House Sparrows Passer domesticus and Tree Sparrows Passer montanus: fine-scale distribution, population densities, and habitat selection in a Central European city

Populations of House and Tree Sparrows have rapidly declined in various breeding habitats throughout their European distribution range; however, the strongest decline was recorded within urban environments. In our study we investigated fine-scale distribution, population densities and habitat selection of both sparrow species within a 200 x 200 m squares in a medium sized city (Ceske Budejovice, Czech Republic) during the breeding season. The total population density of House and Tree Sparrow was 11.7 and 2.8 individuals/10 ha; however the densities of both sparrow species markedly differed among various urban units. The highest density of House Sparrow was recorded in residential areas (33.3 ind./10 ha) and Tree Sparrows were mostly found in garden colonies (10.3 ind./10 ha). After removing spatial effects, we found that numbers of both sparrows were negatively correlated with area of artificial surfaces (e.g. pavements, streets, railway networks or parking spaces) and positively correlated with area of city green. Built-up area did not affect numbers of House Sparrow, but there was a slight negative relationship with Tree Sparrow numbers. However, maximum numbers per square for both species were found in the areas where city green represented ca 50 % of all habitats. This suggests that mix of built-up areas and city green is more important for sparrow numbers than each habitat per se. Comparison of use/availability for studied habitat reveals that both sparrow species clearly avoided artificial surfaces. House Sparrow showed preference for built-up areas and Tree Sparrow showed similar preference for built-up areas and city green. Different habitat selection can be explained by a combination of different requirements for nest sites together with the nutritional needs of sparrows during the breeding season. The majority of nest sites were located in artificial structures such as roof tiles (80% for House Sparrow and 50% for Tree Sparrow), followed by nests located in crevices and holes on buildings. Both sparrows nested in older buildings: 92% of House Sparrow and 85% of Tree Sparrow nests were situated in buildings older than 30 years, i.e. built before the 1980s.