Estimation of feeding frequencies by periodic weighing of chicks: evaluation by video-observation of burrow-nesting Wilson’s Storm-Petrels (Oceanites oceanicus)
Anja Gladbach A B C , Christina Braun A , Anja Nordt A , Hans-Ulrich Peter A and Petra Quillfeldt BA Institute of Ecology, Polar and Bird Ecology Group, Friedrich-Schiller-University Jena, Dornburger Str. 159, D-07743 Jena, Germany.
B Max Planck Institute for Ornithology, Vogelwarte Radolfzell, Schlossallee 2, D-78315 Radolfzell, Germany.
C Corresponding author. Email: anja.gladbach@gmx.de
Emu 109(4) 316-320 https://doi.org/10.1071/MU09043
Submitted: 22 May 2009 Accepted: 22 September 2009 Published: 4 December 2009
Abstract
We used video-observations of nesting burrows to determine if periodic weighing of chicks (once per day) accurately captured feeding events in Wilson’s Storm-Petrel (Oceanites oceanicus). We found that, compared with video-recordings, periodic weighing and correction for metabolic loss correctly estimated whether a chick had been fed for 99.3% of all nights. It underestimated the number of feedings on 14.8% of nights and overestimated it on only 4.7%. The most common error in our study occurred in the discrimination between single and double feedings, classifying 22 (35.5%) of all double feedings as single feeding owing to their small size. However, the method gives good results at the population level, as the error rate (0.7% for fed v. unfed) is well below the variance in feeding rates observed between good and poor seasons. Thus, periodic weighing of chicks is an easy and reliable method for monitoring feeding rates, which is especially important in burrow-nesting species where a direct observation is difficult. We show that, following the establishment of a metabolic mass-loss curve by weighing chicks over short intervals, weighing of chicks once a day provides reliable results, and thus disturbance to feeding adults can be minimised. This can be especially useful in species where adults feed during a restricted time of the day, such as nocturnally.
Additional keywords: seabirds, provisioning.
Acknowledgements
We thank Thomas Lubjuhn for sharing his knowledge and providing laboratory facilities and Tim Schmoll, Steffen Hahn and Markus Ritz for their contributions to logistics and fieldwork. The manuscript benefited from the comments of three anonymous referees and Timothy Greives checked the English. We received logistic support from the Alfred-Wegener Institute of Marine and Polar Research (Bremerhaven, Germany), the National Antarctic Institute of Argentina and Hapag Lloyd Seetouristik. This study was partly funded by grants provided by the Deutsche Forschungsgemeinschaft (Pe 454, and Qu 148), BMBF-DLR, Studienstiftung des Deutschen Volkes and the State of Thuringia, Germany (Landesgraduiertenstipendium).
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