Abstract
Non-native Monk Parakeets (Myiopsitta monachus) are invasive birds widely distributed in European urban parks. Studying the nesting sites of urban populations is mandatory since these areas often serve as initiation of colonization processes in surrounding non-urban environments, posing a risk to agricultural crops and commercially valuable orchards. Therefore, understanding the density and distribution of nesting sites, as well as the structural characteristics of both the nests and their host trees, becomes crucial. In this study, we surveyed all Monk Parakeet nests in the five largest urban parks in Rome. Our data provides new insights for urban habitats supporting previous findings on nest-tree selection in Monk Parakeets. We recorded 66 nests on 30 trees belonging to four ornamental species: Cedrus libani, Phoenix canariensis (or P. dactylifera), Pinus pinea, and Trachycarpus fortunei. Cedars and palms were the most frequently used host trees, with nest density varying among parks (2 nests per 10 hectares, approximately). Nests were typically located at heights of around 13–14 meters, and parakeets showed a preference for taller trees with larger trunk diameters. These larger trees offer increased stability (e.g., during adverse weather) and, for highly social species like this, allow to build nests in higher (and then sure) positions, in terms of group dynamics and predator avoidance. Differences in tree architecture may account for the variation in relative nest height (nest height/tree height ratio, %) among species: in palms, nests are placed higher in the canopy (87.76% ± 7.03) compared to those in cedars (64.7% ± 16.4). Cedars hosted a significantly greater number of nests per tree (2.8 nests/tree ± 1.82; n = 20 nest trees) compared to palms. Our findings, combined with citizen-science data, could contribute to more effective management and control strategies—not only within urban parks but also at finer spatial scales, such as private gardens and residential areas.