Abstract
Increasing urbanisation and human pressure on lands have huge impacts on biodiversity. Some species, known as “urban exploiters”, manage to expand in urban landscapes, relying on human resources. The House Sparrow (Passer domesticus) is the perfect example of a human-commensal species. Surprisingly, this urban exploiter has been declining all over Europe over the past decades. The proximate causes of this decline remain poorly understood. We particularly lack understanding about urban habitat characteristics that are particularly unfavourable for House Sparrows. In the present study, we analysed fine-scale habitat characteristics of House Sparrow population sizes and trends using a fifteen-year House Sparrow census (2003–2017) covering the urban diversity of Paris (nearly 200 census sites), one of the densest European cities. We documented for the first time the dramatic decline (−89%) of the species in Paris over the study period. The temporal decline over the whole city correlates with the concomitant increase in the number of breeding Sparrowhawks. We could not detect statistical influences of annual variations in weather conditions and pollution. The decline of House Sparrows is spatially heterogeneous. Indeed, site-scale analyses revealed sharpest declines at sites that initially hosted the largest numbers of sparrows, which are areas with a relatively high proportion of green spaces and new buildings. Further experimental studies are now needed to disentangle the exact impact of specific characteristics of the urban environment on House Sparrow populations.
Highlights
With the growth of the world human population and the increase in human pressure on lands, cities are constantly expanding, often leading to a reduction of biodiversity with increasing urbanisation (Marzluff et al 2001; Chace and Walsh 2006; Clergeau et al 2006; McKinney 2006, 2008; Clanché and Rascol 2011; Seto et al 2012)
The strong correlation between random intercept for site effects and random slopes for site-specific linear Year effect (r = −0.43, M1, Table 1) reveals that the sharpest declines occurred at sites with the highest numbers of House Sparrows at the beginning of the study period, whereas the numbers of House Sparrows were relatively stable at sites with low local abundance (Fig. 2b)
The strength of the decline seems to depend on locations, as urban House Sparrow populations would have ceased to decrease in the United-Kingdom where they are stabilising at very low population size (Woodward et al 2018) while they are still declining in Southern European countries like France, Belgium (De Coster et al 2015), Germany (Witt 2000) or Spain (Murgui and Macias 2010)
Summary
With the growth of the world human population and the increase in human pressure on lands, cities are constantly expanding, often leading to a reduction of biodiversity with increasing urbanisation (Marzluff et al 2001; Chace and Walsh 2006; Clergeau et al 2006; McKinney 2006, 2008; Clanché and Rascol 2011; Seto et al 2012). The proportion of people living in urban places is higher than 80% in developed countries (Antrop 2004). This is a global phenomenon as in developing countries land areas occupied by cities are increasing even more rapidly (UN-Habitat 2016). Urbanisation can affect wild vertebrates, and especially wild birds, because it leads to habitat fragmentation (Antrop 2004) as well as an increase in disturbances such as air (Eeva and Lehikoinen 1995, 1996; Llacuna et al 1996; Eeva et al 2009), noise (Meillère et al 2015a, b) or light pollution (Dominoni et al 2013).
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