Spring migration at the southmost stop-over site in Europe, the Gavdos Island (Crete, Greece)

The island of Gavdos, located south of Crete and only 250km north of African coast plays an important role for migratory birds in spring being the first land where birds can re-fuel and rest after the long open-sea crossing. Bird ringing surveys conducted in spring of 2002-2004 revealed that the island funnels migrants from a very wide range of Eurasia, probably reaching east to Siberia. The survey was initiated again after 18 years in early June 2021, and carried out in full intensity in spring 2022, with 500m of mist nets used for 75 days from mid-March to end of May. The nets were opened from 06:00-19:00 at two ringing sites on the island, covering all the major habitats for birds on passage, excluding the shore. A total of 3103 individuals of 63 species were ringed, with 49 individuals of 19 species retrapped, and a single foreign recovery (Germany) obtained. The most trapped species was Hirundo rustica (15.5%), followed by Sylvia borin (14.44%) and Motacilla flava (8.5%). A notable number of Sylvia communis (7%), Muscicapa striata (6.9%), Anthus trivialis (4%) and Ficedula hypoleuca (4.16%) were also trapped. Noteworthy were also the records of Merops persicus (N=2), and Sylvia ruepelli (N=7). Sylvia species were the most common genus trapped (28%). These results call for an intensification of mist-netting of birds at Gavdos, as the study of migratory patterns on this remote island can provide a unique window into the bird migration across the central Aegean migratory corridor

The timing of the spring migratory passage of Sylvia species over the southernmost point of Europe, Gavdos Island (Crete, Greece)

Spring migration phenology is shifting towards earlier dates in response to climate change in many bird species. However, the patterns of change might not be the same for all species, populations, sex and age classes. The patterns of change could differ between species with different ecology and different lengths of migratory routes. We analyzed the timing of the spring migratory passage of seven species of the Sylvia genus on the island of Gavdos, Greece from mid-March to the end of May 2022 in order to determine specific species’ phenology following the crossing of the Mediterranean Sea. The first migrant Sylvia species that appeared on Gavdos during March were Sylvia rueppelli and Sylvia melanocephala, followed by Sylvia cantillans and Sylvia atricapilla. At the beginning of April, two more species were present on the island: Sylvia communis and Sylvia curruca, while during mid-April, Sylvia borin started migration across Gavdos. The first Sylvia warblers during spring passage were species wintering in Northern Africa and the Mediterranean (i.e. short-distance migrants) and in the Sahel zone, followed by long-distance migrants. The most numerous species during spring migration was Sylvia borin. The results of our study call for an intensification of data collection in the form of year-round tracking and long-term data sets at a large geographical scale to determine the impact of climate change on the timing of migration and its consequences on bird populations across Europe

Spring migration of Sylvia species over the southernmost point of Europe Gavdos Island (Crete, Greece)

The island of Gavdos, situated only 250 km north of the African coast, is the first land birds reach flying across a long stretch of the open sea in spring and acts both as a refuelling as well as an emergency landing site for northward bound migrants. We report here patterns of the spring migration of the genus Sylvia trapped on Gavdos in mist-netting surveys conducted in three successive springs in the period 2002-2004, and in 2022. Out of a total of 7983 individuals of 17 genera and 74 species ringed across the four years, there were 2211 individuals of eight Sylvia species, making up to 30.7% of the total catch per season. S. borin was the most commonly trapped species among the nine (S. atricapila, S. borin, S. cantillans, S. communis, S. curruca, S. melanocephala, S. nana, S. rueppelli, S. nisoria), accounting for 62.2% of the total Sylvia catch. The longest mist-netting period covering 75 spring passage days carried out in 2022 in which seven Sylvia species were trapped, including Sylvia melanocephala (N=7) trapped for the first time on Gavdos. Differences were also observed in the phenology of the passage, albeit not for all species. The late onset of the passage is most likely attributable to an unusually cold spring with long periods of strong, opposing north-westerly winds rather than an actual shift in the spring passage timing

Nesting Habitat Selection and Breeding Distribution of Two Sympatric Insular Eagle Populations: The Golden Eagle and the Bonelli’s Eagle on the Island of Crete, Greece

In the current study we present data collected during the last two decades on the island of Crete (Greece) regarding the nesting habitat of two sympatric species namely the Golden Eagle (Aquila chrysaetos) and the Bonelli’s Eagle (Aquila fasciata). The factors that determine the species nest site selection were identified via a logistic regression model and nesting habitat suitability maps were constructed by using maximum entropy models and a Geographic Information System. At the spatial scale considered, the best predictors of nesting habitat were topographical variables such as altitude and slope indicative for the requirement of rugged terrain. The predictive maps represented by the subset of topographic variables were also able to predict nest-site selection by both species more adequately than subsets of bioclimatic or human disturbance variables. Based on the overlap of the available nesting habitat of the two eagle species, an ecological separation was detected most probably related to their diet spectrum and consequently foraging range. Compared to the Golden Eagle the Bonelli’s Eagle was found breeding on lower altitude, more often on sea cliffs or the ends of gorges and in the periphery of mountain areas. In the latter case human-induced mortality and land use changes are regarded as significant factors for the observed pattern

Looking at the Expansion of Three Demersal Lessepsian Fish Immigrants in the Greek Seas: What Can We Get from Spatial Distribution Modeling?

A big number of Red Sea species have entered the Mediterranean Sea since the opening of the Suez Canal. Some of them quickly establish local populations and increase their abundance, forming a potential threat for local biodiversity and fisheries. Here, we use habitat modeling tools to study the expansion of three alien, demersal fish species that entered the Mediterranean basin at different times: Pterois miles, Siganus luridus and Siganus rivulatus. Georeferenced occurrence data from the eastern Mediterranean over the past ten years were compiled using online sources, published scientific literature and questionnaires and were correlated with environmental and topographic variables. The maximum entropy modeling approach was applied to construct habitat suitability maps for the target species over all of the Greek Seas. Results emphasized the three species’ strong coastal nature and their association with the presence of Posidonia oceanica meadows. Probability maps evidenced that for all species there is a higher likelihood of presence along the southeast and central Aegean and Ionian Sea coasts and a lower likelihood throughout the North Aegean Sea. For Siganus spp., predictions in the Thracian Sea were highlighted as highly uncertain, as the environmental conditions in this area partly fall outside the range of values occurring in locations of their current presence

Selection of Nesting Habitat and Insular Niche Separation of Two Sympatric Aquila Species

Aquila chrysaetos and Aquila fasciata are two congeneric eagle species distributed in the Mediterranean region which are supposed to compete for similar breeding and foraging resources. In the present study, bioclimatic, topographic, and human-related habitat parameters were investigated for 64 and 75 nest sites of Golden and Bonelli’s eagles, respectively. The nests were found during fieldwork undertaken from 1995–2020. Overall, the habitat parameters that best discriminated nest site selection were associated with elevation, temperature, and land use with topographic variables being most powerful for niche separation. Univariate analysis, regression, and species distribution modeling identified a strong association of the species with altitude pinpointing the Golden eagle’s mountainous and continental character and the Bonelli’s eagle being a lowland and coastal species. Golden eagle nests were situated away from human settlements on steep cliffs in higher altitude areas with transitional woodland-shrub vegetation. In contrast Bonelli’s eagle nests were located on low-altitude warmer zones, closer to the coast and human settlements with more natural grasslands in their vicinity. The ecological niche separation of the two species was best described by altitude and temperature, though no clear-cut evidence was detected for their competitive exclusion. Inter-specific nearest neighboring distance was found statistically significant only for the Golden eagle which seems to be less tolerant in its co-existence with the Bonelli’s eagle. Conservation measures for both species should target territories under human pressure, though more research should focus on the species range use and habitat heterogeneity within overlapping territories