The Uskmouth Savi’s Warbler

A Savi’s Warbler (Locustella luscinioides) at the RSPB’s Uskmouth Nature Reserve has now entered the third week of its stay. The bird was found by Mathew Meehan and is the first record for Gwent. It is holding territory in a small strip of reedbed in the centre of the reserve, flanked on one side by a track and on the other by open water, so (unusually for this species) it is quite easy to observe. If visiting, please keep to the paths: as well as the Savi’s Warbler, nesting Bearded Tits (Panurus biarmicus) and Cetti’s Warblers (Cettia cetti) are present in the same area.

Savi’s Warbler, 1 June 2014, Uskmouth Nature Reserve, Martyn Hall (www.martynhallphotography.com)

If the physical appearance of Savi’s Warbler is a little dull, its song certainly isn’t: it sounds like a loud, prolonged cricket. I emphasise loud: on my first visit, I could hear the bird from at least 100 metres away as I approached. Click here to listen to a recording of the Uskmouth bird by Darryl Spittle.

Savi’s Warbler is at the northwestern end of its world range in Britain, and numbers have fluctuated considerably since it was first discovered here in the early 19th Century. Back then, it bred in Norfolk and Cambridgeshire, but with drainage of the fens, this population died out by around 1850. It remained a rare migrant for the next 100 years, but then established a breeding population again, initially in Kent, then in Norfolk, Suffolk and a few other southern and eastern counties, although still in tiny numbers: the peak population was of c.30 singing males at a total of c.15 sites in 1977-1980. Numbers have since declined, to the point where ten singing males constitutes a good year.

Most of our local birds have occurred on the Somerset Levels, where around a dozen have occurred, with two clusters of records: four birds at the gravel pits around Bridgwater between 1970 and 1988, and five birds in the Ham Wall/Meare Heath area between 2005 and 2010. Chew Valley Lake has had four, the last of which was in 2001. In Gloucestershire there have been just two: at Frampton in spring 2001, and at Coombe Hill Meadows in 2013. Wiltshire has also had just two, at Coate Water, Swindon in May 1965, and at the Cotswold Water Park in 2006. Almost all of these birds have been singing males in spring, so no doubt other individuals have occurred undetected. With the increase in records from the Somerset Levels in the last decade, there’s perhaps a good chance that Savi’s Warbler will become a regular breeding bird here one day.

Fly Orchids in the Avon Gorge

Fly Orchid (Ophrys insectifera) is in flower currently in the Avon Gorge. To see the most accessible plants, head north on the towpath on the west side of the gorge, to an area of rock falls about half a mile north of the Suspension Bridge. I counted 10 plants in flower today by the fence at the bottom of the rocky slopes (see map & photo below). Here they grow in the open, in limestone grassland, but at other sites Fly Orchids occur in woodland.

Fly Orchid is a scarce plant around Bristol. The Avon Gorge is the only site in close proximity to the city: the location I visited on the North Somerset side is the most well-known, although Fly Orchid has also been found occasionally on the Bristol side. Elsewhere in the region, there is a cluster of sites in the Avon valley southeast of Bath, including Browns Folly and Avoncliff. There are several other sites farther south and east of here into Wiltshire and east Somerset, including Cleaves Wood near Wellow, Morgans Hill near Devizes, and a grassy bank on the north side of the A303 near Wincanton. Elsewhere in Somerset, Fly Orchid is only found on cliffs near Blue Anchor. Its stronghold is in the Cotswolds, with around 10 sites in the Stroud area and others southeast of Cheltenham. Although it formerly occurred in the Wye Valley, it is now extinct there.

Pollination is carried out by male digger wasps of the genus Argogorytes, which are attracted to the flowers by a pheromone; they mistake the flower for a female digger wasp and attempt to mate with it. In doing so, the orchid’s pollen sacs attach to the wasp, and are then transported to the next orchid the wasp visits. The Avon Gorge Fly Orchids are of particular note, as in the past, this process went a little awry and hybridisation occurred with Bee Orchid (Ophrys apifera): when these hybrids were first discovered here, in 1968, they were new to science. Hybrids are not known from the Avon Gorge currently, but they are present at the Wincanton site. Hybridisation has also occurred in Kent with Early Spider Orchid (Ophrys sphegodes).

A Siberian Chiffchaff on a Bristol dung-heap

Common Chiffchaff (Phylloscopus collybita) is a leaf-warbler familiar to birdwatchers in Britain, as a common summer visitor, and in much of the country as a winter visitor in small numbers. Its eastern cousin tristis, Siberian Chiffchaff, also regularly winters in Britain, and there’s currently one in Boiling Wells Lane, at the north end of St Werburghs. The stream from which the lane gets its name, and a nearby dung-heap, are attracting plenty of insects, keeping our Siberian visitor loyal to a very small area. Here’s a photo:

A lot of confusion surrounds the status of Siberian Chiffchaff in Britain, more of which below, but they are pretty distinctive birds, especially if you have the opportunity to compare one with Common Chiffchaffs, of which there are up to four at Boiling Wells currently. Siberians are paler birds, particularly on their underparts, which are whitish, lacking the yellowish-buff colours present on Common Chiffchaff. The upperparts are pale grey-brown, usually without the green tones of Common Chiffchaff, although the flight-feathers and the tail can be finely edged with green. Usually there is a warm buff colour on the cheeks and breast-sides, and there can often be a narrow pale wingbar. The bill and legs are black and so are conspicuously contrasting compared with the pale plumage. Finally, both songs and calls are different: the St Werburghs bird gives the typical call of Siberian Chiffchaff, a soft single-syllabled ‘peep’, neither rising nor falling, different from the rising, slightly disyllabic ‘hueet’ call of Common Chiffchaff. If it’s a male, it may start singing later in the winter: instead of the repetitive ‘chiff … chaff’ song, Siberian’s song has a more varied structure to it.

The confusion I mentioned above has a long history. First, in the 1950s and 1960s, several SIberian Chiffchaffs were mistaken for Greenish Warblers (Phylloscopus trochiloides), something that seems hard to believe today, with improved knowledge and better optical equipment. More recently, there has been a wide-ranging debate about the identity of non-calling birds, especially those which differ from the typical appearance described above. Midlands birder Alan Dean has highlighted several such birds which he terms “grey-and-white chiffchaffs”, and believes that these are not Siberian Chiffchaffs, but either eastern Common Chiffchaffs or the result of hybridisation where the two meet.  This has caused many birders to doubt the identity of many of the birds they’ve seen.

Thankfully, things may not be as bad as Alan suggests. Birders based in Poole, Dorset have been studying their wintering chiffchaffs, and concluded that at least some of the birds which do not conform to the typical appearance still call and sing like Siberians. More recently, ornithologists in the Netherlands looked at the DNA of birds trapped for ringing, and discovered that not only did birds identified confidently as Siberian Chiffchaffs have the right DNA, so did a large number of other birds, all of which had been tentatively identified by their ringers as Scandinavian Common Chiffchaffs (Scandinavia is one area the “grey-and-white” birds have been thought to come from). Interestingly, none of the birds in this study had DNA which matched birds from Scandinavia, even though the Dutch ringers had specifically been looking out for them, and all of the normal-looking Common Chiffchaffs trapped were just that.

There has also been a study in western Russia, looking at if and how frequently the two hybridise. The answer? Yes, just like us humans, some chiffchaffs are confused about chiffchaffs and hybridisation does occur. However, it only occurs in a narrow zone some tens of miles wide where the two populations overlap. West of this for several thousands of miles are normal Common Chiffchaffs, while normal Siberian Chiffchaffs are found east almost all the way to the Pacific Ocean. Numerically, hybrids are so rare that they can’t really be the cause of Alan Dean’s puzzle.

There are dozens of other Phylloscopus warblers in Europe and Asia, and many of these are difficult to tell apart visually, but have distinctive calls and/or songs – indeed, several new species have been described based on this in the last twenty years or so. Siberian and Common Chiffchaffs seem to be another one of these species-pairs. Historically, Siberian Chiffchaff has been considered a geographical race of Common Chiffchaff, however given what we now know this is not really appropriate. Because of the narrow hybridisation zone, they are probably best considered “semispecies” (biological jargon which means that, although not everything’s completely sorted out in the overlap zone, evolution has basically done its job and the two are on separate future trajectories).

I did a little bit of birding PR today with the owners of the dung-heap: they had wondered if all the people with cameras who had been visiting this week were from Bristol City Council and were eyeing up their land for house building. I showed the bird to them and explained why it was attracting interest, and I think they’re now happy that their visitors are all just perfectly normal people who just happen to like looking at birds on dung-heaps. They regularly turn the dung, exposing more of the chiffchaff’s food, so hopefully it will hang around for quite a while.

Here’s a map showing the area the bird frequents:

Uskmouth Reserve’s Penduline Tit

This male Penduline Tit (Remiz pendulinus) is entertaining the crowds at the RSPB’s Uskmouth Nature Reserve, near Newport, at the moment, feeding on dead flowerheads of Bulrush (Typha latifolia), right by the reserve’s visitor centre.

Eurasian Penduline Tit (to give it its full English name, as there are about nine other species in Asia and Africa) is one of several bird species which have spread northwest from eastern Europe in recent decades. The first British record was in the 1960s, at Spurn, the famous migration watchpoint in Yorkshire, but now almost 300 have occurred here, including several small flocks. There has long been speculation that Penduline Tits might colonise southeast England, but so far it hasn’t happened – and we can say this with a fair amount of certainty as the nest is a conspicuous pouch which is constructed hanging from a tree branch above or close to water, and one of these would surely have been noticed considering how well-watched Britain’s wetlands are.

The Uskmouth bird can be identified as a male by its large black mask, with a rusty bar across the forehead, whitish head, intense chestnut upperparts, and small reddish-brown breast-streaks. Females have a narrow face-mask, pale grey head, paler upperparts and plain underparts, and juveniles have a completely plain pale brown head.

Uskmouth’s bird is the first for Gwent, but there have been several on this side of the estuary (see below), and with the trend towards increasing numbers, plenty more can be expected.

• Westhay Moor, two birds from January to March 1997
• Berrow reedbed, three birds in December 1997 and February 1998
• Shapwick Heath, two birds in December 1999
• Ham Wall, four birds in January 2004
• Portbury Wharf, two birds in January 2012

Uskmouth reserve is just west of the small village of Nash, east of the river Usk, south of Newport, and is signposted from junction 24 of the M4 motorway.

People? What are they?

I’m stretching my geographical boundaries a little farther than normal to the northwest with this post, but I think the subject deserves it. This is a juvenile Long-billed Dowitcher (Limnodromus scolopaceus), which turned up last week on Rhaslas Pond, just east of Merthyr Tydfil, and has spent the weekend entertaining birders and photographers at point-blank range. Rhaslas is a small artificial reservoir in the middle of bleak moorland, which goes to show that rare (i.e. lost) birds can turn up anywhere.

Long-billed Dowitcher is generally thought of as a North American bird and those occurring at this time of year are most likely to have originated in the Canadian Arctic and been brought across the Atlantic by low pressure weather systems. However, there is also a significant population in Arctic Russia, and some Long-billed Dowitchers occurring here, particularly adult birds in late summer, probably come from that direction. The third possibility is that once here, they stay and migrate up and down the East Atlantic flyway, with godwits or other European shorebirds.

There are much better photographic efforts than mine on the Cardiff Bird Club blog. The photo below shows just how close everyone was able to get (the red arrow points to the bird); indeed, while I was there it kept walking towards the photographers rather than away from them.

Arctic-bred shorebirds have been known on previous occasions in Britain to be just as tame: there was a Buff-breasted Sandpiper (Calidris subruficollis) in Somerset a few years back which allowed an equally close approach, for example. Most famous of all is an Upland Sandpiper (Bartramia longicauda) which occurred on the Isles of Scilly in the 1980s which was so tame it took a worm out of a birdwatcher’s mouth. These birds are invariably juveniles on their first southbound migration and the theory is that because they’ve never seen people before, they don’t associate us with danger: bad news for the individual bird, but great news for birdwatchers.

Little Gulls at Chew Valley Lake

These two Little Gulls (Hydrocoleus minutus) were at Chew Valley Lake this afternoon. Usually, when Little Gulls turn up at Chew, they feed over the centre of the lake, way beyond camera range, but for some reason, these two birds chose to frequent Herriott’s Pool, the small body of water separated from the main lake by the A368.

These two are a non-breeding-plumaged adult (left) and a juvenile (right). Little Gull is the world’s smallest gull, much smaller than a Black-headed Gull (Chroicocephalus ridibundus). Adults have deep dark grey underwings, and the pale grey upperwings lack the finger of white along the front edge that Black-headed Gull shows. In breeding plumage they have black hoods and pink-washed underparts. Juveniles have a contrasting pattern of black, grey and white, lacking the gingery-brown tones of juvenile Black-headed Gulls. The black stretches from wing-tip to wing-tip across the back (the bird in the picture above has its wings fully outstretched; when the wings are in normal beating mode, the black forms a ‘W’ shape). Juveniles moult into first-winter plumage later in the autumn, replacing the black on the upperparts with pale grey, but the black on the wings remains, so the W is a good feature throughout the winter (note that juvenile and first-winter Kittiwakes have a similar pattern, but as long as you have a Black-headed Gull nearby for a size comparison you shouldn’t get the two confused).

Little Gulls do not regularly breed in Britain. Their main breeding colonies lie to the east of us, in marshes from eastern Europe and Scandinavia into Russia. They mainly occur in Britain on migration, in April and May, and then again from August to October. Flocks at Chew Valley Lake are usually of single-figures, or occasionally into double-figures. These numbers are typical for large wetland sites in Britain. There are two areas in Britain which regularly attract much large numbers, however: the Mersey coast, and the east Yorkshire coast. The former often attracts hundreds, and the latter has been known to host thousands. Small numbers of (usually first-summer) birds oversummer in Britain, mainly on the east coast, and occasionally make nesting attempts, although so far these have all been unsuccessful. Interestingly, breeding Little Gulls have successfully colonised the east coast of North America in the last hundred years, so the establishment of a British colony may be a possibility one day.

For more information on birds at Chew Valley Lake, Rich Andrews’ CVL Birding website is highly recommended.

Lanceolate Spleenwort in Oldbury Court woods

The fern in the photo below is Lanceolate Spleenwort (Asplenium obovatum), a scarce species which is mainly found in coastal locations in southwest England and Wales, but which has a small population in the woods on the Oldbury Court estate (a location sometimes also referred to as “Glen Frome”), where it was first found in 1835.

There are several features which enable Lanceolate Spleenwort to be told apart from its more common relative Black Spleenwort (Asplenium adiantum-nigrum). To make this easier to follow, I need to introduce a few bits of fern terminology. The stipe of a fern is the main stalk of a fern frond. In most fern species, the frond is divided up: the main segments are called pinnae, and the lobes on each pinna are called pinnules.

Lanceolate Spleenwort has an elongated oval or oblong frond, with the pinnae nearest the base usually shorter than the ones further along, and these are often bent back towards the base of the plant (you can see this on some of the fronds in the photo if you look carefully). By contrast, in Black Spleenwort, these lowest pinnae are usually the longest, giving the frond a triangular shape. On Black Spleenwort the stipe is also usually much longer than on Lanceolate Spleenwort. I’ve included a photo of Black Spleenwort below, taken at a nearby location, and both of these features are obvious. There are other differences visible when you examine the fern close-up: the sori (spore-bearing bodies) on the underside of the leaf of Lanceolate Spleenwort are found only around the edges of the pinnules, whereas in Black Spleenwort they spread in a fan shape from the vein in the centre of the pinnule. Black Spleenwort gets its name from its solidly black stipe, whereas Lanceolate Spleenwort’s stipe is a green colour above, with a dark brown stripe below,

Lanceolate Spleenwort grows in sheltered fissures and crevices on acidic rocks, although in the warmer far southwest, it is also found on hedgebanks in lanes. The largest British populations are on sea cliffs in Devon, Cornwall and northwest Wales. The Oldbury Court site is the easternmost extant site in Britain for this species, and is isolated from other populations of Lanceolate Spleenwort by many tens of miles. In southwest England it is not found again until Exmoor, and in south Wales, not until the Gower peninsula, although there are old records from Beachley near Chepstow. Its northernmost locations, in Cumbria and southwest Scotland, are also very isolated. Globally its range extends south through France, Spain and Portugal to the Canary Islands, Madeira and the Azores, a distribution-type that is shared by a number of other fern species. Black Spleenwort is nowhere near as fussy, liking all rock types (loads of it grows on the limestone in the Avon Gorge, for example); I have even found it on walls in the city centre, near the Bristol Royal Infirmary and Old Market.

Here is the location of the plant I photographed (and a photo of the outcrop on which it was growing). If you want to visit it yourself, take care as it is on a steep muddy slope, high above the river. The best approach is to head up the zigzag footpath from the weir, and then take a right turn when you reach some railings. However, there are lots of similar-looking outcrops in the valley, from Eastville Park northeast to Winterbourne and it wouldn’t surprise me if some of these had their own mini-populations of Lanceolate Spleenwort too.

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.

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.

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.

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).

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.