This dataset contains information on the distribution of geese and swans and the three-dimensional flight trajectories. The former was obtained through vehicle field surveys, interviews, and a literature review. The latter was obtained using ornithodolites.

Collection of bird distribution

The foraging and resting flocks of swans and geese were located and recorded at the stopover sites and in the wintering areas by vehicle. A cumulative total of approximately 60,000 km² of farmland (including pastures, rice fields, and cropland), in addition to bodies of water, including rivers, ponds, and lakes was covered. The surveys were carried out for a total of 101 days: nine days in Niigata Prefecture (from November 2018 to February 2019), four days in Yamagata Prefecture (in February 2019); 10 days in Akita Prefecture (in February and November 2017); 11 days in Akita Prefecture (in December 2018 and February 2019), 10 days in Aomori Prefecture (March 2018 and March 2019); five days in Miyagi Prefecture (in November 2017); and 52 days in Hokkaido (in March and April 2017, March and April 2018, and March 2019). The surveys were carried out in daylight between 08:00, after the birds left their roosts in the morning, and 16:00, before they roost in the evening. The approximate sunrise and sunset times during the study period were from 04:30 to 06:30 am and from 15:30 to 18:00. During the surveys, species and flock sizes on the ground were recorded and locations were mapped. Birds in flight were recorded only when they passed directly above the researcher.

Fixed-point observation using an ornithodolite

We used ornithodolites (VECTOR21, VECTOR21 AERO, and MOSKITO manufactured by SAFRAN Vectronix; 1σ distance error: ± 5m, 1σelevation error: ± 0.2°, 1σ azimuth: ± 0.6°) capable of obtaining highly accurate three-dimensional location data. These devices accurately measure an object's azimuth, elevation, and oblique distance and calculate the latitude, longitude, and altitude using the built-in compass and infrared laser illuminator. When used for birds, the tracking data is acquired at 3 to 6-second intervals. The response of flight altitude to terrain and landscape can be understood. During March and April 2018 and February and March 2019, fixed-point ornithodolite surveys were conducted at 93 sites within the study area to obtain location and flight altitude data. We measured flight altitudes in various environments, including farmland, water bodies, urban areas, forests, and mountainous areas, to elucidate the effects of landscape and terrain factors on flight altitude. The maximum measurable range according to the device's specifications was 12 km for structures. However, for the target species of geese and swans, the measured range was approximately 2 km for individual birds and approximately 3 km for flocks.