Enrico Merli

Long-term trends of heron and egret populations in Italy, and the effects of climate, human-induced mortality, and habitat on population dynamics

Factors affecting bird population dynamics include climate, harvesting by humans, and habitat changes. Here, we describe the long-term (1972–2006) population trends of seven heron species in NW Italy, an area holding important European breeding populations of these species. Grey (Ardea cinerea), purple (Ardea purpurea), and squacco (Ardeola ralloides) herons, and little egrets (Egretta garzetta) exhibited a strong logistic increase, leveling off around year 2000 at 3–23 times their initial level. Black-crowned night herons (Nycticorax nycticorax) began by increasing like the former species but then dropped to initial levels. Such trends were found to be influenced by several candidate ecological factors, as assessed by ARIMA models. Specifically, grey herons increased following a decrease in human-induced mortality, as quantified by an index of hunting pressure, and an increase in winter temperatures. Little egrets increased mainly with the increase of the extent of ricefields, whereas squacco herons increased with increasing rainfall in the African wintering range. Black-crowned night herons were also positively affected by increasing African rainfall, but only during 1972–1988, whereas in later years competition with other herons could have affected the species’ decline. The improved protection of colony sites by special reserves was unlikely to be the primary trigger of the observed increase, although obviously important for the long-term population persistence. In conclusion, our study shows that heron populations of southern Europe are sensitive to environmental and climatic changes, as well as to temporal variation in human disturbance and changes in foraging habitats, though the importance of the different factors differs among species.

Using harvest data to predict habitat-population relationship of the wild boar Sus scrofa in Northern Italy

The relationships between the wild boarSus scrofa, Linnaeus 1758 density and the habitat characteristics were investigated by collecting bag records in 18 hunting areas during the 1995 and 1996 hunting seasons. The study areas were located in the Northern Apennines (N-Italy) from 470 to 1160 m a.s.l. In each study area a Density Index (DI) was calculated by weighting the number of wild boar culled in each hunting season on the number of hunting days and on the surface of the study areas. Moreover 16 habitat variables were measured in each study area. Correlation and regression analyses were performed considering the DI as a dependent variable. Mixed deciduous woods were positively correlated with wild boar density together with chestnuts woods and conifer reafforestations. No significant negative correlations were found. Twelve multiple regression models each including three habitat variables were ranked by the information-theoretic approach (modified Akaike’s information criterion). The study stressed the importance of mixed woods for wild boar and the usefulness of hunting data as a mean to predict the habitat suitability for the species.

The reintroduction of grey and red‐legged partridges (Perdix perdix and Alectoris rufa) in central Italy: a metapopulation approach

The grey partridge became extinct in the province of Siena (central Italy) in the late seventies, whereas the red‐legged partridge had already disappeared by the beginning of the twentieth century. Some reintroduction attempts of both species carried out in the 1980s gave encouraging but not definitive results, and failed after an initial success. This was probably due to the low number of birds released, the small size of the re‐introduction areas, their isolation, the farm‐bred origin of the partridges, and hunting. In the province of Siena, for the first time in Italy, a large‐scale reintroduction program of grey and red‐legged partridges was experimented. The project started up in 1995 with seven reintroduction areas for grey and four for red‐legged partridge, and was extended to 19 areas (22,562 ha) for grey and 7 (6858 ha) for red‐legged partridge in 2002. Population viability analyses for both species showed that if reintroduced populations were isolated they would be extinct in a few years. Therefore, a metapopulation approach was adopted (contemporary releases in reintroduction areas close to each other). In each area, 100–1000 partridges per year were released for a minimum of 3 years, from different farms in order to achieve the maximum initial genetic diversity. Releases were effected in late summer (August–September) in acclimatization pens containing 10–20 aviaries. The reintroduced population showed marked variability of some demographic parameters, such as pair density and brood production rate; instead, average brood size was relatively constant across the study areas, but with annual variations. Reintroduction success was limited to a few areas only, mainly depending on the habitat characteristics of the areas, their surface area and isolation, and on the degree of care for the birds during the acclimatization period.

Rana dalmatina and R. latastei: Habitat selection, fluctuation in egg clutch deposition and response to exceptional floods in northern Italy

Abstract A ten year census was carried out on Rana dalmatina and R. latastei egg masses deposited in 36 reproductive sites in a 10‐hectare area, subject to periodic flooding, on the banks of the Ticino River. The vegetation type surrounding reproductive sites was noted. There were no signs of decline in the populations of either frog species. The number of egg clutches fluctuated widely from year to year but no correlation between clutch number and either flooding or climate parameters were detected. R. dalmatina preferred partly open areas for reproductive sites, whereas R. latastei selected areas characterized by hygrophilous vegetation and a high tree canopy.