On 4th June I spent the day at Dundreggan with Tony Hunter, one of the entomologists from Liverpool Museum, who’s carrying out some further sawfly survey work for us at Dundreggan this year. Tony had been up at Dundreggan last year with his colleague Guy Knight, and they made some interesting discoveries, particularly of sawflies associated with dwarf birch (Betula nana) on the higher ground on the estate. Guy wasn’t able to come up this time because of health reasons, but Tony had been up in May, to set out some Malaise traps in the dwarf birch exclosure, and this visit now was a chance to check on the traps and look for sawfly larvae and adults on the plants as well.
We drove up the Bhlaraidh track – an old hydroelectric road on the boundary of Dundreggan. It gives good access to the eastern side of the estate, including the area where we erected a 10 hectare fenced exclosure for the regeneration of dwarf birch in 2002, while Dundreggan still belonged to the previous owner. On the way up the track, we saw a bird that I didn’t recognise at first, right on the track itself. It was a partridge of some sort, and didn’t seem too bothered by our presence, as long as we stayed in the vehicle. This enabled me to get some good photos, and I subsequently identified the bird as a red-legged partridge (Alectoris rufa), a non-native species that is reared and released by the neighbouring estate to the east, as a game bird.
Reaching the exclosure, we could see that the dwarf birch plants were in full leaf, unlike our previous visit in May, when the buds were just beginning to swell, but had not yet burst. Many of the dwarf birches also had catkins on them, and the growth of the plants, plus the abundance of catkins, was noticeably much greater on the plants inside the exclosure than on those outside.
After 10 years of protection, the majority of the plants there are not substantially taller than the unprotected ones, but they have put on a lot of lateral growth, as can be seen in some of these images.
As we walked around in the exclosure I spotted a moth on the ground, and although I didn’t recognise the species I could see it was a male, as it had beautiful feathered antennae. I subsequently had it identified by a moth specialist as a common heath moth (Ematurga atomaria). This is a widespread heath and moorland species, occurring throughout the UK, and typically on the wing in May and June.
Although this exclosure was put up specifically to help the dwarf birch there grow successfully without being overgrazed by red deer (Cervus elaphus), a number of other tree species have begun regenerating there spontaneously, including rowan, downy birch, juniper and Scots pine. This is very exciting as the area is at an elevation of 450 metres, and provides the opportunity for the natural re-establishment of the tree-line vegetation community, consisting of both stunted trees and montane shrubs such as dwarf birch. On one of the small pines I spotted an adult sawfly, which no doubt was looking for a place to lay its eggs. I’m still waiting to learn the exact species that this is, but it is one of two in the genus Diprion that feed on pines and are hard to tell apart – this requires close examination under a microscope.
The largest and tallest dwarf birches there are those growing on the drier ground of some of the slopes. Most dwarf birch plants that we find on Dundreggan and neighbouring areas are on wet, boggy ground, but my suspicion is that isn’t the species’ preferred habitat – rather it’s where it’s been able to survive, as the deer don’t go there as often as the drier sites. This is something that we plan to do some more monitoring and research on, to determine the best sites for dwarf birch, so that we can target our protection measures for them.
The main purpose of the visit was to look for sawflies associated with the dwarf birch, and Tony dug up a small plant to take back to Liverpool with him, so that sawfly larvae he and his colleagues have collected at Dundreggan can be reared on to adults there, and then identified – many sawfly species cannot be properly identified from their larval stage alone.
In last year’s surveys, some larvae were collected which couldn’t be identified to species level, so there’s a two-fold strategy to address that this year. One part is by hopefully rearing some larvae to adulthood, and the other is by using a Malaise trap to catch adult specimens. This trap is somewhat like a tent that is open at the sides. Insects are attracted by the white fabric, and then move upwards on the underside of the fabric, eventually reaching the peak at the front, where a hole leads into a container of alcohol. The insects fall into this, where they are preserved from decay and can be studied after the containers are emptied each month. Tony was up just now to change the containers, and was pleased to see they had quite a number of sawflies in them. At the equivalent time last year, the traps had been damaged by very strong winds, and no adult specimens were caught then, which is why some of the sawflies couldn’t be identified to species level.
We also carried out some detailed searches of the dwarf birch plants themselves, and Tony found sawfly larvae on several of the bushes. These were of a species that was found last year and successfully identified – it is a sawfly (Pristiphora borea) that had only been found 3 times in the UK, and only once since 1931, before it was discovered at Dundreggan in 2010, when we had the first sawfly survey carried out there.
Another sawfly found by Guy Knight on Dundreggan last year proved to be a species (Amauronematus tristis) that had never been recorded in the UK before at all. We didn’t see any sign of that species this day, but the larvae for it were only seen later in the season last year, so it’s possible that it appears later on than the Pristiphora borea sawfly, thereby providing a phased sequence of herbivory on the dwarf birch by the two species.
It was a third species that provided the mystery last year, and which Tony is hoping to find specimens of this time. In addition to the adult sawflies that were in the Malaise trap containers, he also managed to catch some adults with his sweep net, and he’s taken all of those back to Liverpool, so that Guy (who is the sawfly expert at the museum there) can identify them.
The larvae that we did see are all very well-camouflaged against the green leaves, so they are difficult to find until you get your eye in for them. They are also very small – to give an indication of scale, the dwarf birch leaves they can be seen amongst are all about the size of an adult’s little finger nail. The specimens we were seeing this day were relatively large, and we suspect they were almost fully grown and would soon be pupating – the transformational stage in which insects change from being larvae into adults that have a completely different form.
Tony will be back up with some of his colleagues from Liverpool in July, and I’ll make another trip out with them then. By that time, there may also be some news about the mystery sawfly from last year, which they suspect will prove to be another species that hasn’t been recorded in the UK before. All this serves to emphasise the importance of the dwarf birch population at Dundreggan, and the need to ensure that it grows successfully, without being held in check by the grazing pressure from deer.
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