We left UV early on 26 August, the day after he had flown 90 km south from the Langue de Barbarie to an area near Lompoul. The reason for his move was the presence of a large silt outflow from upriver areas of the Senegal river literally muddying the waters for many kilometres around the Langue. It seemed likely that UV would not return to his base for possibly several weeks given the density of the outflow apparent on a satellite image (here it is again for ease of reference).
However UV knew best and he went ‘home’ on 26 August! As mentioned in the last post about him he could have moved under half that distance and found clear water, so the first question was ‘why go so far?’. On the 25 August UV roosted literally metres from a spot he had used before on his travels up and down the coast. He must have felt comfortable in an area he knew pretty well.
The next question is ‘was he wise to return to the Langue so quickly?’. On 26 August he took his time returning, with several stops before heading more purposefully north in the early afternoon. He was at elevations of over 400m ASL virtually all the way, with a maximum recorded altitude of 857m so seems to have been checking out what lay ahead. He was back in his usual area before 15.00 UTC and sitting on well used perches on the beach and in the mangroves. How would he find fishing? Harder than before seems to be the answer. This image is 27 August.
UV travelled about 2.5 km out to sea to forage. But the extent of the thick silt plume was 10km on 24 August, so could he see prey? The strong currents in the area must have dissipated the silt much more quickly than anticipated. The rainy season means clear satellite imagery is infrequent, but Paul has produced this graphic showing the area on 28 August. Light cloud affects the sharpness but there is a marked difference in extent and density of the plume.
Although diluted the outflow is still significant enough to have affected UV’s behaviour. He is hunting further offshore, has never been recorded fishing in the lagoon which will be muddy and isn’t perching in areas near the lagoon but using new places much further south along the beach (between 3 and 6 km from his roost). His hunting is now almost exclusively to the south which will be clearer water than near the estuary. This image is 31 August.
The orange patch below the red fixes is all the paths from 1 July to 31 August, an indication of the shift in his area.
Since returning UV has made one trip to the mainland. On 30 August he set out soon before noon, not returning to the Langue until late afternoon. He spent time both on his outward journey (yellow arrows in the next image) and inward trip (red arrows) flying over the mouth of the Senegal river, often high, as well as sitting right by the mouth for half an hour.
On the mainland he didn’t bother with the tributaries he has previously favoured, they too would be muddy, but he had a couple of stops in marshy areas quite near an irrigation channel and the Ngalam river. They are circled on the overview of the day.
As you can see he went hunting once he was back home. The last question is ‘will UV revert to previous behaviour as the sea and lagoon return to normal clarity?’. Time will tell!