Introduction

Most common survey methods employed to estimate the abundance of reptiles involve capturing individuals (Table 8.1). This is for two reasons: (a) reptiles tend to be mobile and/or shy and cryptic, so not all members of a population will be visible (and therefore amenable to counting by sight) at any one time; and (b) much more information can be obtained from an animal that has been captured than can be obtained from an animal that has simply been seen. For example, the animal may be weighed and measured, have its sex and reproductive condition determined, and have its parasite load assessed. An identifying mark may also be placed on the animal so that it can be re-identified, should it be recaptured at a later time. As well as providing advice on capturing reptiles, we also provide information on common techniques for marking individuals.

Reptiles are ectotherms. That is, they obtain their body heat from the external environment. This has major implications for any survey technique, in that weather conditions may greatly affect the activity and therefore the catchability of reptiles. The effect of weather can vary seasonally, as well as on a daily basis. This should be kept in mind when designing a survey programme.

Because it is unlikely that the whole population will be counted in any one census period (some individuals will be missed), statistical mark–recapture methods should generally be used to estimate population sizes/densities or survival probabilities for reptile populations (see Chapter 3).