Accuracy of geolocation estimates for flying seabirds

Abstract

Geolocation (Global Location Sensing or GLS logging) using archival light-recording tags offers considerable potential for tracking animal movements, yet few studies of flying seabirds have exploited this technology. Our study evaluated its effectiveness for determining foraging ranges of black-browed albatrosses Thalassarche melanophrys fitted simultaneously with GLS loggers and satellite-transmitters (Platform Terminal Transmitters, PTTs). After some preliminary validation, the position of an albatross could be determined by geolocation with a mean error ± SD of 186 ± 114 km (SDs of 1.66°and 1.82°of latitude and longitude, respectively). Errors from identical static loggers were lower (mean ± SD of 85 ± 47 km, with overall SDs of 0.61°and 0.99°of latitude and longitude, respectively) and less variable, with the difference attributable to variation in sensor orientation, intermittent shading by plumage, and the difficulty of correcting for extensive, potentially non-linear movements of flying birds. Iterative smoothing reduced both the mean error and the inflation of kernel ranges derived from GLS data, but over-smoothing contracted the extremes of the range. This reduced the overlap with radial cores apparent in the control data, and should be avoided for multinuclear GLS fix distributions. The accuracy of GLS tags is more than adequate for tracking migration and breeding-season foraging ranges of pelagic species, and for identifying broad-scale habitat preferences, overlap and potential conflict with commercial fisheries.

Individual variability in the migratory path and stopovers of a long-distance pelagic migrant

“…In short, the analysis of light data provided by the geolocators delivered (a maximum of) two positions per day for the whole migratory period. The tracks were double-filtered (following Phillips et al 2004) to remove any outlying positions, resulting in an estimated locational error of 186 AE 114 km (Phillips et al 2004). …”

Post-breeding dispersal of Adélie penguins (Pygoscelis adeliae) nesting at Signy Island, South Orkney Islands

“…At the end of each 10-min period, the maximum (truncated) light reading and the sum of positive saltwater tests (between 0 and 200, where 0 indicates that the logger was always dry and 200 that it was always wet) were recorded (Afanasyev 2004). Light level data were processed following the approach of Phillips et al (2004). The times of sunrise and sunset were determined from thresholds in the light curves and converted to location estimates using TransEdit and BirdTracker (British Antarctic Survey, Cambridge, UK); latitude was derived from day length and longitude from the time of local noon.…”

“…Previous studies have deployed ARGOS satellite transmitters (Platform Transmitter Terminals or PTTs) on small numbers of adult and fledgling Adélie penguins to investigate their post-breeding dispersal (Kerry et al 1995;Davis et al 1996Davis et al , 2001Clarke et al 2003) but limited battery life and the need to attach such devices to feathers which are subsequently shed at moult has meant that complete movement over the winter period cannot be documented. In recent years, however, technological advances have resulted in the production of miniature Global Location Sensor (GLS) loggers; battery-powered devices that enable the movements of seabirds to be tracked on a year round basis (Phillips et al 2004;Bost et al 2009;Ballard et al 2010).…”

From Ice to Penguins: The Role of Mathematics in Antarctic Research

“…equinoxes, and the precision is relatively low, with an average error of 186 km 14! estimated for free-ranging albatrosses (Phillips et al 2004).…”

“…large migration studies), geolocators or Global Location 6! Sensing (GLS) loggers are extremely useful (Phillips et al 2004;Croxall et al 2005). 7!…”