Investigating temporal and spatial correlates of the sharp decline of an urban exploiter bird in a large European city
Résumé
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.