Comparison of trip duration, activity pattern and diving behaviour by Red-tailed Tropicbirds (Phaethon rubricauda) during incubation and chick-rearing
Julia Sommerfeld A B and Janos C. Hennicke AA Department of Ecology and Conservation, Biocentre Grindel, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany.
B Corresponding author. Email: julia.somma@gmx.de
Emu 110(1) 78-86 https://doi.org/10.1071/MU09053
Submitted: 15 June 2009 Accepted: 4 December 2009 Published: 24 February 2010
Abstract
In the tropical marine environment food resources are scarce and often patchily distributed. Consequently, nesting tropical seabirds must balance travelling to productive areas and sharing incubation or providing food to the chick. Changes in foraging behaviour occur when adults switch from feeding only for themselves during incubation to feeding a chick and fulfilling their own energy requirements. Externally attached data-devices were used to compare the duration of foraging trips, flight activity and depth of dives of incubating and chick-rearing Red-tailed Tropicbirds (Phaethon rubricauda) on Christmas Island, Indian Ocean. Adults with chicks had a bimodal pattern of foraging, with alternating short and long foraging trips (mean duration ± s.d. of short trips = 3.0 ± 4.1 h, of long trips = 57.4 ± 41.1 h), whereas incubating adults undertook only longer trips (mean duration ± s.d. = 152.9 ± 47.2 h). This strategy is stimulated by partner behaviour, rather than body mass as reported for many other seabirds, and may enable the optimisation of simultaneous food delivery to chicks and self-feeding when local resources are poor. The proportion of time spent in flight (flight activity) by adults with chicks averaged 90.1% during short trips whereas incubating birds spent only 62.4% of their trips flying. Overall mean depth of foraging dives by adults with chicks averaged 0.6 ± 0.3 m during short trips; mean maximum depth of dives by incubating adults were recorded using maximum-depth recorders and were significantly deeper at 10.7 ± 8.7 m, reaching a maximum depth of 25.6 m.
Additional keywords: bimodal foraging strategy, Christmas Island, dive-depth, flight activity.
Acknowledgements
This work was conducted within the framework of the Christmas Island Seabird Project (see www.seabirdproject.cx) supported by the University of Hamburg, Christmas Island Tourist Association, Christmas Island Explorer Holidays, Christmas Island Territory Week Committee and Christmas Island Care. We thank David James and Parks Australia North Christmas Island for their support in all aspects of the study. The Christmas Island Hospital kindly donated material for the maximum-depth recorder. We thank Mirjam Becker, Jessika Garzke and Annika Müller-Burbach for their help in the field. We also thank Mark Holdsworth, Barry Baker and Sue Robinson for comments on an earlier manuscript and Mary-Anne Lea, Tim Reid and David Priddel for comments on this manuscript. Special thank to Louise Oxley for providing English assistance. Further, we also thank two anonymous reviewers for providing useful comments. We greatly thank Ross Cunningham who provided valuable assistance with statistical analyses. All experiments were carried out under permission of Parks Australia North Christmas Island and in accordance with the principles and guidelines of the German and Australian laws on animal welfare.
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