Optimisation of reintroduction protocols for cryptic species: Reintroducing the sand lizard Lacerta agilis to a lowland heath site

Abstract

At a time of high biodiversity loss and in the light of global climate change, some species are at particular risk. Geographically restricted specialists may undergo biotic homogenisation. Less charismatic and smaller taxa are often under-studied, with cryptic species raising additional monitoring challenges. The close links between reptile biological cycles and temperature and moisture leave many populations facing an uncertain future.
Following dramatic population declines of the sand lizard Lacerta agilis in the UK due to habitat loss, fifty years of captive breeding and reintroduction efforts have focused on returning populations to sites in their former range. Ongoing presence of the species shows reintroduction efforts are broadly successful, but the cryptic nature of the sand lizard has raised post-release monitoring difficulties. This research addressed the challenges associated with this species, offering a more quantitative assessment of reintroduction practice to determine efforts are best-placed and to inform protocols going forward.
Microhabitat preference of the sand lizard was studied in the light of monitoring difficulties. Detectability of sand lizards varied, with less dominant adults spatiotemporally restricted to less optimal environmental conditions. Juveniles showed aggregative behaviour as a thermoregulation mechanism, the benefits of which may influence post-release movement. Survey methodologies ere assessed at the receptor site, Eelmoor Marsh SSSI in Hampshire, UK. Recommendations were made for the sand lizard as well as the wider reptile community, including the more generalist common lizard Zootoca vivpara and slow worm Anguis fragilis, and predators adder Vipera berus and grass snake Natrix helvetica. Refugium materials of felt and slate proved favourable to sand lizards and common lizards, both species highlighted as being poor users of traditional tin refugia. eintroduction protocols currently focus on hatchlings. Hatchlings, yearlings, and a small number of two-year-olds were released in this study. Releases were undertaken in September 2017 and September 2018, of 80 and 86 lizards respectively, and post-release monitoring occurred for a year following each. Overwinter survival favoured yearlings over hatchlings. Yearlings also showed predictable post-release movement and survival; hatchlings did not. Yearlings displaying higher locomotor performance and those that showed a less exploratory and less active behavioural response to the novel release site, were more likely to survive overwinter. The furthest travelled yearlings pre-winter showed more exploratory and active traits. Many yearling lizards showed release site fidelity, remaining in or returning repeatedly to the area, highlighting the importance of maintaining this as optimal, structurally diverse habitat. Released yearlings were observed having successfully bred within a year, at two years of age; released hatchlings would likely not breed until their third year. Observations of sand lizards in less favourable environmental conditions and beyond the normal active season indicated release may be favourable earlier in the year; this would benefit from further study. Continued monitoring is recommended to observe longer-term trends.
This research highlighted the potential and benefits of developing a rigorous post-release monitoring approach for cryptic species. It showed the importance of building on current understanding of species ecology and biology at demographic and individual levels to aid conservation initiatives.

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Identifiers

ORCID for Rachel Sarah Gardner: orcid.org/0000-0002-4911-7731

ORCID for Judith Lock: orcid.org/0000-0002-1673-4207

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