The researchers believe the creatures must be capable of shrinking their bones as well. So we don't entirely know how they shrink. The iguanas in the study became shorter during the climate phenomenon known as El Ni o, which occurs every two to seven years. This results in heavier rainfall in the Galapagos archipelago and the destruction of the red and green algal blooms that are the favoured food of Amblyrhynchus cristatus . But those animals that shrink their size can live through the famine.
Smaller iguanas fare better because their foraging and use of energy is far more efficient.
Females also do better because of their apparent ability to shrink further than males. The researchers found that adult marine iguanas can switch repeatedly between growth and shrinkage, depending on the environmental conditions. In adult humans, in contrast, re-growth after skeletal shrinkage, as happens in osteoporosis, is impossible. Dr Wikelski says other animals could share the iguanas' shrinking ability as previous observations in other creatures have probably been dismissed as data errors.