The observations are collected by using country-specific and standardized ...protocols, validated, summarized and finally used for the production of continent-wide annual and long-term indices of population size changes of 170 species. Here, we present the database and provide a detailed summary of the methodology used for fieldwork and calculation of the relative population size change estimates. We also provide a brief overview of how the data are used in research, conservation and policy. We believe this unique database, based on decades of bird monitoring alongside the comprehensive summary of its methodology, will facilitate and encourage further use of the Pan-European Common Bird Monitoring Scheme results.
Abstract
This study presents the results of conservation measures undertaken and their impact on the eastern imperial eagle population in Bulgaria. The species is distributed in the south-eastern ...part of the country, as there is only one known pair in central Bulgaria. During the period 2009-201 3, 28 different breeding territories were occupied. The population increased by 20%, as the number of pairs that occupied breeding territories increased from 20 in 2009 to 24 in 201 3. In general, the mean values of the breeding parameters of the eastern imperial eagle population for the period 2009-201 3 were as follows: productivity (P) 1 .03±0.1 8; breeding success (BS) 1 .1 8±0.21 ; and fledgling success (FS) 1 .68±0.1 6. The annual survival rate of breeders varied from 0.795 to 0.932. The most important factor causing the mortality of immature eagles was electrocution. Shooting and poisoning have become important mortality factors, too. Guarded pairs had a higher mean breeding success (1 .32±0.88) than non-guarded pairs (1 .06±0.91 ). As a whole, 39% of all artificial nests installed in the period 2009-201 3 were occupied by birds of different species. During the period 2008-201 3, a total of 23 juvenile eastern imperial eagles were tagged with satellite/GPS transmitters. In addition, 608 hazardous electric poles in the territories of seven pairs were insulated. Supplementary feed was provided for 1 4 pairs once a week during the autumn-winter seasons (October - March). A total of 483 supplementary feedings took place, 450 ofwhich also included monitoring in order to record the effectiveness of this activity.
Abstract
During the period 2008-201 3, 32 different breeding territories were occupied by eastern imperial eagles (EIEs). These territories were mainly distributed in two regions: the Dervent ...Heights/Yıldız Mts. and the area to the north of the Marmara sea coast. The nearest neighbour distance established was 4.2 km. The mean distance between pairs was 1 0.44±2.95 km. The mean value of breeding success for the period 2008-201 3, including 1 07 cases of incubation, was 1 .01±0.1 0. The mean breeding success of birds in the Marmara region (1 .05±0.78) was higher than that in the Dervent Heights/Yıldız Mts. (0.91±0.84). The present study on the diet of the EIE was based on the remains of 582 prey items of at least 70 taxa. Mammals were the most common group (46.5%), followed by birds (32.4%) and reptiles (20.3%). The white-breasted hedgehog (Erinaceus roumanicus) was the most common prey, followed by two tortoises - Hermann's tortoise (Eurotestudo hermanni) and the Greek tortoise (Testudo graeca) - which together accounted for a total of 1 4.4% of the prey caught. The prey species particularly represented in the food spectrum of the studied pairs were: the yellow-legged gull (Larus michahellis), the European souslik (Spermophilus citellus), the chicken (Gallus gallus f. domestica) and the white stork (Ciconia ciconia). These species together accounted for 67.8% of the prey caught. There was a statistically significant difference (Z=2.52, p=0.01 ) in the food preferences of the EIEs in the two studied regions.
Since 1990, nature conservation NGOs are the main players in the running of nation-wide research and monitoring schemes for raptors in Bulgaria. Among them, the Bulgarian Society for the Protection ...of Birds (BSPB) and Green Balkans are most active, covering the most threatened diurnal raptors in the country. The key species covered by comprehensive monitoring schemes are the Imperial Eagle Aquila heliaca, White-tailed Eagle Haliaeetus albicilla, Egyptian Vulture Neophron percnopterus, Griffon Vulture Gyps fulvus, Black Vulture Aegypius monachus, Saker Falcon Falco cherrug and Red-footed Falcon F. vespertinus. Information on their distribution, numbers, breeding success, productivity, diet, movements etc. is gathered on annual basis. The Buzzard Buteo buteo and Kestrel F. tinnunculus are also regularly monitored at the national level by the Common Bird Monitoring scheme. Distribution of all raptor species has been studied for the purpose of the Atlas of Breeding Birds in Bulgaria. The contemporary satellite telemetry methods revealed important aspects of movements and threats to eagles and vultures from Bulgaria within the country and abroad. Main threats for the raptors in Bulgaria are related to habitat loss, unnatural mortality and disturbance. The main gaps in raptor monitoring in Bulgaria are related to the lack of coverage of most of the diurnal species and owls. There is a strong national and international cooperation in conjunction with the work concerning Imperial Eagle, Egyptian and Griffon Vultures. However, further enhancement of cooperation on other raptor species and issues such as lobbying for implementation of raptor-friendly agricultural practices and enhancement of various economic sectors are needed
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.
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