Lake Michigan common loon dive data

Breeding common loons for the movement and foraging pattern study were obtained from lakes in central and northern Minnesota and Wisconsin, and the Upper Peninsula of Michigan during summers 2010-2012. 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 (0.02o C accuracy, ≤ 0.05o C 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 were capable of storing 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. Geotag temperature data also provided indication of major flights (characterized by prolonged drop in temperature). Flight times were used to set bounds on the distances of migration events. Location estimates were used to determine gross movement patterns and generalized location (i.e., Green Bay, northern Lake Michigan, southern Lake Michigan) of loons while using Lake Michigan. Attributes of dives (i.e., proportion of time underwater, depth of dive, ascent and descent rates, duration of dive, time within 2 m of maximum depth, post dive surface interval) were extracted from pressure data, where depth (m) = pressure (dbars) * 1.019716 (http://www.seabird.com/document/an69-conversion-pressure-depth). Dives were considered to be submergence below the water surface, which we define as recorded depth of >0.8 m (typical body length of adult common loons in this study). Because pressure data were collected at 20-sec intervals, we interpolated the times of both dive initiation and surfacing. Average ascent and descent rates were estimated individually for each loon and used to interpolate these times, where rates were based on median values derived from dives > 47.25 m (n = 1,214). The descent rate used for interpolation was 1.056 m/sec and the ascent rate was 1.605 m/sec.