Birds minimize flight energy by utilizing atmospheric conditions such as dynamic soaring (using wind gradients) and thermal soaring (using updrafts). A previous study estimated wind speed and direction using the flight paths of streaked shearwaters (Calonectris leucomelas), applying the hypothesis that ground speed is minimized in headwinds and maximized in tailwinds. Lagrangian environmental data collection via bird flight paths offers distinct advantages for gathering information in coastal areas where conventional observation methods, such as satellites, suffer from low spatiotemporal resolution due to complex land-sea boundaries, or in fine-scale areas that are difficult to observe.

Unlike pelagic migratory seabirds such as streaked shearwaters, black-tailed gulls (Larus crassirostris) are resident species inhabiting coastal areas year-round, often sharing habitats with humans. We aimed to verify the feasibility of continuous environmental data collection in coastal areas using this species. We captured gulls using noose-mat traps in Kamaishi City, Iwate Prefecture, Japan (September-November). They were released after solar-powered remote data transmission loggers were attached to six individuals via harness. To optimize battery efficiency, 1 Hz (1 data point/sec) data were collected during daylight hours. A total of 769,618 data points were recorded from three individuals from October to January.

Following the method of previous studies, we estimated wind speed and direction by fitting a sine curve to flight direction and ground speed. A comparison with 10-minute average data from a nearby AMeDAS station exhibited similar trends, although validation was limited by the spatial distance between the flight area and the AMeDAS station.

Additionally, we identified 23 thermal soaring events (total 2,102 sec), which were distinguished by a spiraling ascent. Although thermal soaring has been reported in other gull species, this is the first record of thermal soaring in black-tailed gulls. Thermal soaring was defined within continuous flight ( > 3 min) segments > 60 sec with ascent and angle change > 60° over 10 sec (unidirectional turn > 60%), allowing for < 5 sec data gaps. The maximum ascent during thermal soaring was 165.6 m (duration: 70 sec), and the maximum flight altitude was 243.4 m. In contrast to flapping or gliding, the circling birds drifted horizontally, indicating advection of the updraft by the wind. These results suggest that wind estimation is also possible through the thermal soaring of black-tailed gulls.