Saturday, 20 July 2013

Butterflies emerge as it warms up

The warm spell, whose arrival was perhaps uncharacteristically timed to the nation’s favourite sporting event, has delivered an upturn in the number of butterfly sightings locally. Most evident of these have been the small tortoiseshells, with numbers reaching double figures in a few chosen gardens around the Brecks. Further afield, in ungrazed grasslands and the scruffy margins of forest rides, the first of the summer skippers (small, essex and large) are being seen. There have even been reports of clouded yellow butterfly and hummingbird hawk-moth, both a sure sign of some decent summer weather.

This fine spell of weather suggests that it is also the time to be out looking for some of our more overlooked butterflies, including both white admiral and purple hairstreak. Both are woodland butterflies and both spend much of their time up in the tree canopy, only coming down to a lower level to nectar and take other nutrients. The graceful white admiral is on the wing from June to August, depositing eggs on the leaves of honeysuckle. The white admiral caterpillar begins its journey towards adulthood in late summer but then hibernates through the winter, resuming its growth the following year. A patch of oak or mixed woodland, with some flowering bramble and some honeysuckle, provides an ideal site at which to seek out this large and attractive butterfly. I have seen them at various sites across the county but tend to favour Holkham in the north and Knetishall Heath in the south, in part because of the other species they hold.

The purple hairstreak is a much smaller butterfly, darkly coloured and with a deep sheen that flashes purple when caught in the light. The species is associated with oak, though adults may sometimes be seen around ash, and they spend most of their time in the canopy feeding on honeydew or basking, wings open, in the sun. This arboreal association makes them difficult to see well but they can be watched through binoculars as they flit around the canopy, silhouetted against the summer sky. Populations have a colonial structure and numbers can vary greatly from one year to the next but it is worth putting in the effort to catch up with these delightful little butterflies.

Friday, 19 July 2013

Looking at the skins of dragons

One of my tasks over the coming months is to go through the many hundreds of damselfly cases that have been collected as part of our reed warbler study. The warblers feed their young on a range of insects, damselflies included, and we need to secure a measure of how the availability of these changes throughout the reed warbler breeding season. The cases are collected from a standardised area of reed bed on a weekly basis, a task that can take several hours of careful searching.

As you probably already know, damselflies spend a greater part of their lives in water as larvae, emerging only when they are ready to transform into an adult. At our site, with its extensive fringing reedbeds, much of this emergence takes place on the reed stems themselves, the larval damselfly hauling itself out of the water ahead of the transformation.

The delicate case left behind after emergence is known as an exuvia (plural exuviae) and this forms a perfect replica of the larva, still showing a series of features that can aid identification. Thanks to the incredible efforts of Steve Cham, we now have two guides dedicated to the identification of dragonfly and damselfly larvae and exuviae, Simple to use and full of illustrations the guides are going to be well-thumbed this year as I work my way through the hundreds of sample tubes packed with specimens.

These are not be the only samples to be tackled this season, as we also have measures of the availability of other insects, notably small flies, collected via a series of pan trans. These traps, which take the form of yellow bowls placed on posts and which are filled with water, sample flying insects using the reed beds. Not only do we plan to examine the seasonal availability of potential reed warbler prey but we also want to look at how it varies across the site. This should enable us to relate characteristics of individual nesting attempts to prey availability and to establish whether some parts of the site are better for breeding reed warblers than others. The answer to that question is some way off, however, not least because we have all these specimens to go through first.

Thursday, 18 July 2013

Orchids offer a taste of the exotic

A thriving colony of bee orchids, discovered by a friend within the last fortnight, has brought a taste of the exotic to my local patch. The bee orchid is one of our most showy orchids, its elaborately patterned flowers used to attract the bees that act as pollinators. This is one of four Ophryus orchids to be found in Britain, the others being the fly orchid, early spider orchid and late spider orchid. Despite their name, the spider orchids also have flowers shaped to attract bees. Interestingly, these flowers do not offer the bees any reward since they do not contain nectar. Instead, male bees are fooled into ‘mating’ with the flower through a series of visual, tactile and olfactory deceits. In addition to looking and feeling like a female bee, the flower releases a scent which mimics the pheromones produced by a virgin female. The quantities of these chemicals produced may even be such that the flower becomes more attractive to a male bee than a virgin female.

Somewhat surprisingly, the bee orchid has largely abandoned this method of pollination and is now self-pollinated – the three related species continue to use bees. Quite why this has happened is unclear, although it is a fairly recent phenomenon and does not seem to have hindered the success of the bee orchid, which is found across most of England. Bee orchid shows a preference for areas of disturbed ground, presumably where it can cope with the competition, and old grassland or scrub sites on chalky or sandy soils can support sizeable colonies. These days it is the only one of the four species likely to be encountered in Norfolk, occasionally even turning up in gardens.

The wider group of orchids to which these species belong contains in excess of 240 species, making this the largest of the European orchid groups. Although members of the group can be found across Europe, reaching as far north as Scandinavia, the greatest diversity is to be found around the Mediterranean. This underlines the complex relationships that must exist with particular pollinators, the orchids diversifying to exploit the range of potential pollinators present. We may be some way from the Mediterranean but at least we have the bee orchid to bring a taste of the exotic.

Wednesday, 17 July 2013

The river runs low

The river is at her seasonal low, the run of dry weeks restricting the amount of water reaching her. The sluggish water sits well below the level of the bank and, in places, larger stones breach the surface. The sluice that guards a looping arm of the river, normally a roar of noise dropping into a turbulent pool, has been reduced to a trickle and the water below is dark and silent. With less water now passing through this arm of the river, the shallows have been reduced to a slither of silver that glints and chuckles through pebbles and stones. The otters that passed this way earlier in the year would now have to walk rather than swim.

A little upstream the river has more depth but even here the riverbed can be seen, a paler floor between the rippling weed that has grown dense with the season. A family party of mute swans has held court on this stretch for several weeks now, the adults displaying aggressively at any goose or duck that ventures too close to the swans’ fluffy grey chicks. This level of parental care bodes well and, despite losing one of their seven chicks very early on, the six remaining youngsters are doing well.

Here and there the yellow globes of water lily break the surface, their buttercup yellow flowers standing bright against the dark shadows cast by the riverside willows. Other gems, in the form of banded demoiselle damselflies, glint in the shafts of light that pierce the shade. The metallic emerald green of the females is particularly striking. Clouds of small flies can be seen hanging in the air above the water’s surface. In places these are picked off by the grey wagtails which, nesting nearby, use the floating vegetation as a platform from which to feed.

The summer river provides an idyllic scene, albeit one that is perhaps a little tatty around the edges. There is a sense that the river is bursting with life, crowded as it is with plant growth and supporting a wide community of creatures. I like the seasonality of the river and its changing moods. Right now it is drowsy but its character will soon change with the arrival of the rains.

Tuesday, 16 July 2013

Eyes on the bramble

The bramble is alive with insects at the moment, its flowers the lure that attracts flies, beetles and a multitude of bees. Although many of the visiting insects are familiar enough it is always worth spending some time at a flowering bramble to see what else might be attracted in. Over the years, for example, bramble has provided me with some of my best views of white admiral and black hairstreak butterflies, not to mention several interesting species of beetle.

Today though, it is the commonplace insects that are my focus, the bramble providing an opportunity to brush up on my bumblebee identification and to try out a new identification ‘app’ developed for the ipad by TouchPress . The most common bumblebee on this particular patch of bramble is the tree bumblebee Bombus hypnorum, a recent colonist whose populations here in the Brecks appear to be going from strength to strength. This attractive bee was first recorded in Britain back in 2001 but was not recorded from Norfolk until 2008, when an individual was found in Earlham Cemetery. Being one of the easier bumblebees to identify, with (in queens, workers and most males) a ginger thorax, black abdomen and white ‘tail’, you stand a good chance of spotting one this summer here in Norfolk. Tree bumblebees, as the name suggest, usually nest above the ground in holes in trees or buildings. They have also taken to using nest boxes of the type erected for hole-nesting birds like blue or great tit.

The arrival of the tree bumblebee is perhaps unsurprising given that its distribution elsewhere in Europe sees it established as far north as the Arctic Circle. The colonies of this species can be sizeable with perhaps as many as 200 workers supporting them, which might explain the numbers that I am seeing here on the bramble where they outnumber the white-tailed and buff-tailed bumblebees flying alongside them. Some of the other bees present will need more careful scrutiny, however, if I am to pick out some of the cuckoo bumblebees that might be present. Cuckoo queens take over the nests of true bumblebees, ousting the resident queens to secure the labour of their workers, which then help to raise cuckoo males and females.

Monday, 15 July 2013

The stillness of dawn

Even by my usual standards it is early; the combination of an elderly dog and a warm and stuffy night sees me up and about not long after four. Outside, in the garden, the air is delightfully cool and the town sits under a stillness that, for now, seems to suggest that its ownership rests with me. The dawn chorus of earlier in the year has subsided and it is the hypnotically drowsy calls of woodpigeons that echo across the dawn, disturbed only by the occasional chaffinch or dunnock.

The male from our resident pair of blackbirds sits in silhouette on the fence, a stroke of orange bill on an otherwise flat canvas. His plumage shows the signs of a long breeding season and the efforts of raising more than one brood of chicks. Scruffy in his appearance, it will not be long until the annual moult and the replacement of rough and battered feathers. The young from the latest breeding attempt are somewhere in the garden and they will soon start to call for food with the nagging persistence of hungry children which, after all, is what they are. Other young birds will soon arrive; streaky-plumaged young greenfinches in the company of their parents will come to take sunflower hearts from the hanging feeders and yellow-cheeked blue and great tits will join them to take advantage of this reliable food source.

All of a sudden there is a brief moment of commotion as the jackdaws arrive. This gang of a dozen or so avian ruffians squabbles over scraps of food and tufts of discarded dog hair. For these birds the breeding season continues and there are hungry young to feed and nesting attempts to be completed. The jackdaws are always an early visitor, a pattern repeated in many other gardens across the county, and they only rarely visit the garden later in the day. It is a little too early for many insects to be on the wing. Once the sun makes her appearance and stirs the borders with her warmth, the bumblebees and hoverflies will emerge to jostle around the blooms. It is going to be another warm day but for now I can enjoy the cool stillness of dawn.