Galapagos land iguana (Conolophus subcristatus)
|French:||Iguane terrestre des Galápagos|
|Spanish:||Iguana Terrestre De Las Galápagos|
|Size||Male weight: up to 13 kg (2)|
Length: over 1 meter (2)
Classified as Vulnerable (VU D2) by the IUCN Red List (1) and listed on Appendix II of CITES (3).
There are two species of land iguana found in the Galapagos; this species Conolophus subcristatus, is found on six islands and Conolophus pallidus is found only on Santa Fe (2). This species is very large, growing to lengths of over a meter (2). The short head is blunt and the back legs are thick and powerful, with long sharp claws on the toes (4). It is yellowish in colour with blotches of white, black, rust and brown (5) and a row of spines passes along the centre of the neck and back (4).
Land iguanas are endemic to the Galapagos Islands off the coast of Ecuador (4). Conolophus subcristatus is native to six islands (2). In 1835 when Charles Darwin first went to the Galapagos, land iguanas were extremely numerous; he wrote: “I cannot give a more forcible proof of their number, then by stating that when we were left at Santiago Island, we could not for some time find a spot free from their burrows on which to pitch our single tent”. Sadly, this once thriving Santiago Island population has become completely extinct (6).
This iguana lives in the drier areas of the islands on which they occur, in scrubby habitats (5) (4). Females require access to areas of sandy or loose soil in which to lay their eggs; some females even use the ash around dormant volcanic craters (4).
Galapagos land iguanas are active during the day. They maintain their body temperature by basking in the sun to warm up and seeking shade when they become too hot. In the morning they can be found basking, but during the heat of midday they tend to retreat into shade. At night they sleep in burrows which they dig themselves (5). This species is omnivorous but tends to mainly eat plants and the fruits and pads of cactus trees. They may remove the spines with their claws, and these cacti provide them with plenty of moisture during dry spells (2) (5). This species has an interesting relationship with Galapagos finches; the iguanas often raise themselves from the ground and allow the finches to remove ticks from their bodies (2).
Males defend territories, with displays involving head bobbing, biting and tail thrashing (5). During courtship, males aggressively court the females (4). After mating, the females set off on a migration to suitable egg-laying habitat. On Ferdinanda Island, females are known to travel up to 15 km to reach a suitable nesting site (4). They then lay two to 20 eggs in a 50 cm deep burrow. The nest site is guarded for a number of days after laying, in order to prevent other females from laying in the same place and damaging the eggs (5). The young hatch after 85 to 110 days; it then takes them up to a week to dig their way out of the burrow (5). Maturity is reached between eight and 15 years. If they survive the first years of life, when they are most vulnerable to predation and food scarcity, land iguanas can live for up to 50 years (2).
In the early 1800s, whalers and settlers came to the Galapagos Islands. It is likely that they ate land iguanas, but the most serious problem they caused resulted from the introduction, both accidental and deliberate, of predators such as cats and dogs and domestic animals such as goats and pigs (6). Introduced animals are still the main threat facing this species today (2). Cats and rats hunt eggs and young iguanas and introduced goats destroy food plants (4). The natural predators of land iguanas include hawks, herons, and snakes, all of which cannot prey on young after they reach around one year of age, as they become too large. However, cats can continue to kill young iguanas until they reach three or four years of age; cat predation is a huge problem preventing the natural success of the species (5).
In 1976, wild dogs wiped out the last colonies of land iguanas around Conway Bay on Santa Cruz Island. This prompted the Charles Darwin Research Station (CDRS) and the Galapagos National Park Service (GNPS) to initiate an emergency rescue scheme for the 60 remaining survivors. They then discovered that a similar level of destruction was occurring on Isabella Island. The GNPS and CDRS established a recovery programme, including a captive breeding scheme based on Santa Cruz. The captive breeding programme continues today, and land iguanas are returned to the wild when they reach a size beyond which they are safe from cat predation (2) (6). This breeding programme is accompanied by a campaign to work towards the eradication and tighter control of introduced animals. Other important measures include the maintenance of suitable habitat for the species, and continued monitoring of the populations (2).
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- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Omnivorous: feeds on both plants and animals.
World Conservation Monitoring Centre 1996. Conolophus subcristatus In: IUCN 2003. 2003 IUCN Red List of Threatened Species. (March 2004)
Galapagos Conservation Trust- land iguana (March 2004)
CITES (March 2004):
Bruin, T (2000) Conolophus subcristatus (On-line), Animal Diversity Web (March 2004)
Land iguanas: a natural history. The Darwin Foundation (March 2004)
Galapagos land iguanas and their protection. The Darwin Foundation (March 2004)