Just before Christmas, battling the after-effects of my first dose of man-flu for over two-years, I plunged into the flooded waters of the Rivers Wye and Irfon in order to check a few more roost-sites of Dippers (not a wise move on your own really as I ended up soaked to the skin and almost got swept away!).
Earlier this year we ringed 535 nestling Dippers, an all time high, and checking all known roost sites in the autumn/winter is a great way of finding out how well these birds have survived and where they have subsequently settled following their post-juvenile dispersal. It also allows us to colour-ring the survivors as we don't colour-ring chicks in the nest due to the naturally low survival rate.
Spray-covered Dipper roosting on a rock-face near a waterfall. Nearby (and impossible to photograph unfortunately) was a bird roosting behind a raging torrent!
So far this season we have checked 257 roost sites and recorded 342 roosting Dippers of which 301 have been caught or identified from colour-rings. Well over 50% of all birds caught were retraps or controls. Dippers are pretty sedentary but females especially will swop river catchments. The furthest movement recorded so far this year is of a nestling that I ringed on the River Rea near Neen Savage in Shropshire and then re-rapped on the upper reaches of the River Teme, a straight-line distance of over 53 km.
The Dipper equivalent of a Sandwich Tern in Namibia!
Roost counts at occupied roosts were as follows:-
1 x 12
2 x 9
2 x 7
4 x 6
5 x 5
15 x 4
22 x 3
34 x 2
55 x 1
The remaining 117 suitable or previously used roost sites had no birds present. We still have about 50 odd known sites to check if/when the waters subside.
It is clear from this monitoring that the Dipper population locally is continuing to recover from a population dip in the 1990's almost certainly caused by the use of new powerful Synthetic Pyrethroid (Cypermethrin) sheep-dips (withdrawn from sale in the UK in 2010) and undoubtedly helped by the provision of well over 100 purpose-built nest-boxes.)