Orientation, movement and thermoregulation in the giant tortoises (Testudo (Geochelone) gigantea)of Aldabra Atoll, Seychelles
| Autor: | Malcolm Coe |
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| Rok vydání: | 2004 |
| Předmět: | |
| Zdroj: | Transactions of the Royal Society of South Africa. 59:73-77 |
| ISSN: | 2154-0098 0035-919X |
| DOI: | 10.1080/00359190409519165 |
| Popis: | The giant tortoises of Aldabra engage in feeding activity in the early morning and late afternoon, with variable periods of inactivity in the middle of the day. On clear days a high proportion of tortoises orient their long axes away from the sun. Sun orientation responses of 676 tortoises were measured in coastal mixed scrub and coastal grassland habitats in July 1978. These orientations showed that a significant number of tortoises faced away from the sun. The length and area of the shadow cast in front of the carapace was calculated for eight size classes of tortoise, assuming that the animal's long axis was in parallel with the sun rays. If a tortoise seeks shade when the shadow length has been reduced to less than 50% of the carapace height, we may predict that this would occur between 09h00 and 10h00. The shadow area at 09h00 and 10h00 was reduced respectively to 8.7 and 3.8% of that produced at 07h00. The shadow cast in front of the carapace allows a tortoise to feed in the shade, through which mea... |
| Databáze: | OpenAIRE |
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