Sunday, 28 April 2013
Saturday, 27 April 2013
Tephritids and the feasibility of identification from photos
25th April 2013 - Topsham
I'm trying to catch up on work but still finding the time for a quick trip down the garden with my camera and tripod. Most of the insects visible and photographable right now are flies, one of the more colourful was this Tephritid.
This is Euleia heraclei (Linnaeus), sometimes given the common name of Celery Fly (Colyer & Hammond 1968). The larvae also leaf mine many other umbellifers including Hogweed (Heracleum sphondylium) hence the specific part of its name. This male was parading about on a nettle leaf waving his wings to attract a female. Although I was fairly confident I knew it, I confirmed its identity using the key in White (1988). The wing pigmentation is a little faint on this one and I wonder if it's not long emerged. It's quite a variable species, some are reddish-brown, others are dark brown to black (White 1988, Colyer & Hammond 1968). According to White (1988) the first is the Spring generation, the latter black form is the second late Summer generation. This one has a dark brown thorax and a black abdomen. The next two were both taken in April a few years ago.
These two are both females (from the shape of the abdomen) but are definitely Euleia heraclei - the wing pattern is diagnostic. They are presumably all the same generation but they differ markedly in colour. From discussions over at Diptera.info I suspect that, of the two colour forms, the black is the 'normal' one, the reddish brown is a 'Summer' variant.
As an aside I wonder just how many of 76 British species can be identified from photos. Many have distinctive colours and wing markings - in fact they're probably no more difficult than most Hoverflies. Looking at White's Handbook (1988); 22 species and all British genera are identified using his first 'Simplified key'. From a brief look, none of the characters used in the key appear to be impossible to see on photos.
The remaining genera are keyed to species as follows:
Myopites - 2 spp. separated by wing pattern and abdomen.
Urophora - 7 spp. 4 separated by wing pattern, 3 spp. only by genitalia.
Platyparea - 2 spp. separated by wing pattern.
Rhagoletis - 3 spp. separated by wing pattern.
Trypeta - 3 spp. separated by wing pattern, thorax pattern and head bristles.
Vidalia - 2 spp. separated by wing pattern, thorax pattern and head bristles.
Cerajocera - 3 spp. 2 only separated as larvae/pupae*
Chaetorellia - 2 spp. separated by wing pattern.
Terellia - 6 spp. 4 separated by wing and thorax pattern, 2 by size and proportions.
Oxyna - 3 spp. separated by thorax bristles.
Paroxyna - 7 spp. separated by wing, thorax and leg characters.
Campiglossa - 2 spp.separated by wing, thorax and leg characters.
Dioxyna - 1 spp. separated by wing, thorax and leg characters.
Tephritis - 10 spp. separated by wing pattern and bristles.
Trupanea - 2 spp. separated by wing pattern.
*Cerajocera is now included as a subgenus in Terellia; the two difficult spp. ceratocera and plagiata can now be separated using the key in Korneyev (2003).
I realise the exact arrangement of genera and species has changed but the argument is still valid. Of the British total of 76 spp.it appears that 3 can only be separated by terminalia examination, 2 spp. can only be separated on the basis of size and relative length of oviscape (female egg-laying tube). Given that the egg-laying apparatus of Tephritids is often quite easy to see, it's possible that identification is quite feasible. The remaining 71 spp. are, in theory, identifiable based on wing pattern, pattern of thorax, and head and leg bristles. Bristles can be tricky to get right on such small flies but not impossible; the wings and thorax are relatively straightforward. I think I need to find more Tephritids.
ReferencesColyer, C.N. & Hammond, C.O. 1968 Flies of the British Isles Warne.
Korneyev, V.A. 2003 New and little-known Tephritidae (Diptera, Cyclorrhapha) from Europe. Vestnik Zoologii, 37(3): 3-12.
White, I.M. 1988 Handbooks for the Identification of British Insects Vol.10 Part 5a: Diptera: Tephritidae. Royal Entomological Society.
Sunday, 21 April 2013
Return to Macro
20th April 2013 - Topsham
When I'm out and about in 'birding mode' my approach to photography is simple. I carry a modest lens - just an old Nikon 300mm f/4 with a x1.4 teleconverter - which is a compromise between weight and magnification. I almost never use a tripod for birds - I can usually hand hold at the shutter speeds needed for moving birds. And of course, I scan the middle distance and the sky, not the ground at my feet. Photographing insects is so fundamentally different that, as well as different equipment, I almost need a quite different frame of mind. I suppose It's just like switching a camera's mode option from 'birding' to 'macro'. Except it's more complicated: set to manual focus, minimum aperture, lowest ISO, mirror lock-up and cable release. Of course I also need a different lens - I use a Sigma 180mm f/3.5 macro - and a sturdy tripod and head - a Uni-loc with a Manfrotto Proball 468 RC4; which is one of the reasons I tend to walk slow and not far when looking for insects.
It's been far too long since I did any macrophotography so I wondered if I'd have to learn it all again. Yesterday I dusted off my macro lens and tripod, and tried to remember the techniques.
At this point I remembered two of the problems that used to make life difficult: bright sun and wind. Insect cuticles are often shiny - not so much here but think of bluebottles and leaf beetles - and exposing for dazzling highlights gives black shadows and can kill detail. The effect of strong sun on green vegetation is, if anything, even worse. The simplest solution is to shade the subject - a hand often works - but there's a risk the insect will move. The tiniest of air movement can cause leaves to shake but it's rarely continuous and sometimes I just wait for the lull. If that doesn't work then I just look for insects on the ground or on tree trunks.
I spent a little time in the garden re-familiarising myself with the method and found a few things to photograph. This fly was fairly co-operative, it sat still while I positioned the camera and shaded it. I'm not too disappointed with the result; it could be sharper but it is cropped quite a bit. The species looks like Scathophaga furcata (Say, 1832) based on the dark shaded cross-veins on each wing and the dark stripe on the front femur; although I'm not sure it's possible to be certain from this photo. My tentative identification was made using Stuart Ball's provisional key (Ball, 2007).
References:Ball, Stuart G. 2007; Key to the British Scathophagidae (Diptera), Version 3.1
Thursday, 18 April 2013
18th April 2013 - Topsham
We've got Jackdaws nesting in our chimney pots. Actually it seems they're mostly just dropping sticks down the chimney but I guess they know what they're doing. And they are lovely birds, fun to sketch in watercolour, no need to worry about colour - Payne's Grey and a touch of Cobalt Blue. I like the way the pale eye looks in the black face, the top of the iris in shadow but there's still a highlight on the surface of the cornea.
Temporarily immobilised by a cold, not getting out and not getting any serious work done. I've been amusing myself with some sketches - Sandwich Terns on Marazion Beach from last month.
Monday, 15 April 2013
Ringed Plover sketches
12th April 2013 - Sker Point, Glamorgan
A couple of days in South Wales visiting Carolyn's dad was a great excuse to get out at dawn and walk along the beach before things got too busy. There were a few signs of migration with Golden Plovers in the fields, a Whimbrel, a Wheatear and a couple of Ringed Plovers on the beach. Looking at these two, clearly a male and a female, I wonder if they were a pair or was that just coincidence?
Wednesday, 10 April 2013
9th April 2013 - Exeter Canal
About 4pm I was sitting at my desk having just finished correcting rough layouts for a couple of Pterodroma plates. I needed a break and decided I could spare an hour or so to make a quick trip to the 'other side' (of the Exe, that is) to maybe get some photos of this Red-throated Diver. I normally see them at some distance on the sea but this one, evidently liking the fishing in the canal, has been giving very close views for a couple of days or so. I couldn't resist.
No signs of any breeding plumage appearing so not yet in moult; although I suppose it could be a 2nd calendar year bird, which means any newly moulted feathers will look just like those of a winter adult. I noticed a difference in the feathers of the left and right flanks. The left side of the rear of the bird appeared much more disordered, I guess this could be just the effect of wetting but it didn't seem to be the case on the right side. I wonder if it's oil?
Monday, 8 April 2013
6th April 2013 - Exminster Marshes
Cetti's Warblers are hard to see, never mind photograph. I've only twice managed to get images worth keeping - and my standards are not high. I wouldn't even attempt draw them in the field. These sketches were made from my own distant, overexposed but useable photos. It's a male trying to attract the attentions of a female, singing occasionally but mostly waving his wings around, in the process showing quite nicely on top of a bramble patch.
Friday, 5 April 2013
4th April 2013 - Topsham
One of the few upsides of the cold is the chance to photograph Chiffchaffs, at close range and near ground level. I know it's a sign that they are having serious difficulty finding food but it's too good an opportunity to miss. While standing in the back garden hoping to pick up a distant Waxwing, I got a few lucky shots of this bird. Lucky because it was close, the light was good and I got it more or less in focus - not that usual in my experience of bird photography. Not wanting to let a half-decent photo go to waste, I thought I'd try to age it.
First, I should make it very clear that I am no expert. I'm not a ringer but I do have some experience of handling birds - or rather bird specimens. I have a modest ornithological library, I obviously have access to the internet and I have, to be honest, slightly nerdish tendencies. I like to look things up and I like to apply that to birds I photograph. What I'm really doing is thinking out loud, making notes and interpreting what I can see in the photo based on what I've found out. So when I write that adult Chiffchaffs have a complete post-breeding moult and a partial pre-breeding moult, that's shorthand for "I've just read in Svensson that Chiffchaffs have a complete post-breeding moult...etc." I find this stuff really interesting, I hope others do too.
First, why is it a Chiffchaff and not a Willow Warbler? That's the sort of thing everyone should know but, surprisingly, doesn't seem to be in the National Curriculum. It's a Chiffchaff because it's got dark legs, a short primary projection, an eye-ring more obvious than the weak supercilum, a plain face and four emarginated primaries. If it had called that would have helped, but it didn't - waste of valuable energy, I guess. Incidentally, this last paragraph is not something I had to look up - I have picked a few things up over the years.
Here's a different view of the bird. You can see the short outermost primary (P1), the next (P2) is actually emarginated along its full length but is not counted (?). P3-6 are emarginated towards the tip - I find it helps to think of the indentations. A small digression; in passerines the primaries are conventionally numbered ascendantly - going up on the closed wing the outer is P1; on non-passerines it's descendant - e.g. in gulls the outer primary is P10. There are logical reasons for both systems and I'll follow convention rather than consistency and use whichever is appropriate.
So that's its identity established, what about its age? As ever, the key is moult. Adult Chiffchaffs have a complete post-breeding moult (typically finished by September) and a partial pre-breeding moult (head and body and sometimes tertials and a tail feather or two, usually finished by January). Juveniles have a partial moult in autumn (head/body and tertials, some greater coverts and sometimes the central tail feathers), followed by another partial moult, like the adult, in winter (Cramp 1992). So the key to ageing in spring is going to be the condition of the primaries and the retrices and the presence of moult limits in the greater coverts (Svensson 1992).To even my inexpert eyes, this bird's primaries and tail feathers have seen better days. They are brown (compare them with the fresher tertials) and the tips are frayed. A moult limit in the greater coverts is harder to be sure of but I think the two inner coverts look fresher and more green fringed than the outers. So on the state of the primaries and tail feathers at least this has to be a 2nd calendar year or first summer bird.
Now a different Chiffchaff from the next day. I can't see an obvious moult limit in the greater coverts, the primary coverts look rounded - although the fringes look thin at the tips - and the primaries appear to have reasonably unworn tips. This, I would say, indicates an 3cy or older. However the longest upper tail coverts are very worn as are at least a couple of the tail feathers. At least one tail feather - the slightly (displaced ?) darker one at the top - looks fresh and, by the length of it, is still growing. So, with wing pointing to adult and tail saying first spring, I'm going to pass on this one.
Cramp, S (ed.)1992. The Birds of the Western Palearctic. vol.6. Oxford.
Svensson, L 1992. Identification Guide to European Passerines.
Fourth edition. Stockholm.
Winter (and winter birds) still here
3rd April 2013 - Topsham
Blue sky and bright sun but the Siberian wind still numbs fingers and ears. Early morning at Topsham Rec brought back fond memories of the warm days of December - seriously. The Long-tailed Duck was still on the river, a couple of Redpolls were still looking for seeds on last years reeds and a single Common Gull wondered where all its friends had gone.
I'm sorry to say I'm getting blasé about Waxwings these days - I go years without seeing one, now I see them while walking the dog. I heard the familiar liquid, trilling, whistling....whatever I write is not going to do it justice...and saw a flock of about 30 or 40 in roadside trees. I tied the dog to a fence, grabbed my camera and got a couple of shots before they flew. I was only 170m from my house, I measured it on the map - yes, I know - and all I could think was that if I'd been in my garden, I might have heard them, then I'd have Waxwing on my garden list.
Thursday, 4 April 2013
Here's one I made earlier
Just for the sake of posting something different; here's a watercolour sketch I did last year of a Little Egret hunting fish in the Exe at Topsham.
Monday, 1 April 2013
Topsham 30th March 2013
It's becoming almost a weekly ritual now, I drop by Bowling Green Marsh, usually early morning (when no one can see me?) a day or two after some half decent birds have turned up, fail to see anything and wonder why I bother. I even went in the hide this morning, for the first time in several years, to try and get a better view of a Little Ringed Plover - I didn't and promptly left. I don't like hides, hides are basically sheds. I've nothing against sheds, I have a shed in my garden, it not somewhere I'd choose to sit though. So, distant waders proving unsatisfying - they're always at the far side of the pool - I returned via the Goatwalk and found something more interesting.
I noticed a wagtail and managed to get a handful of shots before it flew off. It was impossible to get more than a cursory look and I clearly didn't have time to take notes or sketch it, but I had the photos. Now I can analyse the bird at leisure. Here is a composite of the most useful photos.
Like most people I used to think White Wagtails Motacilla a.alba* were fairly easy to identify, at least in Spring, but it now seems that things are a little more complicated - which is always interesting. Before I get stuck in, a word about references; the Identification Guide to European Passerines (Svensson 1992) is always a good place to start but for this family the primary source now has to be Pipits and Wagtails (Alström, Mild & Zetterström 2003), a marvelously detailed book with nearly 50 pages on Pied/White Wagtail alone (not counting illustrations and photos). The other important work is White Wagtail and Pied Wagtail: a new look (Adriaens, Bosman & Elst 2010), really nice critical look at variation in the two forms, the safest field characters and some difficult intermediate birds.
Clearly it's not black or even blackish on the mantle which it would be if it were an adult Pied Motacilla a.yarrellii. But what about a first summer bird? In fact, can I age it from these photos? At the risk of overkill, I'll give it the third degree - hey, it's more fun than doing the crossword!
It's got a black crown but there are a lot of grey feathers on the nape - still moulting? The mantle and scapulars are mid-grey, there appear to be some darker marks but these are just the feather shafts and an optical effect. The back and rump are hidden when standing but on the flight view are seen to be the same colour as the mantle, it's the upper tail coverts that are blackish. The chin, throat and bib are black with only a few whitish feathers, the breast sides and flanks are extensively grey - the same colour as the mantle or perhaps slightly paler.
On the closed wing I can't see the lesser coverts so I'll start with the medians; there's a clear difference (both wings) between the inner (black with white tips) and outer (not quite black with narrower grey tips) feathers. The greater coverts show a similar appearance; the inners (black with grey fringes and broad whitish tips) contrast with the outers (shorter, greyer with thinner fringes and tips). The two longest tertials are much fresher (black with broad whitish fringes) than the shortest (quite brown with very thin fringes). The secondaries look a little paler than the longer tertials and there are only thin pale fringes not the solid white patch shown by adults. The primaries are hard to see but the tip of the longest (just appearing beyond the tertials) is brownish grey, not black, the fringes (also those on the primary coverts) are thin and look worn.
In late March both adult and first summer birds will have just finished (or be about to finish) a partial moult. So all head and body feather will be new, also a variable number (none to all) of secondary coverts and tertials and sometimes a few tail feathers will be replaced. During the previous autumn an adult will have had a complete post-breeding moult, a first year will have had a partial moult - i.e. not including it's juvenile remiges and usually not including some juvenile coverts and tertials. So moult contrast/limits in the coverts isn't going to work as it does in Autumn, the key to ageing in spring is detecting the presence of retained juvenile feathers. A bird hatched last year should still be carrying its first set of flight feathers and possibly some juvenile coverts.
Those outer median and greater coverts look very much like juvenile type feathers (as shown in Svensson, and Alström et al.) and the shortest tertials do look convincingly faded and worn. The secondaries don't look black like the longer tertials and they don't show the solid white patch as on , for e.g. this adult Pied from earlier in the week - also showing fairly fresh black primary coverts with neat white fringes.
Bearing in mind all the caveats about ageing spring birds, I'll stick my neck out and call this a first summer. But is it alba or yarrellii? Adriaens et al. rather complicate matters by describing a number of intermediate birds, some of which are certainly hybrids. They also critically analyse those characters useful for identification. Here's how I think their seven characters (A-G) work out on this bird:
- The colour of the mantle and scapulars and the percentage of blackish feathering shown in these areas (characters B,C and D) - it seems there is some overlap in colour between the subspecies and my bird is not pale enough to be an obvious alba; there's definitely no blackish colour though, other than on feather shafts (an optical effect) which seems to rule out yarrellii.
- The colour and extent of the flank pattern (characters E and F) - again there seems to be some overlap in colour between forms so unless the flanks are greyish white (alba) or really dark or black (yarrellii) this is less helpful, as is the case with this bird.
- The whiteness of the belly (character G) - clean and white in most birds of both subspecies but in some yarrellii there are a few dark spots. Certainly no spots apparent on this bird.
- The colour of the rump (character A) is last as this still seems to be the safest character. There is a little overlap though, some alba can show a fairly dark grey rump (specifically the area above the upper tail coverts, which are blackish in both forms, and roughly between the tips of the middle tertials). This area was difficult to see as the tail is raised on the one blurred flight shot making it hard to judge the exact extent of the grey feathers but my guess is that the rump is the same colour as the mantle.
* I like scientific/Latin names, they're not hard to learn, they tend to change less than common names and they're often shorter. It's my blog and I'm going to use them.
Adriaens, P, Bosman, D, & Elst, J 2010. White Wagtail and Pied Wagtail: a new look. Dutch Birding 32: 229-250.
Alström, P, Mild, K & Zetterström, B 2003. Pipits & Wagtails of Europe, Asia and North America: identification and systematics. London.
Svensson, L 1992. Identification Guide to European Passerines.
Fourth edition. Stockholm.
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