Abstract
Urban planning and management need long-term population level studies for evaluating how urbanization influences biodiversity. Firstly, we reviewed the current population trends of the House Sparrow (Passer domesticus) and the Eurasian Tree Sparrow (Passer montanus) in Europe, and evaluated the usefulness of citizens’ science projects to monitor these species in Finland. Secondly, we conducted a long-term (1991–2020) winter field study in 31 urban settlements along a 950 km north–south extent in Finland to study how latitude, weather and urbanization influence on sparrow’s growth rates. The House Sparrow is declining in 15 countries, and increasing in 5, whereas the Eurasian Tree Sparrow is declining in 12 and increasing in 9 European countries. The trend of the House Sparrow was significantly negative in continental Europe. However, the trend of the Eurasian Tree Sparrow was not significant. Both species have declined simultaneously in six countries, whereas in four countries, their trends are opposite. Citizen-based, long-term (2006–2020) winter season project data indicated that House Sparrow has decreased, whereas Eurasian Tree Sparrow has increased in Finland. However, the short-term (2013–2020) breeding season citizen-based project data did not indicate significant changes in the occupation rate of sparrows. Our long-term (1991–2020) field study indicated that wintering populations of the House Sparrow have decreased, whereas the Eurasian Tree Sparrows have both expanded their wintering range and increased their population size. Based on our winter count data, latitude and weather did not significantly influence the growth rates of sparrows. When the human population increased within the study plot, House Sparrow populations decreased, and vice versa. There was also a trend that a decreasing number of feeding sites has decreased the House Sparrow numbers. Urban-related factors did not influence the growth rate of the Eurasian Tree Sparrow. Our results indicate that the colonization of a new, even closely related species does not influence negatively on earlier urbanized species. It is probable that the niches of these sparrow species are different enough for allowing them to co-occur. The House Sparrow mainly nests on buildings, whereas the Eurasian Tree Sparrow can easily accept, e.g., nest boxes. Urban planning should take care of both the food availability and nest sites availability for both sparrow species.
Highlights
Increasing urbanization and human pressure on lands have important impacts on biodiversity, species distribution and abundances
Using our winter count data, we studied whether the latitude, weather conditions and urbanization influences the population trends and population growth rates of the wintering House Sparrows and the Eurasian Tree Sparrows
The Eurasian Tree Sparrow population size has been stable in continental Europe (One Sample t-test; t = −0.24, df = 26, p = 0.814)
Summary
Increasing urbanization and human pressure on lands have important impacts on biodiversity, species distribution and abundances. At the same time, some synanthropic species thrive well within human settlements [4,5]. Many different mechanisms, such as human-induced food availability, milder micro-climate and reduced predator abundance, have been suggested to be responsible for positive changes in urban bird species richness and population abundances [1,3]. The total number of buildings was lower during the first study winter than the later winters (Table 1). The snow arrived later on the study sites during the winter of 1990/1991 than the other winters (Table 1). There were no differences in the amount of the snow (cm) between the study winters (Table 1)
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