Ahead of Squirrel Appreciation Day (21 January), the National Trust shares an insight into the unlikely frenemy of the red squirrel and pine marten.
The 2,000-acre estate at Crom, on the shores of Lough Erne in County Fermanagh features the largest surviving area of oak woodland in Northern Ireland and a protected nature reserve. Home to a wealth of wildlife it remains one of only a few places in the country where the native red squirrel continues to thrive.
Managed by the conservation charity National Trust, Crom has a healthy and long-established population of red squirrels whose stronghold has proved to be largely resilient to the invasive grey squirrel.
Grey squirrels were first introduced to Ireland from North America in 1911 and rapidly spread. Grey squirrels transmit the squirrel pox virus to reds, a deadly virus to which greys are immune and compete with reds for food, threatening the very survival of the red squirrel here.
So why is the red squirrel population at Crom proving resistant to this hostile take-over?
One theory is that the red squirrel has formed an unlikely alliance with another native species, the pine marten.
Dr Joshua P Twining, a postdoctoral researcher at Queen’s University, Belfast spent many years conducting research at Crom. Joshua’s research included collecting scat (droppings) to investigate pine marten diet and interactions with squirrels, to collaring and radio-tracking pine martens to examine population health and behaviour.
“We know pine martens are opportunistic omnivores, switching food throughout the year and consuming whatever is available, including squirrels. Closer inspection of pine marten scats revealed that while this small predator eats both red and grey squirrels, they eat proportionally more grey squirrels than red ones. This apparent preference was likely linked to the availability of the grey squirrels as prey.”
Joshua conducted experimental research throughout Northern Ireland that investigated squirrel behavioural response to pine marten scent at feeding stations, revealing that red squirrels display a clear fear response, and developed anti-predator behaviours to pine marten scent while greys didn’t respond at all.
Joshua explains: “Reds avoided feeders, and when visiting fed for shorter periods of time and were more vigilant – standing on their hind legs with their head upright and tail twitching from side to side, giving a clear warning to others that a predator was in the area.
“Meanwhile, the greys generally continued to visit and feed as if nothing had changed. In some cases, grey squirrel visits to feeding stations actually increased while their vigilance decreased around pine marten scent.”
Red squirrels and pine martens have co-existed for thousands of years and, as a result, reds are adapted to pick up on these chemical signals, taking evasive action when they know a pine marten is nearby. But grey squirrels, a relative newcomer to the Ireland, don’t respond to pine marten scent in quite the same way. They don’t appear to recognise the scent cues of the predator, which likely makes them much easier prey for the pine marten.
“We don’t know exactly how many reds live at Crom, but we have a healthy, established population,” explains National Trust Ranger Matthew Scott. “We also have a stable pine marten population; we think there are around 12 on the site. Thankfully there’s no established population of grey squirrels, though we do have the occasional grey turn up and then disappear soon thereafter.
“We’re confident that the continued presence of the pine marten at Crom is helping to keep grey squirrel numbers down and giving the more vulnerable red squirrel a chance to grow in numbers.”
The continued success of the reds at Crom is also helped by geography, as ranger Matthew reveals: “The landscape that Crom sits in, peninsulas and islands surrounded by Upper Lough Erne and other lakes and rivers, helps reduce the likelihood of grey squirrels making their way into the estate. I like to think of the water like a moat around a castle.”
As a conservation charity the National Trust are also committed to managing the woodland at Crom in a nature friendly way, supporting the habitat to allow pine marten and red squirrel populations to thrive.
“Crom has been in the care of the Trust for the last thirty years and during that time there has been an ongoing programme of tree planting, as well as non-native conifer, rhododendron and laurel removal in our woodlands,” continues Matthew. “We also retain veteran trees and dead wood in our parkland and woodland, many of which contain holes, hollows and ivy cover that provide important denning sites for pine martens.
“Each winter we monitor our red squirrel and pine marten populations across the estate. We use sunflower seeds at baited feeder stations and capture the visitors on camera traps. We also stand ready to undertake grey squirrel control should that be needed.”
This land management has helped to develop and support the continued success of Crom’s oak forest, an incredibly biodiverse woodland that provides a valuable habitat for pine martens and red squirrels.
The National Trust is making an appeal to the public to help reverse the decline in nature by donating to the Everyone Needs Nature campaign via the website: www.nationaltrust.org.uk/appeal/everyone-needs-nature-appeal