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.
And here is the same period in 2015.
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.
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.
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.
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.
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…
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.