Mike Smart and Chris Wells
We have been trying for a couple of years now, with much help from local observers, to read colour- rings on Curlews in the Usk estuary. We have made special efforts over the latest high tide cycle from 6 to 10 October 2021, and thought it might be of interest to summarize our observations.
Background
In winter 2015/16 on the Usk estuary 41 Curlews were caught (using cannon-nets) and colour-ringed, as part of a BTO project looking into the possible effect on water birds of tidal lagoons in the Bristol Channel. 15 Curlews were caught at Newton Farm (near Rhymney Great Wharf) and 26 were caught near the West Usk lighthouse at St Brides. Little attention was given to recording these colour rings in the intervening years, but studies of colour-ringed Curlews on the Severn estuary in Gloucestershire, with John Sanders taking a leading role in ring reading, revealed much interesting information about the birds’ behaviour: birds were extremely site-faithful, returning year after year to the same wintering area, indeed often to the same high tide roost and feeding area; survival of adult birds was very high; the breeding range stretched from nearby sites in the Severn Vale in Gloucestershire and Worcestershire, across Yorkshire and Breckland, to the Low Countries, with an appreciable number going to breed in Finland and Sweden.
In autumn 2019, therefore, we began to look more closely at the Usk-ringed birds. The main observation points have been at Peterstone and Goldcliff, where Curlews go to roost on the highest tides. On lower high tides they may roost around St Brides or along the foreshore of the National Nature Reserve, where it is more difficult to approach and observe them. In winter 2020/21, we recorded 32 of the 41 birds ringed in 2015/16, which demonstrates a very high rate of adult survival, and the expected site fidelity. Birds ringed at Newton Farm show a very strong tendency to join the roost at Peterstone; birds ringed at St Brides normally roost along the foreshore of the National Nature Reserve east of the Usk (and in particular at the mouth of Goldcliff Pill), but are pushed onto the Goldcliff Lagoons by the very highest tides. Just one bird moved on elsewhere, being seen in autumn in both 2019 and 2020 at WWT Llanelli, but returning to the Usk (perhaps after moulting?) in winter 2020/21; none of the others have ever been recorded anywhere else in winter. Four of the birds have been recorded away from the Usk in spring or summer: two were clearly on their breeding grounds, one in Sweden, one in Poland; two were probably on migration, en route to their breeding grounds: one on the Gloucestershire Severn in April, the other in late March in two different years in Lancashire.
There have also been observations of birds from other colour-ringing schemes: one that breeds in Germany; one that breeds in Poland; one ringed (and perhaps breeding) at Caersws in mid-Wales; and one of the birds raised in captivity and released into the wild (the so-called “head-started” young) at Slimbridge in 2019. Frustratingly, we have not yet got close enough to the Slimbridge bird to read its ring and so to identify the individual concerned.
Observations in October 2021
Chris Wells, observing from the sea wall, has had much greater success in reading rings, because the high tides generally (though not always!) push the roosting Curlews out of the Spartina belt so that their legs and rings can be seen. Of the 15 birds ringed at Newton Farm, Chris has so far this autumn recorded 11 (not – yet- including the one that goes to Llanelli; nor two others that have never been seen since 2015/16 and are thought to be dead). He has recorded two birds not seen in 2020/21, thus bringing the total of birds surviving to at least 34 out of the 41 ringed.
Mike Smart, recording at Goldcliff Lagoons, has had minimal success, because the water levels there have been so high that, when the birds are sitting in the lagoons, their legs are under water and cannot be seen. Natural Resources Wales have authorised him to use a portable hide around the lagoons, so as to get closer to the birds, but so far it has not been feasible to use it because of the high water levels. However, Terry Winter managed to photograph one colour-ring from the first hide on 8 October (see below), where levels were a little lower than on Becs Lagoon near the seawall.
Observations at first light at Goldcliff Lagoons have provided some interesting information. At times in the past, there have been observations of large numbers of Curlews (300 to 400) at dusk, and there have been questions as to whether these birds actually stayed all night to roost on the lagoons, or just came in for the period of high tide, returning afterwards to the foreshore when the tide dropped. On 6 October in the half light at 06h20, well before the high tide (forecast for 07h51) there were two groups of 35 and 50 Curlews on the first lagoon; they flew out, disappearing over the seawall towards the mouth of Goldcliff Pill at 07h25 and 07h35, and did not return on the high tide. At the same time the next morning, 7 October, with the wind very light indeed, only 13 were roosting on the first lagoon, and flew out at the same time; on the high tide about 300 came into Becs Lagoon, staying belly deep throughout the high tide period. At the same time on Friday 8 October, none were roosting on the first lagoon, but 350 to 400 came to Becs Lagoon at the height of the tide. This indicates that some may roost overnight at times, but that it is by no means a regular event, and that the whole wintering Curlew flock rarely does so. It seems more likely that when there is an evening high tide, the main Curlew flock may come on to the lagoons for the high tide period, but probably then returns to the mudflats. Further investigation required!
Numbers of Curlews coming to high tide roosts are governed not only by the height of the tide, but also by the strength and direction of the wind. At Peterstone, there generally appear to be 150 roosting Curlews. At Goldcliff there are sometimes no Curlews at all (e.g. on 6 October, when none returned to Becs Lagoon after the roosting birds had moved out), but on 7 and 8 October numbers reached 350 to 400, which probably represents most of the Curlews which normally roost and feed to the west of the West Usk Lighthouse.
If water levels at Goldcliff Lagoons remain high, it will be of interest to look at the Curlew roost around the West Usk lighthouse, even on lower high tides.
We would be very pleased to receive any comments, additions or amendments, and of course, any new readings of Curlew rings.
For further background information about Curlews, please consult the Curlew Forum website at www.curlewcall.org .
Black Blue Blue at Goldcliff on 8 October (photo: Terry Winter)