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Norwegian University of Science and Technology (NTNU) 2008

The ecology and behaviour of the Masai Ostrich (Struthio camelus massaicus) in the Serengeti Ecosystem, Tanzania

Magige, Flora John

Titre : The ecology and behaviour of the Masai Ostrich (Struthio camelus massaicus) in the Serengeti Ecosystem, Tanzania

Auteur : Magige, Flora John

Université de soutenance : Norwegian University of Science and Technology (NTNU)

Grade : Doctoral thesis 2008

Résumé partiel
This thesis focuses on the ecology and behaviour of the ostrich (Struthio camelus massaicus) in the Serengeti Ecosystem, Tanzania. Ostrich is a large, flightless, cursorial, communal breeding bird, endemic to a variety of open habitat types of Africa. It is classified as ‘Least Concern’ under the IUCN Red List. Nevertheless, wild ostrich populations have been declining and considered ecologically extinct in most parts of western and northern Africa due to habitat loss, egg collection and illegal hunting. The first section of this thesis (Paper I) investigates the effect of topography, rainfall and predation on breeding success of ostriches in the Serengeti ecosystem. Differences in the altitude and amount of rainfall in the ecosystem affect the breeding success of the ostriches. In the low altitude western area, ostriches laid eggs earlier than in the high altitude eastern area. The differences could be attributed to the rainfall and food gradients, which increase towards western area. In addition, high breeding success observed in the western area could be atrributed to the vegetation type that conceals the nests. Following this section, the Paper II and III of the thesis examines the possible biological reasons why ostrich eggs are white in colour and whether female ostriches are able to recognise their own eggs when confronted by intraspecific brood parasitism. During the egg laying period, ostriches leave their eggs unattended for approximately two weeks before the incubation start. In this period the eggs are exposed to high levels of predation due to their conspicuousness. The reasoning of the eggs being white has been attributed to reduce and overcome heat stress. The temperature experiments on painted and control eggs revealed that the inner temperature of the brown painted eggs reached lethal temperatures. Developing embryos would die, should ostrich eggs have been brown in colour. White painted and control eggs were below the threshold temperature where the embryo mortality starts to increase, indicating that white eggs prevents overheating. However, white colour increases predation risks due to high visibility. In addition, following communal nesting behaviour of ostriches, nests commonly end up with many more eggs than can be incubated. Since the ostrich can only incubate less than 20 eggs, at the onset of incubation the ‘major’ female (the first female to lay the egg in the nest and subsequently undertakes guarding and incubation), ejects some of the eggs. The ejected eggs are presumed to belong to the ‘minor’ females (females that subsequently lay eggs on the same nest). There was no clear pattern of movement of eggs in the nests, and ejection of eggs was random. Ejected eggs that were experimentally put back in the nest were never ejected again. Spectorophotometric study compared inner central eggs in the nest and ejected eggs in colour variance. Results revealed no significant difference in colour between the eggs, indicating that ostriches do not recognise their own eggs but eject eggs randomly.


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