Navigating With The Sun / by Michael Johns

One of the easiest ways to study basic life-history and behavior of seabirds is to outfit them with devices the passively record data for you. The tricky part is getting those devices back in order to download and analyze those data. So far this season, we have recovered 19 geolocator tags that were secured to the legs of Cassin's auklets breeding in artificial nest boxes last year. These tags are designed to be very small and light, and have zero affect on the breeding performance and survival of birds that carry them. Geolocators record ambient light levels experienced by the bird as it flies around it's environment. These light level recordings are later used to estimate roughly where the bird was twice a day throughout the deployment period, using the timing of sunrise and sunset (which varies depending on longitude) and the duration of day-length (which varies by latitude). The photo above shows a row of tags calibrating in the sun on SE Farallon Island.