Tuesday, 27 December 2016

Butterflies and moths overwintering in the Newhaven Fort tunnels

Our third year of surveying overwintering insects and bats in the tunnels at Newhaven Fort started on 14th December. The Fort management team kindly allows us access to the tunnels which are closed to the public at a time when the Fort itself is closed for winter maintenance. 

Peacock in diapause (Vanessa io)
Of the few butterflies which spend the winter in diapause, species like the Red Admiral (Vanessa atalanta) tend to prefer the cover of thick vegetation rather than a subterranean hibernaculum. They are the last species on the wing in most years and often one of the earliest seen the following year. We have never found Red Admirals in the tunnels. Peacocks (Vanessa io) and Small Tortoiseshells (Aglais urticae) are often seen on a warm morning in February or March basking on the bare ground around rabbit warrens, having emerged from within the holes. The Newhaven Fort tunnels offer a similar refuge and we find both species in small numbers here.

Bloxworth Snout (Hypena obsitalis)
Of all the insect species found overwintering within the tunnels, we are most interested in the Bloxworth Snout (Hypena obsitalis), a moth which is in the process of colonising coastal Britain from the south. It feeds as a larva on Pellitory-of-the-Wall, a nettle which grows in walls and crevices, hanging on along the edges of things - a bit like the Bloxworth Snout itself. The Newhaven Fort tunnels are emerging as one of the best spots in the UK known for this moth.

Bloxworth Snout (Hypena obsitalis)
Another notable moth we find is a well-known overwinterer, The Herald (Scoliopteryx libatrix). This species feeds on poplar and willow and there are a few of these trees in the northern edge of the Fort and Castle Hill Local Nature Reserve. This species has been seen in single figures in previous surveys. It is a common but beautiful moth which looks like an autumn leaf.

Eristalis tenax hoverflies clustered beneath a paint blister
In addition to these core species, we usually also see good numbers of the Twenty-plumed Moth (Alucita hexadactyla) which feeds as a larva on the abundant honeysuckle growing at Castle Hill LNR, a few Common Flat-body (Agonopterix heracliana) and a few individuals of the Fleabane Smudge (Digitivalva pulicariae), which are curiously found deep within the tunnels far from an obvious point of entry. All the other moths and butterflies we see are found fairly close to the open air, in the company of bristletails (Petrobius maritimus), various woodlouse species, slugs and snails, several species of midge and lots of spiders. Their prerequisites appear to be a stable temperature and some ventilation with protection from the weather, predators and pathogens. Some light intrusion to indicate changes in day length is probably also an important guide to the right time to re-emerge the following Spring.

So to 14th December 2016. Five of us ventured underground on what was a sunny winter day with a moderate southerly breeze blowing warm air across the English Channel from the continent. This weather pattern had been in place for several days prior to our visit and followed a period of colder weather with a number of overnight frosts. It's a shame the frosty weather hadn't lasted until our visit as this would have allowed an interesting comparison with previous years' surveys, which have always taken place during mild weather, but the mild weather did allow a direct comparison this year with the previous two. The thermometer read 13°C, which is pretty warm for a clear December day. Temperatures in the tunnels ranged between 12°C and 13.5°C. Here's what we saw:

Peacock (Vanessa io) (17)
Small Tortoiseshell (Aglais urticae) (9)
Twenty-plume Moth (Alucita hexadactyla) (67)
Herald (Scoliopteryx libatrix) (31)
Bloxworth Snout (Hypena obsitalis) (10).

Five species is the fewest we have seen since we started surveying the tunnels, yet we saw more individuals overall and beat our previous record of 112 by quite a margin: this time we saw 135. The reason for this was a significantly greater number of Twenty-plume Moths (December average is 40) and Herald (December average 7.5). It is misleading to place too much relevance on only a few years' data, but this December we saw a 67% increase of Twenty-plume Moths and a more than 400% increase of Herald.

The value of regular surveys grows with the accumulation of comparable data from year to year and we are beginning to see some interesting patterns emerge now that we are into our third year of monitoring. Observing overwintering insects also reveals a surprising insight into different species' behaviour. Predictably perhaps, warmth-loving butterflies tend to be in a much deeper state of diapause than moths, which are more tolerant of cooler temperatures. The Bloxworth Snout is particularly tolerant of low temperatures, often entering a shallow state of torpor rather than proper diapause. This ability to remain active at times when predators or competitors may be less active might offer a selective advantage as it radiates northwards into new territories, but it might consequently also be more at risk of severe cold snaps. If more people were able to inspect overwintering sites each year it would almost certainly help improve the understanding of how weather and climate influences the population dynamics not only of moths or butterflies but also all those species associated by a complex web of interaction.

The reasons for the increases in some species this December might be that the weather was good when the adults we saw were progressing through their earlier life-stages; it might be that predators and pathogens were fewer; it might be that previous years were influenced by adverse conditions at the time and we are now witnessing a regression to the mean. Whatever the reasons, the other species we saw this time were at much the same levels as in previous surveys. Questions arising from the collected data are exactly what is hoped for. Some of these questions might be answered if we can continue to collect data in future years.

A cluster of Herald (Scoliopteryx libatrix)

Monday, 26 December 2016

Bishopstone Boxing Day-break

Daybreak on Boxing Day. Cool, calm air; a sky mostly clear of cloud. That restful feeling of the morning after the night before. The wind and rain delivered by Storm Barbara on Christmas Day had skimmed past and the world was sleeping in. As the sky lightened from the east above The Rookery, long streaks of cloud lit up like glowing embers on logs rekindled by the approaching sun.

Something was passing with the Rooks. They were up and abroad early. As the dogs and I made our first pass of the trees, they returned above us making enough noise to scare away the spirits of the dwindling dark and with them the fears of the long winter night. The world was theirs again. The tawny owls were silent; the jackdaws nowhere to be seen.

The rooks were still at it when we passed by on our way home. I paused and watched them in the throes of what could have been the corvine equivalent of our Boxing Day hunts - all excitement and chatter as they rode the canopy, breaking the surrounding silence. I put aside the automatic enquiry of what was happening and why and just watched, enjoying the pell-mell.

Leaving the rooks to it, I followed the path homeward and their sound subsided. We reached the crossing of a holloway and its parallel hawthorn-dotted modern track which connects the hamlet of Norton with Foxhole. Here, by the line of hawthorns, a meditative moment. It is chilly - maybe 5° Celsius - and yet a cloud of winter gnats hung in the air, silent, rising and falling in waves, peaking and troughing as though the countryside was gently sleeping, breathing out, in, out, in.

These midges are  males, dancing to attract females. They hang around the protection of the hedge or in a state of torpor, emerging in low light when it is mild and quiet. It is mesmerising to watch them, trying to pick out an individual from the cloud and follow it as it rises and falls in a starling-like murmuration. Rise and fall, like breathing. It's still early. I'm the only person around. I have the world to myself. It's a good time to take a breather. To just be instead of be going somewhere. The midge-cloud shares its gift: a lesson in pausing and noticing the rythmic rise and fall of the breath, the ability to let everything else fall away and focus only on the self. Nothing matters beyond the hypnotic, rhythmic dancing cloud. Just breathe and be at one with the world.

Saturday, 10 December 2016

Rough Music at Bishopstone

Walking the eastern downs is a relatively treeless and bird-light pastime, especially in winter. Gulls and game are often seen along with my indifferent friends the rooks, but there are sometimes few other species to keep them company, save for an occasional jolly of wagtails. It is always with great pleasure therefore that a walk takes me through the trees at Bishopstone with its abundance of ash, elm and sycamore alive from canopy to ground with avian chatter.

I set out a few weekends ago beneath a dark, clear, moonless sky to enjoy the late-November dawn. A gentle climb from South Heighton up to and along the crest of the Firle plain to Bo-peep, along the gentle sweep of the Cradle Hill escarpment, where the first pale light seeped out of the eastern horizon and, before heading home, a final plunge back down into Bishopstone and its wet meadows and trees. By this time the day had beaten the darkness away, the stillness in the air stirred by the dawn breeze from the east, and the robins and blackbirds had had their say, leaving the soundscape to later risers. Rooks and jackdaws could be heard from a distance in the treetops, their indiscretions a banner to all within earshot that this land belongs to them, the trees of Bishopstone Wood their palisade wall.

I skirted up and around the rookery so that I could climb and look down on the leafless canopy, swept clean the week before by the first winter storm of the season. Leaving the wet meadows behind me, I climbed alongside a scrub fringe towards what sounded like a disagreement involving jays and magpies. Jays established themselves here only in recent years, but have become a regular and welcome sight. A few weeks earlier I saw between Stanmer and Ditchling Beacon what I thought was a terrible disagreement between a mischief of magpies and jays. I suspected a raptor of some sort - a buzzard is often the subject of their scorn - but the pell-mell was hidden in the privacy of autumn leaves and I walked on without learning whether they were collaborating against a common foe or facing-off against each other. Seldom do birds muster such a cacophony as jays and magpies.

Today I was able to creep unseen up to the melee. As I rounded a bush the scrub opened up and I saw two jays, which straight away saw me and sat silently upright like children caught in the act of something naughty. The magpies, though, were oblivious in the pell-mell: ten of them screeching around the scrub. I stood still as a sleeping horse, hoping not to send every bird scooting into cover. Next, a surprise in dozens of mixed tits: great, blue and long-tailed, all busy uttering alarmed calls amidst the jays and magpies. The scene was chaotic, the noise confusing and wonderful to behold, like rough music! Not, then, a fight between jays and magpies; more likely cooperation on some level involving more species than I might see along all of the previous nine miles.

My question of where the raptor was hiding was quickly answered: it wasn't a raptor, but it was a predator and another recent arrival in the Rookery. A tawny owl broke cover low down, flew directly towards me and shot into the deep scrub just a few metres before where I stood, blowing my cover to all present. The corvids retreated to a safer distance and the tits melted back into the scrub edges. The owl, a creature which feeds on small rodents and insects rather than other birds, was now perceived as less of a threat than I. But there was no rough music for me, only a hush.

Rough music is one of folklore's popular rituals for dealing with bad behaviour, keeping a community safe, and something that might have been borrowed by people after watching birds like those before me. The origins of this might be found in the wassail - a similar ritual in which a cacophony was made to scare off evil spirits from apple trees before they were blessed at the end of Christmastide. A rough music ritual may have been popular with those dishing out the punishment, but it was less so for the person at the receiving end; a wife- husband- or child-beater. A noisy procession would be led after dark through the village to the wrongdoer's house, clashing metal tins or sheets and chanting along the way. The procession would stop outside the culprit's house and a chant was made warning them to mend their ways. Sometimes an effigy would be carried and burnt outside the house. The ritual would be repeated over several nights if required until the person relented. Sometimes they packed up and moved away, unable to cope with the naming-and-shaming and rejection by a close-knit community. With little else to entertain a village at night, rough music was an attractive pastime to those who might already have taken a few liveners at the local inn and this no doubt helped instil their determination to mete out a traditional form of justice, even in later times when told to desist by the local policeman. It was the peoples' form of justice and their right to give it.

Rough music lives on today in the tradition of Bonfire. Everything is there: a culprit, the effigy, processions, chanting, loud noise, fire, the burning. Every Bonfire in Lewes gives rough music to politicians and the Pope, just at that time of year when the days darken and the world plunges into the long, uncertain, winter. A time when dark spirits walk the land.

Back at the rookery the owls have the trees only by night, their hoots answered only by the occasional complaining jackdaw or rook. There is no place for them during daylight hours, nor any place for people. The rooks and jackdaws, the magpies and jays and the little birds all give us rough music and move us on. Following the hollow way out of the trees, I headed out over open ground again. Amongst the rooks and gulls I counted a jolly of thirty wagtails bobbing along the drills.