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Marine Biology

, Volume 145, Issue 2, pp 215–223 | Cite as

GPS tracking a marine predator: the effects of precision, resolution and sampling rate on foraging tracks of African Penguins

  • P. G. Ryan
  • S. L. Petersen
  • G. Peters
  • D. Grémillet
Research Article

Abstract

We used a prototype GPS logger to track the movements of breeding African Penguins (Spheniscus demersus). The loggers also recorded temperature and water depth, which allowed us to reconstruct foraging tracks in three dimensions, although GPS signals are interrupted when the birds dive. Here we report the logger’s performance in the field and assess the effects of GPS error, resolution and sampling rate on estimates of foraging track length and speed. There is a trade-off between sampling rate and battery lifespan. We tested loggers at sampling intervals of 1 s, 10 s, 1 min, 2 min and 10 min. Sampling less frequently increases the chance of tracking an entire foraging trip, but it slows uplink times, slightly decreases the accuracy of positional fixes, and significantly reduces the ability to measure fine-scale aspects of foraging behaviour. Compared with radio or satellite tracking, GPS loggers offer unprecedented detail about animal movements. The results of our analysis suggest that techniques that sample relatively infrequently, such as satellite tracking, underestimate actual track lengths by up to 50%. However, caution is needed when interpreting fine-scale sampling for relatively slow-moving organisms. Re-sampling 1-s tracks suggests that c. 35% of apparent movements at this scale are due to measurement error and, more importantly, the limited spatial resolution of GPS (1.85×1.54 m at the study area). We recommend that researchers use a 1-s sampling rate for fine-scale studies, but resample at less frequent intervals to remove spurious noise for slow-moving animals. At current levels of resolution, animals should move at least 4 m per sampling interval. We provide empirical correction factors to compare inferred track length sampled at different rates, but caution that these are idiosyncratic and strongly dependent on the animal’s behaviour. Overall, GPS loggers offer a significant advance for studies of fine-scale animal movement patterns.

Keywords

Global Position System Global Position System Data Track Length Satellite Tracking Dead Reckoning 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

Field work at Boulders was conducted under permit from the Cape Peninsula National Park, and with the support of Marine and Coastal Management. We are grateful to Marta de Ponte and the wardens at Boulders, especially Crecilda van den Berg, Lennox Zosela, Chris Clift and Monique Ruthenberg, for assistance with the field work. The Everinghams kindly provided accommodation at Boulders, and the Southern African Foundation for the Conservation of Coastal Birds allowed us to test dummy devices on captive penguins under their care. This collaborative project was initiated thanks to a joint fellowship of the Direction des Affaires Internationales du CNRS and the South Africa National Research Foundation to P.G.R. and D.G. S.L.P. received financial support from the Bob Blundel Memorial Scholarship and Ocean Basket Scholarship. The project was approved by the animal experimentation ethics committees of the University of Cape Town and South African National Parks.

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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • P. G. Ryan
    • 1
  • S. L. Petersen
    • 1
  • G. Peters
    • 2
  • D. Grémillet
    • 3
  1. 1.Percy FitzPatrick InstituteUniversity of Cape TownRondeboschSouth Africa
  2. 2.earth&OCEAN TechnologiesKielGermany
  3. 3.Centre d’Ecologie et Physiologie EnergétiquesCentre National de la Recherche ScientifiqueStrasbourgFrance

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