Abstract
The Brown Skua Stercorarius antarcticus lonnbergi is an opportunistic species that displays a high degree of flexibility in foraging tactics. We deployed global positioning system (GPS) and immersion (activity) loggers on breeding Brown Skuas of known sex, body size and condition at Admiralty Bay, King George Island with the aim to examine the impacts of spatial and seasonal fluctuations in prey availability on movement and foraging behavior. We also investigated whether reversed sexual size dimorphism (females larger than males) in this species leads to differences between sexes in foraging behavior and whether this or other factors contribute to variation in breeding success. Analysis of the GPS data highlighted the high degree of plasticity in foraging behavior among individuals. Although most Brown Skuas were flexible in their feeding tactics, this was not enough to ensure a successful breeding season, as few pairs fledged chicks. During early chick rearing, Brown Skuas spent most of their time on land, feeding almost exclusively on penguin chicks. By late chick rearing, when the availability of penguins had diminished, Brown Skuas supplemented the food obtained on land by traveling to the ocean. All foraging trips to sea occurred during daylight, mostly during the early morning. Despite marked sexual size dimorphism, we failed to find any difference in foraging tactics between males and females. Furthermore, although laying date affected the number of chicks hatched (earlier pairs were more successful), no relationship was found between breeding success and male or female body size, condition or degree of dimorphism within pairs.
Zusammenfassung
Flexible Nahrungsstrategien von Skuas als Reaktion auf lokale und saisonale Nahrungsengpässe
Skuas Stercorarius antarcticus lonnbergi sind Opportunisten, die hoch flexibel sind in ihren Nahrungsstrategien. In der vorliegenden Studie, durchgeführt in der Admiralty Bay auf King George Island, wurden brütende Skuas mit bekanntem Geschlecht, Körpergröße und Kondition mit GPS- und Immersions- (Aktivitäts-) Datenloggern ausgestattet, um die Auswirkungen von räumlichen und saisonalen Fluktuationen in der Nahrungsverfügbarkeit auf das Bewegungs-und Nahrungssucheverhalten zu untersuchen. Außerdem wurde untersucht, ob der umgekehrte Sexualdimorphismus bezüglich der Körpergröße (Weibchen größer als Männchen) bei dieser Art zu Unterschieden zwischen den Geschlechtern im Nahrungssucheverhalten führt und ob dieser oder andere Faktoren zu Variationen im Bruterfolg beitragen. Die Analyse der GPS-Daten stellte einen hohen Grad an Plastizität im Nahrungssuchverhalten zwischen den Individuen heraus. Obwohl die meisten Skuas flexibel in ihren Fresstaktiken waren, sicherte dies nicht automatisch eine erfolgreiche Brutsaison, da nur wenige Paare Küken aufzogen. Während der frühen Phase der Kükenaufzucht verbrachten die Skuas die meiste Zeit an Land und erbeuteten nahezu ausnahmslos Pinguinküken. In der späten Phase der Kükenaufzucht, als die Verfügbarkeit von Pinguinen vermindert war, ergänzten die Skuas ihre Landnahrung durch Nahrungsflüge auf dem Ozean. Alle Nahrungsflüge auf dem Meer waren tagsüber, meistens am frühen Morgen. Trotz des ausgeprägten Geschlechtsdimorphismus in der Körpergröße konnten keine Unterschiede im Nahrungssuchverhalten zwischen Männchen und Weibchen gefunden werden. Und obwohl das Legedatum die Anzahl der geschlüpften Küken beeinflusste (frühe Paare waren erfolgreicher), konnte keine Abhängigkeit zwischen dem Bruterfolg und der Körpergröße und Kondition von Männchen und Weibchen oder dem Grad des Dimorphismus innerhalb der Paare nachgewiesen werden.
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Acknowledgments
We are grateful to the field team on King George Island (Matt Henschen, Brette Soucie and Caitlyn Bishop) for assisting with device deployments and recoveries, and to Sue Trivelpiece for helping with all logistical preparations. This research was supported by logistical and scientific funding from the US AMLR Program and from OPP grant #0739536 to W. and S. Trivelpiece from the National Science Foundation. This work complies with, and was completed in accordance to, an Antarctic Conservation Act permit, provided by the US National Science Foundation.
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Carneiro, A.P.B., Manica, A., Trivelpiece, W.Z. et al. Flexibility in foraging strategies of Brown Skuas in response to local and seasonal dietary constraints. J Ornithol 156, 625–633 (2015). https://doi.org/10.1007/s10336-015-1156-y
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DOI: https://doi.org/10.1007/s10336-015-1156-y