Importance Of Nest Sites Availability For Abundance And Changes In Number Of House- And Tree Sparrow In Warsaw

Abstract House- and Tree Sparrows were censused on 55 plots (684 ha), representing 3 habitats: housing estates, parks and allotment gardens in Warsaw from 2005-2009 and in 2012. Also, the data on nest sites of both species were gathered. Data from 70s/80s of the other authors enabled to determine the changes in number of sparrows. The population of House Sparrow decreased on average by 48% and the sharpest decline was found in allotment gardens. The decline continued in the period of studies, i.e. in 2005-2012. Tree Sparrow showed an increase from 70s/80s by 68% although in 2005-2012 the population was stable or even decreased. House Sparrows nested mainly in crevices in buildings, and suboptimal nest sites – such as nest-boxes and holes in trees – were occupied only in these areas where food condition were particularly good. Resources of optimal nest sites on studied area was almost entirely sufficient for House Sparrows population. Number of House Sparrow was related to area/presence of buildings. Renovations of buildings strongly influenced local number of this species, however they were not the main cause of its decline. Although nest-boxes were occasionally used by H. Sparrow, their presence could not stop the decrease in numbers caused by loss of nest sites. Tree Sparrow showed greater plasticity in their choice of nest sites. In parks their abundance was correlated with the number of nest boxes. It was suggested that in this habitat, the observed decrease of House Sparrow with simultaneous abandonment of nest-boxes (and other nest sites) may have contributed to the increase in Tree Sparrows.