UV: overview and detail!

UV completed his third Autumn migration yesterday. An unusual view of it.

courtesy Paul McMichael

His total distance travelled was… let Paul explain:

“How far has UV flown during his migration?

You’d think this would be a fairly simple question – and it can be provided with a simple answer. Problem is: there are rather a lot of different answers…

The reason is that “how far” is capable of being measured in several different ways – all of which give the “correct” result according to their method. For example, do we include all his changes of altitude, while flying? Should we take into account the height of the terrain he was flying over at various points? He covered a significant amount of distance while foraging to and fro at his stopover locations – should this be included as well? Does it even count if he was flying backwards?

Not so simple after all, this “how far” business.

My usual way of arriving at a total distance is to take the recorded track and (using computer software) lay it flat onto a mathematical model of the Earth’s surface known as the WGS84 ellipsoid. This tends to give a result that is the distance made good over the ground, but ignoring transient changes of height (in thermals, and so on.) I also take out any local movements during stopovers. Applying these criteria, UV’s overall migration distance works out at 5354 km. (3327 statute miles)

At the other extreme, I can load ALL his individual recorded points, take the distance between each one (vertically as well as horizontally) and tell my PC to add them all up. This give a result (stopovers, thermals, mountains AND flying backwards, all included) of 5741 km. (3567 statute miles)”

UV’s migration took him 38 days. In 2016, his ‘record’ Autumn migration lasted 32 days. Both are significantly slower than his Spring 2017 migration time of 19 days, and that included 4 days stopover.

In Autumn 2016, UV had 2 stopovers totalling 18 days. This Autumn the same number of staging posts lasted 20 days.

Lots of numbers!

Let’s go back to UV’s last couple of days leading up to arrival in Senegal. The last detailed update saw UV out of true migration mode on 13 October, as he made his way slowly south. On 14 October, he had about 260 km to fly in a direct line to the Langue de Barbarie. He travelled 236 km in the day, but ended up just short of his final destination as night fell.

pottering down the coast!

The first part of his day consisted of multiple short stops along the coast.

taking his time

UV reached the coast by 10.20 UTC, but flew slowly south before the period in the image above. At 13.42, he headed offshore and took advatage of a thermal to gain height and speed. He kept up his pace once back over land. By 16.44 he was about 1900m above the terrain as he approached the Senegal River. He stopped at the first irrigated land just north of it for around an hour. At just after 18.21 UV crossed the river into Senegal. He roosted at twilight near the Diama dam.

first night on Senegalese soil since April

UV was in no rush to reach his wintering grounds yesterday, travelling west to the sea initially, then perching at several points. He was across the river boundary and back in Mauritania during that time, but at 11.43 he returned to Senegal and was soon over the city of Saint-Louis.

courtesy Paul McMichael

UV spent the rest of the day refamiliarising himself with the northern part of the Langue de Barbarie.

the narrow spit of the Langue de Barbarie is just visible below the red fixes

UV perched overlooking the sea to the west, the river to the east.

is the landscape like this now?

The Google Earth image was taken in April, just after UV had begun his Spring migration. Now, it is likely the land will look rather different because of the rapid erosion – and sand accretion – in the area.

a year earlier

Comparing the two images, you can see the small island just SE of UV’s perches has now merged with the spit. Filau trees have been planted to try and reduce the speed of erosion. Their growth is visible. On Doune Baba Dieye, the island to the right of the image, the filaus may prevent the separation of the northern tip from the rest of the island.

Later in the afternoon, UV perched at the southern end of the spit before heading inland to a familiar roost area used at times last winter.

There were few fixes in a late morning email today – the atmosphere has been thick with dust, affecting the charging of the battery. UV was still inland, although he had probably foraged early in the day and returned with a meal. Some lazy days ahead – probably!


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UV is in his wintering grounds tonight

UV arrived at the northern part of the Langue de Barbarie in Senegal, his wintering area, at lunchtime today.

courtesy Paul McMichael

As the sun set yesterday, UV was only 20 km from his regular foraging grounds, but he roosted, and was in no hurry to complete his migration this morning! He arrived 38 days after setting out from northern England.

There’ll be more tomorrow about UV’s last couple of days, right now, we’re thrilled he has successfully completed his third Autumn migration.

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UV’s desert travel

The patchy downloads of data recently meant that it wasn’t until last night that we were finally able to see the whole picture for UV’s travel from 7 October onwards. This post covers aspects of interest.

Eventually, we can see his full day on 7 October.

across one of the major landmarks

The Oued Draa is Morocco’s longest river at approximately 1100 km. It features in most satellite tagged osprey’s routes, including Archer’s a few weeks ago. UV roosted just south of the course of the river, which will be dry at this time in his area.

below the cliffs

On 7 October, UV flew 307 km. On 8 October, he covered 220 km as he crossed into Western Sahara. He wasn’t getting much help from winds.

into the Es-Semara Desert

dry water courses

On 9 October, UV crossed into Mauritania. And out again.

276 km travel

On 10 October, UV flew 317 km.

SW travel

another water course roost

Awsard is home to a UN Team Site in the disputed territory of Western Sahara and is also a refugee camp.

UV covered 339 km on 11 October, ending his day near the Banc d’Arguin.

ever nearer ‘home’

Shortly before UV crossed his 2016 route, he was soaring high on a thermal.

courtesy Paul McMichael

One of the distinctive landmarks he would have seen was the gold mine at Tasiast.

UV roosted inland. He had a slightly ‘greener’ view than of late.

a bit greener

On 12 October UV encountered the dust storm. He flew 168 km in the day.


As you can see, initially, UV headed for the coast. He may have eaten for the first time in almost a week.  In migration mode, when stored reserves are converted to energy, a week without food is not a problem. 

perhaps a meal

Whether UV ate or not, he didn’t forage at his next opportunity.

no need to feed

Yesterday, UV travelled 159 km. His strategy was almost out of migration mode, with little high or fast flying.

about 260 km left to ‘home’

His activity near the coast is interesting.

perhaps lunch

UV arrived far too high to forage, but around 13.00 UTC he may have caught a fish.

After that interval, he flew high over the sea for a few minutes, then headed on inland.

Data today came early. UV had just left his roost area. He should have reached his wintering grounds by now.

Compare his route with juvenile Archer’s path.

so close

Archer had more favourable winds than UV, but her first migration was well judged for a juvenile honing skills.



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UV: more on his detour

Paul has been analysing weather data to establish why UV took a detour away from his normal migration route – and into a headwind – on 12 October. Over to him:-

“We were interested in why UV took a fairly long detour on the afternoon of the 12th October. A detailed analysis of his track shows that this was quite a sudden and clearly-defined change of course. UV did not “want” to go this way – his route on previous migrations lies southwards along the coast – so there must have been a reason for it.

courtesy Paul McMichael and earth.nullschool.net

The weather conditions in northern Mauritania were unusual at that time. A local weather front extended N-S, just inland from the coast, and it marked the boundary between two air masses. One, consisting of dry air from the desert interior, and another which was dense moist air from the Atlantic ocean. This maritime air had come down from further north, where the usual Azores high-pressure anticyclone has temporarily “gone missing”. (The same conditions that have allowed hurricane “Ophelia” to generate extra power and start moving NE towards Europe – the first named storm to do this since TS “Vince” in 2005.)

There can be no hurricanes in the desert, but turbulent convection along frontal systems such as this can generate small, intense squalls of winds that produce localized dust storms. Known as a “haboob” in Arabic, such an event can appear from nowhere, last a couple of hours, and then subside as suddenly as it appeared.

(c) CNRS Photothèque, Françoise Guichard and Laurent Kergoat

These dust storms are too small to show clearly on satellite images, but we can infer their effects by seeing plumes of dust that are entrained into the upper atmosphere and carried forward from the origin location. One such plume is clearly visible on the MODIS pictures from the following morning…

courtesy Paul McMichael

Our interpretation is that UV saw this haboob ahead of him on the 12th and tried to fly inland in order to go around it. This didn’t work, so he landed in an area of scrub vegetation at 15:45z and remained there overnight. By morning the air would have been clear and his track shows that he headed straight back to the coast, there to pick up his normal migration route again…”

courtesy Paul McMichael

Many thanks to Paul for a great deal of work. And if – like me – you have wondered why a dust plume could be north of the origin, given northerly winds offshore for UV, the answer is that the dust in the image above is high level dust. It was carried up into the 700 hPa layer, where prevailing winds would have taken it NE.

There’ll be a blog later today covering interesting aspects of UV’s travel through the desert.



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UV: a detour

We didn’t receive data from UV’s GSM/GPS transmitter yesterday. This was unexpected as his course appeared likely to follow the coast, where there are more cell towers than inland.  We found out why there was no update in an email tonight.

courtesy Paul McMichael

The easterly route yesterday took UV away from cell towers – and his 2016 route. This still from an animation of weather shows why he altered course.

20171012 winds:paul

courtesy Paul McMichael and earth.nullschool.net

We’ve received all the backfill data that has been missing since 7 October, so a huge amount to analyse tomorrow.

Tonight, UV is about 250 km from his wintering grounds in northern Senegal. He should arrive tomorrow, but the data may well be earlier. Tenterhooks time.

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UV: more partial data, but very welcome

We’ve received another partial download of data from UV’s GSM/GPS transmitter.

courtesy Paul McMichael

By the last fix at 13.41, he was under 2 km from Mauritania.

As Paul’s graphic shows, this morning UV crossed over his 2016 route. He will probably follow a similar course now.

The winds have been light and variable. UV has been conserving energy by repeated thermal soaring today.

courtesy Paul McMichael

The forecast is for similar conditions over the next couple of days. UV has about 550 km further to travel to his wintering grounds in northern Senegal. He should arrive on Friday. Safe onward journey, UV, from us all.

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Brief update: UV, Aln and Archer

There was no data yesterday from UV, who is crossing the Sahara Desert. It may be another day before he gets within range of a cell tower.

As predicted, Aln returned to the Sierras de Cazorla for a stopover.

courtesy Paul McMichael

She’s spent the last six days enjoying sun and mid 20°C temperatures. We’ve mentioned before the very low levels in the embalses (reservoirs). This graphic illustrates the point.

courtesy Paul McMichael

One of the reservoirs Aln has visited, Negratin, is featured in this article – it now has a natural outdoor spa for the public to enjoy!

Archer is still in the wetlands south of the Senegal River. She has had a couple of  small expeditions in the last couple of weeks, including a flight over the Grand Lac in the Parc National des Oiseaux du Djoudj.

at times Archer was over 500m above the terrain

The main hide overlooking the lake is very near Archer’s departure point in the SE corner. The water levels at this time of year will still be high, in contrast to a visit halfway through the dry season at the beginning of March 2017.

the measuring pole is a handy perch for Pied Kingfishers
(c) V J Paine

Archer flew along the shoreline on the right of the photo
(c) V J Paine

In the photograph below, the islands in the water may not be visible at the moment.

a view towards the west
(c) V J Paine

Archer wouldn’t have been alone as she flew around the lake, that is a certainty!

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