Sea change

The last few posts about UV described his quite settled existence. He has no fixed routine -spending different amounts of time in several places – but he uses familiar spots and he can sit for hours! Just like most over-wintering ospreys.

On Wednesday UV flew further south than he has done since arriving back in Senegal. At his most southerly point he was offshore near the area that was his home for several months in 2015.

Familiar territory

Familiar territory

Yesterday UV was back there and went further, higher and for longer! He was in the air for around 2.5 hours with a 3 minute break perched on a tree by the river. His maximum altitude was 1036m ASL. Especially when over the river UV could have been hunting. But about 40% of the time he was over 150m ASL, far too high to see fish especially as the water is not clear. Perhaps UV was observing where other birds were hunting given he hasn’t been flying over the area recently. Whatever the reason for his behaviour it is interesting data.

It’s impossible to capture UV’s activity in an image. Paul has spent hours, literally, creating an animation of UV’s outing. UV’s altitude is shown at each point of his journey. Click to follow his route.

play

 

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Overview and ‘microview’

Since the last update on UV he has continued to spend his days in a few familiar places but without having a settled routine. Sometimes he is at the coast for most of the daylight hours, occasionally he is barely recorded away from a roost area. An interesting aspect is where he still hasn’t been – no recent recorded activity on the south spit of the Langue de Barbarie, no travel to the southern end of the National Park where the river mouth used to flow into the ocean. His foraging areas have varied but before looking at a couple of examples an ‘overview’. Paul has prepared a migration map which will go up in A2 and A3 versions at Kielder Castle. It is also in the Location Maps section of the blog. 

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

Whilst in ‘overview’ mode the daily MODIS weather satellite data for 20 November showed a red dot at the top of this graphic indicating thermal activity very near Djoudj National Park.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

The smoke billowing out to sea covers as large an area as the patchy cloud near the Senegal River mouth. The red dot is in an agricultural area and the likeliest explanation is that the crop is sugarcane. Sugarcane field burning commences in November, the start of the dry season. The fires burn the leaves off the stalks which makes harvesting the sugarcane easier.

Back to UV. His foraging activity has  ranged from just offshore to around 4.75 km out over the ocean. On 25 November he went further south offshore than usual.

checking different areas of the ocean

checking different areas of the ocean

When there are one minute fixes the change from slower foraging to moving on to try a different area is clear. After speeding south UV slowed down from 15.14, when he circled over a spot before carrying on south then east and north to a shallower area.

In contrast many of his forages look more like the image below.

another fishing trip?

another fishing trip?

That shallow area is a popular one.

Data arrived as this blog was being finalised. UV had two excursions today into the deep blue of the ocean, about 3.25 and 4.75 km offshore. Where tomorrow, UV?!

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Busy doing nothing much!

In the ten days since the last update UV has lived up to the title of this post! He hasn’t visited anywhere new nor has he travelled south in the Langue de Barbarie National Park, an area he used regularly late last year and early 2016. But he has no set routine. He may spend two or three days flying between a couple of beaches but the next he could be inland all day – as far as the data reveals. He is quite restless at night and has been moving before midnight to a different tree a few hundred metres from his initial roost.

In the first image UV looks as though he was perched in water rather than on the beach.

Dipping his talons?

Dipping his talons?

Probably the 12.41-13.16 area was above the water level given the low tide time. But it is possible it is permanently above water now. The image is of the southern end of the northern section of the Langue de Barbarie. The tip of the mainland is just left of the North symbol. This slideshow with the island of Doune Baba Dieye at the centre reveals how rapidly the landscape there is changing.

This slideshow requires JavaScript.

UV has spent many hours on either the Langue de Barbarie or the area circled in the last image. He only settled in the Langue de Barbarie in April 2015, the date of the first image, when the area he now frequents was still submerged.

Regular readers may recall previous mention of the devastating impact of an attempt to reduce flooding in Saint-Louis. In 2003 a 4m breach was cut in the Langue de Barbarie peninsular. It is now 6 km wide as the sea erodes land to the south of it and sand accretes to the north. Several villages have been destroyed including the one on Doune Baba Dieye and the ecology of the area has been adversely affected. By the end of the year the Senegalese government will decide which of several alternative measures to implement to try to alleviate the situation.

In the April 2015 image in the slideshow the sediment flowing downriver and into the Atlantic is apparent. Recently there has been more rain in West Africa than usual at this time of year. Paul has made a graphic showing the percentage above normal of the rain.

courtesy Paul Wildlifwriter

courtesy Paul Wildlifwriter

As you can see the white, green and blue areas are all affected by higher than usual rainfall. The Langue de Barbarie is in the blue area just below the Senegal-Mauritania border. As there is mostly no rainfall in November even a small amount produces a very high ‘percentage above normal’ reading.

Latterly days have been cloudy so weather satellite imagery is often unrevealing over coastal Senegal. But on 13 November it was possible to see the sediment leaving the river and dispersing to the south carried by the prevailing current.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

UV had been foraging nearer shore but he has been further out to sea at times in the last week, possibly in part because of the opaqueness of the water.

UV

UV almost into the deep blue

By the end of November Project Tougoupeul will have begun their month long survey of birds in the Langue de Barbarie National Park. Last year UV was photographed a couple of times but he’ll have to change his habits to get in the picture again!

 

 

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Thunder and … foraging!

In the previous post we described UV changing behaviour slightly and foraging along the shoreline of the northern part of the Langue de Barbarie. On 3 and 4 November data didn’t show UV foraging activity in any detail.  There were very few fixes on 4 November, a day of unseasonal thunderstorms.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

UV sat tight inland most of the day although the showers could have missed his spot altogether. The daily recorded rainfall at Saint-Louis airport was 0.51mm. Podor airport (about 180 km upriver in a straight line) recorded 6.10mm.

NASA weather satellite imagery had been showing quite a small area of silt (carried downriver as a result of the earlier seasonal rains) around the Senegal River mouth although it looked dense. Today looks rather different.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

The silt is extending about 20 km offshore, well past the 6 km distance UV has been foraging sometimes. The silt plume is heading south. This slideshow of graphics prepared by Paul shows the seasonal currents. Green is cooler water, the arrows show the direction of the currents.

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Paul: “The prevailing direction is north-south – “The Canary Current”. This flow starts as an upwelling of cold water from the deep ocean, and gets warmer as it travels south near the surface. The cold source is nutrient-rich, which is why that whole region along the west African continental shelf is such a rich fishing area. (For ospreys and people.)”

Is it possible to discern a change in UV’s behaviour caused by the currents carrying the sediment south and out to sea? On 5 November UV flew further north along the shoreline than previously since his return. The data doesn’t show him heading out to the deeper ocean – blue – at all.

UV's foraging areas

UV’s foraging areas

The single offshore fix to the south was at 13.00 UTC when the frequency of fixes was 15-20 minutes apart, so he could have been further afield during that sortie. UV also foraged just off the SW of the spit, a popular place for him.

On 6 November there were many more fixes for much of the day. He had two foraging trips near land to the south of his usual areas. This image shows the longest.

Around 50 minutes of foraging

Around 50 minutes of foraging

An animation can bring alive so much better than an image how UV foraged. Many thanks to Paul for this one.

play

 

 

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Going fishing… and more

Since UV’s long excursion south on 28 October, so eloquently described by Paul in the previous post, he has reverted to quite settled behaviour. His foraging strategy is still one of the most interesting aspects of his behaviour. Before discussing that, this image shows UV stopping off at the Ngalam River on his way back ‘home’ on 28 October.

Back to familiar territory

Back to familiar territory

UV flew low over the same small area of the river as in the image above during his ‘high flying’ outing on 19 October. On 28 October UV ventured north of the Ngalam into the Trois Marigots, a marshy haven for birds. He perched at the bottom of the Marigot Khant-Sud in the same spot as a visit about a month before he migrated in Spring. Then he flew past Toddé, where Nest 2 hatched Blue 1H was seen in November 2013. UV has also been there before, so more reacquainting himself with ‘old haunts’.  He has shown no daytime interest so far in the coastal area to the south – the Langue de Barbarie National Park – which was his heartland for several months in 2015.

Back to UV’s foraging. As mentioned in previous posts seasonal fish migration and silty waters in the river mouth at this time of year will influence behaviour. Paul has created two ‘heatmaps’ of UV’s flying activity – March and October 2016.

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A note of caution: all flying activity is not foraging, even when over water. But the heatmaps do reveal changes in that behaviour. Before UV left in Spring he was foraging over quite a small area relatively near the river mouth just off the north spit of the Langue de Barbarie. Now he is venturing much further offshore during part of most flights over water although the area in question is not red, but misty blue, in the heatmap. UV’s inland flying is around Lac Guembeul. He may forage there but there is less clearcut evidence – mainly he is just moving from one perch to another!

Analysing the data we can see that some days UV is looking for fish – or could be – more often than others. At this time of year there are many large fish and a good size catch, say 600g, could satisfy an osprey in winter quarters for almost a couple of days. It may be significant that the day after UV made his 182 km journey he was potentially foraging 7 or 8 times – perhaps he’d built up an appetite!

During the last few days UV has changed his strategy slightly.

Two flights over water

Two flights over water

UV’s  more distant flight took him 4 km out to sea. The 1-2 minute fixes suggest he was looking for prey. The area just off the end of the spit appears quite productive. UV often spends several minutes there, as can be seen above. The water is shallow so silt is less of a problem. He also flew along the shoreline, a rare event since his return. Fish shoals are likely to be in different areas according to currents and wind shifts, so are they nearer the shore now?

Further along the shoreline

Further along the shoreline

Several times yesterday UV flew a greater distance than previously up and down the shoreline. GSM trackers with their wealth of data allow much to be learnt about probable fish movement as well as ospreys.

 

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Just because …..

Soon after publishing yesterday’s post about UV settling back into his usual range – quite large in itself – new data arrived. UV flew 182 km on a round trip to the south! Interpreting behaviour can be a real challenge. Yesterday was a good example as Paul describes so effectively below:-

Ospreys. Gotta luvvem, right? Just when we thought that UV had settled down to a winter of comparative idleness at his winter quarters in north-west Senegal, he decides to prove us wrong.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

Just before 7:00 UTC yesterday morning he left his roost site and headed off – not westwards towards his usual hunting grounds, but south-east into the rural interior. What was going on?

Joanna and I have been analysing osprey behaviour for a long time, and we have developed some standard methods and protocols to help us understand it. We check the weather for that location. We study the terrain features being traversed. We consult maps to see if there are rivers or lakes on the route which might attract one of our birds. We did all those things yesterday, and we were baffled.

Moving at a brisk clip, UV flew for almost 50km, down to an otherwise unremarkable area of farmland near the town of Gueoul. No lakes here. No irrigation canals, no flooded mine workings – nothing fish-related at all. As the morning breeze died away, UV began to circle. He gained almost 600 m of height before gliding down and away northwards over fields and Baobab trees new-greened after the seasonal rains.

(c) tinofrey courtesy Panoramio

(c) tinofrey
courtesy Panoramio

Another 50 km, and the autumn sun began to generate rising air currents – “thermals” – above the flat landscape. UV flew. Using little or no excess energy, he soared in graceful arcs to the apex of these thermals. On my screen, his GPS track forms cathedral spires of altitude, and the glides between them are flying buttresses – an architecture of the air, made visible.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

Technical analysis went out the window. There is only one interpretation that fits what we saw UV doing yesterday. He is a young, strong creature, back home in his adopted land. His flight back to the river was not merely a journey – it was a virtuoso performance by a master of the aeronautic art. UV had no destination in view, no special reason to make this trip…

He did it because he could. … Ospreys. Gotta love them.

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Settling in again, UV style

UV returned to his wintering grounds in northern Senegal just over a couple of weeks ago. He has been to many familiar places. Here is an overview of his activity.

Not just sitting on the beach!

Not just sitting on the beach!

The range shown in the image is 510 sq km. If the excursion east and north on 19 October is removed UV is travelling around 140 sq km of land and sea with an ‘average’ day encompassing roughly 100 sq km. Many overwintering ospreys have a range under 10% of that – for example the Loch of the Lowes 2015 male FR3 has spent most of his time in an area of about 5.5 sq km although he does venture further afield.

Since his return UV has occupied perches mainly on the north spit of the Langue de Barbarie and an inland area near Lac Guembeul. He has roosted in several different habitats including within the National Park on the south spit of the Langue de Barbarie – a rare occurrence since he more or less abandoned that territory in autumn 2015. On 23 October he roosted in the same trees he used many times from April to October last year. But there are no daytime fixes of UV in the National Park.

One of the interesting aspects of UV’s behaviour is his foraging, but first we’ll examine that excursion. UV flew east then north at altitudes of over 400m ASL, much higher than normal when in wintering grounds.

High flyer UV

High flyer UV

UV’s high flying ceased at the Ngalam river which he has explored before.

Checking conditions

Checking conditions

He flew on without stopping and headed for the north spit of the Langue de Barbarie. He reached over 500m ASL. Most of his flying in his first two of three journeys over the sea was too high for foraging.

Here is a NASA satellite weather image.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

The wind direction in weather websites was N or NE so why was there dust from the Sahara in the atmosphere? Paul explains:-

 “Ordinary” weather maps are useful, but they don’t always tell the whole story. On the 19th October, ground-level winds followed the usual pattern of onshore sea breezes during the afternoon. But in the layers of atmosphere between 1500 and 3000 m, the winds were blowing in the OPPOSITE direction, carrying high-altitude dust from the desert interior.

UV’s high flying to the Ngalam river and back was probably unrelated to dust above him but that, coupled with silty water below (inset in the weather image), might have made it even harder to forage off north spit. He could have been looking for better conditions further afield. Frequently since his return to Senegal UV’s foraging has been some distance offshore with many flights between 2.5 and 5 km from land. Paul has made an animation which shows this clearly.

play
This graphic shows where there will be plentiful fish supplies.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

UV isn’t fishing in the river at all because although the seasonal rains are now over sediment is still being carried downriver (the inset in the NASA image above). Observer on the ground and friend of Kielder Ospreys Jean-marie Dupart writes a blog about wildlife in northern Senegal and on 26 October described the ospreys foraging at sea, not in the murky river. If you read Jean-marie’s post you’ll see he had over 50 osprey sightings albeit as he says some could be the same bird twice. A great place to visit!

Last autumn UV changed his foraging areas from ‘close to shore’ to further afield, reinforcing the view that fish migration and the clarity of the water are the reasons for alterations in behaviour. Fishing in the mostly clear and quite shallow rivers of northern England must seem a long time ago to young UV!

 

 

 

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