Grosso, G. | Search bioRxiv

bioRxiv2026

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 {degrees}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 {degrees}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.

ecology↗

bioRxiv2026

Beyond the urban surface: bird-borne sensing reveals the atmospheric structure of urban heat

Urban heat is commonly characterized near ground level, while its vertical atmospheric structure remains difficult to observe across cities. We used bird-borne temperature sensors on homing pigeons (Columba livia) and yellow-legged gulls (Larus michahellis) to investigate the horizontal, vertical and daytime structure of the lower urban atmosphere over Rome. The dataset comprised 61,917 air-temperature observations from 47 individuals of gulls and pigeons, spanning 17 km and altitudes up to 400 m above ground level. Generalized additive models related air temperature to distance from the city centre, altitude, time of day, land cover, tree-patch area and topography, and reconstructed three-dimensional temperature fields. Air temperature showed a centre-to-periphery gradient that weakened with altitude and through the daytime period. At 20 m above ground level, its magnitude declined from -0.40 {degrees}C km--1 at 09:00 to -0.30 {degrees}C km--1 at 13:00 and -0.19 {degrees}C km--1 at 17:00, with weaker gradients at higher altitudes. Reconstructed isothermal boundaries showed a complementary vertical pattern. At 13:00, median heights decreased from 135 m for the 34 {degrees}C boundary to 76 m for 35 {degrees}C and 37 m for 36 {degrees}C. The 34 {degrees}C boundary reached its greatest extent around midday, rising from 57 m at 09:00 to 135 m at 13:00 before declining to 14 m at 17:00. Horizontal thermal contrast and the vertical development of high-temperature air represent complementary dimensions of urban heat. Bird-borne sensing offers a promising approach for resolving three-dimensional atmospheric temperature patterns that conventional monitoring networks cannot capture.

ecology↗