Visual display of the Ecology of giant tortoises (Geochelone elephantopus) in the Galapagos Islands

				

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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

 

					
				
					

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  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