Breeding common loons were obtained for the movement and foraging pattern study from lakes in central and northern Minnesota and Wisconsin, and the Upper Peninsula of Michigan. Both adults of a territorial pair were fitted with archival geolocator tags (Model LAT 2500; 34.6 x 8.3 mm, 4.4 g; Lotek Wireless Inc.). A combination of adhesive and plastic cable ties were used to affix the geolocator tag to a modified lock-on aluminum leg band. Tags were programmed to collect daily location estimates for up to two years, tag temperature (0.02 oC accuracy, ≤ 0.05 oC resolution) at 30-min intervals, and pressure data (±1% accuracy, 0.05% resolution) at 20-sec intervals during daylight hours to document foraging patterns (dive profiles) while on the Great Lakes during fall migration and on the wintering grounds. Data stored on geolocator tags were not transmitted, requiring that the marked loon be recaptured to recover the tag and download the data. The geolocator tags could store data for several years before the devices needed to be downloaded. Geolocator tag data collected over the previous year(s) were downloaded from tags using LAT Viewer Studio software (Lotek Wireless Inc.). Geolocator tag location estimates were based on light-based geolocations using the template-fitting approach (Exstrom, 2004), in combination with tag temperature (sea surface temperature) and pressure (dive depth) data. Template-fit error estimates were used to filter aberrant geolocation estimates. Sea surface temperature (derived from NASA Moderate Resolution Imaging Spectroradiometer [MODIS] imagery) across North America inland lakes, Atlantic coastal waters, and the Gulf of Mexico, coupled with diving depth information were used to improve or obtain location estimates and timing of migration movements when light-based geolocation estimates were unreliable.