Let it shine for butterflies

The run of poor weather through the early part of the month is likely to have had some effect on our butterflies, potentially limiting their development and reducing opportunities for active flight in search of a mate. On the few occasions when the sun has shone it has been reassuring to see familiar butterfly species on the wing. One particularly pleasing sight has been the presence of several small heath butterflies over the short turf of my local nature reserve.

The small heath is a somewhat inconspicuous species and easily overlooked. Even when located it remains a somewhat fidgety butterfly, quickly on the move and reluctant to reveal its upperwings. Often, all you will see are the grey and brown hind underwings and, if you are lucky, a glimpse of the eye-spot that appears on the underside of the forewing.  As the name suggests, this is a small species and one that is associated with grassland habitats on well-drained soils, where the sward is short and rather sparse. Some might refer to this species as being rather drab but I prefer to think of it as understated.

Small heaths are colonial in their habits and the males gather together within a breeding area to form what is known as a lek. Here they compete with each other for the best positions and the resulting access to visiting females. The best areas seem to be those with some form of landmark, perhaps a bush or small tree and it appears that the females visit these specifically to mate, as opposed to feed. Once mated, the female will leave the lek to lay her eggs on the leaves of fine grasses.

Although easily overlooked and, as a result, unfamiliar to many casual butterfly watchers, the small heath is very widely distributed across Britain. It also shows a greater tolerance of altitude than most of our other species, occurring in upland areas across parts of northern Britain. For me though it is a species of lowland heath and rough grassland, a butterfly that I can recall from my childhood and one for which I have a good deal of affection. It is wonderful to have what appears to be a thriving colony here on the Nunnery Lakes Reserve in Thetford.

Live traps reveal small mammals

The rich, waist high vegetation of the riverside meadow has proved a good hunting ground. The small mammal traps deployed here over the weekend have yielded good numbers of mice, voles and shrews. Other traps, set along a woodland edge, have proved equally successfully. The traps were being used as part of a workshop on small mammal identification and trapping, organised by the Norfolk & Norwich Naturalists’ Society to give more people the skills and confidence to get involved in wildlife recording. Small mammals are a group that I have worked on for many years, so it was rewarding to be able to pass on some of my skills to a new generation of small mammal enthusiasts.

The traps, known as Longworths, consist of a small aluminium nest box, attached to a tube that contains a trap door and a trigger. A small mammal entering the box, trips the door and then is caught and held until the traps are checked a few hours later. In the meantime, the mouse, vole or shrew has bedding and food available, which seems fair compensation for its inconvenience.

The woodland edge traps were dominated by captures of Bank Vole, neat creatures with rich, chestnut red fur in the adults. Also present in a smaller proportion of the traps were Wood Mouse and Common Shrew. The success of these traps was remarkable; with two traps set at each of the trap points we managed to catch in every trap and, incredibly, we even managed to catch two animals (a Wood Mouse and a Bank Vole) together in one trap. This high capture rate ensured that each of the dozen participants got to see and handle various small mammals. Handling your first small mammal, especially when the eyes of the rest of the group are on you, is not the easiest thing in the world but folk grew in confidence as the morning progressed. The riverside traps were dominated by captures of Field Vole, hardly surprising since the rank vegetation was classic Field Vole habitat and the matted vegetation dominated by their network of interconnected runs.

Each trap was emptied in turn into a large, clear polythene bag. This allows you to see what you have caught and then to manoeuvre it into the corner of the bag where it can be more easily removed. This involves holding the small mammal very gently through the bag with one hand, while the other is placed in the bag, your finger and thumb used to pick the animal up by the baggy skin at the back of the neck. This provides a brief opportunity to determine age, sex and breeding condition before release. It was a morning well spent.

The be-witching hour

We are huddled around a moth trap on the southern margins of Thetford well after midnight, yet there is still the drone of traffic on the road to Bury. It has been a steady night so far, with a good mix of species in reasonable numbers, each drawn to the bright mercury vapour light of our traps. A low purr hints at the portable generator that provides us with the power needed for the traps, but it will only be when the fuel runs out that we become wholly aware of its intrusion into the still night. By that stage, dawn will not be far away and the passing traffic long ceased.

The strength of the light makes the darkness beyond all the more intense, our night vision gone. Moths buzz past our ears, occasionally blundering into us, pulled in by the light. You get a sense of the size of the moths as they approach, the more robust species trailing a whirr of heavy wings. We have with us some folk who are new to mothing and they are soon astounded by the colour and diversity of the moths on show. While the pink and ochre of an Elephant Hawkmoth creates a stir, it is the size of a Pine Hawkmoth that draws the most comment. This smart, but rather neutrally toned, species is a common catch in the Brecks at this time of the year, but this was not always the case.

The Pine Hawkmoth favours areas of open or mixed pine forest and is most strongly associated with the dry heaths and poor soils which have been devoted to timber production. It is the spread of these plantations that has really benefited the species. A century ago it would have been a rare vagrant here, but now Norfolk is well within its core range, a range that extends west into Dorset and north to Yorkshire. As its name suggests, the larvae of this impressive moth feed on pine trees, favouring the needles of Scots Pine. When small, the larvae lie along the length of a needle, relying on this slender camouflage for protection. They grow in a rather sluggish manner, becoming more conspicuous, before later descending to the ground where they overwinter as pupae under a carpet of moss or needles.

Adults are on the wing from May through into early August and are attracted to both light and to sweetly scented flowers. The females are initially reluctant to fly and remain on the trunks of trees where they await a male who will pair with them. The males, however, are more mobile and it is these that you tend to see in the traps.

Winter wonder

The ice changes everything; it shifts the focus away from familiar sites that I would normally search for wintering waterfowl. The lakes, so often packed with Coot and duck, are empty. Instead they carry a crisp skin of newly formed ice, highly polished thanks to the lack of wind and reflecting the bank side willows with photographic precision. The fishermen, quite sensibly, are nowhere to be seen and I have the reserve to myself.

Much of the activity is on the river which, ever in motion, remains ice-free. Small groups of Mallard drift away at my approach, while the more nervous Teal take flight, leaping into the air and away with a flurry of wings. Canada Geese and feral Greylags wander about the margins of the pits, unsure and seemingly bemused at the sudden change of state to their watery haunts. As they move across the shiny surface they slide each webbed foot forward, pushing down onto the ice. Am I imagining this or are they really indulging in something that resembles gentle skating? There is a sound to their somewhat unsteady movements, a harsh scratching noise, and I cannot work out if this is caused by their claws or comes from the ice itself, moving under the stresses of this additional weight.

In some places the ice is thinner and the occasional goose falls through; with much flapping of wings it tries to move forward, the ice sometimes breaking further but more often the goose shakes itself free of the cold, dark water. A larger area of open water holds a few dozen coot, a handful of Tufted Duck, a single Goosander and, amazingly, a drake Goldeneye. This stunning black and white duck is a rare visitor to the lakes, being more commonly encountered on the flooded margins of the East Anglian coast. This is probably only the second or third record for the site and a welcome one it is too. Although there is a small but expanding breeding population of this delightful duck in Scotland, this bird may have come from the larger Scandinavian population which breeds on freshwater lakes and pools surrounded by conifer forest. It is also remarkable that this particular bird is an adult male, since it is the females, which winter further south than the males, that dominate our wintering population.

Since the light is pretty good I get a decent chance to watch the Goldeneye through my telescope as it dives deep into lake in search of food, buoyantly erupting from the surface at the end of each dive. It won’t remain here for long, especially if the ice increases its grip on the lake, so I am fortunate indeed to stumble across it.