Back to the beach

The last update about UV was written on 12 February before data for that day’s activity had arrived. We commented on UV’s tendency to spend most of the day inland so you can guess what he did on 12 February!

A few hours on the beach

A few hours on the beach

Since 12 February UV has spent much more time at the coast in different spots. He has also rarely been recorded flying at heights of over 200 m ASL. He has been airborne for much less than the 3-4 hours a day than he had been averaging.

Is he starting to build up reserves ready to start migration? Possibly – time will tell.

You’ll notice UV kept close to shore in the image above. He has seldom ventured far from land in the past week. Paul’s weather analysis has identified one possible reason.

credit: OSCAR/NASA JPL courtesy Paul Wildlifewriter

credit: OSCAR/NASA JPL
courtesy Paul Wildlifewriter

In contrast with much of the winter until now, the SSTA (sea surface temperature anomaly) for 15 February shows a distinct patch of cooler-than average sea around the coast of Senegal – the green in the image. There is also a north-going current.

These changes could be affecting the type and numbers of fish available near the coast, or their distribution. Cooler water near the coast could be attracting some pelagic species which normally feed in the rich cold water of the ocean. Another colourful chart from Paul.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

The red at the coast denotes more plankton presence than normal because of the additional nutrients and oxygen in the cooler water. So there could be plenty of prey for UV and his fish eating companions!

It will be interesting to see whether the SSTA continues and where UV forages over the next period.

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Comparisons

UV’s activity in the first ten days of February has been similar to last month with most of his perches being inland rather than on the coast of northern Senegal. He is still flying for up to four hours a day. How does 2017 so far compare to 2016?

In 2016 UV had a more extensive range as these two images show.

UV's range: from the northern part of the Langue de Barbarie to it's southern end

UV’s range: from the northern part of the Langue de Barbarie to the southern end

UV's range: more inland activity and a more compact area

UV’s range: more inland activity and a more compact area

Despite travelling much further south on many days in early 2016 – and doubless catching fish on his offshore forays there – the current hunting ‘hotspot’ between the two sections of the Langue de Barbarie featured in 2016 too.

2016: nearly 2 hours flying

2016: nearly 2 hours flying near the northern end of the south spit on 18 Jan

2017: a longer sortie

2017: a longer sortie in a similar area

The top image was made in January 2016. Although the scale is slightly different you can see the change in the coastal landscape between the two images. The tip of the south spit is gradually receding and the sandy lump on the mainland at the right of the images is growing. Both are the result of the creation of the breach in the Langue de Barbarie in 2003, an event we’ve mentioned many times before.

When UV travels to the most eastern area of his current range he often meanders there yet flies high for part of that trip. On return he frequently races back towards the coast. The return journey is usually downwind so he has a ‘helping hand’ to achieve some impressive speeds. A helpful graphic by Paul of one excursion.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

56 knots is 103 kph or 64 mph. Not bad going!

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UV in January

The last post described an unusual day when UV was airborne for as many hours as during migration. This one looks back at his activity in January as a whole. No better way to start than with a heatmap created by Paul by inputting thousands of flying fixes. A lot of work.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

You can see from the bright red that UV’s foraging is focussed on an area just offshore and which is opposite the ever expanding breach which severed the Langue de Barbarie.

Here is the map for the period covering his arrival in his wintering grounds.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

In January UV has concentrated on foraging further south, with some limited activity in the north.

As January progressed the red area became his main area for low level foraging. It still is, this is the area in close up yesterday. UV hovered several times and could have caught supper.

Maybe a catch

Maybe a catch

Many of the other fixes, especially the ones further from land, are too high to be foraging and we’ve commented before on UV’s long periods at higher altitudes. Is he looking for fish shoals when high in the sky? UV will have mastered the technical process of catching fish, but he will still be adding to his experience of how the overall landscape works for foraging.

In January 2017 UV spent more time inland than during January 2016. Last year he went to the southern end of the Langue de Barbarie often towards the end of the month, this year he has only been there early in the month.

UV has found new inland areas to perch this January. Overall, the data seems to suggest that he is still maturing and gaining experience as an adult osprey, which can only bode well for his possible future as a nest provider.

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Energy to burn

The typical image of an overwintering osprey is of a bird feeding once or perhaps twice a day, maybe having a short fly around now and again but mainly perching by or near water.
GPS trackers are the main source of this information. We have already mentioned how the ARGOS trackers which are usually programmed to give fixes 4 hours apart can ‘hide’ activity revealed by the 2nd generation GSM trackers. But even an ARGOS model would have shown more activity by UV than his ‘normal’ on 27 January.

He flew for as many hours as he would on an average day of migration. First he took a 75 km circular inland excursion as Paul’s graphic shows.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

Early in the day fixes are between 20 and 40 minutes apart – you can see the shorter time intervals as he neared the coast on return. The data indicates that during his exploration UV wasn’t at particularly high altitude nor travelling at speed. He’s gone inland around this area before so would remember there is no fish source. So was it just a ‘wander’ before perching for much of the day?

On his return UV didn’t land but travelled up and down the coastal strip of the Langue de Barbarie. Here is just one part of that activity, much of which was at altitudes over 200m ASL.

Up and down for an hour

Up and down for an hour

UV was flying over the coastal area at a maximum altitude of 1015m ASL for over 4 hours.
He wasn’t done for the day, though, and was airborne for almost 2 hours in late afternoon.

Weekend data revealed UV was back to ‘normal’ for recent days which means mainly perched inland but extended sorties, often at high altitude, around the coast. Another graphic from Paul contrasts UV’s Sunday midday ‘probably foraging’ trip at low level with a later ‘overview’ flight.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

If there is one certainty from UV’s recent activity it is that he is a fit young osprey!

There’ll be a January overview post later this week.

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Out and about

It has been nearly two weeks since an update on UV and mostly his activity can be summed up as ‘more of the same’.  Over several consecutive days he can perch for most of the time in one small area then desert what appeared a favourite place. Whilst a few sites – for example the island of Doune Baba Dieye  – are frequent destinations UV has found some new perches recently. Mostly they are in scrub rather than right on the coast.

There are exceptions but UV returns to a roost area at or after sunset – around 19.00 – most days and he is recorded over water just before sunrise (about 07.30) often enough to conclude he usually forages early.

As we’ve said previously UV flies over the river or sea more times each day than is necessary for his energy requirements. The following images show different behaviours.

out to sea

out to sea

These high flying trips out to sea could be looking for shoals of fish. Still the authority, the University of Edinburgh 1982 PhD,  The Wintering Ecology of Ospreys by Yves André Prevost had this to say:- “When foraging 1 to 5 km out at sea, for sardines or flying fish, Ospreys often rose up to an estimated height of 300 m, apparently to locate fish, then came down slowly before diving from up to 100 m.”

But today UV flew about 3.5 km out to sea at relatively low altitudes.

low and slow

low and slow

The fixes were between 5 and 10 minutes apart and UV could have been higher and faster in between them. The group of fixes below 09.34 were mainly 20 minutes apart and he could have been perched somewhere between them, but that area is a favourite hunting ground.

Until recently UV hadn’t been going so far out to sea. We’ll explore why this change may have occurred in a future post.

On 13 January UV displayed more typical behaviour for recent weeks, staying fairly close to shore.

a typical foray over water

a typical foray over water

The yellow-circled fixes appear to show UV perched in water but the sand in all those areas is probably above sea level most if not all of the time nowadays.

Finally, on 16 January UV explored around the National Park area of the Langue de Barbarie, his original ‘home’ there.

a change of mind?

a change of mind?

It looks as though he was heading inland when something attracted his attention – perhaps ospreys or gulls showing interest in a shoal? – and off he went to join in!

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Have wings, will fly

Now we’ve entered a new quarter – and year – Paul has created heatmaps showing UV’s daytime activity from October to December 2016. (UV arrived back from migration on 11 October.) Here is the overview heatmap – the redder the colour on the map the more fixes there are in the area.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

And here is the same period in 2015.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

UV was still residing on the southern spit of the Langue de Barbarie for much of October 2015, which explains the ‘hot spot’ near the bottom of the 2015 map.

One image can’t show the whole story and Paul has made a week by week animation of the last quarter of 2016 which is much more revealing.

play

You can see that during November UV started foraging further east – in the river mouth rather than at sea.  In December there are also new areas to the south attracting UV. The reducing fish migration from upstream could be part of the reason for UV’s changes. Satellite imagery shows plankton bloom very near the coast in much of the last two months so fish should still be plentiful in both sea and river estuary.

The last post described how UV’s behaviour appeared unaffected by the Harmattan, the dry and dusty seasonal wind. So far in January the weather has been mainly clear and the tracker battery is now much more fully charged. The plentiful fixes show UV has been even more active than usual including travelling 28 km south for the morning on 5 January.

An early morning trip south

An early morning trip south

Early in the day fixes are 10-40 minutes apart so there isn’t much detail about how UV spent his 4 hours at the southern end of the Langue de Barbarie National Park. The likelihood is he was mainly perched. He spent many hours in that southern patch for a couple of months from late January 2016.

After noon the number of fixes reach a frequency of  1-2 minutes.

More fixes after noon and plenty of activity

More fixes after noon and plenty of activity

UV was airborne for over two hours after heading back north, flying up and down the area from the breach in the Langue de Barbarie to a point opposite Mouit on the mainland, but he wasn’t foraging given most of the altitude readings were over 100m ASL.

But in late afternoon after a period of perching he could well have been hunting in two separate low level flights in the river.

Typical foraging behaviour

Typical foraging behaviour

The previous day, 4 January,  UV had spent over three hours with just a one minute pause flying over the sea and river. His behaviour was similar to that described above – elevation gains then a few foraging level fixes. Was he searching for fish shoals? It doesn’t seem likely as he stayed in a relatively small area, patrolling up and down. He only ‘needs’ one reasonable sized fish a day – although with all his exercise recently he’s burned many calories – so his extended forays may be for no particular reason.

Sometimes UV perches in one spot or a very small area for several hours but lately there are many more ‘busy’ than ‘quiet’ days.

His behaviour on 4 January also serves to highlight something we have noticed before:- previous versions of tracking technology may have given the impression that over-wintering ospreys are more sedentary in their daily routines than is actually the case…

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

This pair of images use exactly the same data set, but the first one shows the “old style” activity analysis – where fixes were only available at intervals of three to four hours on any given day. Our 2nd-gen tracking units show how much of this daytime activity was “hidden” in the gaps between positions.

 

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Sand and dust

Since the last update on 24 December UV has continued to travel between various coastal and inland day spots. On 28 December he appeared to be perched in the water, not on the sandy shore, near Lac Guembeul.

UV perches around the shoreline

UV perches around the shoreline

The Google Earth image was taken in early July during the wet season so the water levels will be lower now with more sand exposed.

There have been fewer fixes over the past week – some days only every 20 minutes or so at best – because the tracker’s battery voltage level has been relatively low as this graph by Paul shows.

courtesy Paul Wildlifewriter

courtesy Paul Wildlifewriter

The tiny battery in UV’s tracker unit is charged by solar energy and the charging system is only just enough to maintain battery condition under good direct sunlight. High-altitude dust can attenuate the power of the sun by as much as 20% – even when the sun ‘appears’ to be shining.

The reason for the relatively low voltages is the amount of dust in the atmosphere. At this time of year the Harmattan affects West Africa. Paul has created an animation which shows how the dust eventually reached South America.

The Senegalese authorities issued a ‘red alert’ health warning, a relatively rare event. The fine dust reached ground level as you can see in this powerful photograph by ornithologist Frédéric Bacuez.

The Harmattan (c) Frédéric Bacuez/http://ornithondar.blogspot.com

The Harmattan
(c) Frédéric Bacuez/http://ornithondar.blogspot.com

There are some Osprey photographs in the most recent post on Frédéric’s blog, click the link under the photograph.

Despite the impact on his battery UV’s behaviour seemed unaffected by the week long Harmattan and he was recorded at altitudes over 300m ASL on several days. In this image he was only at foraging level for a couple of fixes during an offshore flight and he flew inland at over 600m ASL.

Was UV foraging briefly?

Was UV foraging briefly?

Today’s data arrived just as this post was being finalised. UV had a busy morning visiting several inland sites but he was at foraging level just offshore for the last few fixes, perhaps finding some lunch!

 

 

 

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