Challenges in alpine lizard conservation: evaluating monitoring methods for cryptic alpine geckos

Long-term monitoring is pivotal to understanding population trends in threatened species and quantifying the impact of conservation interventions. Effective monitoring methods are generally underdeveloped or absent for taxa inhabiting the alpine zone. In Aotearoa | New Zealand (NZ), the alpine zone covers c. 11% of the land mass and supports a diverse fauna of at least 34 native lizard species. We developed and tested the effectiveness of footprint tracking tunnels and rock lifting for monitoring two cryptic alpine gecko taxa, cascade geckos (Mokopirirakau “Cascades”) and orange-spotted geckos (Mokopirirakau “Roy’s Peak”), in NZ’s Southern Alps during the austral summer. Field sampling occurred within defined strip transects and included two variants of rock lifting (one highly constrained involving lifting just 30 pre-selected marked rocks per transect; the other involving lifting all rocks judged suitable) and baited footprint tracking tunnels. All sampling methods resulted in low capture rates, plus highly variable detection rates for tracking tunnels. Rock turning counts of cascade geckos were consistently higher than those of orange-spotted geckos, and marked rocks returned counts 2.5–6.3 times higher than other rocks lifted within the transects. We used simulations to assess the ability of our trialled methods to detect a 20% change in gecko counts (hand searching via rock lifting) or detection rates (tracking tunnels) over a 10-year period, across 10 years for rock lifting and 15 years for tracking tunnels. None of our methods were capable of reliably detecting a rate of change equivalent to a 20% increase or decline, even if sampling effort was increased. Our results highlight the difficulties in developing effective monitoring methods for species that are sparse or difficult to detect. We conclude that alpine geckos will require longer monitoring timeframes than their lowland counterparts due to their slow life histories and cryptic nature.