In the region of Brittany, house sparrows have adapted to urban environments, with 80 percent of them nesting in buildings rather than natural cliffs, according to the encyclopedia cited in a recent census. These nests are commonly built in chimney flues, which can lead to serious issues such as blocked flues, carbon monoxide buildup, or even fires. A nest constructed in the spring can remain in the flue long after the young birds have fledged, typically between 30 to 45 days after hatching. This situation has prompted local authorities to consider alternative solutions to address the problem without harming the birds. The house sparrow, now more commonly found in urban areas, has seen a significant population increase between 1954 and 2010. In addition to nesting issues, the birds are also known to cause damage to crops, particularly maize seedlings, leading to tensions with local farmers in Brittany and the Pays de la Loire. To prevent carbon monoxide poisoning and fire hazards, some communes have advised residents to inspect their chimneys before the first fire of the season. Recommendations include insulating chimneys, covering them with solid grilles, and installing smoke and carbon monoxide detectors. In 2026, four Breton prefectures authorized the shooting of 10,500 house sparrows, but this was quickly challenged in court. The administrative court in Rennes suspended the orders, citing concerns about the legality of the action and the lack of proof that alternative methods had failed. Similar rulings had previously been made in 2024 and 2025 by other courts, following appeals from environmental groups such as Bretagne Vivante, the LPO Bretagne, and One Voice. These groups have pointed to a 2022 study by the University of Rennes 1, which found that shooting sparrows was largely ineffective and recommended focusing on preventing access to nesting sites and managing feeding areas in agricultural zones. As an alternative to shooting, the Green Fund project, supported by the DREAL for the years 2025–2027, is testing solutions such as grilling chimneys to prevent sparrows from nesting. This initiative involves collaboration between the LPO Bretagne, the University of Rennes 1, and the Regional Agricultural Chamber of Brittany. The goal is to block access to the cavities that sparrows use for nesting, thereby reducing the risk of blocked flues in the fall. While the project is still in its testing phase, it represents a promising approach to resolving the issue without harming the birds. For now, the effectiveness of chimney grilles remains under evaluation, but they are being considered a viable option.