Bird-assisted sampling of air temperature reveals three-dimensional cooling effects of urban vegetation

Air temperature in cities is highly variable horizontally and vertically, reflecting the complexity of the urban landscape. Yet, studies of urban temperature still depend largely on ground-based meteorological stations and satellite-derived surface temperature products, both of which provide limited information on near-surface air conditions and vertical structure. We tested a bio-assisted monitoring approach to characterise fine-scale three-dimensional patterns of summer air temperature in the city of Rome, Italy, using homing pigeons (Columba livia) equipped with lightweight GPS loggers air-temperature sensors. Flight data collected during summer sampling campaigns between 2023 and 2025 revealed pronounced spatial, vertical, and temporal variability in air temperature over the urban area. Modelling results showed that vegetation had a measurable cooling influence within the lower urban atmosphere with grass cover and wooded patches were both associated with lower air temperatures. Thermal contrasts between land-cover types were the strongest at low altitudes and during morning hours, when air above artificial surfaces was up to approximately 5 °C warmer than above vegetated areas. We also observed a buffering effect associated with green areas: air temperature, particularly near wooded vegetation, remained relatively stable up to approximately 300 m from the patch edge before increasing by as much as 3 °C. These findings suggest that animal-borne sensing can complement conventional monitoring by capturing air temperature variability across urban landscapes and heights, while also helping to identify when and where urban vegetation most effectively mitigates heat exposure. This approach offers new opportunities to support climate-resilient urban planning and targeted heat mitigation strategies.