Scree skinks, what happens over ten years?

A lot can happen in the world in, say, politics and technology, in 10 years.

Arguably, changes in the environment are slower-paced but that is not always a good thing. A 10-year study of New Zealand’s endemic scree skink in mid-Canterbury has recently been completed. At first, the research aimed to increase our understanding of scree skink ecology and the impacts of the predators that threaten them. However, two years into the study, a devastating flood nearly wiped the population out, leaving us with unexpected insights into population recovery and the possible impacts of climate change on this species.

Scree skinks (Oligosoma waimatense) are known to live in dry rocky areas – such as scree slopes – as well as on rocky bluffs and in stream beds. They are found from South Marlborough through to North Otago in montane to sub-alpine areas. They are one of our largest skinks, with a tail that is longer than their body and very long toes to help them move about their unstable habitat. Mice, cats, mustelids and hedgehogs are all found in scree skink habitat and the invasive spread of weed plants also endangers these lizards. The species is classified as ‘Threatened, Nationally Vulnerable’.

So, what does it take to study a skink over 10 years? Marieke Lettink says “commitment, some discipline and the love of it”. Marieke is an external science advisor in DOC’s Lizard Technical Advisory Group (TAG), which is dedicated to the conservation management of skinks and geckos. “I use the same methods to monitor the skinks at the same site each year, and the work is done under similar weather conditions to give the most accurate picture of changes occurring over time.” The work may be precise, but Marieke enjoys getting into some remote and beautiful landscapes.

An aim of the long study was to understand more about the threats to scree skinks and options for management. It is very challenging to control the numbers of invasive mammalian predators over large sub-alpine landscapes, but even more to control the weather. The flood event in the second year resulted in an 84% drop in the number of scree skinks caught by Marieke. “I wasn’t confident that the population could bounce back from such a massive crash” Marieke said. As she continued with the annual monitoring, she found that it took eight years for the capture rates to return to the same level it was before the flood. That is a concerning length of time for a species that is already low in numbers and at the same time under continual attack from predators. How do we think the population will cope with increased chances and intensities of flood events from climate change?

The formal 10-year study finished in 2018 but monitoring will continue. There is still much to find out about threatened lizards and the causes of their population declines. And it’s never certain what is around the corner: “We were pleased at the end of the scree skink study, we had learned a lot and the population appeared to be doing well. But our joy was short-lived. Last summer another flood hit the site and preliminary data suggests the scree skink population has been devastated yet again”.

A study that gathers data over a long period is valuable so that we can understand the threats to these valuable species, and it is especially important for long-lived species like scree skink. It demonstrates to us how easy it could be to lose an entire population in a ‘freak’ weather event. Because, remember, these days, as we face the reality of the implications of climate change, ‘freak’ is becoming ‘frequent’ – and more intense.