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3.2 Lizards and snakes

3.2.1 Iguana iguana and Ctenosaura similis (green and brown iguana)

Neotropical lizards and snakes are both highly diverse and particularly abundant and variable. In addition to their myriad functions within their respective ecosystems, the most valuable species are also fairly important in economic and nutritional terms.

The snakes most prized for their skins are the anaconda (Eunectes murinus) and the boa (Boa constrictor), and the lizards; Iguana iguana, Tupinambis nigropunctatus and Dracaena guianensis (105, 191, 334, 452, 479). Venomous snakes are used in the pharmaceutical industry, and some snakes and lizards are in demand as pets. The species most widely used for food are the iguanas Iguana iguana and Ctenosaura similis (98, 191, 207, 400, 431, 511).

3.2.1 Iguana iguana and Ctenosaura similis (green and brown iguana)

Local names: Camaleo (Brazil), gallina de palo, iguana, iguana verde (various countries), leguaan (Suriname) Iguana: garrobo, gallina de palo, Ctenosaura iguana negra (Central America).

Geographical variation and distribution: Iguana iguana (green iguana) is widely distributed throughout Latin America from the Mexican states of Sinaloa and Veracruz, through Central America, and in South America as far south as Peru, Paraguay and northern Argentina, including many neotropical islands. The more restricted range of Ctenosaura similis (brown or rock iguana) runs from southern Mexico to Panama, including various nearby islands (187). Iguana iguana is monotypical (333) but is smaller in arid zones (35, 416). Continental brown iguana ("garrobo") populations are Ctenosaura s. similis, but other species are also used as food, e.g. C. pectinacea in western Mexico (98, 207).

Elevational range: Green iguana are found from sea level up to 1 000 metres in Colombia, and brown iguana up to 800 m in Central America (187).

Size and weight: Green iguana vary by sex and location. Adult males can weigh 4 kg and grow to 1.8m (head/body length 45 cm). Adult females are 1.2-2.6 kg with an average head/body length of 33 cm (155, 260, 400, 629). On the arid island of Curaçao most adults reach a head/body length of 23-26 cm (maximum 33 cm), with sexual dimorphism by size (35).

Brown iguana are smaller, the adult females weighing an average 0.65 kg, with a head/body length of 27.6 cm. The maximum weight for males is 2 kg (155, 629).

Habitat: Green and brown iguanas inhabit different types of wooded areas, including very arid habitats. Green iguana prefer to be close to water and near forests, particularly gallery forests. Brown iguana, however, seem less dependent on a riverine habitat (155). They are not found in very moist forests and appear only sporadically or not at all over most of the Amazon forest. One apparent limiting factor in brown iguana distribution is suitable communal nesting sites.

Abundance: Iguana may be abundant in their preferred habitat with populations of up to 90/ha (548), although deforestation and intensive hunting are making alarming inroads (207, 400, 511).

Behaviour: Most green iguana are diurnal, sedentary, and arboreal, except for females with mature eggs on the move to communal nesting sites (260, 493). During the breeding season adult males are territorial, living with several females. Iguanas remain inactive 90-96 percent of the time (167, 394) and move slowly, although they can run very fast and dive into the water when pursued. The more terrestrial brown iguana use their burrows as refuges. There are quite a few studies on iguana behaviour (88, 158, 166, 416, 493).

Feeding habits: Green iguana are specialized and selective leaf-feeders, eating the tender green leaves and flowers of various trees and shrubs and herb vegetation in savannah ecotones (34, 400). Newly-hatched brown iguana are insectivorous and gradually shift to an herbivore-omnivore diet as they grow (155).

Reproduction: Green iguanas breed during the dry season (494): the nuptial period and fecundation coincide with the onset of the season. A month or two later, the females lay a clutch of 14 to 76 eggs weighing 9-14 g (629) in burrows excavated in communal nesting sites. At the end of a three-month incubation period, the newly-hatched iguana emerge from the nest. This is timed to coincide with the onset of the rainy season, an ideal strategy for leaf-eaters (206, 494). Brown iguana lay an average clutch of 43 small eggs (12-88), weighing 4-8 g (629). Peak reproduction in the wild is thought to be five to eight nesting seasons (416).

Growth: Newly-hatched green iguanas have an average head/body length of 7.6 cm and weigh 11-6 g. Their growth during the first two years of life averages 0.273 mm/day (fluctuating at different times and in different places from 0.22-0.58 mm/day). They reach sexual maturity in two to three years (155, 260, 494, 511). The brown iguana grows faster during the insectivorous phase (0.362 mm/day (155)).

Mortality: Brown and green iguana hatchling predators include various species of reptiles, birds and mammals (155): only about 2.6 percent live to the age of one year (260). Adult iguanas may be killed by stray dogs and other carnivores, flattened by vehicles, or hunted (260, 511).

Hunting: Green and brown iguanas are the neotropical reptiles most frequently hunted for food (98, 191, 207, 400, 511). The methods used are rifles, particularly the 22, or dogs trained to capture iguanas shaken out of their trees. Live iguanas are captured for trade with a long rod tipped by a lasso, or they may be pulled out of their nesting burrows or refuges: this latter appears to be the method of choice for brown iguanas. The captured animals are tied up and immobilized. Iguanas, a fairly visible prey in many habitats, are relatively sluggish and easy to hunt, particularly in the dry season.

Products: Green and brown iguana are hunted for their meat and eggs, to feed the family or for sale, or for their commercially valuable hides, and newly-hatched iguana are sometimes captured for the export pet trade. Iguana eggs are a highly prized local food throughout the animal's range. Iguana eggs are often extracted from live females by a ventral cut. The animal is then released. The fate of female iguanas subjected to this treatment is unknown - sometimes the incision is sewed up to facilitate recovery.

Iguana meat is white and flavourful though rather tough. It is widely eaten but with local variations. In some Central American countries, iguana meat is not only daily subsistence fare, it is also in demand for the typical dishes of the Lenten period (511). Large quantities of live green and brown iguana are sold in the local markets where the consumption of this saurian is a long-established tradition (191, 144).

Management: Hunting intensity in densely populated areas has combined with deforestation to decimate iguana populations, prompting closed seasons and commercial hunting restrictions in Costa Rica, Panama, Nicaragua, Suriname and Venezuela. In some countries the hunting season (and an increase in poaching in others) coincides with the iguana nesting period: the target is the eggs.

Both brown and green iguana are highly valuable in subsistence hunting from the social and nutritional standpoint. As local producers of animal protein they deserve priority attention given the following: 1) these large exothermic herbivores have an excellent plant matter/meat conversion ratio; 2) the geographical and ecological distribution of iguana is vast, including many islands and other arid habitats where native fauna is scarce; 3) iguana prefer and tolerate modified environments; 4) they are widely accepted as food; 5) iguana reproductive capacity is relatively high once sexual maturity has been reached. The negative side is that slow growth, high hatchling mortality, vulnerability to hunters and depredation by dogs are a hindrance to management. Recently, the Smithsonian Tropical Research Institute began an applied research programme in Panama to develop iguana management and production systems for breeding under natural conditions and captive breeding (494, 619).

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