Reptile surveying and monitoring can be problematic; reptiles are active, shy creatures, which do not aggregate for breeding as do amphibians. Their behaviour is also heavily influenced by the weather. Most methods for surveying and monitoring reptiles do not generally produce sufficient data to enable population size to be estimated, unless mark–recapture techniques are used.

ATTRIBUTES FOR ASSESSING CONDITION

Population size

Estimates of population size for reptiles are made during April–October. Most methods for estimating total population size employ mark–recapture studies. Population indices can be obtained without mark–recapture work, but results are less accurate.

Breeding success

Whether or not reptiles are breeding successfully can generally only be ascertained by counting the number of young animals entering the breeding population each year.

Survival and mortality

Estimates of survival and mortality can only reliably be made by mark–recapture studies; the survival of individually marked animals from one trapping occasion to the next can be estimated. Unless dead animals are found, it is not usually possible to distinguish between mortality and emigration. Similarly, immigration and births can be easily confused, unless you are certain that the population is isolated.

GENERAL METHODS

A survey for reptiles should start with an assessment of the habitat suitability for different species, to establish which, if any, reptiles are likely to occur in the area. For example, Grass Snakes Natrix natrix are more likely to occur in areas with freshwater bodies; a summary of the habitat requirements of the different species can be found in Gent & Gibson (1998).