Natural history of the Frog
The lifecycle of the frog has four main stages which are: egg, tadpole, metamorphosis and adult. The mating call of the frog is well known and is executed by the male frog. He will locate a watery area deemed suitable for spawning of eggs and will then call out to the female to attract her to this area that he has located. After laying the eggs some species of frogs, though not all, will stay with the eggs to look after them.
Female frogs lay many thousands of eggs at any one time as they are very highly vulnerable to predation. For this reaction frog reproduction tends to happen 'en masse' to ensure the maximum number of young survive. Despite this, the vast majority will be eaten by predators when still an egg or tadpole. Some frogs lay their eggs on a leaf on the surface of the water and the tadpoles then drop into the water when they hatch. Some species of frog produce eggs that are able to detect the vibrations of nearby predators in the water and will then hatch early to avoid being caught. The cane toad for instance, produces poisonous eggs which deter predators. Every species of frog has a slightly different gestation period for eggs but on the whole this is around one week. Environmental factors can also influence this.
Following the tadpole stage the young frog undergoes a metamorphosis period to develop into an adult frog. There is some evidence that some species become carnivorous while still in the tadpole stage (i.e. the common frog) and for this reason it is usually the late developers that will survive as any early developers could be eaten by their peers! After they have fully developed the young frog will either leave the watery habitat that they have grown up in and take to land or may stay in the water. Most frogs will eat small bugs and insects but some of the larger species can east fish and small mammals.
Frogs live in a variety of habitats worldwide excluding Antarctica and the Oceanic Islands. Since the 1950's a lot of species have declined and some are even thought to be extinct, such as the golden toad. More than 120 species are believed extinct since 1980. This is due to environmental factors such as climate change, pollution, introduction of non-native predators and infectious diseases. Scientists now think that frogs may provide an excellent indicator of the state of the environment and habitat as a whole.