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

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.

Automated summary

The study revealed a drastic decline of House Sparrow populations in Paris over the past 15 years, which contrasts with the patterns seen in other cities. The increase in breeding Sparrowhawks was found to be correlated with the decline in House Sparrows, while weather conditions and pollution showed little statistical influence. Additionally, areas with initially high numbers of sparrows, characterized by a high proportion of green spaces and new buildings, experienced the sharpest declines in population. Further experimental research is needed to clarify the exact impact of urban environment characteristics on House Sparrow populations.