Find information on spaces, staff, and services.
157 DISCUSSION Daily activity patterns and time budgets of giant tor- toises in the Galapagos Islands are strongly seasonal, and are correlated with temperature and moisture, as has been found for most terrestrial turtles (Auffenberg and Iverson 1979). Changes in daily activity patterns coincide with changes in temperature, with a bimodal pattern corresponding to the hot season, and a unimodal pattern corresponding to the cool season. Time budgets, which also vary seasonally, are more strongly related to precipitation than to tempera- ture. Under extremely dry conditions with little available food, tortoises will spend little of the day in the active mode. The decrease in activity should curtail the majority of their energy expenditures, enabling them to live for a longer time on stored fat without additional food. They become more active, feeding for a greater portion of the day, with increasing precipitation, available food, and water content of the food. In the Galapagos Islands, the bimodal pattern, although occurring in the hot seamon, is not as crucial to tortoise survival as it is on Aldabra. On Aldabra, feeding areas and shaded resting areas are generally separate and those tor- toises that do not seek shade at midday on all but the coo- lest days are likely to die from overheating (Swingland and Frazier 1979, Coe and Swingland 1984). Shade, from trees, cactus, shrubs, or rocks, is much more dispersed in the Galapagos Islands, and tortoises may often feed in shaded
158 areas. The midday peaks in resting, although present and apparently due to high ambient temperatures, do not reach 100% in the Galipagos, as they do on Aldabra. Study area had little effect on either activity patterns or time budgets of tortoises. The slightly greater levels of travel at La Caseta and on Pinzon may be related to the distribution of preferred habitats. At both El Chato and SCNZ, preferred areas are highly concentrated, while on Pin- zon and at La Caseta, they are much more dispersed. In the latter two areas, tortoises may have to travel farther to reach preferred resting and feeding areas. Although sex was not analysed as a factor in the instan- taneous observations, it had no significant relationship to the time budgets of tortoises for any activity. The ability of tortoises to store fat and to live for months without food or water was well known to whalers, who collected thousands of tortoises in the 1800's to supply their ships with fresh food for long periods of time at sea (Townsend 1925). Tortoise hunters often resorted to drink- ing the water in the pericardial sac, as well as the liquid in the bladder of the tortoise, to refresh themselves while traveling across the arid islands (Darwin 1860, Townsend 1925, Pritchard 1979a). This ability to store food and - watery and to live for long periods of time without them, enables tortoises to change their behavior patterns to cor- relate with seasonal changes in temperature and precipita- tion, and the corresponding changes in both food and water