Monday, December 8, 2008
Taken on the same morning as my Blue Tit photo, photo 1 shows a Coal Tit (Parus ater) on my garden birdfeeder.
Averaging around 9-gm, Coal tits are the smallest British tit and easily recognised by their black crown and the white patch at the back of their head: No other British tit has the same. They are common in the UK, often inhabiting conifer woodland, the RSPB website giving the number of breeding pairs as 653,000.
What other I know about coal tits I've learned from reading The Titmice of the British Isles (John A.G.Barnes, publ. David&Charles 1975), this includes the rather charming fact that once mated a male-female pair will tend to remain bonded across the years, assuming both manage to survive that is; Annual mortality for coal tits is around 80%.
I was surprised to learn that coal tits make their nests very near to ground level in tree stumps or even in holes in the ground. I've spent many hours walking through woodland and don't recall ever having seen one, which I suppose must mean they're well concealed. Females lay on average 9 eggs around April-May. Coal tits are diligent parents and have been recorded making upwards of 60 visits to the nest in a single day to feed their chicks.
Coal tits spend a great deal of their day - around 90% - feeding. Given their small body size and slender beaks they consume the smallest insects (typically 0-2mm according to the book above) among the tits, an example of evolution driving different species to specialise in different feeding habitats and foodstuffs to best survive in one another's company. An exception to the rule is beech mast, which is so plentiful in Autumn that many different tit species come together to enjoy the glut.
Something I didn't know is that coal tits will sometimes store food (seeds etc.) for later consumption. Typical hiding places might be holes or under moss on tree trucks. There is a record of one bird digging up a seed that it had hidden more than a fortnight previously.
Finally, I have often wondered about the time at which birds go to bed. Of course 'late in the day', but is that as light is dimming, or say, a little after sunset? Dr. Barnes' book has answered my question: the coal tit is on average an early rooster, typically abed 1.7 minutes before local sunset. Good night!
Saturday, December 6, 2008
Some of you may recall that in my posting on White Tipped Bristle Moss I mentioned being impressed at the performance of the camera I was fortunate enough to borrow on that occasion. Well, I'm pleased to announce that the birthday fairies have since visited and I am now the proud owner of a fancy digital SLR. I offer this in explanation for why I have spent the greater part of Saturday morning, crouched in a 'birdhide' (a.k.a my garden shed!) my zoom lens trained on my garden birdfeeder.
Blue Tits (Parus caeruleus) are small birds (around 11gm, 11cm), easily recognised by the yellow breast, black eye stripe on a white face, blue crown, and blue and green dorsal (=viewed from back) feathers (photo 2 - click to enlarge). With experience (which I don't have!) it's apparently possible to distinguish males from females by the slightly smaller size and less vivid colourings of the latter.
The Blue Tit's call is a high pitched 'tsee-tsee-tsee' or occasionally a scolding 'churr'. They are one of Britain's commenest birds: The RSPB website gives the number of breeding pairs in the UK as approximately 3.5million.
According to my copy of The Blue Tit (Jim Flegg, Shire Natural History) female Blue Tits normally lay a single batch of between 5- and 16-eggs, during March or April. As with Robins, life is hard, and annual mortality in Blue Tits is around 90%. I had not hitherto realised that predators of the chicks include the Greater Spotted Woodpecker. Late summer and autumn see the highest mortality rates. More happily for my blue tit, birds that make it into Winter have a decent chance of reaching the Spring.
During Spring male Blue Tits defend terretories. During Autumn these break down and Blue Tits join large flocks of small birds roaming the hedgerows. During Winter a sort of 'half way house' emerges with birds forming smaller flocks and confining their travels to smaller (300-400m^2) areas. Again, like Robins, UK Blue Tits tend not to travel any great distance during their lives, <1% moving more than 100km although every few decades climate conditions lead to mass influxes ('irruptions') of birds from the European mainland.
A puzzle about Blue Tits, described in the book above, relates to their dietary fondness for Winter Moth (Operohtera brumata) and Tortix caterpillers. In some years in Oak woodlands, these attain epidemic proportions. Blue Tits seem able to predict (or to state things less anthopromorphically - there is a correlation between) when, and how many eggs to lay to take best advantage of the arrival of the caterpillers. How they do this isn't known, or at least wasn't when the book was written.
Finally, a fact well know to Brit's of a certain generation, which I include here for the interest of overseas readers, was the tradition (now rendered largely extinct by the ubiquitous supermarket) of having milk delivered to the doorstep in glass bottles capped with aluminium foil. It was to a national hazard to find Blue Tits had pecked through the foil to get at the cream below. You can find a photo of this here. Charming at first, but the householder soon learnt to leave empty youghurt pots out for the milkman to place over the bottles to thwart the theives!
Wednesday, November 12, 2008
For those of an inquisitive disposition, one of the wonderful things about natural history is its ability to generate an inexhaustible supply of questions one doesn't need to be a professional to either ask or investigate: Noticed something alive!? O.k., so what is it?...and what does it eat?... what eats it?...when does it mates, how does it mates?...You get the idea.
To supply a germane example: In a previous posting on my garden's holly tree, I reported being struck by the small number of creatures reported to derive nourishment from holly's tough and spiny leaves. This started me wondering about what creature might surmount the seemingly even tougher problem of eating dead holly leaves...
...photo 1 (click on photos to enlarge) shows a holly leaf I found in the leaf litter beneath my tree. Photo 2 shows a 100x magnified version of some of the small black dots decorating the surface upper-centre, and photo 3 some of the larger ones covering the remainder of the leaf.
It's perhaps no surprise to learn that the agent of decay of dead holly leaves is a fungus. Fungi are separated into two great divisions ('phyla'), the basidiomycota (=most of the familiar 'mushrooms') and the ascomycota which are typically small, cup shaped fungi (see a previous posting for more details). Clearly photo 2 shows my fungus to be one of the latter. The cup's inner surface (hymenium) is the site of spore production.
In the case of my holly-leaf, a little web searching (specifically of the encyclopaedic bioimages site) suggests the species of fungus at work is Trochila ilicicola. (A smaller question I do have however, is whether the two types of black spots - the smaller dimples of photo 2 , and larger pustules of photo 3 - might conceivably be two different species. Can anyone comment?)
I'm led to understand my cup fungus has a rather neat trick up it's sleeve, namely a hinged lid which it can open when conditions are damp (and hence good for liberating spores), and close when conditions are dry. I didn't get the opportunity to try observing this under the microscope, but you can find some photos on the fine mycolog site.
So there you have it. The next time you take a walk on an late autumn day when interesting natural history might seem in short supply, try picking up a dead leaf!
Sunday, September 14, 2008
No, despite appearances to the contrary I have not abandoned my blog. I hope one or two of you may still be visiting.
Some time ago you'll recall I was pleased and surprised to be visited by a white budgerigar. It seems that the larger exotic birds are not to be outdone however, as around six-thirty one morning in recent July, I was delighted to encounter a couple of Peafowl pecking around on my lawn. I hastily grabbed my camera and achieved the not-very-good photo (left) before they fled over the wall. I assume my birds came from a local farm or some country estate, but I do not know from which.
A few minutes internet searching informed me that my birds are Indian Peafowl (Pavo cristatus), as opposed to the endangered Green Peafowl (Pavo muticas) from Java and Burma. Males of the latter species can be identified by a tall, spiky crest on their heads.
Much the most famous feature of peafowl is of course the peacock's fantastic fan tail (sadly mine didn't display). Ever since Darwin, naturalists have been fascinated to understand what possible evolutionary purpose it can serve to sport such an unwieldy appendage; The benefit of carrying around a large iridesceant sign, seemingly pefect for announcing to predators "Here I am! Eat me!", isn't obvious!
My quest to understand a little more led me to an excellent review paper by one R. Gadakar (here). In brief, my understanding is as follows: As a Peahen, one approach to selecting a mate is to choose those males who most strongly advertise their health and vitality with a large fan. So far so good, but the question this poses is whether the extravagant fan we see today has arisen because at some point in history females selected to breed with males with a slightly longer tail, which led to male-offspring with slightly longer tails, from which later females again selected the longest...i.e. whether today's fan is a result of 'run-away selection' (in which case the fan is beautiful but it is not, per se, an honest indicator of the male's health). Or whether an alternative hypothesis holds i.e. the so-called Zahavi's handicap idea, which states that any male able to carry around such a huge encumbrance and yet still survive (evade predators etc.) must somehow be truly fit and strong i.e. the tail is not only beautiful but also honest indicator of the fitness of the male.
I have failed to think up a simple way to restate this (indeed, as the paper above says, the trend in biology these days is to get away from the vagary of mere words and express things in terms of mathematical models where possible), but a (very incomplete) analogy might be following: some female humans prefer their men well muscled, as a sign of their vitality. For the humble male there are then two routes to getting-the-girl: One, a regime of healthy food and physical exercise. Two, steroids and plastic surgery! The latter may achieve the visible appearance of the 'body beautiful', but it could hardly be called an honest statement of the chap's health and fitness. By contrast, in seeking to achieve the rippling musculature beloved of the ladies, the former approach requires males to accept the 'handicap' of limited diet and punishing gym sessions, but in the long run this 'handcap' is actually likely to positively benefit both their own and their offspring's health.
The existence of this, the (Zahavi's) handicap hypothesis out there in nature however was controversial amongst evolutionary biologists when it was first suggested, and therefore it has been important to find ways to test it. Which brings us back to peacocks: Glass-jawed weaklings beneath steroid-inflated shells, or supermen in both looks and deeds?
Some of the definitive studies of peafowl have been performed on a feral population at Whipsnade Zoo here in the UK Firstly it is known that peahens select those peacocks with the most symmetric tail fans. High symmetry is strongly correlated with a large number of eye spots. And what have the studies at Whipsnade concluded about those males with the highest eye spot count? That they i) have better reserves of body fat ii) have higher survival rates (against loss to foxes etc.) and iii) father healthier, fatter chicks.
In short, no preening primadonna he, the male peacock really is both both beautiful and honest!
Saturday, May 17, 2008
Photo 1 shows a fly I found sunning itself on my bird-table late last summer.
I have no expertise when it come to fly-identification. With the help of the very nice colour plates in my copy of Insects (Michael Chinnery, Collins) however, I'm fairly certain my fly is a member of the Sarcophidae family of so-called Flesh-flies.
In general, identifying flies down to species level is a job for the experts. Page 27 of this book (The Sarcophagidae of Fennoscandia and Denmark, Thomas Pape), partly available online, gives you a flavour of what's involved. Dipterists spend a lot of their time looking at genitalia (!) -that of flies being an important aid to species recognition. I didn't subject my fly to the indignity of this, so can't be confident about its species, though from the book above a guess might be Sarcophaga carnaria (can anyone confirm or correct this?)
There are some 120,000 species of fly (Diptera), with 15,000 occurring in Europe. Chris Thompson's Diptera site contains a wealth of information, including specifics on the Sarcophagidae.Flies are distinguished from other insects in part by having only two wings, their hind pair having shrunk down to vestigial 'stumps' called halters.
There are some 2600 Sarcophagidae flies, about 300 occurring in Europe (this site lists them) and about 60 in Britain. As the name Flesh-fly implies both adults and larvae (maggots) are often associated with carrion, though in fact there is considerable variation in feeding habits across species: some concentrate on small corpses (this site has some closeups of an adult feasting on a dead caterpillar); some larvae are parasites of other insects; some predate snails, others earthworms; some species are able to live on a purely vegetarian diet. Sometimes of course, Flesh-flies become associated with human corpses. As a consequence the Sarcophagidae have been well studied by the science of forensic entomology which aims to get information about the time of a person's death by the rather grisly process of analysing any insects infesting the corpse.
The Sarcophagidae are viviparous (=females give birth to live young, the larvae). This book (Natural Enemies of Terrestrial Molluscs, G.M. Barker) explains this as an adaption to give the flies a speed advantage when it comes to getting their their young established on an ephemeral food item such as a corpse as rapidly as possible.
A final question I am left with is what purpose it serves my fly to sport the "zebra-like" black and white stripes on its back. Can anyone enlighten me?
Monday, May 12, 2008
After a goodly absence (apologies dear readers) it's time to return to the task of cataloguing my garden's life.
The first piece of news is that sadly I've had to remove (to my compost bin) a good proportion of the ivy I blogged here. This proved necessary as the sheer weight of ivy caused the collapse of my garden fence! A sad aspect to this is that, as I commented previously, my ivy has proved a popular nesting site with my garden birds (in clearing the foliage this time I uncovered a bird box I had previously stuffed into the ivy, containing an old robin's nest). The good news is firstly that ivy grows so aggressively in my garden that it's certain to recolonise swiftly as soon as I re-erect my fence, and secondly that in clearing it away I came across the subject-matter for today's posting, growing on some old logs: the mushrooms seen in photo 1 (click to enlarge).
I have a little knowledge of British fungi, so I was quickly able to identify my fungus as a Coprinus mushroom. The little "mica-like" flecks on the young caps helped me to identify my mushroom as Coprinus micaceus.
As the great majority of mushroom guides will tell you, there are more than a dozen British Coprinus species, all readily recognised by the characteristic that the whole cap of mature mushrooms "autodigests" and turns into a thick, black, inky, spore-laden liquid, as opposed to the more typical mushroom habit of liberating spores as "dry, airborne powder". You can see "ink" starting to ooze from the mushroom in the centre of photo 1 (the one with its stipe ("stem") touching the coin)...
...Except it turns out the books are wrong! More specifically, although it is true that several hundred mushroom species world-wide share this 'inky' habit, the approach that mycologists have traditionally taken of classifying them all as members of the genus Coprinus seems to be wrong: following DNA sequencing, Hopple and Vilgalys published a scientific paper in 1999, showing that many of the traditional "Coprinus" mushrooms are in fact unrelated to each other (at genus level at least). Worse still, the Coprinus "type species" (i.e. the species most neatly embodying the features of the Coprinus mushrooms = Coprinus comatus) turned out to be genetically rather atypical!
All of this means that mycologists are having to do some serious thinking about how to re-write the textbooks. The current approach is to divide the previous Coprinus genus, into four genera: a small collection of true Coprinus mushrooms and additionally the Coprinopsis, Coprinellus and the Parasola mushrooms. There's a very readable account of all this at Tom Volk's site.
I've known amateur naturalists who get rather heated about splitting and re-naming species, genera etc. on the basis of genetic analyses. 'Species', they say, 'should be defined according to what things look like in the field!'. I don't personally agree with this. To replace one genus with four, superfically identical genera may be inconvenient for the amateur, but at the end of the day if that's the scientific truth of things, I say 'so be it'. Mother Nature isn't obliged to set things up in a way that's convenient for the amatuer and the fact that she sometimes doesn't surely increases the fascination of the studying things?
One final thing that intrigues me is the phrase "mica-like flecks" that all the books seem to use when describing my mushroom, and lends itself to the species name "micaceous". Had I been the first to discover and name my mushroom, I imagine I might come up with "cottony" or "bobbley" to describe the young caps. I doubt the mineral mica, would have entered my head! Just about the one thing I know about mica comes from school physics lessons: namely that that it exhibits a curious optical phenomena known as double refraction (birefringence). You can see a nice photo here. I regret I didn't get a chance to experiment with my mushrooms to find out, but I just wonder whether the flecks on the caps perform any similar "optical magic". Does anyone know?
Saturday, March 29, 2008
Photo 1 shows another of my garden-wall-top's community of mosses. For this photo I was fortunate to be able to borrow a fancy digital camera. I'm most impressed with the close-up ability, as compared with the results from my own humble little 'point and click' camera, normally responsible for the snaps on this site. The Walloon bank balance may need to take a hit at some point!
Photo 2 (click to enlarge) shows a 40x magnified view of a single leaf. Distinguishing features are the circular leaf cells, the central vein that fades out just before the end of the leaf and the 'recurving' (folding over) of the leaf edge. Another obvious feature is the long, white 'hyaline' (=clear) hair at the end of the leaf. Quite a number of mosses sport such hairs (see my previous postings on S.intermedia, G.pulvinata and T.muralis for example). A pure guess on my part is that these hairs act as condensation sites for droplets of dew, thereby helping the moss to collect water. I've no evidence for this however. Can anyone comment? Anyway, regardless of their purpose, these features taken all together identify my moss as Orthotrichum diaphanum in my trusty copy of British Mosses and Liverworts (Watson, Cambridge).
For those of you unfamiliar with the art of moss identification (which included me when I began this blog a year ago ) clicking on 'moss' under the 'labels' menu on the left this screen and scrolling down, you'll easily be able to compare the leaf shapes of the different species I've blogged so far. You'll see that far from being all the same, different species of moss really do have their own individual and characteristic leaf features (some short and fat; others long and thin; some with hairs; some without etc.) - a strong aid to their identification.
O. diaphanum is a fairly common moss. According to my copy of The Moss Flora of Britain and Ireland (Smith, Cambridge) "[it] has been found on such unlikely materials as old linoleum, corrugated iron and tarmac". It is most common on trees and wooden fences.
Another feature obvious in photo 1 are my moss's brown setea (fruit stalks and capsules). The site of the Bryophytes and Buildings project - cataloging mosses in Edinburgh, Scotland - has some superb closeup photo's of the capsules and the 'peristome teeth' that are revealed when a capsule loses its lid. Experts use the shape and number of peristome teeth as another aid to species identification. I've read (though I can't remember where) that a moss's peristome teeth act as little mechanical devices, bending and flexing in response to passing air currents and changes in humidity and actually 'reaching inside' the capsule, 'scooping up' the spores therein, and flicking them out, away from the moss. Another of nature's tiny miracles!
Sunday, March 23, 2008
In my previous posting I talked about the appearance of daffodils here in Oxford heralding the arrival of Spring (though I might add that when I wrote the posting, the weather was warm and sunny, whilst today we're experiencing strong Arctic winds and snow - there is nothing so changeable as the British weather!).
Another pretty indication of Spring's arrival is the masses of blossom breaking out on the trees and hedgerows. One common example, found everywhere in parks and gardens here in the UK, is the blossoming of ornamental 'Myrobalan' Cherry-plum trees. I have one in my garden (at (0,1.1) - see here) - photo 1 (click on photo's to enlarge)
The botanical name for my tree is Prunus cerasifera, and on the basis that the blossom is pink (photo 2) and the leaves purple-red (see photo 3 taken late last summer), it is an example of the subspecies P. cerasifera nigra. (Were the blossom to be white, it would more likely be an example of the second common cultivar: P. cerasifera Pissardii).
Together with showing the toothed leaf margin (another feature aiding identification) photo 4 shows a closeup of one of my tree's 'fruits' (or, to give them their correct botanical name, drupes - see my previous explanation here). I've no idea what, if any, culinary use it's possible to make of these. Can anyone comment?
Though I intend to make an effort to observe more carefully this year, I also don't know what animals, if any, like to eat the drupes. I guess blackbirds, squirrels and pigeons, at least, might give them a try.
For completeness, photo to 5 shows a closeup my tree's bark, and photo 6 a view of the buds in late January, a few weeks before they blossomed.
And that would appear to be that! Those who follow my postings will know that I normally make some effort to link to websites providing interesting snippets of information on the 'lifeform' under discussion. When it comes to Myrobalan cherry-plums however I've drawn something of a blank! There is a fair amount of scientific literature out there devoted to trying to sort out the genetic relationships between all the various plums, cherries, peaches, apricots and almonds that constitute the Prunus genus. Specifically on the Myrobalan's however, I've found next to nothing of say which the amateur naturalist like myself might find interesting (any suggestions anyone?)
I'll therefore end with my own observation: returning to the closeup of the blossom in photo 2 it's apparent the flowers have 5 petals (5 fold symmetry). Recently I watched a streaming lecture on the physics of crystals on the superb M.I.T., open course-ware, website (as you do!). The lecturer, one Prof. Wuensch, explained that star-fish have evolved five legs since objects with a 5-fold symmetry lack an 'easy' or 'weak' direction along which to tear or rip them (if startfish had, say, 4 legs they'd present a weak axis along which a fish could easily tear them into two, symmetric, 2 legged sections). I will end my posting therefore with The Walloon Myrobalan Blossom Conjecture:
Fruit-tree blossom commonly has 5-petals to make it more difficult for birds (such as Bullfinches) to dismember it.
Friday, March 21, 2008
Spring has sprung here in Oxford in the U.K. One of the cheeriest signs of its arrival is surely the great profusion (I'll spare you references to "hosts of golden-" etc.!) daffodils that pop up in our gardens, woodlands and on roadside verges. Photo 1 shows some of those appearing anually in my garden.
In fact, a number of different types of daffodil appear at this time of year in my garden. That I should find more than one is perhaps no surprise since, as I learn from the Warwick Daffodil Genetic Resource webpage, breeders have developed a staggering 25,000 daffodil cultivars! The Royal Horticultural Society site hosts a searchable database. The same site also gives details of the horticultural code system used by daffodil aficionados (narcissists?!) to label varieties. In brief, it works like this:
Firstly, decide which of the 13 divisions of daffodil yours belongs to. In the case of the daff in photo 2, though not obvious from the photo, I measured the central 'trumpet' (corona') as longer than the outer petals ('perianth segments'). This puts it in Divison 1. By contrast, the corona of the daffodil in photo 3 is more than 1/3, but less than the full length of the petals, putting it in Divison 2.
Next, write down a letter for the colour - White, Green, Yellow, Pink, Red or Orange - of the perianth segments. So, photo 2 becomes 1Y, and photo 3 2W. (There are rules on the RHS page above for what to do if your daffodils petals are multicoloured)
Finally, repeat for the corona (adding a hyphen '-'). So finally photo 2 = 1Y-Y and photo 3=2W-Y.
Simple! (Or at least that's my understanding - as always, my amateur identifications come with a health warning - I'm always happy to be corrected. )
Of course it's also possible to be more 'botanical' about things - working through phrases like 'dentate coronal rim'. The ultimate goal must surely be to pin down one's daff's to one of the >25000 listed varities. Breeders have come up with some great names - "Her Majesty Queen Alexandera"; "This Little Piggy" and "Singing Pub" being three that caught my eye. I'd be delighted if any expert out there can tell me the name of the daffodil's in Photos 2 and 3 .
For those interested in doing more than simply naming their daff., the definitive textbook would appear to be "Narcissus and Daffodil, The Genus Narcissus" (Edited by Gordon R. Hanks, publ. CRC Press). I don't own a copy, but rather helpfully, the publishers have put a substantial chunk of the book online. From this I learn that there are about 80 species (as opposed to sub-species cultivars) of Narcissus, forming part of the Amarillidacyeae family of plants that also includes the snowdrops and lillies. Something I'd not really considered was how bulbs grow and expand. The book gives a rather detailed account of this and explains that each year new flesh appears in the centre of the bulb, with progressively older flesh being found further out from the centre. The very oldest flesh ends up as the papery, thin skin one often finds on the outer surface of bulbs. Finally, it seems that daffodil bulbs contain some rather nasty, toxic, alkaloid compounds. This no doubt explains why, although bulbs in my garden commonly get dug up and eaten (by, I assume, squirrels or badgers), this never seems to happen to my daffodils. Britain's wild daffodil is Narcissus pseudonarcissus.
The 1st March is St. David's Day - the patron saint of Wales - and it's common for people to wear a daffodil buttonhole.
I'll leave two last words to William Shakespeare:
When daffodils begin to peer,
with heigh' the doxy, over the dale,
why, then comes in the sweet o' the year.
The Winter's Tale (Act 4, Scene 3)
and from the same play
That come before the swallow dares,
and take The winds of March with beauty
The Winter's Tale (Act 4, Scene 4)
Monday, February 11, 2008
February is seeing Oxford hit by a succession of clear, frosty days. The cold weather means that many of my garden's plants, fungi and animals are tucked away out of sight or sitting out the winter in a dormant state. As I've remarked before, this is a good time for the amateur to take an interest in those humble lifeforms the mosses and lichens which, far from lying dormant, seem to positively relish the winter and the lack of competition it affords. My garden wall for example, is currently layered with a vibrant mat of fruiting mosses.
Photo 1 shows a closeup of two more denizens of my wall's stonework. For the uninitiated, no, this is not a mistake! What appears from a distance to be little than a collection of stains on the stonework is in fact my blog's first example of a crustose (=flat, crustlike - see here for more explanation) lichen. In fact there are two in photo 1. Photo 2 shows a zoomed-out image of the same region. Personally, I find it little short of miraculous to see life thriving on bare rock.
Photo 3 shows a 40x magnified view of the tiny black dots peppering the surface of the uppermost lichen in photo 1. These are perithecia - tiny flask shaped 'salt cellars' from which the lichen shoots out spores.
When it comes to species, as always, my identifications come with a health warning: I'm far from expert in identifying lichens and furthermore, without going to the lengths of studying spores under the microscope and applying chemical tests (lichenologists take these seriously: I even have a book - Microchemical Methods for the Identification of Lichens, Orange, James and White - that teaches the amateur how to perform chromatography!), it can be well-nigh impossible to definitively identify some lichens by visual appearance alone. With this disclaimer, let me say that my lichen's fruit bodies being set in little craters in the surface, and the black line delineating the thallus perimeter in photo 1, are both features that fit with the description of Verrucaria baldensis in my copy of Lichens:An Illustrated Guide to the British and Irish Species (F.S.Dobson).
A similar analysis for the lower, 'less spotty' (though you'll still see some perithecia if you look closely) lichen in photo 1 inclines me to an identification as Verrucaria muralis.
The Verrucaria genus of lichens is noteworthy for including a number of freshwater and maritime lichens. The next time you're at the seashore, look towards the high-tide line and in all likelihood you find the rocks everywhere stained black. This isn't oil (as is sometimes thought) but a result of the ubiquitous seashore lichen V.maura.
Amongst the many extreme features of the life of a crustose lichen is the extraordinarily slow growth of some. According to my copy of Lichens (O. Gilbert, New Naturalist series) lichens are amongst the oldest and slowest growing organisms in the world: Rhizocarpon geographicum, for example, puts on a mere 0.09mm of growth-radius per year. A patch of the lichen Aspicilia calcerea, growing on the Rollright Stones, a stone circle in Oxfordshire, is estimated to have begun life there in 1195AD. It's thought some Icelandic lichens might be 9000 years old! I'll have nothing quite so extreme in my garden, but I am curious to track the growth rates of at least a few of the crustose patches on my garden wall. Watch this space!
Early last October I found a pair of ladybirds sitting on some of the rust-afflicted Groundsel growing in my garden (at (0.2,1.9) - see here). Photo 1 shows a front view and photo 2 a view from the side which more easily permits my ladybird's 19-spots to be counted.
In seeking to identify my ladybird I turned first to my recently acquired copy of Ladybirds (Richmond Publishing, 1989) by Majerus (he of moth book fame) and Kearns. Despite the book containing beautiful colour illustrations of all 42 of the traditionally accepted British species of ladybird, I was surprised to find my 19-spot not included. All became clear however when a search of the internet bought me to David Element's webpage and I learnt that my ladybird is The Harlequin Ladybird (Harmonia axyridia), an invasive alien species that has only recently arrived in Britian (it was first recorded here in summer 2004).
In fact, H. axyridia comes in a variety of subspecies with different colouring and number of spots. My 19-spot variety is termed H. axyridia succinea.
Sadly, despite it's attrative appearance, it's a bad sign to find a Harlequin ladybird in my garden. The Harlequin is a voracious aphid predator, so varacious in fact that there is considerable concern about the damage the Harlequin may do to the native ladybird- and lacewing-species that also rely on aphids for their food. The Harlequin ladybird survey has been set up to monitor the invasion threat and people are encouraged to register sightings (I have).
To cheer us all up I'll leave us with the nursery rhyme, which, though I used to recite the first two lines as a child, I enjoyed learning from Majerus' and Kearns' book contains two extra lines
"Ladybird, ladybird fly away home,
Your house is on fire and your children all gone,
All except one, and her name is Anne,
And she crept under the porridge pan"
Sunday, February 3, 2008
Growing on a stone next to my vegetable patch (at (0.2,1.6) - see here) is the moss seen in photo 1 (click photo's to enlarge).
For this posting I was fortunate enough to gain access to a low power stereo dissecting microscope. My usual technique of balancing my cheap digital camera on the eyepiece didn't deliver such good results as it does with my own higher-power microscope, but the stereo' did allow me to capture some photo's at 16x magnification of the moss in its wet state (photo 2) and (photo 3) the remarkable 'twisted-rope' structure the leaves adopt if the moss is left to dry out. Mosses are able to withstand considerable drying incidentally, all that's needed to bring them back to full greeness being a few drops of water.
Previously, I've talked at length (here, here and here) about some of the features to look for when identifying mosses. For this posting, suffice to say that the combination of elongated leaves with their circular cells and nerve running their full length, together with a few other features and reference to my copy of British Mosses and Liverworts (Watson, Cambridge) and a recently acquired copy of The Moss Flora of Britain and Ireland (Smith, Cambridge), leads me to conclude I've got Didymodon (Barbula) vinealis growing in my garden (though as always, my identifications come with a 'health warning' - I'm always happy to be corrected). The website of the British Bryological Society gives the common name as Soft-tufted Beard Moss.
Though I realise the following will be decidedly 'old news' to the experts out there, I can't end today's posting without relaying a fascinating feature of mosses that I discovered recently from leafing through some botany textbooks. As most people know, DNA inside living cells gets packaged up into chromosomes. Human cells contain 2 sets of 23 chromosomes (i.e. 46 in all) and are said to be diploid. The exceptions are sperm and eggs; These contain only 1 set of (23) chromosomes and are said to be haploid. This pattern is common across almost all mammals. Mosses do things differently however; When you look at a moss you are seeing a mass of haploid cells, except, however, where you see stalk-like setae (you can see a number in photo 1. Photo 4 shows a closeup). These are the a moss's spore-filled fruits. In contrast to the rest of the moss, the cells comprising the setae are diploid. In a sense therefore, your or my diploid arms 'sprouting' from our diploid torsos, are a genetically 'closer match', than a moss's diploid setae sprouting from its haploid host.
There are more things in heaven and earth, Horatio, than are dreamt of in your philosphy!
Friday, February 1, 2008
Have you spotted it yet?
Photo 1 (click to enlarge) taken in late summer, shows, squatting camouflaged against the undergrowth, my blog's first amphibian, (at (0.8,0.4) - see here).
Identification wasn't difficult. There are only two native British toads: the Common and the Natterjack. These have warty skin and an altogether more robust stature than my amphibian. There are also only two frogs: The Common and the Pool Frog. The latter is rare and in fact has only recently been recognised as an indigenous species. There are also a handful of introduced alien species of frog and toad in Britain, but again none is like mine. In all therefore, I've little heitation in indentifying my frog as The Common Frog (Rana temporaria).
To learn something about frogs I have been reading The British Amphibians and Reptiles (M. Smith, New Naturalist). Published in the 1950's, the book has a more 'robust' (a.k.a. cruel!) approach to studying nature than most amateurs would find acceptable today. I learn for example, that toads dropped into formalin will (surprise, surprise!) adopt a defensive posture; that Goldfinches injected with toad venom, die; and that a convenient way to mark frogs for identification is to cut one of their fingers off! Despite this, the book contains a lot of fascinating and surprising information: For example I hadn't previously known that, lacking a rib cage, frogs are unable to inflate their lungs as mammels do. Instead they absorb oxygen through their skin and by rhythmically 'gulping' air, which they can do up to 140 times a minute. Croaking is achieved by passing air backwards and forwards over the vocal chords. Since this does not require air to be expelled from the body, frogs can, and commonly do, croak underwater.
The skin colouring of the Common Frog is highly variable. Black patches (see photo 2) are due to accumulations of melanin. More melanin is produced in colder weather and during hibernation (typically mid October to early March) Common frogs may turn quite a dark brown. As they grow, frogs periodically moult a thin outer layer of their skin.
Male Common Frogs can be distinguished from females by the presence of thickened black nuptial pads on their hands. These help the male to grip onto the female's back during mating. As the female releases her eggs, the male fertilises them by releasing sperm into the water. Common Frogs can spawn suprisingly early in the year. March and April are most common, but the book describes records of spawning as early as mid-January and says that it is not uncommon to find spawn floating amongst the ice on freezing ponds.
Frogs have a 'homing instinct' and can find their way back to breeding pools from some distance. When the book above was written (the 1950's), how they achieved this wasn't known. Can anyone comment on whether this problem has been solved since?
Wednesday, January 30, 2008
After a series of postings on some of the smaller and arguably more curious lifeforms present in my garden, today's posting features something I suspect most of you will find all too familiar: a garden weed.
Growing in my vegetable patch (at (0.1,1.7) - see here) is the weed seen in photo 1 (click photos to enlarge). It has quite happily survived the British winter frosts.
Working with my copy of The Wild Flower Key (F. Rose, Penguin), I had no difficulty in identifying my plant as a member of the (amusingly named) spurge family (supposedly a word derived from 'to purge' - a reference to the plant's laxitive effect). There are over a dozen British spurges however, so identifying the species involved slightly more work, but on the basis that my plant has a smooth (non-hairy) stem; leaves edged with tiny teeth, arranged in alternating fashion along the stem; and a "flower head" (umbel) with five-fold symmetry - together with a few other features relevent to the key in the book above - I'm identifying it as Sun Spurge (Euphorbia heliscopia).
Sun Spurge is normally a single-stemmed plant. Occasionally however, as in photo 2, it may banch from the base (since this plant is a common weed in my garden I felt no compunction in pulling it out to photograph it).
Photo 3 shows Sun Spurge's five-fold symmetric 'umbel'. The five leaves at the base of the umbel are known as bracts. The individual 'cups' containing the tiny central flowers are known as involucres.
An obvious feature of Sun Spurge is that the flower-head is almost entirely green. Since much of any plant's effort goes towards harvesting sunlight, it clearly makes sense to pack every available surface with green chlorphyll. What puzzles me is that most plants don't do this however. Instead they use up precious resources producing brightly-coloured flowers, the said purpose being to advertise their presence to pollinating insects (or so I understand). The question I then have however, is why Sun Spurge doesn't need to do the same? Can anyone comment?
Reminding me of piece of surrealist sculpture from an Yves Tanguy painting, Photo 4 shows a closeup (40x magnification) of one of the tiny flowers of Sun Spurge, peppered with yellow pollen grains. My understanding is that the small, green, plate-like 'petals' nearest to you are nectar producing glands. The round object in the background is the plant's ovary-containing female fruit. The three forked prongs sticking up from it are stigmas. A pollen grain landing on one of these will fertilise the ovary, causing the fruit to swell up, eventually to the point of bursting when it explosively scatters seed over the surrounding soil.
Sun spurge is part of the large Euphorbiaceae family of plants comprising some 7,50o species. The leaves are a favoured food of the caterpillars of the Spurge Hawk moth (a migrant visitor to Southern Britain). When broken, the stem bleeds a milky-white sap and from my copy of Medicinal Plants In Folk Tradition (Allen and Hatfield, Timber Press) I learn that our ancestors used the sap to cure warts. I certainly don't advise anyone try this however since the sap is a serious irritant and worse, a carcinogen. If that isn't enough to deter casual experimentation, as the book describes, one man given a dose 'as a joke' (!) in the ninteenth century:
'ran up and down the street like a madman, and swelled so big that his friends had to bind him round with hay-ropes lest he shall burst'
With friends like that who needs enemies!
Tuesday, January 29, 2008
I promise to return to more sizable and familiar lifeforms soon, dear readers! For today's posting however: another lichen.
The lichen seen in photo 1 (click to enlarge) decorates many of the branches of my garden apple tree (at (1.2,1.5) - see here) and I'm almost certain (see shortly) in identifying it as Physcia tenella ('it' being either of the two greyish patches below the coin, as opposed to the yellow lichen left of the coin which - though I've not examined it is detail - is probably our old friend X. parietina)
The meaning of the Greek physcia (pronounced 'Fisk-ee-a') seems to be a matter of debate on the internet. I have come across it variously translated as "bellows", "breath-like", "sausage-shaped" and "blister"! Can anyone clarify the true meaning?
P.tenella is my blog's third example of a foliose lichen. According to my copy of the scholarly Lichens (F.S. Dobson, The Richmond Publishing Co.), Physcia lichens can be distinguished from other foliose lichens, in part, by their narrow (<~2mm) lobes, and septate spores (septa being thin, internal dividing walls - see here for some examples) - though I confess I've not looked for the latter.
Two further distinguishing features of P.tenella are i) the presence of eyelash-like cilia on the edges of the lobes. You can see these in the 40x-magnified photo 2. (Can anyone tell me what purpose it serves to lichen to 'sprout' these?) And ii) the presence of granular soredia (see here for my explanation of what these are) decorating the ends of the lobes. Were I to observe the soredia 'packaged' together inside little 'hoods' I understand I'd be looking at the closely similar lichen P.adscendens (since its not obvious they are, I'm sticking with my identification as P. tenella).
Finally, two nice facts about P.tenella I got from reading my copy of Lichens (O.Gilbert, The New Naturalist series). Firstly, P.tenella is one of three British lichen species favoured by long-tailed tits (Aegithalos caudatus) in building their nests (on average each nest contains nearly 3000 lichen flakes!). Secondly, being fairly acid- and nitrogen-tolerant (not all lichens are), in areas where people walk dogs, P.tenella is one of the commonest lichens to colonise the region marginal to that patch of tree-trunk known to professionals as "the canine zone" . It shouldn't be hard to imagine what this is!
Tuesday, January 1, 2008
What better way than to start 2008 than with my second lichen (photo 1 - click to enlarge).
This one is growing on a bough of my garden apple tree (at (1.2,1.5) - see here) and is once again an example of a foliose (flakey, 'leaf like') lichen.
As explained in my previous posting, lichens are an organism that comprise a combination of a fungus and an algae. You might expect a curious life form such as this to have some unusual means of propagation and dispersal. In fact, lichens have at least three. The method(s) a given lichen favours can be a handy hint towards identification.
One method by which lichens disperse, as discussed last time, is via spores produced from fruit-like bodies called apothecia. The white bumps peppering my lichen's surface (thallus) in photo 1 are a second. As photo 2 (40x magnification) shows, these bumps consist of small white granules known as soredia. Soredia are little lumps of lichen (some fungal hyphae and a few algal cells) whose purpose is to flake away, hopefully to land somewhere new where they can set up home.
With regard to reaching a species identification, as I've said before I'm basically a novice when it comes to lichens. Based on the very handy A Key to Lichens on Twigs (Wolseley, James, Alexander) - a leaflet produced by the excellent Field Studies Council, together with a copy of the highly scholarly Lichens (F.S. Dobson, Richmond Publishing Co.) that Santa was generous to deliver me recently, I'm going with the identification Punctelia (Parmelia) subrudecta. I'm not 100% confident in this as the books above describe this species as having a grey thallus, whereas I'd definitely say that in my photo is greenish. That said however, the photo of P. subrudecta on the excellent site of the Botanical Museum of Oslo seems a good match. Furthermore, as I mentioned in my previous lichen posting, another handy tip for the identification of lichens is the use of chemical tests: according to the books, P. subrudecta turns red when exposed to a drop of sodium hypochlorite (=household bleach). The reaction was small and fleeting, but as shown in photo 3 (you'll want to click to enlarge), removing a small piece of my lichen and testing it resulted in just such a reaction. In short, I'll stick with identification for now and inmvite the experts out there to correct me!