Wednesday, 20 November 2013

THE CURIOUS CASE OF CAPTAIN LIZ



Some things are easier than others. Getting your local Renault dealer to only charge for servicing work that they've actually done is quite easy. Climbing Mount Everest is fairly easy.

Telling one of the world's most eminent ornithologists that he has made a series of mistakes in his data analysis is far from easy. Fortunately, Rob Bierregaard was very good about this, and we have been able to sort out the known facts of this rather sad story, and draw certain conclusions from it all.

Osprey Cap'n Liz left her natal area at Cape Cod on the 8th of October. As many juvenile ospreys do, she headed directly south, over the ocean and down the eastern seaboard of the USA. With the wind in her favour, the little bird made excellent progress – no doubt thinking that this whole migration deal was a piece of cake and that far too much was being made of it. Rather than turn west to make a landfall in the Carolinas, Liz continued on her southward track, at which point things started to go wrong...

The winds that had been helping her died down to almost flat calm for three days – an unusual bit of weather for that area at that time of year. Suddenly, Liz found that maintaining speed was much harder work than it had been. More wing-flapping was needed and she was using up her “fuel” reserves at an alarming rate. By the evening of the 10th, with no change in the conditions, Liz would have been almost exhausted. She even tried to retrace her course, turning back north, but by that time it was far, far too late. 

Thirty nautical miles away, the oceanographic vessel Atlantic Explorer was steering ENE towards her home port in Bermuda. Some days earlier, an osprey had landed on the ship and had kept company with her for a while. Rob Bierregarrd's team thought that this bird MUST be Cap'n Liz.

It wasn't. My analysis of the ship's daily positions shows that Liz never came to Atlantic Explorer, although at one point they were only twenty miles apart. Flying northwards in the darkness, Liz would not have seen the ship and their courses diverged rapidly. What happened next is a matter of some speculation: at 13:00 hrs on the 11th, Liz came down to sea level and her speed dropped almost to zero. She could not fly any further.



It seems certain that Liz had landed on some kind of floating item, although of course we don't know what this was. To the science team back in New Hampshire, the GPS track looked like the course of some powered vessel but it wasn't. I was able to demonstrate that ocean currents and tides would produce the same pattern effect, all on their own.

The PTT tracker continued to transmit but, stranded alone on her raft – whatever it was – exposed to a blazing sun and with no source of fresh water, Liz would not have survived for very long. Dehydration is lethal to birds, almost every time.

Liz was unlucky. Many other juvenile birds – not just ospreys – take this trans-ocean route to the Carribbean and Central America and the vast majority of them survive the attempt. Taking this path saves both time and energy, provided that the wind and weather do not turn against them. To us, this seems like gratuitous risk-taking but that's what birds do.


And they always will.

---------------------------------------------------------------------------------------------

Additional edit: 20 Nov 2013...

There is an intriguing postscript to this story which came to my notice after the above article had been finished.  Of course we don't know what it was that the osprey was cast away on during her final days, but there are more things floating about in the the empty corners of the ocean than coconuts...

Wolfhound adrift in April 2012. (Charles Page)
In February 2013, the Irish-registered 48ft sailing sloop Wolfhound was abandoned by her crew to the west of Bermuda after she got into difficulties during an offshore race.  All personnel were rescued, but Wolfhound continued to drift around the area.  She was seen in April by a passing vessel and found again in July by Matt Rutherford and Nikki Trenholm on their schooner Ault. Rutherford attempted to take Wolfhound in tow but, after an almost-unbelieveable series of misadventures that are detailed HERE, was forced to give up and cast her adrift again.

As far as anyone knows, the yacht Wolfhound is still adrift somewhere in the same area that "Cap'n Liz" was lost.  Could it be...?  We may never know.




Sunday, 29 September 2013

Home for the Winter


 I'm only human. I can easily become enamoured of pretty things, new things, unexpected or wonderful things - Ospreys and eagles and all the endless variety of birds. But first love endures, and these are mine...

The brent geese of Strangford Lough are back.


This morning I was up and out at stupid o'clock, driving the 20-odd miles to an isolated parking spot near the market town of Comber. It was still almost dark, and autumnly cold. A chill east wind whipped in off the slate-grey water, bating the full tide. Not a bird to be seen, on it or by it - they have more sense. But this is Northern Ireland – if you don't like the weather, wait fifteen minutes.

In fact it took twenty for the daily miracle to happen: the sun rose over Greyabbey – well named the place, so it is – and with that a flurry of charcoal wings, low and fast out of the indistinct horizon, and that unforgettable sound...


Of all geese, the brents have the sweetest voices. The new arrivals call to those already paddling in from their hidden roosts back in the saltmarsh. Together they merge into rafts of birds, stem-to-stern and head-to-wind. Last week there were a few hundreds. Today there are thousands.


I've already got my camera coupled to a Televue Ranger 90mm astro refractor. I hate using it for this – focusing is a nightmare, there's no depth of field worth talking about, and the whole set-up is optically snail-like at f8 on a good day – but nothing else in my kit will reach out the 500m to where the geese are starting to feed.

The species is Branta bernicla “hrota” - the pale-bellied race that breeds in the high Canadian Arctic, further north than any other of its kind. They have migrated almost 3000 miles by way of Greenland and then Iceland to spend the winter here in Ulster. It's estimated that 95% of the entire population returns to Strangford and Lough Foyle – a conservation challenge of epic proportions, for the dwarf eel-grass zostera noltii that they prefer grows almost nowhere else in any quantity, except - happy coincidence - the estuary of Afon Dyfi in Wales.

The tide is racing out now, exposing more than 40 hectares of mud flats. The geese follow it and so must I, round the shoreline to Castle Espie WWT where there are higher viewing points – and also hot coffee to be had. The mug goes down well and there's a chance to chat with the staff.

 What's the overall count on the Lough?

22,700 brent geese as of Friday – a good total with the peak month of October not yet reached. It looks like the birds have had a productive breeding season, unlike last year when numbers were down on average.

A few more shots from the shore hide. Curlew are in massed ranks at the edge of the saltmarsh, waiting for their particular cafeteria to open. A leavening of shelduck and wigeon have joined the geese, taking advantage of their vigilance. The sun is almost overhead now and it could even be called warm (with a little imagination).

Sunday afternoon visitors are pouring into the WWT centre, whooping and hollering, and I take the long route round the south perimeter of the reserve to avoid them, pausing only to wince at the recently-completed “Limekiln Observatory”: a well-intentioned but horribly misguided design that merges with the shoreline landscape like a fart in a diving suit.

But not even duff architecture can spoil this day: the geese are back and that's all that matters.



Links:

Ulster Wildlife Trust - Strangford Lough Campaign

Irish Brent Goose Research Group (Site)

Wildfowl & Wetlands Trust - Castle Espie

Saturday, 14 September 2013

Skyscanner

The weather-awareness of migrating birds



Giovanni Vitali (1876-1963)
Giovanni Vitali was a brilliant scientist but his timing was terrible.  In 1911, he had announced the discovery of a new sensory structure in birds – one that he named the “organ of flight”, although we now call it the Paratympanic Organ, or PTO for short.  The original theory was that this PTO was involved with directional control and balance – but why birds would need a second balance sensor when they already had a perfectly good one (in the inner ear) remained a puzzle.  Nonetheless, Vitali's findings caused a sensation at the time, with many follow-up papers and nominations for the Nobel prize flying around even faster than the birds he was studying.  But even then, things were changing... in a few short years, war would stalk across the face of Europe and the mainly Italian and German science journals in which Vitali's work was published fell silent, some of them never to reappear.

During the middle part of the 20th century, the strange story of the “organ of flight” passed quietly into the annals of Science and was almost forgotten.  Almost - but not quite...

Satellite tracking of bird migration has answered many questions – but it has also raised new and unexpected ones.  The latest generation of tracking equipment gives very good positional accuracy and can return data at hourly intervals.  This high-resolution data has shown that birds – even young raptors on their first-ever migration – appear able to make choices about their routes to take advantage of tailwinds and other favourable weather conditions.  More remarkably, they seem to be assessing the conditions several hundreds of kilometres down-range from a given position.   But how is this possible?

This chart shows the migration of osprey Blue YZ – a first-time migrant out of Loch of the Lowes in Scotland, being tracked by Scottish Wildlife Trust. On 6-09-13, YZ left the Isle of Man and flew south over the Welsh coast before veering south-west, and out to sea.   To all outward appearances, young YZ had made a terrible error of navigation and was now in danger of becoming lost.  But a study of the prevailing weather conditions at that time paints a completely different picture...

The plot (red line) shows YZ's course overlaid on a chart of wind speeds and direction. If the young bird had followed a “normal” course – east and south to the the mainland coast – it would have encountered adverse headwinds in the English channel and almost certainly would have had to pause its journey at that point.  But the course actually selected took YZ along the edge of an incoming weather front, with strong tailwinds at an altitude of around 300m which eventually brought it safely back over land in northern France.  By doing this, the bird saved at least one whole day's flying time – and a heap of energy into the bargain.  With the weather still in its favour, YZ continued on over the Bay of Biscay, repeating the same trick again during the following afternoon.

This is NOT an isolated example: every season, we see young migrants doing this kind of thing and there can no longer be much doubt that it is an innate “programmed” behaviour for them.

But how can a young and inexperienced creature obtain and correctly interpret something as notoriously complicated as European autumn weather patterns? One possible way is by looking at high-level cloud formations.

Alto-cumulus clouds ahead of an incoming warm front. (NOAA image library)

These patterns in the sky often presage the arrival of weather systems from the Atlantic Ocean.   They form at a height of between 5000 and 9000 metres – which means that they are visible from considerable distances.  A bird flying at (say) 300m ASL can command a view of the sky for two hundred kilometres in any direction.   What does that mean? On the next chart, I have plotted circles of 200 km radius and centred them on some typical migration “hot spots”.  


In each case, you can see that the “dangerous” sea crossings are in fact well covered by this range: a bird on the Solway Firth can get a view of weather systems well down in the Irish Sea; a bird at Portland Bill in Dorset commands weather info right over to the far side of the English Channel.

That explains some of the weather-awareness that birds seem to posses, (given thirty-odd million years of evolution, of course) but on its own it is not enough. To do everything they seem able to achieve, something else is needed. Remember Prof. Vitali's “paratympanic organ”?   Let's take a closer look at it...

On microscopic examination, the cells comprising the PTO look oddly familiar to today's anatomists.   In fact, they resemble the sensory cells found in the lateral lines of some fish species.  If that is so, and if the PTO isn't an organ of balance, then it might be something that senses pressure.

Barometric air pressure.

And – although conclusive proof still waits on some ongoing research – many scientists are becoming convinced that THIS is the missing piece of the puzzle.[2]  Satellite tracking has shown that long-distance migrants can maintain a constant altitude, even when flying over sea AND in total darkness.  They are able to do this within a few tens of metres – at least as accurate as the instruments set up to measure this performance. Without visual cues, the only way this could be possible is if birds have a built-in “altimeter” - and the PTO as air pressure sensor fits the bill perfectly.

And if THAT is true, then we can also credit birds with a real method for doing something that we humans have believed them capable of for thousands of years – sensing the weather in advance.

It doesn't have to be very sophisticated: here in western Europe, the general principle is that LOW or falling atmospheric pressure means changeable weather, with stronger south-west winds. HIGH or rising pressure generally means stable conditions, more northerly and lighter winds.

And for a young bird on its first epic journey south – that may be all it needs to know.

-Wlw

  • [1] Image 1 - Background: sunset over the Sine Saloum Delta. Photo: John Wright, used by permission.
  • [2] The Paratympanic Organ: A Barometer and Altimeter in the Middle Ear of Birds?  C.S. von Bartheld & F. Gianessi, Exp Zool B Mol Dev Evol. 2011 September 15; 316(6): 402–408.
  • [3] Scottish Wildlife Trust Website:  Loch of the Lowes
  • [4] Vitali is not to be confused with the notorious Mafia don Giovanni "Big John" Vitale, boss of the Detroit crime syndicate in the 1920's - who was never at any time nominated for the Nobel Prize.

Saturday, 17 August 2013

Not Small, Possibly Far Away



Head movements and range-to-target...







Both osprey youngsters are almost fully grown and taking a keen interest in the various things to be seen around their nest. This is not idle curiosity – in a few days (weather permitting) they will be obliged to avoid some of these structures while in flight, and perhaps land and perch on others.

They need to get a good appreciation of the size and position of all such things, and how to apply Dougal's Rule to them (“These are small, but the ones out there are far away”), otherwise known as perspective.

You will often see ospreys moving their heads from side to side when they are studying an object at medium range. They do this in order to get a better estimate of distance and size. Like almost all birds of prey, ospreys have binocular vision (two eyes working in unison for forward vision) but the difference in perceived position of objects (parallax) is not very great – the effective range for parallax alone is only about two metres, whereas we can use the same method out to almost three metres because our eyes are further apart.

Something else is needed.

Doing the head-wiggle gives additional scope to this method of judging distance, known technically as “qualitative stereopsis.” It includes the picking up of many different visual cues, including shadows and colour-based edge detection.

To land on a perch, or to avoid objects at speed, birds need to integrate all this visual information very rapidly. It has recently been discovered that structures in the optic nerves of birds contribute to this “image processing”, without all the work having to be done in the visual centres of their brains.




Tuesday, 23 July 2013

Integrating the Impossible

The complexities of resource exploitation in a littoral ecosystem

Estuary of Afon Dyfi looking south-west.
(Picture E. Evans, used by permission)

It's not the Amazon rainforest, despite all the rain. It's certainly not the high Serengeti under Ol Doinyo Lengai.  And yet these estuaries around the British coast are some of the most biologically productive ecosystems anywhere on the planet.  Each cubic metre of glorious glutinous silt down there contains over 25000 kJ of calorific energy – about the same as a dozen (large) bars of chocolate.  Fish base their entire life cycles around these places.   Wading birds flock to them in winter because there's no food resource that compares.

The Dyfi estuary supports not just one food chain but hundreds.  At the bottom of each are microscopic organisms living in the mud and, near the top, one osprey nest.   It seems like a perfect location for ospreys to live and breed, so why only one nest so far?  That's an interesting question – but first, a shaggy dog story...

 
This is Polky, a good-natured little pooch who lives with one of my neighbours across the road. Polky and his almost-identical brother Cobblers (don't ask) go for walkies twice a day, and their favourite game is catching a thrown tennis ball on the grassy area between our respective apartments.  To be honest, this is the only time I can tell the two dogs apart because Cobblers is brilliant at catch ball. He makes it look easy and he never misses.  Polky, on the other hand, cannot catch ball for toffee. His eyesight is fine, his technique is sound and his timing appears to be good. He really tries but he just sucks at it.  If the ball hits him on the nose and rolls away, that's a good effort by Polky's standards. Both dogs have been playing this game since they were pups.  It's a game of skill and co-ordination; one that involves instinctive AND acquired abilities.

Some animals are better at learning how to do stuff than others.

In Britain, many osprey nests are close to reservoirs or freshwater lakes. Catching fish in such places is by no means easy, but at least the birds know where the fish are.  Given the innate hunting skills they were born with, any reasonably competent male osprey ought to be able to produce fish for his nest.   However, rivers and their estuaries are different.  The overall food resource there is greater and more varied, but accessing it can be much more complicated.   In a tidal estuary and river, the behaviour and distribution of fish changes on an hour-by-hour basis, AND varies over seasonal time scales as well.   Weather patterns far upstream can change the salinity of the seawater offshore, or affect its temperature and transparency.  At any given spot, there may be dozens of sizeable fish present on one day, and not a single one at the same time on the next.

In such a complex environment, instinctive hunting skills are not enough – not by a long chalk. There is no inherited information that says..

“Flounders can be caught along the sandy areas south of the estuary, for an hour either side of low tide.”

“Hunting migratory sea bass in mid-May is a waste of time because there aren't any.”

“If visibility is poor today, there's a well-stocked trout lake about 12 kilometers north-east from here."

“If it's been sunny for three days, shoaling mullet will be taking plankton near the surface in the mornings.”


All this, and much else, has to be learned.  The reason that Monty - and his neighbour at the Glaslyn nest to the north - are so successful is that they have achieved a complete mastery of all these factors.  They know and understand the dynamics of foraging on the Dyfi, or Tremadog Bay, and it has taken them years to amass all the detailed information needed to do this.


Other male ospreys may not be so proficient, because it's one thing to catch sufficient food to feed yourself – quite another to collect enough for a female and a brood of ravenous youngsters as well.

The nest-provisioning stats collected in Wales illustrate this problem.  A solo osprey only needs about 400g of fish per day to maintain condition.  That's two small trout or one very moderate mullet.  This graph shows the weekly take required when three chicks are being supported.   And it's not just about quantity: if conditions are unfavourable, the solo osprey might go hungry for a couple of days until fishing becomes easier.   This state of affairs won't do when there are young to be fed – the incumbent male has to be able to produce something every day, and only a bird that knows his home range like the back of his own talon can do this.

Unringed osprey "Dai Two-Dots" 26/8/12  ( (c) Dyfi Osprey Project)


Perhaps this is the real reason that “Dai Dot” and other satellite males have not attracted roving females and set up nests of their own in west Wales.   They can live along the estuaries in the summer quite comfortably, but they have never acquired the EXTRA skills and knowledge to be successful providers for a family.

Like Polky, they just don't have what it takes to catch the ball.

Saturday, 6 July 2013

Song of the Osprey

This year there's been a lot of interest in the various sounds and calls (“vocalizations”) that ospreys make, and in particular their responses to intruders. Take a look at this video with the sound turned well up...

  

 … it's from a camera at an osprey nest in Latvia. The audio quality isn't great but we can forgive that. (The ESTLAT Conservancy do a tremendous job with their monitoring, considering that the nests are among forests in the middle of nowhere.) Listening carefully, we can hear that there are two markedly different calls being given by the adult. Monty and Glesni use these same sounds and it might be interesting to figure out what they are “saying”...

The first type of call is a short, melodious chirp on a rising tone. This seems to be a territorial call and it appears to be specific to ospreys, directed at the incoming intruder as a kind of identifier. Although ospreys don't defend a feeding territory as such, many other bird species do, and they sing to define the range of the territory. A bird's territorial song – which we merely listen to and enjoy – is a very serious matter for it and its neighbours. Millions of years ago some ancient common ancestor of Monty and Glesni might have had similar behaviour, and it could well be that this little chirp is all that evolution has left to us of the osprey's song. It says: “I can see you. We are here, and this nest is occupied.”

The second call is very different: it is the true “alarm call”: a strident challenge and a warning. It says: “Go away! You are too close to my nest and we will chase you if you approach!”

Unlike the “song”, this call is not specific to other ospreys, but is employed generally. The alarm call does something else, too... Watch the behaviour of the nearest chick as the adult's “chirp” song changes to alarm-calling. The chick immediately lies down in the nest and keeps very still. This is an instinctive response to the alarm, technically known as “thanatosis” or playing dead. The young will remain in this posture until the alarm-calling stops – although it can be seen that they are not very good at pretending to be dead, as they keep raising their heads to see what is going on! Osprey chicks tend to do this, even though it rather spoils the effect...

 Chick "doing a Ceulan" and looking around during the alarm call phase.
(Click for larger)  Image: ESTLAT Conservancy

Nest intrusions are a part of life for paired ospreys during the breeding season – and few things are more often misinterpreted by casual observers. On blogs and social networking pages, we regularly see words like “attack” and “fighting off” being used, the users of them assuming that the intrusions are always being perpetrated with hostile intent.

It's much more complicated than that...

“A good place for ospreys is one that already has some ospreys in it.”

With the small (but gradually rising) population density here in the British Isles, it's natural to view the osprey as a solitary nester. But in other parts of the world, nest sites can be separated by only a few hundred of metres, with as many of them occupied as are available and/or can be supported by the local food supply. In this context it would not be wholly wrong to describe ospreys as being communal (or at least, semi-communal) nesters. And in birds, communal living inevitably means the evolution of a social hierarchy and the behaviours to moderate it.

There is plenty of evidence that this is happening among European ospreys, too. Young unpaired birds, both male and female, are fascinated by occupied nests of their own species. They feel compelled to investigate them and it's not just a matter of prospecting for sites: the very presence of a successful nest gives information about the availability of fish, construction material, local prevailing weather and much else besides.

Visiting other nests also enables a roving individual to gauge its own social status as it gets older and more experienced. (You know you're at the bottom of the heap when the local dominant breeding pair can't even be bothered to chase you away!) Although it's true that some “homeless” bonded pairs might attempt to oust an incumbent male from a nest he has just finished building, this doesn't often happen unless the overall pressure for nest sites is very great.

Blue 24(10) inspecting the nest at Cors Dyfi 26/6/13
Click for larger (c) DOP 2013

None of the foregoing means that intruders are WELCOME at an active nest – no matter how peacably-intentioned the visitor might be. The dramatic response of the incumbents demonstrates that - especially if they have eggs or chicks in the nest.


Increasing intruders

Recently, Dyfi Osprey Project revealed that they have seen more than 30 different individuals interacting at the Cors Dyfi nest site (to 2/6/13), compared with 25 by the same period in 2012. Does this mean that the UK population of ospreys has suddenly increased by 17%? Perhaps not...

A significant observation is how few of these visiting birds were ringed. Given the overall UK ringing rate, we might reasonably expect that 30-40% of them would have visible rings but in fact it was only a handful. It's possible that the appearance of these “extra” ospreys is a consequence of the unusual migration weather and the late spring, and that a proportion of them were in transit to other countries – most likely, Scandinavia and the Baltic.


Thursday, 20 June 2013

REVIEW: Barr & Stroud "Sprite" 10x50 Monocular





Simple question: can you get decent birding optics for less than fifty quid?  Simple answer: no, of course you can't – the whole idea is ridiculous...

(Image courtesy of The Dreadnought Project wiki)
Back in the 1920's, when Britannia really DID rule the waves, her Majesty's navy went to one place and one place only for the supply of binoculars, telescopes, and optical rangefinders – Barr & Stroud Ltd of Glasgow. Equipped with these beautiful (and largely hand-made) instruments, British diplomatic policy consisted of loading up the main armament and letting Johnny Foreigner know who was boss. But times have changed. There are no battleships left to impose order on the poor benighted heathen, and there are no companies left like Barr & Stroud either. These days your MG car is made in China, your Webley & Scott shotgun is made in Turkey, and this new range of B&S “Sahara” optics originate in South Korea – via a new import firm and a smart bit of re-branding to cash in on the famous name.



I have many pairs of binoculars – far too many, if I am honest.  And I can't look through any of them any more.  Recent illness left me with a medical problem called “strabismus” which means that I get double vision when using them.  Although this doesn't affect my daily life to any great extent, it is a nuisance when out birding.   What I really need is HALF a pair of binoculars – so when I saw this 10x50 device being advertised, I decided to grab one and test it.  Unlike most monoculars on the market today, the B&S 10x50 “Sprite” is exactly that – whereas most of them are really cut-down cheap spotting scopes.  It is a roof prism design and features fully coated lenses, BAK4 prisms and an off-axis focusing system.  Supplied are a captive front lens cover (at last!), rip-stop nylon pouch, and a mini-tripod – of which more later.

A quick trip out to my local nature reserve on a dull and overcast day – perfect for optics testing.   First impressions are more than favourable: this glass is GOOD.  Images are bright and punchy, and the colour fidelity is well-nigh perfect.  Field of view is also excellent at 103m/1000 – as good as anything in its class.  The teeniest trace of chromatic aberration could be detected on brightly lit subjects but even this is a lot better than usual.   For a 10x50, edge distortion is minimal.  Up against my old Zeiss 10x50 porros – which cost ten times as much – the B&S Sprite matched them on optical performance in every department.  Of course there is no “stereo image” impression with a monocular but we pretty much lost that years ago, when roof prisms became the standard layout.

So far, so excellent.  But what really impressed me was the ergonomics
and handling - someone has really put some thought into the design, and it shows.  The frame is polymer, for a total weight of 420g.  This is covered with a rubberised armour giving good grip.  The tube is fully waterproofed and even nitrogen purged (something we just never see at this price point) so fogged-up lenses will not be a problem.  Overall, the exterior moulding fits my (rather small) hands well, with my index finger falling naturally onto a focus control which is both light, and as smooth as a double-glazing salesman's patter.

I really like this thing.  It's not perfect: compact dimensions and 10x50 usually mean critical eye relief, for the laws of Physics cannot be altered, but at 17.5mm this is better than average.  The eyepiece has a four-position click stop arrangement with positive detents.  With my mismatched eyes I would have preferred an extra two stops, but this would have increased the overall length.  For normal people – and spectacle wearers – it should be fine.  The other imperfection is the included table-top tripod.   It's cheap and rattly and very nasty, and will probably stay in the box.

I also did some quick experiments with “digiscoping”, for which the Barr & Stroud monocular is surprisingly well suited.  Even with adapters, proper digital SLRs don't like it: the vignetting upsets their fancy metering unless pulled back to full manual control.  Much better results came with a Samsung Galaxy S3 phone: its autofocus was quite happy to look through the Sprite and it figured out the correct exposure with no adjustments at all.   A couple of extremely boring test shots are included here.

Digiscoped shot with Galaxy S3. The houses facing are exactly 220m away.

So what about the price?  Pacific-rim optics have come a long way in the last ten years and, in the medium price bracket, are now a match for anything made in Europe.   Last season, the same range of bins and monoculars was being brought in through Bresser in the USA and the equivalent model retailed at around £90.00.  The new importer has done some aggressive discounting and I bought this one (new and boxed) from Amazon for £49.00 including delivery, which is just a steal.   Even better, unlike some cheap instruments with their orange lenses and go-faster stripes, the “Sprite” 10x50s will not embarrass you down the bird hide: its black and green finish looks the business, and it still has that historic name on the side.  Truly “second kind of cool” and, if anyone asks – show them the receipt and watch their faces...


Barr & Stroud “Sprite” 10x50 Specification
Magnification: 10x
Objective: 50mm
Minimum focus distance: 2.3m
Field of View @1000m: 103m
Prism type: BAK-4
Lens Coating: Fully Multi Coated
Exit pupil: 5mm
Eye Relief: 17.5mm
Tripod bush: Yes
Waterproof: Yes (Fully immersion tested 1m for 60sec)
Nitrogen gas filled: Yes
Case supplied: Yes (Nylon with belt loop)
Dimensions: 165x88x60mm
Weight: 420g

[All images except #2  (c) Wildlifewriter 2013]

Sunday, 16 June 2013

Great steaming piles of... bark?

Glesni chews some bark.
Image (c) Dyfi Osprey Project 2013

During this early part of their nesting season, the Dyfi ospreys – Monty and Glesni – have been bringing some strange items back to their nest.  As well as conventional materials, they have also been collecting dried cow pats, seaweed, and pieces of tree bark.  A lot of the bark appears to be silver birch, though other species have been sampled as well. Not only have they been collecting this stuff, but on occasion they have been eating it – and on camera, as well

As might be expected, this hasn't gone down very well with the legion of dedicated osprey fans.  They have been disapproving of the selected “nibbles”: ospreys eat fish and only fish, and birch bark and cow poo are not supposed to be on the menu.   So what's really going on...?

This is a kind of detective story.
Almost everything that animals do, they do for a good reason.  That reason might not be obvious to us, ensconced in our little anthropomorphic bubbles as we are, which is why we often misinterpret their actions.  But on other occasions, even a close and objective study of the behaviours cannot provide the correct answer: to get to THAT, we have to think outside the box – and even right outside the nest.  But first, let's define the problem. Fish, we are told, is an almost complete foodstuff in itself and ospreys shouldn't need anything else to sustain them.  That's what it says in all the books.  And here's the thing...

The books are quite right. They don't.

And yet is seems unlikely that Monty and Glesni are eating cow dung and chewing bark just because they like the taste.  I mean, would YOU? That means they must be getting something important from these things – something to do with nutrition or the maintenance of good health. And there, my dear Watson, is our first clue.   A second clue comes from something that cow pats and bark have in common, and that fish don't.   The cow dung consists of partly digested vegetable matter.  Once it has lain around for a while, and the urea and sulphide compounds have degraded or been leached out by the (very occasional) Welsh rain, it doesn't smell too niffy nor taste too acrid.   The birch bark includes an inner layer of woody cells (part of the cambium) which contains and transports many of the nutrients used by the tree during its own development.

Molecular structure of
unbound thiamine pyrophosphate
(c) Warwick University
There are some substances vital for life which animals (with a few rare exceptions) cannot synthesise for themselves.   One of these is vitamin B1, or thiamine.  Thiamine is important stuff: it is needed for the production of ATP, a molecule which supplies energy to the cells of the body, and also plays a role in the correct functioning of the heart, kidneys, and central nervous system.  Chronic B1 deficiency is a serious and potentially fatal condition in all animals, and in humans it has a disease name: Beriberi.

So perhaps the ospreys are getting this and other substances from direct ingestion of plant material, to supplement their typical diet.   If this is so...

Hold on just a cotton-picking minute there, Sherlock. Uncooked fish contains LOADS of B-complex vitamins. Everyone knows that!

And so they do. But some of them might contain other things as well. This is where we need to think outside the box (or nest) because the answer doesn't lie on the green pastures of Derwenlas, but out there in the grey waters of the Irish Sea...

Grey mullet
A favourite prey species of the Dyfi pair is the Atlantic grey mullet Mugil cephalus, which form more than 50% of their total catch.  Mullet are an ideal osprey food: rich in fats, protein and easy to catch because their habit is to feed at the top layer of the water-column.   There they graze on plankton – microscopic plants and animals – and small free-swimming crustaceans. It's been found [1] that mullet also contain quantities of enzymes called “thiaminases”.[2]  The thiaminase enzyme splits B1 molecules in situ, making them biologically inactive.  The amount of enzyme contained in mullet seems to vary seasonally and by location, and may depend on what the fish themselves have been eating. [3]

So this may be the answer to our little mystery: the wonderful mullet which ospreys adore also hides a sinister secret. By eating so much of it, the birds may actually be getting less available vitamin B1, because enzymes in the fish itself are blocking it. To redress their dietary balance, Monty and Glesni need to nibble at an alternative “top-up” source – one that is already part-processed (by tree or cow) but which doesn't contain any thiaminase. This would explain why other fish-eating birds, or other ospreys in different parts of the country, don't have to nibble on cow pats.

No shit, Sherlock?

None at all Watson. Pass me my violin, there's a good fellow....


Notes:
[1] Source: Cornell University Dept of Animal Sciences
[2] NEOPYRITHIAMINE AND THE THIAMINASE OF FISH TISSUES R Sealock & J White; J. Biol. Chem. 1949 181: 393-403.
[3] Or it is possible that this could be an evolving anti-predator adaptation. Other marine organisms use vitamin-busting enzymes as part of their chemical weaponry. Ferns - especially bracken - contain large amounts of thiaminase, which helps them to deter browsing herbivores.

Tuesday, 11 June 2013

The Puzzle of Portmore Lough





The view from the lower hide is oddly familiar, yet rather strange. We overlook a freshwater lake surrounded by low-lying wetlands of fen carr and unimproved grassland. Summer waterfowl chase each other around the shoreline, while nesting terns and gulls are busy on a couple of nearby nest rafts. The sky is big and open, though a few birch and alder trees stand to our left. It's sunny and getting rather hot out there. But where are we? It could be Cambridgeshire or somewhere else in East Anglia, or even northern Germany. But listen... from beyond the high ground on the far side of the lake, the sound of racing motorcycle engines drifts down from the roads where morning Qualifying is already under way. Behind the hide, a squadron of military transport helicopters is wheeling down from an air force station towards the army barracks about twelve miles to the south. Wherever we are, it's a long way from Norfolk...
 

This is the Portmore Lough nature reserve in Northern Ireland, and you can bring me here to die.

Gulls and terns at Portmore Lough
(c) Wildlifewriter 2013
On the first sunny weekend of the whole summer, more than 20,000 visitors have arrived at the Oxford Island centre down the road, and their car parks are already overflowing – yet here we have the place to ourselves. Like most fenlands it's remote and difficult to access, although RSPB who have the management of the reserve area, have done a lot of work on paths and boardwalks since last year. Wellington boots are no longer obligatory. This type of wetland habitat is rare in Ireland but, where it exists, Nature takes full advantage. As biodiversity hotspots go, the place is almost incandescent: 317 species of insects at the last count, including bembidion clarki and a colony of rhinoceros beetles found nowhere else. Tree sparrows Passer montanus are nesting in boxes by the upper boardwalk. On the water, common terns are still incubating: testament to the late spring and their difficult migration this year, but the black-headed gull chicks have hatched over the weekend. They stagger among the tern nests, trying to find their feet and avoid being pecked at the same time. The project to increase lapwing breeding is also paying off and numbers are already up on last year.

Anything could appear here – and usually does, if you time it right. In spring and autumn, the big-ticket items are passing through: ospreys are regular visitors, though none have stayed to nest as yet. It would be an ideal place for them, with perch and pike abundant in the water and minimal human activity. Short-eared owls feel secure enough to hunt in broad daylight and, after dark, rare Daubenton's bats are active along the gullies and hedgerows. By winter, internationally important numbers of wildfowl roost overnight on the lough, safe from ground predators and humans disturbance. Whooper swans and some Bewick's will be here, with gadwall and pochard occupying the cheap seats at the front.

Up at the observation platform, local birder Paul Toner is catching a few afternoon
Juv female marsh harrier, Portmore Lough, Jan 2012
(c) Ed O'Hara
rays and we stop to ask what the “craik” is: in January last year, Paul, Ed O'Hara and the local group recorded (and photographed) marsh harriers on the reserve – a good tick anywhere but big potatoes for Ireland where they are never regular. We talk about ospreys again, and the issues about getting planning permission for a nest platform. Bureaucracy will have its due course, and nothing will speed it up. A few other enthusiasts wander in and, as ever, the conversation turns to the mystery of the Lough itself: why is it here, and why is this place so different from the surrounding landscape?

No-one knows. The lake itself is almost circular, which is an odd thing for a natural formation. It is certainly not glacial in origin, as existing textbooks claim.
Google Earth 2013
Old maps and written descriptions from the sixteenth century make no mention of it, and recent core samples have confirmed that there was no large body of water present at that time, yet one seems have appeared - almost overnight - around the mid 1580's. It's even been suggested (quite seriously) that an airburst meteorite might have exploded there, excavating the circular depression in which Portmore now lies, but leaving no physical trace of what would surely have been a spectacular event at the time...

You'd think someone would have noticed.



RSPB Portmore Lough, Aghalee, County Antrim.
N 54.570768, W 6.299629
Open year round. Parking, wheelchair access.
Ph: 028 9049 1547


Sunday, 12 May 2013

HUNKERING and BUNKERING


The unseen design elements of bird nests.

((c) Dyfi Osprey project 2013)


Many species of birds build nests which – to our eyes – seem unnecessarily vulnerable to the elements. Herons, most corvids, ospreys and many others choose to make their nests in exposed trees or other high places. Given the vagaries of typical British weather, we worry about them and their broods when the rain falls (as it usually does) and strong winds start to blow. However these nests – or at least the central “egg cup” area of them – could be better protected than you might think. But to understand why this might be, we have to look first at a seemingly unrelated subject: Golf.

All keen golfers will tell you that they love to play on the classic style of seaside course: the “links” - which take their name from the term for an area of sandy, infertile ground between farmland and the sea. Golf courses were first laid out in such places because the land is nutrient-poor and of little use for anything else. Links course are challenging to play on, and test the full skill set of golfers. We rejoice in the wild scenery, the undulating fairways and the tricky sloping greens, and we all agree that seaside courses would be perfect, except for one thing...

Rory McIlroy has a practice bunker


in his back garden at home



Pot bunkers.

We all hate them.

Unlike the wide shallow sand traps found on parkland courses, pot bunkers are small and deep, often with high revetted faces and a cup-shaped bowl of tight-packed sand at the bottom. It is all-too easy to get the ball in one, and difficult – sometimes impossible – to get it out again. Almost every amateur golfer believes that pot bunkers are put there to make the course harder, but that's not the real reason for their existence... 

It's often windy at the seaside, and strong winds would remove the material from a conventional sand hazard in a matter of days, meaning that the grounds staff would be forever having to replace it. The design of pot bunkers means that this doesn't happen: the deeply-shaped recess actually forms a high-pressure area above the sand surface, sheltering it from wind gusts.

Large bird nests have a similar layout to pot bunkers, and the same general aerodynamics. A wide raised rim surrounds a lower bowl-shaped interior, in which the eggs are laid. With this “design”, the weather may be as bad as it likes but the eggs – and later, nestlings – are protected from the worst of the wind, as is the bird which broods them. Rain gets in, of course, but rain itself is not the primary threat to eggs and chicks – as long as there is not too much. It is the WIND, with its effect of carrying away heat, which is the real problem.


So... the next time you watch a poor bird hunkering down in her nest while a howling gale blows around it, don't worry too much. Things may not be quite as bad as they look.


Sunday, 5 May 2013

Seals and Eiders



There's no blog this weekend because my mother is ill in hospital and we have been rallying round, fetching stuff, doing good works and generally looking busy.

To fill the gap, here's a picture taken at Rathlin Island, Northern Ireland, during my last trip out there:  Seals and female eider with brood.  (There were actually 5 eiderlings, but they steadfastly refused to gather for a group photo.)



(Click for full-size)


"TRUE OR FALSE" OSPREY QUESTIONS (2)


(Originally at FB Osprey Webcam Group)


(c) There are no ospreys on the Indian sub-continent 


FALSE. Ospreys are still reported from India and Bangladesh, where they appear to be coastal, confined to specific areas and not common anywhere. One hot spot seems to be the Sundarbans wetland in Bengal, where ospreys are regularly spotted by visitors. The most recent sighting I could find was 2/2/2013 and this photo by Nazul Islam was taken in 2010.
Osprey at Sundarbans lagoon. (c) Nazul Islam 2010
The population appears to be migratory and there have been a few ring recoveries – one from a bird originally ringed in Norway. In their survey in the 1980's, Sakeur & Sakeur listed ospreys as one of 14 raptor species known to be in decline, citing habitat loss as the major factor in all cases.

Things must have been different in the recent past... A young Army officer named Elliot, on posting in the Punjab, complained to his diary of 1891 that there were no interesting or exotic birds on and around the lake outside his kitchen window, “...only the usual ospreys, everywhere to be seen.”

 

(d) GPS bird tracking devices are less accurate when it's raining.

Pretty accurate: Niacom active antenna with Garmin Q3600 using SBAS differential corrections for a combined error of less than 2 metres

FALSE. Occasionally, I am asked to explain to someone exactly how the Global Positioning Satellite System works. I try to avoid this, because usually the explanation is only a quarter way through before the “someone” has fallen into a deep and restful sleep. The GPSS is one of those things like Corporation Tax, or the Immaculate Assumption, or open heart surgery – if you needed to know how it works, you would already know exactly how it works.

The space-to-ground segment of GPS is a radio signal. In fact, two primary radio signals, known as the “L1 and L2 carriers.” When the system was being designed, the wavelength for this signal (20cm L-band) was carefully chosen because these frequencies are least likely to be affected by water vapour in the atmosphere. Clouds and rain have no measurable affect on GPS accuracy, although many internet “experts” will still try to tell you that this happens. The myth probably arose because people that are carrying GPS -equipped smart phones might take shelter from rain under structures or dense foliage. These local obstructions could have some effect on reception, but the rain itself does not.

 

(e) Ospreys don't like flounders because they taste funny and are the wrong shape.


FALSE. Poor flounders... rejected by chefs, despised by ospreys, and as ugly and stupid as Ian Duncan-Smith, they get a universally bad press. The fact that ospreys don't like them is well supported by data, though it might be truer to say that while ospreys are prepared to eat flounders – they'd just prefer to eat other things instead. But why? Well camouflaged bottom-feeding flounders are abundant around the British coast in summer, and you'd think they would be perfect sustenance for a nest full of baby ospreys.


The best theory we have is to do with net energy inputs. Compared with other seasonal estuarine species ( e.g. mullet, bass, sea trout) the flounder has about 8-10% less fat content. And for birds, as we all know, fat = flight fuel. Emyr Evans (who is not keen on eating flounders himself) has pointed out to me that they have tougher skin than these alternative species, and so the upshot of all this is a three-way disadvantage in terms of diet:-

  • More difficult to catch,
  • More energy expended dealing with the food,
  • Less energy obtained after ingestion.

Put together, this would explain why the birds – especially breeding females – have evolved a preference for more energy-rich prey items. Shape and taste are unlikely to have much to do with it.