Abstract
Understanding the spatial dynamics of populations is essential for conservation of species at the landscape level. Species that have adapted to stable environments may not move from their breeding areas even if these have become sub-optimal due to anthropogenic disturbances. Instead, they may breed unsuccessfully or choose not to breed at all. Damara Terns Sternula balaenarum feed off the highly productive Benguela Upwelling System. They breed on the coastal desert mainland of Namibia where development and off-road driving is threatening breeding areas. We report annual survival and breeding dispersal probabilities of 214 breeding adult Damara Terns through capture–mark–recapture at two colonies for 9 years (2001–2009) in central Namibia. Using multi-state models in program MARK, model selection based on AICc favoured a model that suggests local annual survival of Damara Terns for the dataset was 0.88 (95% CI, 0.73–0.96) and the annual dispersal probability was 0.06 (0.03–0.12). High survival and low dispersal probabilities are consistent with other seabirds adapted to stable environments. These estimates contribute to the first baseline demographic information for the Damara Tern. Low dispersal probabilities indicate that current protection of breeding sites is an important management approach for protecting the species.
Zusammenfassung
Jährliche Überlebensrate und Brutortstreuung bei einem an stabile Umweltbedingungen angepassten Seevogel: Auswirkung auf Schutzmaßnahmen
Um Arten auf Landschaftsebene zu schützen ist es wichtig, die räumliche Dynamik der Populationen zu verstehen. Es ist möglich, dass Arten, die an eine stabile Umwelt angepasst sind, ihre Brutgebiete nicht verändern können, selbst wenn diese infolge anthropogener Veränderungen nicht mehr optimal sind. Stattdessen könnten sie dort erfolglos zu brüten versuchen oder gar nicht mehr brüten. Damara-Seeschwalben S. balaenarum ernähren sich im hochproduktiven Benguela Auftriebsgebiet. Sie brüten an der Küste der Namibwüste, wo Überbauungen und Fahren im Gelände ihre Brutgebiete gefährdet. Wir präsentieren jährliche Überlebensraten und Dispersionswahrscheinlichkeiten basierend auf 214 brütenden adulten Damara-Seeschwalben, ermittelt durch Fang-Wiederfang Methoden über neun Jahre (2001–2009) in zwei Kolonien Zentralnamibias. Multi-state Modelle in Programm MARK zeigten für diese Daten, dass die jährliche lokale Überlebensrate von Damara-Seeschwalben 0.88 (95% Vertrauernsbereich 0.73–0.96) war und die jährliche Dispersionswahrscheinlichkeit zwischen den Kolonien betrug 0.06 (0.03–0.12). Die hohe Überlebensrate und niedrige Dispersionswahrscheinlichkeit sind vergleichbar mit anderen an stabile Umwelten angepassten Seevögeln. Diese Schätzungen sind ein erster Beitrag zum Verständnis der Demographie von Damara-Seeschwalben. Die niedere Dispersionswahrscheinlichkeiten legen nahe, dass der Schutz der Brutgebiete, wie er momentan betrieben wird, eine tatsächlich wichtige Maßnahme zum Schutz dieser Art ist.
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Acknowledgments
Funding and support for the protection, management and monitoring of the breeding areas Caution Reef and Horses Graves have been given by the Namibian Coastal Management Project (NACOMA), BirdLife International through its Rio Tinto BirdLife Partnership Action Fund, Rössing Uranium Limited Swakopmund, Namib Film, Big Banana Film, Coca-Cola through its 2041 Antarctica Project, the Ministry of Environment and Tourism of Namibia, the Ministry of Fisheries and Marine Resources of Namibia, Local Authorities and the Erongo Regional Council, CC Africa and various tour companies. J.B. is supported by Namdeb Diamond Corporation (Pty) Ltd, a National Research Foundation SeaChange Research Grant to Les Underhill, a Gordon Sprigg Scholarship and the Sam Cohen Scholarship Trust. R.A. was supported by NRF grant no. 68561. Mark Boorman built the snap-trap enabling the capture and re-capture of breeding individuals. Holger Kolberg made the maps for this study. Comments from Norman Ratcliffe, Jeff Spendelow and Peter Becker considerably improved previous drafts of this manuscript.
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Communicated by P. H. Becker.
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Braby, J., Braby, S.J., Braby, R.J. et al. Annual survival and breeding dispersal of a seabird adapted to a stable environment: implications for conservation. J Ornithol 153, 809–816 (2012). https://doi.org/10.1007/s10336-011-0798-7
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DOI: https://doi.org/10.1007/s10336-011-0798-7