Towards the ecology and conservation of sand lizard (Lacerta agilis) populations in Southern England

Abstract

The sand lizard (Lacerta agilis) is a rare, elusive and cryptic reptile species of conservation importance in the UK. Knowledge of its ecology and behaviour has limited the development of a reliable and effective methodology for population monitoring; this threatens to compromise conservation effort. The behaviour of sand lizards varies seasonally, with sex and with environmental conditions, none of which are fully understood. This aim of this thesis is to further our ecological knowledge of the sand lizard, specifically by investigating factors which influence the detection probability of this species and through exploration of population monitoring and estimation methods.

The detection rate of both male and female lizards in a captive population was found to be heavily dependent on their sex and reproductive stage. The detection probability of males was higher (39%) before mating than after mating (33%): with pre-mated males this was strongly associated with temperature and time of day; and with post-mated males it was linked to changeable conditions with solar radiation values between 200-700Wm-2. The detection probabilities of females were higher after mating (40%) than before (25%) with additional variations in detection rate during and after egg laying. Pre-mated females were most commonly observed basking in a preferred range of ultra-violet light and post-mated they favoured conditions where the ground surface temperature ranged between 17.5oC and 27.5oC.

An intensive capture-mark-recapture study was performed on independent sand lizard populations and pattern matching software was used to assist with the identification of individual sand lizards from their dorsal patterning. The low recapture rate of sand lizards proved problematic and population estimates were generated using Program MARK following amalgamation of the data from each field season: but this nonetheless generated the first estimates of sand lizard populations in the UK, with a maximum mean density of 222Ha-2. The survivorship of males was consistently higher than females (0.67 vs. 0.26) and the detection rates and populations estimates differed between years. A high number of individuals were encountered only once, resulting in wide confidence limits of abundance estimates for this species.

The range of microclimates available within a structurally diverse array of heathland vegetation were quantified and found to be more extensive than previously thought. The range of microhabitats within the preferred temperature range for sand lizards increased from Spring to Summer, so the need for a lizard to be in the open, and thus available for detection decreased.

The obstacles encountered when attempting to monitor sand lizards populations arise from the unpredictable nature of the species. Future sand lizard surveys should be conducted at times when the detection probability maximised, as described in this thesis. A national monitoring scheme should steer away from absolute abundance estimates of populations and consider the use of occupancy estimation to monitor our remaining populations.

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