Lucian Bolboacă

Background/Objectives: The White-tailed Sea-eagle, Haliaeetus albicilla, experienced severe population declines throughout Europe during the nineteenth and twentieth centuries, followed by a remarkable recovery in recent decades. Although the genetic structure of northern and central European populations has been extensively investigated, the phylogeographic history and contribution of the lower Danube population to the mitochondrial genetic diversity of the species remain poorly understood. Methods: We analyzed mitochondrial control region (MT-CR HVR1) sequences from White-tailed Sea-eagles breeding in the Danube Delta Biosphere Reserve (DDBR) and integrated these data with previously published sequences covering the species’ distribution across Europe and Asia; a total of 480 samples were examined. Results: The analysis revealed 47 haplotypes, including 11 haplotypes unique to the DDBR population. Phylogeographic analyses support the Scandinavian Peninsula as the ancestral source area of the species, followed by an early colonization of Central Europe and subsequent expansion into the Balkan Peninsula through the Danube corridor. The Romanian population exhibited the highest haplotype diversity among the investigated regions (Hd = 0.9367) and was characterized by numerous private haplotypes and a predominance of haplogroup C (approximately 76% of individuals), which was rare or absent in most northern and central European populations. Demographic analyses revealed significant evidence of recent population expansion following historical bottlenecks (Fu’s Fs = −5.736, p = 0.006), whereas gene-flow estimates indicated only moderate connectivity with neighbouring Balkan and Central European populations. Conclusions: The high frequency of private haplotypes, the absence of significant isolation-by-distance patterns, and the distinct distribution of mitochondrial haplogroups, characterized by the predominance of haplogroup C, suggest that the current DDBR population may have originated primarily through local demographic recovery rather than recent large-scale recolonization. Our results indicate that the lower Danube region represents an important reservoir of genetic diversity and support the hypothesis that the Danube Delta may have acted as a potential secondary refugium and center of diversification for H. a. in southeastern Europe.

Climate change and altered hydrological regimes are restructuring wetland habitats globally, triggering cascading effects on colonial waterbirds. This study investigates how environmental drivers, including thermal anomalies, water-level fluctuations, and aqueous surface extent, influence the distribution and size of waterbird colonies (Ardeidae, Threskiornithidae, and Phalacrocoracidae) in the Danube Delta Biosphere Reserve. We integrated colony census data (2016–2023) with remote-sensing-derived habitat metrics, in situ meteorological and hydrological measurements to model colony abundance dynamics. Our results indicate that elevated early spring temperatures and water level variability are the primary determinants of numerical population dynamics. Spatial analysis revealed a heterogeneous response to hydrological stress: while the westernmost colony exhibited high site fidelity due to its proximity to persistent aquatic surfaces, the central colonies suffered severe declines or local extirpation during extreme drought periods (2020–2022). A discernible eastward shift in bird assemblages was observed toward zones with superior hydrological connectivity and proximity to anthropogenic hubs, suggesting an adaptive spatial response that was consistent with behavioral flexibility. We propose an adaptive management framework prioritizing sustainable solutions for maintaining minimum lacustrine water levels to preserve critical foraging zones. This integrative framework highlights the pivotal role of remote sensing in transitioning from reactive monitoring to predictive conservation of deltaic ecosystems.

In 2023, we published the first list of birds from the Danube Delta Biosphere Reserve and recorded the presence of 365 species. By that time, eight additional species had been registered. Based on scientific literature, online sources, and field investigations, we identified a total of 373 bird species observed in the Danube Delta Biosphere Reserve, belonging to 61 families (out of a total of 65 families in Romania) and 19 orders. Our interest in publishing such biodiversity lists is not only important from a scientific point of view but also supports reports and presentations in which we refer to the current number of species in published material.

Climate change and altered hydrological regimes are restructuring wetland habitats globally, triggering cascading effects on colonial waterbirds. This study investigates how environmental drivers, including thermal anomalies, water level fluctuations, and aqueous surface extent influence the distribution, size, and diversity of waterbird colonies in the Danube Delta Biosphere Reserve. We integrated colony census data (2016–2023) with remote sensing-derived habitat metrics, in-situ meteorological and hydrological measurements to model site occupancy dynamics using Generalized Linear Mixed Models. Our results indicate that elevated early spring temperatures and water level variability are the primary determinants of nesting success. Spatial analysis revealed a heterogeneous response to hydrological stress: while the westernmost colony exhibited high site fidelity due to its proximity to persistent aquatic surfaces, the central colonies suffered severe declines or local extirpation during extreme drought periods (2020–2022). A discernible eastward shift in bird assemblages was observed toward zones with superior hydrological connectivity and proximity to anthropogenic hubs, suggesting remarkable behavioral plasticity. We propose prioritizing the investigation of sustainable solutions for lacustrine threshold regulation to maintain critical shallow-water foraging zones. This integrative framework provides essential insights for the long-term conservation of deltaic ecosystems, highlighting the pivotal role of remote sensing.

This paper presents the 2024 research results from the Danube Delta Biosphere Reserve (DDBR), including reed bed mapping and typology for fire management, assessment of sustainable use of vegetal resources, conservation status of invertebrates, fish, reptiles, amphibians, colonial waterbirds, and mammals of Community interest, evaluation of species invasiveness under climate change, and studies on human well-being and ecotourism within a sustainable development framework.

The factors that negatively influence the state of the populations of the white-tailed sea-eagle in the Danube Delta Biosphere Reserve and in the surrounding areas are both natural and anthropogenic. Between 2009 and 2018, an intensive study of those limiting factors was conducted. During those ten years, we registered 166 nests in the area, out of which 73 had been destroyed or deserted. The reasons were natural factors related to inclement weather in 73.97 % of the cases and anthropogenic factors in the remaining 26.03 %. Six limiting anthropogenic factors were identified: disturbance caused by fishermen and tourists (16.44 %), forestry works (4.11 %), illegal cutting of the tree supporting the nest (1.37 %), construction of a fishing hut near the nest (1.37 %), fires (1.37 %) and agricultural works and human presence (1.37 %). We present also the results of a spatial analysis aimed at disentangling how human settlements affect the distribution of the nests and how unpredictable settings of different kinds of temporary settlements can affect the viability of the nests. Different conservation actions are discussed with the objective of reducing the negative impact of the anthropogenic factors detected.

Low-intensive agricultural areas of Romania sustain high species diversity. Together with natural habitats, these areas are very important for European biodiversity. The ecosystem´s health is reflected in the predator status because of their position at the top of the trophic networks. The Common Buzzard (Buteo buteo) is the most common bird of prey species in Europe. During the first survey census conducted in Eastern Romania (2011–2012 breeding seasons), 8.55–10.35 breeding pairs/100 square km have been counted. The Common Buzzard density varies between breeding seasons and with differences in habitat structure. Their density is positively influenced by the density of forest edge and Simpson diversity index of habitats but is negatively influenced by the total habitat fragmentation and mean daily temperature. According to this analysis, the selection of breeding territories by common buzzards is positively influenced by a heterogeneous landscape in an area with low-intensive agriculture and with large areas of open habitats made up of natural or semi-natural vegetation.