Overview
- City counts and ornithologists report that house sparrow numbers in Berlin are roughly 70% lower than in 2021, a drop described by Nabu as a “free fall.”
- The decline is unusually rapid compared with other urban songbirds and many suitable nest sites in the city now stand empty, which suggests loss of nesting alone does not explain the collapse.
- Researchers have highlighted Plasmodium (avian malaria) as a leading, unproven hypothesis because parasites and their mosquito vectors do better at higher temperatures, a link supported by a 2019 London study but not yet tested in Berlin.
- Experts also cite interacting pressures that could reduce survival and breeding success, including severe insect loss that starves nestlings, rising pollution, building practices that remove nesting niches, and predation by cats and corvids.
- Berlin conservation groups and BOA plan targeted pathogen and demographic studies to test causes, and the results could change city conservation steps and what to watch for next, such as higher mosquito activity and poorer winter survival in remaining flocks.