Temporal dynamics and spatial patterns of Galliform birds in Trentino – Italy.

Abstract

This study examines the population dynamics of 5 species of closely related galliform birds in the Dolomites, north-east Italian Alps. The aim was to assess the dynamics of these populations at the edge of their European distribution and to investigate the patterns of spatial synchrony. Three main types of data sets were used in the analysis. First, the hunting statistics collected from 210 hunting areas between 1965 and 1994 for each of the 5 galliform species. Second, rock partridge count data from 29 sample areas during the period 1994 to 1998. Third, guts helminths collected from rock partridge shot between 1995 and 1998. Tetraonid populations at the edge of their southern European distribution exhibited a weak tendency to cycle. These cycles only showed significant negative autocorrelation at half the cycle period and were classified as phase-forgetting quasi-cycles contrasting with the more regular oscillations recorded in the same species in Finland. Cycles were not found in time series of black grouse Tetrao tetrix or capercaillie Tetrao urogallus. Rock partridge Alectoris graeca saxatilis exhibited a higher tendency to fluctuate. Rock partridge populations declined between 1965 and 1975 with populations in the western province declining earlier. Total winter loss and spring to summer loss of adults were the most important population parameters influencing the year to year change in numbers. There was some compensation to hunting mortality. The hypothesis that macroparasites may be of significance in destabilising partridge abundance and generating cyclic oscillations was examined by investigating the intensity of parasite infection in cyclic and non cyclic populations. Ascaridia compar and Heterakis tenuicauda were prevalent in the rock partridge populations and significantly greater in cyclic populations than non-cyclic populations. There were large variations in synchrony both within and between species and only weak negative relationships between synchrony and distance. Species in neighbouring habitats were more likely to be in synchrony than species separated by several habitats. A detailed spatial analysis on rock partridge populations found an increase in synchrony with scale from the population to meta-population level. Rock partridge clustered in two groups DRY and WET and synchrony was stronger in populations in the same habitat with populations in the dry habitat showing a higher tendency to cycle. The modelling of the long term dynamics of spatially structured populations indicated that environmental stochasticity was the main cause of synchrony although there is also some dispersal between populations and the importance of this varied between species. Population viability analysis of the grey partridge Perdix perdix in populations in Britain between 1930-1960 and the "declining" continental populations from 1970 to 1994 confirms that the UK populations prior to 1960 were more resilient than the continental populations. Even very small harvesting cannot be tolerated by the present continental populations and this may indicate that the persistence of hunting activity, although with a limited effort, has contributed to the extinction of many sub-populations and is critically threatening the remaining ones.