Recent declines in urban Italian Sparrow Passer (domesticus) italiae populations in northern Italy

摘要

During the last quarter of the 20th century, the House Sparrow Passer domesticus declined greatly in numbers throughout its western European breeding range (Summers-Smith 1988, BirdLife International 2004). This followed an increase during the 19th century that matched the expansion of human settlements (Holloway 1996). Population declines have occurred in both urban and rural areas, but have been more severe in the former, raising considerable public concern (Summers-Smith 2003, Robinson et al. 2005). The reasons for this decline have been investigated in detail on British farmland, where complex source–sink dynamics of local populations were identified (Hole et al. 2002). Food supplementation experiments showed that the decline could be related to a reduction in winter food supplies (Hole et al. 2002), due to the progressive shift from spring to autumn sowing of cereals (Chamberlain et al. 2000, Robinson & Sutherland 2002). In addition, the recent introduction of hygiene regulations and the increased efficiency of harvesting machines has led to a marked reduction of spilt grains and seeds available to granivorous farmland birds, including sparrows (Robinson & Sutherland 2002, Robinson et al. 2005). Factors affecting the decline of urban populations are less well understood (Summers-Smith 2003, Robinson et al. 2005). In Britain, urban populations declined by 60% between 1970 and 2000, although with some geographical variation (Robinson et al. 2005). Among the possible causes, a reduction of nest-site availability due to improvements in quality and insulation of rooftops and a reduction of food availability due to loss of weedy corners from urban areas have both been suggested as likely explanations, as was an increased transmission of epidemicdiseases (Summers-Smith 2003, Robinson et al. 2005).