Habitat changes and dynamics of brown hare populations in western Po Plain (northern Italy)

The decline of brown hare populations recorded in European Countries since the half of the past Century has been observed also in Italy where the main causes are identified in agricultural intensification and changes and overhunting. Other supposed factors of the decline included habitat losses due to the increasing urbanized areas and road networks, and predation impact. From autumn 2005 to autumn 2012 we monitored nine hare populations living in protected areas of the Province of Milan (northwestern Italy) which is characterized by a very high urban density and where arable land is dramatically decreasing because of the expanding urbanization. The aims of this research were : i) to define population trend, ii) to evaluate the effect of habitat losses on hare populations, and iii) to find the main demographic parameters affecting hare population dynamics. We carried out nocturnal counts in March and November of each year and we estimated the densities by Distance Sampling method; using pre and post-breeding densities we estimated the spring to autumn increases and winter losses. For each protected area we measured the percentage of land use classes at the beginning and at the end of the study from two different editions of land use digital map of Lombardy Region (DUSAF, Regione Lombardia). We carried out curve-fit analyses on spring and autumn densities over the time in order to assess population trend and correlation and regression analyses between the percentage change of densities and spring to autumn increases, winter losses, and changes of habitat variables to individuate the main factor affecting population decline. Total spring density was 18.1 (SE=8.43) hares per km2 in 2006 and 17.8 (SE=6.91) in 2012; the difference between the initial and final densities was not significant (t=0.03; P=0.976). No significant trend resulted for spring density (R2=0.001; F=0.003; P=0.956) but we recorded marked fluctuations in the study period (min=11.0; max=24.1). Total autumn density was 33.3 (SE=4.24) hares per km2 in 2005 and 14.6 (SE=6.52) in 2012; the difference was significant (t=2.40; P=0.016). We recorded a significant and decreasing trend in the study period (R2=0.739; F=7.07; P=0.035). Only three out of nine hare populations showed increasing or stable trends and generally the decline of post-breeding populations was more marked than that of the pre-breeding ones. Declining populations were characterized by anomalous dynamics with negative spring to autumn increases and increases from autumn to the next spring. Percent change of post-breeding populations was negatively related to the percent change of urbanized areas (R2=0.921; F=25.10; P=0.002). It seems that hare populations in northwestern Po Plain are mainly affected by a very low recruitment probably due to habitat losses, increasing urbanization and related disturbance.