UV: a bit of a mystery

The last post about UV covered his departure from the Langue de Barbarie for what seemed to be just an overnight excursion. But after one more or less ‘normal’ day he has deserted his small territory in the north of the spit. He has been 30 km south of there and 30 km north, although latterly he has been focusing on two areas nearer what was ‘home’. From 10-13 October he appeared to be very settled again further south on the Langue.

10-13 Oct: UV activity

10-13 Oct: UV activity

The orange patch top right is his original territory. The foraging trips furthest offshore and to the north were both on 13 October. The next day he changed his location to the spit north of the estuary which is also the Langue de Barbarie but not within the National Park. He was still favouring the southern tip of the northern spit when the data arrived this morning. This image is from 14 to 16 October.

14-16 Oct: UV shifts to the north

14-16 Oct: UV shifts to the north

What has happened to cause his move(s)? Regular readers may remember he left the area for a day in late August and then changed his foraging pattern although not his perches/roosts when the rains resulted in a significant plume of silt flowing out to sea. There has been an even larger and long lasting outflow and it seems likely that this is a major influence on UV’s behaviour. Paul has combined weather satellite images (when cloud cover has been minimal) with UV’s foraging activity. Here are some examples.

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And here is an animation created by Paul of the first few days of October.

playThe current is strong in the area; the plume disperses in different directions each day quite noticeably. Although the comparison of its position and UV’s fishing is suggestive of an effect on his foraging it does not explain why he is no longer roosting or perching in his original area on the Langue.

To prevent the city of Saint-Louis from flooding a breach was created in the sand dunes which is now mostly the Parc National de la Langue de Barbarie to the south and the Langue de Barbarie to the north. This article explains in some detail the damaging effect the breach has had in just 12 years. The southern spit is eroding away at its northern end and the northern spit is growing, as is evident in this composite image.

2009-14: the île de Barbarie is growing apace

2009-14: the northern spit is growing apace

In March a plan was formulated to place gabions to protect the Langue for nesting birds especially. Is the plan being implemented now and  therefore UV has been affected by human activity? We just don’t know although we are trying to find out!

It is unlikely a dominant adult returning has resulted in such a dramatic change in behaviour but it could be another factor, as could a level of restlessness – Zugunruhe – seen mostly during the Spring migration period but also in the Autumn to a lesser degree.

Whatever the reason(s) for his move away, UV seems content on the dunes further north. He possibly caught a fish in the ebbing tide on his first day there as shown in this graphic by Paul!

14 Oct: a possible catch

14 Oct: a possible catch

This entry was posted in Abroad, Blue UV, Migration, Osprey updates and tagged , . Bookmark the permalink.

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