Today’s blog by Steven Ewing, RSPB’s Senior Conservation Scientist discusses his new paper looking at the habitat needs of the elusive Mountain Ringlet butterfly.

The Mountain Ringlet (Erebia epiphron) is a small brown butterfly found in herb-rich mountain grasslands in the UK in parts of the Lake District and the western and central Scottish Highlands. It’s truly an inconspicuous little butterfly – you could easily pass through the centre of a large breeding colony on an overcast day during the peak of the flight period and be none the wiser of its presence.

Female Mountain Ringlets, like this specimen, are more sedentary than the males, especially when they first emerge and their abdomens are heavily laden with eggs (c) Steven Ewing 

Only on sunny, warm days do Mountain Ringlets emerge in profusion, males patrolling for females and females searching out suitable host plants for their eggs. The combination of this inconspicuous nature, as well as the remote locations of Mountain Ringlet colonies, is why this species is the UK’s least known butterfly.

The Mountain Ringlet is one of RSPB’s 20 or so All Nature priority species, whose conservation status we are committed to improving in the UK. A key reason for this butterfly’s designation as a priority species is the potential threat posed by climate change. As our only montane butterfly, the environmental conditions and cold-adapted habitats favoured by this species are increasingly disappearing with a warming climate. For example, research shows that low altitude Mountain Ringlet colonies – those most vulnerable to climate change – have suffered higher rates of local extinction than those further uphill in recent decades.

The Lake District is one of the few places with the right conditions for these butterflies (c) Steven Ewing

Part of RSPB’s conservation objectives for Mountain Ringlet is to develop management approaches that reduce the potential impacts of climate change, which can then be rolled out across our reserves and elsewhere. However, our ability to design such conservation measures is severely hindered by the fact that we know so little about the ecology of the Mountain Ringlet.

To address this, scientists from RSPB’s Centre for Conservation Science have had to carry out a bit of detective work, undertaking out a four-year research project to try to inform our understanding of what really makes Mountain Ringlets tick. This project started out studying the Mountain Ringlet colony on RSPB’s Haweswater reserve in the Lake District in 2015 but has since expanded to cover more than 10 other colonies across the Lake District and in Scotland.

How do you even go about working out what a mountain butterfly needs? Well, from personal experience, I can tell you it requires a lot of exhausting running up and down steep mountain slopes chasing after butterflies, and a lot of staring at grass. Our research focused on understanding the needs of Mountain Ringlet caterpillars, as often the larval stages of butterflies have the most exacting requirements.

Steven measuring the height of grass with a highly technical bit of equipment – the trusty garden cane (c) Steven Ewing

As the caterpillars of Mountain Ringlets are even more difficult to locate than the adults, we instead followed female butterflies and watched where they laid their eggs, which you expect to be in locations favourable for their caterpillars. We then compared conditions at these egg sites with random locations within the wider landscape to work out what habitat characteristics female Mountain Ringlets might be seeking out for their offspring.

The results of this research have discovered new insights into the ecology of Mountain Ringlets. For example, we have a far better idea of the range of host plants that the caterpillars are liable feed upon. Whereas Mat-grass (Nardus strictahas always been assumed the key host plant for Mountain Ringlet caterpillars, we now have good evidence that Sheep’s Fescue might also be an important host.

We also now know that Mountain Ringlet caterpillars appear to have far more restrictive habitat preferences than previously realised. They require mountain grasslands with an abundance of host plants, a patchy sward height with areas of short, sparse vegetation, and a reasonable amount of leaf litter to buffer them against extremes of winter temperature. Going forward, this research will underpin the design conservation management measures hopefully enabling Mountain Ringlets to continue to flourish on RSPB reserves and elsewhere well into the future, even in the face of climate change.

The full paper can be read here: Vegetation composition and structure are important predictors of oviposition site selection in an alpine butterfly, the Mountain Ringlet Erebia epiphron 

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