Dottore di ricerca

ciclo: XXXIV

Titolo della tesi: Breeding ecology of Short toed eagle (Circaetus gallicus) in Tolfa Mountains (Central Italy)

We have followed a population of Short-toed Eagle (Circaetus gallicus GMELIN 1788) in “Monti della Tolfa” (Tolfa Mountains; WGS84, E 11.971°, N 42.150°), coinciding with the SPA (Special Protection Area) IT6030005 “Tolfetano-Cerite-Manziate District” (Central Italy). The land cover is composed mainly of farmland and broad-leaved woodland, followed by shrubland, natural grassland, sparsely vegetated areas and urban areas, which extent is probably underestimated, due to the rapid increase in building activities leading to changes in land use from agricultural to residential. The search for nests was carried out in an intensive study area (sample area) represented by an area of 210 km2 in the south-west part of the whole study area (about 1/3 of its total surface). Its landscape is representative of the overall environment. Short-toed Eagle is the only representative of snake eagles that breeds in the Palearctic. The overall European population seems to be stable. Since the 1980s, Italian population of Short-toed Eagle has grown and there has been a territorial expansion. The increase in the breeding population in Lazio, between the early 1980s and the end of the 2000s, was estimated to be 180%. The main purpose of the PhD project was to provide quantitative data on characteristics of the nesting site, breeding calendar, diet, breeding performance and behaviour of the species. In particular we have set ourselves the following goals: a) investigate nest habitat features, habitat suitability and main environmental variables affecting the spatial distribution of territorial pairs; b) estimate population density and breeding success; c) define the trophic spectrum of STE, comparing it with the results of previous studies in the same study area and in other populations from Italy and Europe; d) track the delivery rate of prey at the nest throughout the daily activity and 5) obtain quantitative information about adults and nestlings behavior during the breeding season with a non-invasive system. Between 2019-2021, more the 250 observation days were conducted. Using Generalized Linear Models and the Information-Theoretic Approach, we compared the environmental features (i.e. land cover and topography) that characterize nesting sites in the study area. Additionally, we described the nest-site selection of the species by characterizing nine detected nests and comparing their characteristics with those of an equivalent number of nearby randomly selected sites. We found that, as expected, the short-toed eagle settles on hillsides covered by broad-leaved forests (both evergreen and deciduous) with open areas and away from agricultural areas. Moreover, the nests were found on steeper slopes, on trees extensively covered with climbing plants, possibly to hide them from predators and human disturbance. Our results suggest that, for the conservation of the short-toed eagle, careful management of woodland coppicing is required, as well as greater control of human disturbance and 3 nests were close investigated through the use of camera-traps that have collected more than 87.000 images. Diet was studied during the breeding seasons 2020-2021 with direct observation of hunted prey captured by camera-traps and with collecting of pellets. In the sample area (about 1/3 of the total surface the entire district) we discovered 20 territorial pairs, with density of 10,5 km2/pair. Comparing this data with those deriving from research carried out in previous years in the same study area, it appears that the density of the species in the study area is increasing, and in any case falls within the averages of some areas of Greece and Spain. To study diet we monitored five nests and three roosts between 2020 and 2021, using photo trapping method and the collection and analysis of feeding remains. A total of 247 prey items were identified. The diet of this population is clearly snake-based (93.5% of prey spectrum). The main prey is Hierophis viridiflavus (83% of snakes captured), probably due to its high availability in the environment and its average size, which is positively selected by the Short-toed Eagle. Long-term comparison with previous data shows an overtime contraction of diet breadht with a relative increase of H. viridiflavus compared to other prey. The same pattern is observed in long-term studies on the snake community of our study area and is probably linked to both local anthropogenic impacts and global warming, which tends to increase thermophilic and generalist snake species such as H. viridiflavus. We also investigate behavior and division of adult roles during the entire breeding season. Together with field observations, we note significant role differences between partners. Male is the first to arrive on the nest, it carries mainly dry twigs in the pre-laying period; female, on the other hand, carries mostly leafy twigs, after laying. Brooding task is almost up to the female (83% vs 13%), that always broods in the night. Adult tasks resulted even more distinct during the fledging period: female continued to stay constantly at nest until the young was 22 days old, then her absences regularly increasing up to the 45th day, the first one spent completely in solitude by the young. Female-young relationships are intense and long-lasting, unusual for a diurnal raptor, and sometimes rather similar to the typical effusions of owls. We also note significant differences in pairs behaviour, supposing that this may arise from the fact that some pair is new or others are old and established. We annoted quantitative differences in number of landings, twig transport, nest arrangement and mainly a typical and unmistakability behavior, that we will propose to call "neck display”.

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