They are thought to make long annual migrations between lowland nesting and upland feeding areas. They're long-lived, (life expectancy in the wild estimated to be around 150 years!). The populations of each sub-species fell drastically - due to hunting, introduction of predators and grazing animals - over last 300 years such that only ten subspecies of the original twelve exist in the wild in small numbers. However, recent conservation efforts since the establishment of the Galápagos National Park and the Charles Darwin Foundation hundreds of captive-bred juveniles have been released back onto their home islands. Being cold-blooded, the tortoises bask for two hours after dawn, absorbing the energy through their shells, then becoming active for 8–9 hours a day. They may sleep for about sixteen hours in a mud wallow partially or submerged in rain-formed pools. Perhaps this is a thermo-regulatory response and/or a protection from parasites such as mosquitoes and ticks. Some rest in a 'pallet'- a snug depression in soft ground or dense brush - which probably helps to conserve heat and may aid digestion. To get rid of ticks and other parasites tortoises will raise themselves on all four legs and extend their necks - a visual message to the ever present finches which can then reach otherwise inaccessible spots on the tortoise's body. The tortoises are herbivores eating cactus, a multitude of leaves, vines, as well as fruits but fresh young grass is the favorite food it seems. They have to eat a large quantity of food when it is available - up to 35 kgs a day! By acquiring most of their moisture from the dew and sap in vegetation (particularly the Opuntia cactus), tortoises can go for long periods without actually drinking. They can also survive for over a year being forcefully deprived of all liquids, breaking down their body fat producing water as a side product. They weigh up to 300kg and are by far the largest terrestrial animals on Galapagos and to show their size just look at the photo we took of a man getting into a preserved empty shell ...
After plodding around the 'farm,' in mud (thank god for wellies!), seeing five individual giant tortoises, we moved off to see a lava tunnel nearby; (interesting in that these tunnels are formed because the outside of lave flows cool faster than the inside ... hence tunnels form). Then we moved off to the Charles Darwin Research Station, back in Puerto Ayora. Here we saw Lonesome George - the last of the Pinta sub-species, (he steadfastly refuses to breed with females from other islands genetically matched to be as close as possible ... picky bugger!). We also saw the enclosures where the tortoises are bred for later release ... all very good work but it was incredibly hot and sunny so we skipped most of the outdoor tour and rested in the shade with Nina. See URL for the Charles Darwin Foundation to found out more; http://www.darwinfoundation.org/english/pages/index.php. Note - in spite of these efforts the Tortoises are still on the IUCN Red List of Threatened Species. Margaret & I are members of The Galapagos Conservation Trust - see http://www.savegalapagos.org
We finished our day with lunch at the 'Finch Bay Eco-hotel', where we were heading after the expedition, then back on board the Isabella II.
This is an extract for Wiki on the sub-species:
There were probably twelve subspecies of Geochelone nigra in the Galápagos Islands, although some recognise up to 15 subspecies. Now only 11 subspecies remain, five on Isabela Island, and the other six on Santiago, Santa Cruz, San Cristóbal, Pinzón, Española and Pinta. Of these, the Pinta Island subspecies is extinct in the wild and is represented by a single individual. In the past, zoos took animals without knowing their island of origin. Production of fertile offspring from various pairings of tortoises largely confirmed that they are subspecies and not different species. All the subspecies of giant tortoise evolved in Galápagos from a common ancestor that arrived from the mainland, floating on the ocean currents (the tortoises can drift for long periods of time as they are buoyant and can stretch head upwards to breathe). Only a single pregnant female or breeding pair needed to arrive in this way, and then survive, for Galápagos to be colonised. The closest living relative of the Galápagos giant tortoises is Geochelone chilensis, a small tortoise found in Argentina. The split between G. chilensis and the Galápagos lineage probably occurred 6-12 million years ago based on mitochondrial DNA analysis,[13] before the origin of the oldest extant Galápagos island. Espanola and San Cristobal, the oldest islands, were colonized first; this was followed by several migration events to and between other islands via local currents. The four named southern subspecies on the largest island, Isabela, are possibly not distinct genetic units, whereas a genetically distinct northernmost Isabela subspecies is probably the result of a separate colonization. (...) It is thought that the saddle-backed type carapace evolved independently several times as a reaction to dry environments, although extinction of crucial populations by human activities confounds whether domed versus saddleback carapaces of different populations are mono- or polyphyletic..
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