Osprey Flight Speeds: Are females faster than males?

Monty chases Glesni, Cors Dyfi 2013
(Montgomeryshire Wildlife Trust)

Background 

“How fast can an osprey fly?” is a topic that often comes up when these birds are being discussed. There is, of course, no straightforward answer to this question: all birds have a range of flying speeds, dependent on what they happen to be doing at any given time. Nor is it easy to establish a “maximum speed record” for any species of bird – unless they are pursuing or being pursued, there is no real reason for a bird to fly flat-out over any distance since this would be wasteful of energy. Several attempts have been made to establish a general rate of progress for migrating ospreys, using time intervals between sightings, or by point-to-point measurements from satellite tracking. None of these methods are really satisfactory, since there are so many variables involved. The most significant contributions have come from Sweden, by Alerstam, Kjellen and others. [1] 

In 2006, Lorna Shaw (then an undergraduate at Nottingham University) conducted a study [2] of migrating ospreys pandion haliaetus using data from the Rutland Water translocation project. Taking a sample of 21 individual birds, Shaw concluded that female ospreys might fly slightly faster than males, although the variance was not found to be statistically significant. Given the state of tracking technology at the time, this was to be expected.

We decided to address this question by using a different approach. The latest generation of GSM-type tracking devices record flight speeds directly, and at much shorter intervals. We selected two first-time migrants (sub-adult), one female and one male, that had been hatched (from different nests) at Kielder Forest in the north of England. The birds are hereinafter identified as “UV” (m) and “7H” (f) from their leg ring codes. Both ospreys had been weighed and measured by Forestry Commission staff during the ringing process; they were found to be in good health and well-nourished, and so can be considered representative of the general population. 

Methods

The raw tracking data for both birds was obtained courtesy of ForestryCommission England and loaded into a relational database system. (See sidebar) The object of the study was to obtain an analysis of ALL flight movements since fledging, from September to end December 2014. The hypothesis that female ospreys generally fly faster than males was to be tested. 

The birds had been fitted with 30gm GPS/GSM tracking units manufactured by Microwave Technologies Inc, Mass, USA. These devices output animal movement speeds in knots (nautical miles per hour) and this is the unit referred to throughout, unless otherwise stated. Speeds are “over the ground” in all cases. Since we were interested in all aspects of flight – local, foraging, and migration – these were not segregated. It is recognised that the wind is a major element in bird flight and no attempt has been made to correct for its effects, nor would this have been practicable. 

Record selection and processing 

The initial data tables contained over 20,000 samples for each bird. We filtered out all entries where the speed was recorded as zero, and also deleted all records that were obvious GPS system or transmission errors. We also removed any other entries that appeared to be anomalous for any reason, even if the speeds shown were within acceptable criteria. (In the case of 7H, I manually deleted those records where she was known to be taking a lift on ships, as this might have given her an unfair advantage!)

After this preparation, the remaining sample sizes were: n=9192 for UV and n=9365 for 7H.

To summarise the data, a range of speed classes were selected to construct a univariate frequency distribution. The nominated range was 1-60 knots, in increments of 5. (In the event, no valid speeds in excess of 55 knots were observed.) Corrections were made for the slightly different overall sample sizes, and this resulted in the table and graph following...

Speed Classes (Kts)	Range UV	Range 7H	% Range UV	% Range 7H
1-5	243	255	2.644	2.723
5-10	597	615	6.495	6.567
10-15	1740	1792	18.930	19.135
15-20	2208	2248	24.021	24.004
20-25	2274	2296	24.739	24.517
25-30	1201	1222	13.066	13.049
30-35	634	641	6.897	6.845
35-40	209	210	2.274	2.242
40-45	74	74	0.805	0.790
45-50	10	10	0.109	0.107
50-55	2	2	0.022	0.021

[Click for larger]

Conclusion 

In their daily behaviour, the most common flying speed for young ospreys is in the range 15-25 knots (28-46 Km/h). Velocities higher than this are not uncommon, and wind assistance during migratory passages is probably a major factor.

Although the male bird appeared to demonstrate a preference for slightly higher speeds in the medium range and lower speeds elsewhere, an ANOVA variance analysis of the data indicates that this is not statistically significant. We conclude that there is no effective difference in flying speeds between the sexes.

The birds studied had hatched in the same natal area and commenced their annual migration within a few days of each other. Although they took different routes southwards, and had long stopovers at different locations, these routes and locations (UV in SW Portugal and 7H in NW Morocco) would have had generally similar weather patterns and wind conditions during the period being studied. For this reason, the comparisons between the data sets are probably as valid as could reasonably be expected in the wild.

Links:

[1] "Factors affecting the autumn migration of Ospreys" Shaw L, Rutland water website: http://www.zen88810.zen.co.uk/ROspreys%20site/Satellite%20analysis.htm

[2]  "Timing and speed of migration in male, female and juvenile ospreys Pandion haliaetus between Sweden and Africa as revealed by field observations, radar and satellite tracking." Kjellen N, Hake M, & Alerstam T. (2001 Journal of Avian Biology 32, 57-67.

Sebkhets of the Sahara

Geography Lessons from Ospreys #438

Location: Assouerd Province, Western Sahara

Dama Gazelles (Image: W.A.Z.A. Conservation)

The western coastal margin of the Sahara Desert is a region with almost no rainfall. To our eyes, it appears desolate and lifeless – and yet there IS wildlife here.

Among the dunes and wind-scoured rocky plains, isolated pockets of hardy vegetation grow, flower and set seed. The seeds attract sand grouse and roving bands of migrant finches. Dainty gazelles known as “Mhorro” (Nanger dama mhorr) which are critically endangered elsewhere in the Sahel, still graze there, and the almost-mythical white antelopes (Addax nasomaculatus) - one of the rarest hoofed animals in the world and until recently thought to be extinct in the wild, are also to be found... if you know where to look.

The reason for all this is the presence of sebkhets.

A sebkhet is (in this context) a low-lying area where groundwater from aquifers below the desert seeps to the surface. They can be brackish or can contain fresh water, depending on the local geology. The mendicant camel-drivers have always known about them and some of the larger, more permanent ones have Arabic names. Others are smaller: they can last for only a few years or even months, before the desert wind covers them with sand again and exposes some other sebkhet elsewhere.

Addax nasomaculatus (Image: wildaddax.org)

Ground-reflectance images from satellites, together with LIDAR measurements, have enabled scientists to map the distribution and extent of the desert sebkhets. There are many more of these features than was originally thought, and it is now clear that they are the secret of how large grazing mammals have been able to survive in a place where none should be. At the Parc National de Safia, a closed reserve as been established where the Mhorro and Addax are protected. Their numbers and gene pool have been bolstered with captive-bred animals from European zoos, and the last count was up 23% overall since the project started.

In UV's area, there is a permanent sebkhet and several small un-named ones. Perhaps it isn't such a dull place for an osprey after all!

[Sources:]

Directory of African Wetlands, R. H. Hughes, J. S. Hughes, G. M. Bernacsek
Antelopes: West and Central Africa – action plan, R. East, ed. (WWF)

Wild addax website: http://www.wildaddax.org/description.html

Review: "Ospreys in Wales" by Emyr Evans

This is not your average bird book. Ospreys in Wales – the First Ten Years by Emyr Evans recounts a remarkable conservation success story – but it is far more than that. At its very core, this is a book about faith and inspiration, and about how the combination of these rather abstract concepts brought about the re-establishment in Wales of these rare and charismatic birds of prey.

It is at once a history, a memoir - and a thriller, with all the attributes required: excitement, jeopardy, sex and violence, rivalry, betrayal, tragedy - and flounders. (Though not necessarily in that order.) After an erudite - and lavishly illustrated - introduction has set the scene, Evans expands and develops the story. He writes in an easy, conversational style that seamlessly draws the various locations and events together. Eventually the birds themselves take centre stage, as larger-than-life characters in their own dynastic saga – the englynion of ospreys.

There is plenty here to delight the enthusiast, but the casual reader too is in safe hands. Evans successfully avoids the twin pitfalls of anthropomorphism on the one hand, and dry ascetics on the other. Instead, we are treated to a narrative that carries us along into the fascinating world of ospreys. Details and anecdotes abound, to be sure, but they are presented lightly and with the author's own passion for his subject shining through. Nor is his sense of humour (familiar to all of us who know him) absent, though here it is suitably reined in.

Emyr Evans is a behavioural ecologist by training, but he is also a photographer of rare skill with a sure eye for composition and effect. Ospreys in Wales would be significant for its text alone but the crowning glory of this hardback edition is the stunning collection of colour plates that adorn and inform every page. Drawing on his own library - as well as contributions from professional Andy Rouse and others - Evans shows us why tens of thousands of people around the world now follow every move that these birds make.

This is a true expert's story, expertly and compellingly told. Highly recommended.

"Ospreys in Wales - the First Ten Years" E. Evans (2014) ISBN: 0993099009

Amazon: http://www.amazon.co.uk/Ospreys-Wales-First-Ten-Years/dp/0993099009

Website: http://www.ospreysinwales.com/

Ghost Town

Geography lessons from Ospreys #437

Location: “Puntillas de las Raimas”, Cintra, Western Sahara, N 23.08, W 16.20

Kielder osprey “Blue UV” arrived at the Gulf of Cintra on 11^th December 2014 after an epic 2000 km migration flight from his long stopover in southern Portugal. We were intrigued – few if any tracked birds have ever visited this remote and disputed spot on the edge of the Sahara Desert. As UV looked around his new discovery, I did the same thing on Google Earth. I knew almost nothing about it. Were there any signs of human habitation around the place? There were not.

But there used to be...

Separated in time by nine years, these two aerial photographs of the same location show that there was once a thriving fishing community here at Las Raimas.  Now the hundreds of boats - rough-built inshore craft known as piroques - are gone, and the shanty town that housed their owners and crews is almost buried under the shifting coastal sand dunes. The bay is in a prime position for fishing (and for migrating ospreys) located as it is in the middle of one of the most productive continental shelves on the entire planet. The lee side of the bay is an ideal haul-out for these shallow-draft boats as it is sheltered from the prevailing northerly winds and the powerful Atlantic surf. So what caused these people to abandon their village during this period?

It could have been the local security situation: Western Sahara (formerly Spanish Sahara) has seen sporadic armed conflict for years, victim to the rivalries of its more powerful neighbours: Morocco, Mauritania and Algeria. All of them have coveted its natural resources, but none of them have done its people much good.

Perhaps it was the encroachment of the desert itself, or a failure of the (never reliable) water supply, or the attractions of a less-hazardous way of life in some other line of work. But I don't think it was any of these factors...

The German-registered super trawler "Maartje Theadora" operating off the
coast of Mauritania, 2013. (Greenpeace)

In recent years, the traditional artisan fishing industry in west Africa has been taking a hammering. Locally-owned fish processing stations have closed, boats have been laid up, whole coastal communities have been displaced. The hammering has been administered by large foreign factory trawlers from Europe, from Russia, and now from the Far East as well. Operating around the clock - and on a netting scale that the piroques cannot match - they can take out in one single day, more tonnage than all the fishermen of Cintra would have harvested in their entire season.

The big trawlers need nothing from the land, except fuel oil. They process and refrigerate their own catch, and do not need to sell it at local markets. They respect neither national agreements nor quotas, nor the boundaries of marine reserves. The discarded by-catch includes every creature that swims, and it all goes back over the side – dead. For the countries affected, it's an economic and environmental disaster. But down along the same coast, one man has had enough.

Haïdar el Ali is Senegal's pugnacious and mercurial Minister for Fisheries. Since moving from Environment - where last year he took on Big Timber with devastating effect – he has revoked 29 foreign operating licences, arrested and detained the Russian trawler Oleg Naydenov, and is personally overseeing regeneration projects among his country's artisan fishing communities. You can read more about his exploits HERE.

But what then for Las Raimas? Its people may have moved elsewhere, but they will have taken their disturbance and their pollution elsewhere, too. The lagoon at the north side of the bay - known as the Bajo Tortugo ('little tortoise', after the curiously-domed sandbar that guards its seaward entrance) is now clean and quiet. At least one osprey has come there instead for a visit. And he has come to a very remarkable place, because the Gulf of Cintra is not just blue ripples and an empty beach: its warm shallow waters are thought to be a nursery area for rare marine life and mammals, including Risso's dolphins and the critically-endangered Mediterranean monk seal. With suitable research and protected status, it could be as important to the eastern Atlantic ocean as the Sea of Cortez is to the Pacific.

 I didn't know any of this before UV arrived in the area, but I do now. He is doing a great job.

LINKS:
Forestry Commission England, Kielder osprey blog: https://kielderospreys.wordpress.com/
EU fisheries policy in West Africa (Oli Brown 2009) http://hdr.undp.org/sites/default/files/hdr2005_oli_brown_29.pdf

Biodiversity - Atlantic coastal desert: (WWF) http://www.worldwildlife.org/ecoregions/pa1304

The Migration Merry-go-Round

Migration in Detail - (Part 3)

Way back in 1999, I knew even less about ospreys than I do now. But I did know some things about birds and I had completed my foundation course in Meteorology, so when the Rutland translocation project came to my attention, I – and many other enthusiasts – followed its progress with increasing fascination. Some of the translocated juveniles were fitted with tracking devices. In those days, the units were primitive and highly experimental: they used ARGOS doppler signalling to calculate the positional fixes (which we now know to be a less-than-ideal method.) The trackers were as unreliable and short-lived as a politician's election promises – and only marginally more accurate. But they worked.

When one of the birds, a male tagged as R03(1999), showed some unexpected course deviations over the Sahara Desert, I suggested that he was avoiding a formation of adverse weather systems (which I had detected on weather satellite images) that had developed to the south-west of his position, and that these might affect his ability to use soaring flight while over the desert. This suggestion was put to the Men Who Knew A Lot About Ospreys at the next group meeting. It was not favourably received.

“Ospreys on migration use thermals very little, if at all” was the conclusion of the MWKALAO, although they didn't offer any alternative theory to explain the bird's behaviour. Being a humble and uninformed amateur, I accepted this as being the expert view...

Until now

When the published track from Finnish osprey “Helena” came in for early October 2014, it seemed to show that here again was a bird using soaring techniques while over the desert.

Unlike the examples I produced for previous articles in this series, Helena's sample is not “slope soaring” or any other kind of terrain-following flight. There are no slopes at this point, no escarpments or ridges to provide an updraught. To me, these movements looked very like direct thermal altitude modification. But it was not quite conclusive. To be absolutely certain, I needed to get my hands on the actual data files for an osprey flying over Europe (where there are lots of GSM cell towers) so that the recorded level of detail was as high as could be possible with this new technology. 

Joanna Dailey, who volunteers with the Forestry Commission osprey conservation project at

Blue VV at nest Aug 2014. Blue UV in the background
(Image: Forestry Commission England)

Kielder Forest, arranged for me to get authorised copies of their files for three juveniles. They were carrying GSM trackers and all were operating correctly. The hunt was on.

Two of Kielder's birds followed a mainly coastal and/or over-sea route for their migration. But the third, tagged as “Blue VV”, migrated over land and through central Spain. With light winds and hot sun in late summer, this is prime territory for the formation of thermals. Each day I had been carefully saving the weather charts for this region and these told me exactly when and where to look for the evidence. And little VV did not disappoint me.

Even position fixes at 70 seconds apart does not conclusively prove that spiralling flight has taken place – but adding in the direction of travel at each data point does. During this afternoon flight, there are eight other examples of the same behaviour, roughly at even time intervals.

So... were the Men Who Knew A Lot About Ospreys wrong, fifteen years ago? Well, not really, but they may have been misled by the early technology which - given the comparatively low number of cumulative fixes - seems to show birds flying in reassuringly straight lines across the broader landscape, when in fact they do nothing of the sort. As I have tried to show in this series, we are still learning things about the minutiae of bird migration...

… and there's a lot more yet to be discovered.

In the final part of this series, we will consider the physiology and layout of raptor wings, and see how evolution has adapted different species to have the appropriate “equipment” for their varying lifestyles.

Wildlifewriter acknowledges the use of tracking data supplied by the Natural History Museum of Finland (Luonnontieteellinen Keskusmuseo)and the Finnish Osprey Foundation, and data and images by Forestry Commission England.

Links:

Rutland Water Translocation History: http://www.ospreys.org.uk/osprey-facts/the-translocation-project/

Kielder Osprey Blog (Joanna Dailey): https://kielderospreys.wordpress.com/

Bird's Soaring flight (Technical): http://arxiv.org/ftp/arxiv/papers/1012/1012.0434.pdf

Slope Soaring and Ridge Riding

Migration in Detail - (Part 2)

In the previous article in this series, we looked at one of the energy-saving flight modifications used by ospreys and other raptors during their migrations. Like human glider pilots, ospreys have developed a whole range of techniques that can be used - either singly or in combination – to gain maximum advantage from the prevailing conditions.

Using data from the latest GSM-type tracking units, which can log flight parameters at intervals of minutes - rather than hours, as was typical of the older UHF devices – we can get a much clearer view of what these birds are doing and how they are doing it...

In November 2014, adult male osprey “Tero” was flying south-west down the Arabian Peninsula. After a major diversion to avoid adverse weather south of Iraq, he had reached the Jabal Tuwayq - a long north-south escarpment that marks the eastern boundary of the Asir Highlands in Saudi Arabia. The winds were light but slightly against him. But Tero was able to use the overall rising air current caused by the gentle terrain gradient in a method known to pilots as “slope soaring”

 

As with the “crosswind tacking” technique, this allowed him to gain altitude by turning UP the slope, and then maintain course progress by flying down it at a shallower angle. The advantage of this system is that it works for almost any wind direction that is at a greater angle to the line of slope than 30 degrees.

"Blue 7H" (Image: Joanna Dailey)

A variant of this flight mode is what I've chosen to call “ridge riding”. It is an adaptation to more complex upland terrain where there are many changes of elevation, with steep-sided river valleys and hill crests. And the example chosen this time features “Blue 7H” - a female first-time migrant from nest #2 at Kielder Forest. Blue 7H provides the possible answer to a question that came up on one of the discussion groups, which (in summary) was:

“Do juvenile birds have the innate (instinctive) ability to use these energy-saving techniques, or do they have to learn them as adults?”

Only seven days after leaving her natal nest, 7H had reached the Galicia region of northwest Spain. Crossing this mountainous and forested landscape, she took advantage of local up-currents along the windward side of ridges to maintain the necessary height and made good progress southward and into Portugal. It seems like even a young bird of prey comes equipped with the full repertoire of flight, and only needs to add a modicum of practice. This confirms visual observations of other migratory species on their first migrations.

In the final part of this series, we will look at some other flight modes that are used by ospreys, and see how their anatomy and wing layout influences what they are able to do.

Wildlifewriter acknowledges the use of tracking data supplied by the Natural History Museum of Finland (Luonnontieteellinen Keskusmuseo)and the Finnish Osprey Foundation, and data and images by Forestry Commission England.

Links:

LUOMUS: http://www.luomus.fi/en

Kielder Osprey Blog: https://kielderospreys.wordpress.com/

A Goldfish for Birgit

If I could, I would travel to Senegal, find “Birgit” the osprey, and hand her a halibut in person. And not just any halibut, but a halibut made of solid gold and inlaid with semi-precious stones.

Which she probably wouldn't like.
 

I don't actually have the money or the time (or indeed, a golden halibut) for such an extravagant gesture but the reward would not be unfitting. Not since the time of Ceulan himself has there been such an osprey for the getting of knowledge – and the stories of these two remarkable young birds intersect in a way that could not have fallen out better if I had dared to script it myself...

There are many scientific theories about how long-distance migratory birds achieve their point-to-point navigation. The current wisdom (such as it is) involves a synthesis of various sensory contributions and, over the years, several studies have suggested that birds can “see” the Earth's magnetic field in order to orient themselves. The results have been mixed (to say the least!) and often non-repeatable – which, in Science, is generally A Bad Thing.

The proponents of magnetic navigation have had to take their idea through several iterations: originally it was proposed that birds – and other animals – had some kind of “built-in compass” that told them which way was North. This ran into trouble quite quickly, when experiments showed that animals have no concept of “North” as a specific direction. The next version was that these creatures were obtaining positional information from lines of magnetic force. Unfortunately, this doesn't work very well either: in many places on its surface, the Earth's magnetic field lines lie parallel to each other, which would make them useless for point location.

To get round this problem, the next modification was that animals could sense the “inclination” of field lines – sometime referred to a the “dip angle” which changes with both latitude and longitude. This is certainly feasible (in theory) but even us humans need extremely sophisticated and accurate instruments to measure the dip variation - which is very small – and there was no known sensory apparatus in birds that would be capable of doing this. Meanwhile, researchers who actually know something about birds were studying data from tracking experiments and ring recoveries.[1] In Sweden, an important study looked for the characteristic direction shift that would be evidence of such a navigational mechanism. They did not find it.

The magnetophiles did not give up. Microscopic particles of iron oxide were found in birds' beaks, in the their eyes, their brains, and even in their feet! Weird quantum-mechanical effects were invoked [2] although with a convenient disregard for the actual laws of Quantum Physics. Some experiments were done which were so creative that no animals were involved in them at all. The debate continues and the jury is still out on this stuff.

So – at least as far as ospreys and other raptors are concerned – where does the evidence lie? Is this whole “magnetic navigation” thing the genuine banana, or just a load of haphazard hornswoggle? Can't the birds themselves help us out with this?

Oh yes...

[Click for larger]

 
When Ceulan made his epic migration in September 2012 he passed right over the Kediet al Jill – a 500m-high “guelb” or outcrop hill of magnetite iron ore in eastern Mauritania. This place is one of the most prominent and highly-localised magnetic anomalies anywhere on Earth so if Ceulan's navigational sense was ever going to be visibly affected by anything, this is the place where it would happen.

His course did not deviate by any appreciable amount. But THAT was only one example – until last week, when Birgit came to the same place. (4.11.2014) Not content with a simple pass-by demonstration, she roosted for the night on the north-west slope of the mountain itself. And in the morning, the time when all ospreys take their bearings and direction for the coming day's flight, she simply took off and headed straight towards her eventual wintering site in northern Senegal.
 
If ospreys really did use field lines as a primary navigation method, both of these birds would have been flying in circles around the Kediet until they got far enough away from it.  But there is no sign that it had any effect on their navigation whatsoever.


Magnetic beaks, my ass...

-Wlw.

Wildlifewriter acknowledges the use of tracking data supplied by Montgomeryshire Wildlife Trust, the Natural History Museum of Finland (Luonnontieteellinen Keskusmuseo) and the Finnish Osprey Foundation.

[1] “Satellite tracking of Swedish Ospreys Pandion haliaetus: autumn migration routes and orientation” Mikael Hake, Nils Kjellén and Thomas Alerstam, JOURNAL OF AVIAN BIOLOGY 32: 47 – 56. Copenhagen 2001

[2] “A biomagnetic sensory mechanism based on magnetic field modulated coherent electron spin motion.” Klaus Schulten, Charles E. Swenberg, and Albert Weller. Zeitschrift für Physikalische Chemie, NF111:1-5, 1978

Downwind Tacking

Migration in Detail - (Part 1)

Image 1 - Osprey "Seija" being fitted with her PTT tracking unit by Harri & Joona Koskinen near her home nest in Utsjoki, Finland.  Photo: Tero Niskanen. Used by permission, Osprey Foundation Sääksisäätiö, Finland

The new VO65 yacht has a high aspect-
ratio sail plan, suitable for trans-ocean
endurance racing

On the 11^th October, the competitors in the 2014/15 Volvo Ocean Race departed Alicante on the first leg of their 70,000km round-the world voyage. They left the Mediterranean and, three days later as they were heading down the coast of Morocco, the wind was directly behind them. This was no good at all, and something had to be done.

The class of sailing boats being used – the Volvo Ocean 65 – is no luxury cruising yacht. They are cramped, noisy, uncomfortable, wet, overpowered and undermanned – and ridiculously fast. Despite being over 20m long, the VO65 weighs less than 13 tonnes. It is constructed from carbon fibre and other lightweight composite materials. The sails are not made from sewn cloth panels in the traditional way: instead, they are vacuum formed from high-modulus fabrics such as Kevlar on an enormous mould that creates an aerodynamic profile, like the wing of a bird. 

Migrating ospreys are in a kind of race, too. However, the rules for their contest have been set by Evolution and the winners are those birds who complete the set distance – not in the shortest time, but with the least expenditure of energy. In order to do this, migrant birds seem to have a number of strategies that they can choose from, depending on the conditions encountered along their routes. And one of these methods is very similar to a technique developed by the helmsmen of modern high-performance racing craft:- 

Downwind tacking.

 No sailing vessel can progress directly into the wind. Instead, they must steer a zig-zag course at angles of about 30 degrees to the wind direction, making several “tacks” - or changes of direction – to reach a given point. Sailing directly AWAY from the wind is much easier but, for these racing machines, it is very inefficient because the boat can actually sail faster than the wind which propels it. The crews have worked out that they can achieve a lower point-to-point elapsed time (the velocity made good, or “VMG” for short) by sailing at maximum speed, again at an angle to the wind. They cover a greater distance, but the overall time taken taken to do so is improved.

Millions of years ago, migratory birds discovered the same trick BUT, instead of optimising speed (VMG), they adapt to the conditions and achieve maximum distance per unit of energy expended. Unlike the yachtsmen, birds find that a crosswind has a BAD effect on their flight efficiency, and this is for two reasons: firstly because they have to make constant small course corrections to stay on track, and secondly because the airflow over their wings is disrupted, resulting in excess drag due to turbulence.

In autumn 2014, an adult female osprey named “Seija” was fitted with a GSM satellite tracker by researchers in northern Finland.[1] She migrated strongly down through Europe, crossed the Adriatic near the “heel” of Italy and skipped over the widest part of the Mediterranean in a single 14-hour hop. Rather than resting, Seija continued southwards during the next day before coming to roost at the edge of the Lybian desert. She had flown 5300 km in only thirty days.

Next morning, Seija was up and flying early and within three days had reached the border between Algeria and Niger. How was she managing to cover these distances, across the wind? The chart below shows the details of one hour's flying time, and illustrates that these adult ospreys from Finland know a thing or two about crossing deserts...

[Click for larger]

So what is going on here? The figures in white are altitude (in metres) at each track point where there is a major direction change, and the points themselves are registered at intervals of about 80 seconds. There is no cloud cover. The land surface is about 600m and comprises flat stony desert terrain, with some low-growing scrub vegetation in patches. There are no large-scale thermals here, because the area is dominated by stable high pressure. However, small columns of rising air form locally in the surface layer, and these can be very numerous as the terrain is heated unevenly by direct sunlight. 

 Each time Seija encounters one of these, she turns downwind and uses it to gain height. Her rate of climb is around 200 metres per minute – probably achieved with little or no extra effort AND without wasting time on “classical” spiral soaring. Seija simply flies in the up-current while it lasts. As soon as she reaches the limit of the column, she turns back on her proper course, flying easily with occasional wing-flaps – not gliding, but gradually losing altitude to increase speed and conserve energy. Clever Seija is experienced at this migration stuff and she knows that her path will soon cross another up-current, where she can repeat the trick.

Adding up the figures for this part of her journey, I find that Seija had covered a much larger aggregate distance than a direct start-to-finish route, but in much the same time as she would have done without employing this technique. Meanwhile, back on the ocean, the VOR sailors had achieved overall average speeds of 8.7 knots in a wind that rarely blew over 10 knots. 

I bet they had to work a lot harder than Seija did.
 

So... does all this mean that ospreys never use soaring flight in thermals during migration? No, it doesn't – and in the next part of this article, we will take a look at a different bird in a different part of the desert, some other variants of long-distance bird flight, and see how an osprey's wing-shape is perfectly adapted for these purposes.

Wildlifewriter acknowledges the use of tracking data supplied by the Natural History Museum of Finland (Luonnontieteellinen Keskusmuseo) and the Finnish Osprey Foundation.

[1] Links:- 

LUOMUS: http://www.luomus.fi/en

Sääksisäätiö: http://www.saaksisaatio.fi/en/index.htm 

Volvo Ocean Race: http://www.volvooceanrace.com/en/home.html

“BIRGIT" - a very useful osprey

Image: Google Earth. Data: LUOMOS Finland (University of Helsinki)
*West is up

What's the use of satellite tracking, anyway?

It's a question that regularly crops up on the non-science forums and social media sites. Those who ask it often load the question with some opinion to the effect that “we already know where these birds spend the winter, so what is the point of continuing to track them?” But the birds themselves provide the answer to this... 

Increasingly, ecological research is getting down to the fine details of animal behaviour: things that only advanced technologies – close-up video cameras and microphones, and high-resolution data gathering – can uncover. These days, and probably for the first time in history, we are beginning to study bird behaviour in the wild on the scales at which birds themselves operate. And the observations are revealing.

Osprey “Birgit” fledged from a nest in southern Finland in August 2014 and, as part of a programme run by the Natural History Museum of Finland, was fitted with a GSM datalogger / transmitter unit. She duly migrated south-west over the Baltic and decided to make a stopover near the Ijsselmeer in Holland. Birgit's “2^nd generation” tracker unit is able to record her position, speed and altitude every two minutes, varying this sample rate automatically according to her level of activity.

Birgit found that the flat fields and canals of the Dutch polder were much to her liking, and began to hunt for fish there – probably the first time in her young life that she had done this. The detailed satellite tracking shows that Birgit has instinctively adopted the usual foraging strategy for an osprey. She has some favourite trees for roosting, but does not visit the same places every day to hunt for fish. Instead, Birgit has prospected over a corridor that is some 20km in length, from the towns of Lemmer in the north to beyond Emmeloord in the south.

The fact that even juvenile ospreys – though not the most effective hunters, due to their inexperience – do not repeatedly exploit a single food source is important information, and Birgit has provided confirmation of it. In an increasingly crowded world, people and wildlife can come into conflict, and one charge often levelled at ospreys by the recreational angling community is that they “eat all the fish and then move on, leaving none for us to catch.” But this is wrong, and the latest technological tools are helping conservationists to prove it.

Birgit's autumn sojourn in Holland is just as useful to us as it is (no doubt) to her.

Links: Finland Museum of Natural History (in English): http://www.luomus.fi/en
Osprey “Birgit” tracking page: http://koivu.luomus.fi/info/tracking/index.php/mapper/map/panhal_birgit_autumn2014

Ospreys with Chromecast

Watching the Dyfi ospreys on a computer screen is as good a way as any to while away five months that could usefully be spent doing something else - but it's not always convenient. Like many other DOP fans, I have always wished that I could display the live pictures on my big TV screen, and observe from the comfort of my lazy armchair – or even (heath and welfare permitting) in my bedroom. And now there is a way to do this...

Google's CHROMECAST device is a “streaming dongle” - which sounds like something you'd pay extra for in certain establishments on the seamier side of Greek Street, but in fact describes a gadget that can fetch video files from internet sites such as YouTube, and output them in a format that can display on any compatible TV. (It can do other things, too, but more of this later.)

The Chromecast connected to a Toshiba 22L702 TV

That word “compatible” is the first thing to consider. To use Chromecast – or any other of the growing selection of similar devices, we need a TV that has an HDMI input port. In the case of Chromecast, there is no other option than HDMI. It does have a USB socket but this is solely for the supply of external power, via an adapter. (Supplied.) The TV should also have a minimum resolution of 720p HD, otherwise there is not much point in the whole exercise.[1] (I'm assuming here that our friends at the Dyfi Osprey Project will have been supplied with enough bandwidth next year for their streaming to be in high resolution.) Chromecast outputs a native resolution of 1080p, but it recognises other screen formats from HDMI signalling and adapts itself accordingly.

The Chromecast dongle itself is a small black (or white in some versions) device with a male HDMI connector, an indicator LED, and a small (almost invisible) reset button along one of its chamfered edges. This button is the only external control on the gizmo, and turns out to be quite an important one as lock-ups and hangs are not unusual. This is still emergent technology, and it shows.

The unit plugs into the HDMI slot and, when powered up, searches for a local wireless network and waits to be told what to do next. This can be done via a downloadable app on your PC, but I chose to configure using my smartphone - also running the app - so that I could watch what was going on. Once given the password for a local router, it is time for a nice refreshing cup of tea because Chromecast will immediately connect to the net and start updating it's own firmware – a process that can take up to twelve minutes to complete.

That delay apart, I found the whole set-up to be painless and mostly automatic. However, if you are one of those nerdy types whose home network has several diverse routers, proxy servers, and internal firewalls, you will have to explain all this to Chromecast before it will work – and it probably serves you right.

With everything operating as it should, we can now return to our PC and explore the less well-advertised abilities of Chromecast. In a sentence, it can cast Chrome...

Chrome tab casting to TV via Chromecast, showing
the location of the extra menu icon at top right

 You will need to have the latest version of Google Chrome (36.0.1 at the time of writing) for Windows 7 or 8, Mac OS, or Linux installed. Run this up and log onto the MWT Live Streaming site in the normal way. Now, find the new icon which is at the top-right corner of the browser window. Clicking on this brings up a menu where the “name” of your newly-installed Chromecast device will appear. Select it, and the browser page will be showing on the remote TV set! Chrome and Chromecast recognise what the “Full-screen” control on the LS pane does, and will automatically use the whole screen on the TV to display it.

Running the full LS streaming window on the TV

At this point, I got some very useful cardio exercise while running from one room to another to look at different screens. Once I was convinced that this thing actually did what it was supposed to be doing, I went on to the next stage...

Live desktop mirroring on the TV. Note the high
processor useage (50%) shown on the gauge app
at top right - this is on a 2.7 Ghz quad-core machine.

Now Google's Chrome is a decent-enough browser, but as a personal preference I don't like using it. I prefer good old Firefox with all its extensions and extra facilities. Given that Chromecast's underlying functionality depends on Chrome itself, is there any way round this? Turns out, there is. On the same menu shown earlier, there is a sub-menu – all undocumented - which contains the option “Cast entire screen (Experimental)” I duly experimented with this and it works, sending the entire live PC desktop to a connected TV. With my wireless mouse and keyboard taken into the adjacent room, I can now control the PC from there as well. (Your own mileage may vary with this, as most generic wireless keyboards have fairly short range.)

This mode of operation needs a fairly stout PC to run it, as all the mirror-and-encode work on the live desktop involves some heavy lifting on the part of the CPU. A low-end laptop or netbook device will probably not cut it.

So... there you are: full-screen ospreys on your living room television – and all for £30 quid. (UK pricing.) Chromecast is available from the usual outlets, or Amazon, or Google itself. The price does not seem to vary but, as always, watch out for carriage charges if ordering online.

NOTES:
[1] For older widescreen TV receivers that have composite or RGB video input, it is possible to obtain an HDMI converter.