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Comparative Ethology of the Ciconiidae. Part 1. The Marabou Stork, Leptoptilos crumeniferus (Lesson)

M. P. Kahl
Behaviour
Vol. 27, No. 1/2 (1966), pp. 76-106
Published by: Brill
Stable URL: http://www.jstor.org/stable/4533152
Page Count: 39
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Comparative Ethology of the Ciconiidae. Part 1. The Marabou Stork, Leptoptilos crumeniferus (Lesson)
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Abstract

A breeding colony of Marabou Storks, Leptoptilos crumeniferus, was studied at Kitale, Kenya, East Africa, in January 1964 and from October 1964 through May 1965. Further observations were made of non-breeding individuals at Kitale and elsewhere in East Africa. An adult Marabou was kept in captivity for six months, and nestlings were hand-reared in order to observe their behavioral development in more detail. A brief description of the appearance of the Marabou is followed by an account of the plumage and soft part color changes occurring in breeding individuals. Sexes are morphologically indistinguishable in the field, except for slight differences in size and bill shape. In normal flapping flight Marabous beat their wings slowly, at a rate of about 145 flaps per minute. When conditions permit they rely on thermal soaring and gliding for long distance movements. They are remarkably agile fliers for so large a bird and often perform aerial acrobatics when descending from high altitudes. Marabous are omnivorous, and their feeding technique depends on the type of food being sought and feeding conditions. Their bill is not well suited for tearing flesh, and when feeding on carrion, their main food outside the breeding season, they frequently allow vultures to tear the meat into small pieces before attempting to grab it. Aquatic prey, which is taken in quantity during the breeding season, is sometimes located visually and sometimes by feel (tactolocation), depending on the turbidity of the water. Marabous also habitually forage in freshly plowed fields and near brush fires. Occasionally they kill larger vertebrates for food. Comfort movements are discussed, with emphasis being given to those that seem most typical of storks. Close approach between individual Marabous, either at a feeding area or at a nest-site, often results in ritualized social displays by one or both birds. The specific displays given depend upon the locale of the encounter and the social relationship between the birds. Away from the nest, the Forward Threat is the most common offensive display and the Upright Display the most common defensive display. At or near the nest-site, the Aerial Clattering Threat and Forward Clattering Threat are the most purely aggressive displays, and the Anxiety Stretch and Erect-Gape seem to show the highest escape or fear tendencies. The Snap Display and Balancing Posture are ambivalent displays, showing a near balance between tendencies to attack, flee from, and pair with the other bird. The Up-Down, a common greeting display between mates and between young and parents, appears to be a "friendly" appeasement gesture, serving to reduce hostilities in the opposite member. Swaying Twig-Grasping, most likely derived from nest-building movements, probably helps to strengthen the pair-bond. During copulation the male performs Copulation Clattering alongside the female's bill; this display may have its roots in latent hostility between the members of the pair. Following the description of social displays in adults, a section on the behavior of nestling Marabous is presented. Some adult displays, such as the Up-Down, appear first in nestlings; the development and maturation of such displays are traced. The major elements in Marabou social behavior appear repeatedly, in varying combinations, in many different displays. A summary of these is presented in Table 1. /// Vorstehende Arbeit beruht auf Freilandbeobachtungen in einer Brutkolonie von Marabus, Leptoptilos crumeniferus, in Kitale, Kenya, im Januar 1964 und von Oktober 1964 bis Mai 1965, sowie auf Beobachtungen an nichtbrütenden Marabus in verschiedenen Teilen Ostafrikas und an handaufgezogenen Tieren in Gefangenschaft. Änderungen der Gefieder- und Hautfarbe während der Brutzeit werden beschrieben. Die Geschlechter unterscheiden sich nur unwesentlich in Körper- und Schnabelgrösse. Während des normalen Fortbewegungsfluges werden die Flügel durchschnittlich 145 mal pro Minute geschlagen. Nach Möglichkeit werden Aufwinde zum Gleiten ausgenutzt. Für einen Vogel dieser Körpergrösse ist der Marabu ein erstaunlich aktiver Flieger. Marabus sind omnivor. Das Verhalten der Nahrungsaufnahme richtet sich nach der Art der Nahrung. Sie sind nicht in der Lage, Fleisch zu zerkleinern; deshalb versuchen sie, den Geiern kleine Fleischstücke wegzunehmen. Wassertiere, die namentlich während der Brutzeit aufgenommen werden, werden optisch oder taktil aufgespürt. Marabus jagen ausserdem auf frisch gepflügten Feldern und in der Nähe von Buschfeuern. Gelegentlich töten sie auch grössere Wirbeltiere. Jede Begegnung zwischen Artgenossen führt zu sozialen Verhaltensweisen, die je nach Ort und Status des Vogels verschieden sind. Ausserhalb des Nestes ist Forward Threat die häufigste aggressive und Upright Display die häufigste defensive Verhaltensweise, während auf dem Nest und in seiner unmittelbaren Nähe Aerial Clattering Threat und Forward Clattering Threat beziehungsweise Anxiety Stretch und Erect-Gape angewandt werden. Snap Display und Balancing Posture sind ambivalente Verhaltensweisen, die bei annähernd gleicher Angriffs-, Flucht-, und Annäherungstendenz auftreten. Up-Down ist eine Friedensgeste zwischen Familienmitgliedern. Swaying Twig-Grasping hat sich aus Nestbaubewegungen entwickelt und festigt die Paarbindung. Während der ganzen Dauer der Kopulation zeigt das Männchen das Copulation Clattering, das auf latente Aggressivität zwischen den Partnern hinweist. Die Verhaltensentwicklung der einzelnen Verhaltensweisen beim Jungvogel wird beschrieben. Die verschiedenen Grundelemente des Sozialverhaltens können in unterschiedlichen Kombinationen auftreten, die in Tab. 1 aufgeführt werden.

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