We identified breeding pairs of adult Gambel's white-crowned sparrows and their nests near Toolik Field Station across 2014-2016. We used mist nets and/ potter traps to capture birds and give them unique USFWS metal bands and color bands for individual identification. During the breeding season, we also caught birds and affixed them with backpack radio-transmitters emitting a unique radio-frequency.

We used these radio-transmitters in conjunction with two automated datalogging radio-receivers to confirm the presence or absence of adult birds on the breeding site from the breeding period through onset of fall migration.  We manually scanned records of radio-detections to determine the day of year that birds were last detected on the breeding site and the time of day that these birds were last  detected.  We used hand-held radio-telemetry to validation automated records by visually confirming that radio-transmitters remained affixed to birds.

We also visited nests every 1-2 days to determine whether any offspring successfully fledged the nest and the day of year that nests fledged or failed.

We used data from the NOAA ESRL sunrise/ sunset calculator (https://www.esrl.noaa.gov/gmd/grad/solcalc/) to determine the time of day that sunset occurred at the Toolik Field Station for each day of departure observed in our dataset. We used the time of sunset from this calculator to determine the difference between the time of day that birds departed the breeding site and sunset.

Please see publication for a full description of data collection (Chmura et al., 2020-  https://doi.org/10.1007/s10336-020-01754-z).