The query of one of the major online scientific research databases returned quite worrying data, because a large group of species breeding in Italy, 47 out of 270 (17%) has never been studied and this number grows further (56 species, 20.7% of the total) if we consider that 9 species with published papers have 0 h-index (i.e. do not yet have any citations). These species neglected by Italian ornithological research have been called ‘zero species’. Bird species without indexed studies are 87.2% native and mostly migratory (66.0%). They live mainly in wetlands (36.2%) and forest habitats (27.7%) and generally have an increasing population trend (44.7%). Furthermore, the majority of these species are classified as least concern by the Italian Red List (44.7%), with a lower percentage of threatened species (34.0%). Zero species are more unprotected than protected ones (61.7% vs 38.3%). Finally, 42.6% of them belong to passerines and have a very restricted geographical range (83.0%). Some examples of zero species are reported and discussed, such as the Stonechat Saxicola rubicola, the Common redpoll Acanthis flammea or the Red Kite Milvus milvus, highlighting some of their interesting traits that could stimulate research aimed at conservation.

Territory selection by birds of prey is an essential process influencing survival and productivity. For Golden Eagle Aquila chrysaetos, research in Europe has focused primarily upon migrating and high-density populations, and rarely on the territory selection in low-density populations. We analysed Golden Eagle breeding sites in Central Apennines (Italy), spanning from 29 sites in 1980 up to 38 sites in 2020, verifying in 4 different years (1980, 1990, 2000 and 2020) their status of occupancy or vacancy, through cross-checking data from available literature and field observations. In the chosen years, each site was characterized by land use and neighbouring distances variables, to individuate the presence of a possible common selection process. The different protection status of each area (unprotected or Natural/National Parks) was tested, assuming that habitat protection could have positive effects on Eagles’ territory selection. The so obtained panel data was statistically analysed by means of t-test, χ2 test and probit models. In one hand, Golden Eagles in the Apennines showed a continuous recolonization of territories, including seven previously vacant and two undiscovered sites. On the other hand, half of the vacant sites remain unoccupied. Our results suggest that Golden Eagles, in a low-density population, tend to minimize the effect of lower quality habitats by choosing a breeding territory which can guarantee low intra-specific interferences: 35% of 2020 breeding pairs have, at least, one nearby vacant territory. Depending on the quality of the available breeding habitat, Individual Adjustment Hypothesis (IAH) supports or replaces Habitat Heterogeneity Hypothesis (HHH).