Whinchats

I bumped into three Whinchats (Saxicola rubetra) this afternoon at Stockwood Open Space, in the thistly rough grassland between the sports pitch and the main path. One of them was co-operative enough to enable me to get a photo.

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At this time of year, all ages and both sexes of Whinchats look pretty much the same, with a buffy stripe above the eye (the supercilium), dark droplet-shaped markings on the upperparts, and pale orangey-buff underparts. Spring males, however, are boldly marked, with a distinctive head-pattern (a white supercilium and dark cheeks) and the orange on the throat and breast is more intense, like this bird.

Whinchats don’t breed around Bristol: these birds are on migration, south to their wintering areas. After they leave Britain, these birds are likely to move south through France to Spain or Portugal, where they will feed up, ready for a flight across the Sahara to their wintering zone in the savannah from Senegal eastwards; returning birds in the spring are usually seen from the second half of April.

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Autumn Ladies-tresses on Bristol Downs

There are a few flowering plants that wait till the end of the summer before flowering, and Autumn Ladies-tresses (Spiranthes spiralis) is one of them, never flowering before August and continuing well into September. This is probably the least conspicuous of the orchids which are found in the Bristol area, typically only reaching about ten centimetres tall. The photos below show the way in which the tiny flowers spiral around the stem, a feature reflected in its scientific name.

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I visited the colony on Bristol Downs today, and counted at least 87 plants – although among these were many which weren’t in full flower yet, which I only noticed when I was on my knees next to plants which were in flower, so as I will have no doubt missed other similar individuals, I’m confident the total population here is well into three figures.

Here’s the location: right next to the circular road which runs around the Downs.

Autumn Ladies-tresses is a plant of very nutrient-poor limestone and chalk grassland. In most locations, sheep do the work of keeping the habitat conditions right; on the Downs, in the absence of sheep, the grassland has to be managed by mowing and raking off the cuttings. On the side of the colony closest to the road, the soil has been badly eroded by runners; fences have been erected to encourage people off of this part of the site, in the hope that it will regenerate.

The Downs as a whole are a bit of a curate’s egg botanically, even if you discount the areas which are formally set aside for sports. Although it is certainly the largest area of limestone grassland around Bristol until you reach the Mendips and Cotswolds, that doesn’t necessarily mean it’s good-quality limestone grassland throughout. Some areas are good – I found a few Harebells (Campanula rotundifolia) growing in another spot today, for example – and the stone workings on the southeast side have some botanical interest, as does the area around the observatory. However, other parts are quite species-poor. With the right management to reduce the nutrient levels, though, the Downs could certainly become a lot richer, and complement their neighbour the Avon Gorge.

Two scarce riverbank plants

Earlier this month, I took a walk along the River Avon from Conham to Hanham. to check out some of the scarce plants which occur locally in riverbank habitats. The highlight was this Greater Dodder (Cuscuta europaea), a parasite of the Common Nettle (Urtica dioica): the upright green stems are those of the nettle, and the red stems twining around them belong to the dodder.

This is a nationally scarce plant, found in only a handful of areas in southern and central  England. Locally, it occurs in two areas. It is found along the River Avon from Bristol upstream to Bath, and again to the east of Bath into western parts of Wiltshire; its other stronghold is along the River Severn (mainly around Gloucester but with an outlying site near Frampton-on-Severn).

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The closely-related Common Dodder (Cuscuta epithymum) also occurs in our area, and is also a scarce plant, despite its name. It is found in heathland and dry grassland and parasitises among other things, species of gorse, heather and thyme. It has smaller flowers, although to be certain of the identity of a dodder specimen, a flower has to be dissected under a microscope, to look at tiny features such as the shape of the minute scales at the base of the inner surface of the flower and the relative length of the sex organs.

Here’s the area where I found the plant photographed above:

Also present in good numbers throughout this section of the Avon was Small Teasel (Dipsacus pilosus), the scarce relative of the ubiquitous Common Teasel (Dipsacus fullonum). In and around Bristol, it is found on the River Avon between Bristol to Bath, on the River Frome in northeast Bristol, on the River Chew, and scattered other localities, often in or on the edge of woodland.

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Roesel’s Bush-cricket

It’s the time of year when orthopterans are out in force just about anywhere with any decent vegetation. There are four families represented in Britain: grasshoppers are common and familiar; the larger bush-crickets (which many people just refer to as “crickets”) are less conspicuous but still common; then there are the groundhoppers, which take a bit of searching for, and the true crickets, which are just downright rare. This diversity is the reason for going ever-so-slightly jargony with that first sentence: there isn’t really a single good shorthand name, the best compromise probably being “Grasshopper and crickets”.

They are quite an easy group to get to grips with, as there are only about 30 species in Britain, and the species featured in Vic Savery’s photos below is an easy one to identify: the long antennae and chunky body are characteristic of a bush-cricket, and the pale crescent around the edge of the side-panels of the thorax are a dead giveaway for Roesel’s Bush-cricket (Metrioptera roeselii).

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Roesel’s Bush-cricket, 12 August 2013, Avonmouth, Bristol, Vic Savery (naturenutz.net)

When the last national Orthoptera atlas was published back in 1997, Roesel’s Bush-cricket was largely confined to the Home Counties, with isolated outlying coastal populations in a few other areas. However, like a number of other species of bush-cricket, its populations have expanded since then, and it now occurs around Bristol. It is well-established in Wiltshire and Gloucestershire and has also spread into Gwent in the last decade. Robert Cropper’s 2011 book “The Orthoptera and allied insects of Somerset” documents surprisingly few Somerset sites: a strong population around Bridgwater possibly marks the southwestern edge of the current British range, although the range expansion is no doubt ongoing, so I’m sure that the species will reach Devon soon if it hasn’t already.

The song of Roesel’s Bush-cricket is a high-pitched buzzing, pitched at around 22 kHz. If like me, your hearing has deteriorated to the point where you can’t hear sounds which are that high-pitched, you’ll need to use an electronic detector to track one down. Vic tells me there were three or four singing at his site, on Kingweston Lane near Avonmouth. In all likelihood there are other sites elsewhere in the city too.

Green-flowered Helleborines

Ashton Court, a walled estate just to the west of Bristol is famous for hosting the Bristol International Balloon Fiesta, but it has a botanical claim to fame too: the only accessible Green-flowered Helleborines (Epipactis phyllanthes) in the Bristol area grow here, in a dark wooded part of the estate called Clarken Combe, just a short hop over the wall from a layby on the B3128. I paid the site a very quick visit last weekend and was surprised to find many more plants than I’ve seen here previously, although all were still in bud. This weekend, however, several were flowering: mostly each plant had just a single stem, but one plant had a cluster of nine: here is a photo, and a close-up of some of the individual flowers.

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These plants have an interesting history. Originally found in 1985, they were thought to be Narrow-lipped Helleborines (Epipactis leptochila), a scarce species of limestone beechwoods. They were listed as this species in the Flora of the Bristol Region, published in 2000, and this identification remained unchallenged until fairly recently. I paid the site a visit in late summer 2011, not really knowing any more than to look in the woodlands at Clarken Combe, I narrowed my search by looking under beech trees, and eventually found three helleborine plants, but they were past flowering, so I visited again in 2012 with Martyn Hall, who took some photos. Still none the wiser as to the plants’ true identity, I posted these to the orchid thread at Birdforum. Midlands-based orchid expert Sean Cole posted a reply, asking whether I was sure the plants were Narrow-lipped Helleborines, as they looked to him more like Green-flowered. That afternoon, Richard Mielcarek and I went back to Clarken Combe, gave the plants a very close look, and confirmed that, just as Sean thought, they were Green-flowered Helleborines.

Part of the reason for the confusion is that back in the 1980s, knowledge about the variability of the Epipactis helleborines, and which identification features are most reliable, was still developing: nevertheless, the plants had been visited by many knowledgeable botanists since, and so it’s surprising that it took so long for them to be re-identified.

Green-flowered Helleborine occurs in several varieties (forms of characteristic appearance caused by small genetic differences). The Clarken Combe flowers open quite widely, seem to have a clear distinction between the ‘cup’ (hypochile) and the ‘lip’ (epichile) and in some, the lip is bent back under the cup, whereas in others it is not, and then appears quite long and pointy. As I understand it, this points to them being of the variety known as ‘vectensis’, but I’d be interested in views from others with more knowledge of this subject. The pointy lower lip and the fact that the flowers open widely may be one of the reasons why the plants were originally thought to be Narrow-lipped Helleborines. However, the hypochile of Narrow-lipped Helleborine is filled with a sticky dark purplish liquid, not present in the Ashton Court plants, and the lip of Narrow-lipped is even longer and thinner. There are several other features visible with a hand-lens, which Richard and I checked last year to satisfy ourselves that our re-identification was correct.

In a local context, Green-flowered is only marginally less rare than Narrow-lipped. Narrow-lipped’s nearest population is in the woodlands at the top of Cheddar Gorge; Green-flowered occurred in the past on the towpath below Leigh Woods, but has not been seen here for many years, and only occurs at one other site, a private garden near Stowey. Further north, on the Cotswolds, both species have strong populations, and Green-flowered also occurs at several sites in Wiltshire. Nationally, Narrow-lipped is the scarcer of the two, and its populations are in decline, whereas Green-flowered is if anything on the increase.

Here is a map showing the location of the plants. If you visit, please take great care where you put your feet, as some of the plants are quite small. There are differing views among botanists about the levels of secrecy that should surround locations of scarce plants, and in particular orchids. One orchid site on the edge of Bristol suffered from theft of a very rare species this year, so concerns are very valid. Fortunately, I don’t have to make the decision over the Ashton Court plants, as Bristol City Council have publicised them for many years as one of the features of the site (albeit unwittingly as the wrong species).

Upright Spurge in the Wye Valley

Yesterday I paid a visit to Ravensnest Wood in the Wye Valley, to see one of the rarest plants found in this area, Upright Spurge (Euphorbia serratula). As a native species, Upright Spurge is found in Britain only in an area centred on the Wye Valley and the Forest of Dean. It is also naturalised in scattered locations, mainly in southern England. Although a rare plant in Britain, globally, it is found eastwards to central Asia.

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Upright Spurge’s habitat is woodland on limestone, but not the dense dark parts: instead, it is found in the open, and does best on disturbed ground. Newly created forestry tracks and clearings are where it does best, particularly if limestone chippings are laid. Ravensnest wood held 500 plants in 1997, presumably when the access track there was very new. Yesterday I counted a much more modest 17 plants: along much of the track, grassland had become established, crowding the spurge out, and it was only present in areas where there was still very sparse vegetation. Here is a map of the location:

According to Sell and Murrell’s Flora of Great Britain and Ireland, the most authoritative reference work on Britain’s flowering plants, Upright Spurge occurs in only about 24 British localities. The densest concentration is around Tintern and so, predictably, it has acquired the local name “Tintern Spurge”. Other locations in the Wye Valley are spread throughout a 10km-long stretch from about Wynd Cliff in the south to around Whitebrook in the north. In the Forest of Dean, its main concentration is just to the west and north of Lydney. Much further east, it grows in Highnam Woods, just west of Gloucester. West of the Wye Valley, it occurs in Chepstow Park Wood and in Coed Wen Wood, east of Newport (note that the Grid Reference in Trevor Evans’ Flora of Monmouthshire for this last site is incorrect).

Seeds of Upright Spurge can lay dormant in the soil for years, possibly decades, and so if a site becomes overgrown, fresh disturbance can boost the population. At Highnam Woods, the RPSB does just that, using a rotavator, and so the population there is likely to be secure. At other sites, Upright Spurge has declined or even vanished, but could no doubt be encouraged to flower again if similar techniques were applied. How about it, Gwent and Gloucestershire Wildlife Trusts?

Lamplighters Marsh

Last week, I visited one of my favourite Bristol plant sites, Lamplighters Marsh. This is the strip of land between the Avonmouth railway line and the River Avon, from the M5 Avon bridge southeast to the former Lamplighters pub. It’s got a mix of habitats: lots of scrub and tall herb, one of Bristol’s few reedbeds, and areas of sparse vegetation (and the tidal Avon, a interesting site in its own right, is right next door). Here are a few photos of the site:

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Among the star plants here are a large population of Viper’s Bugloss (Echium vulgare) and a small population of Moth Mullein (Verbascum blattaria), both scarce plants in the Bristol area. Viper’s Bugloss occurs in a variety of habitat types in Britain: chalk and limestone grassland, at the coast in sand dunes, on shingle or cliffs, and in disturbed open ground such as that found in disused quarries or railway lines. Although Lamplighters Marsh could be described as coastal, the habitat here is more like the last of these, and in the Bristol area, it is not really a coastal plant, although in some parts of Britain it is exactly that. My visit was on a sunny evening and many bumblebees were visiting the plants.

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Moth Mullein is an introduced plant. It is distinctive among the mulleins in having large flowers, and not being densely hairy or downy like many mullein species. It occurs in both white-flowered and yellow-flowered forms.  It has been recorded at several other sites in Bristol, but is very scarce away from the city.

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