Problems with multiple colour rings on Curlews Numenius arquata

Twenty and more years ago gull ringers were using multiple colour rings, but there were many drawbacks. Observers had difficulty identifying and recording the different colours, rings faded to appear grey, particularly the pale ones, and many rings were lost altogether. This was an unsatisfactory situation for long-lived species. In addition, the combinations available ran out, so that eventually three different projects, two in Britain and one abroad, were using identical sequences, causing immense confusion. Once coded rings became available the gull ringers quickly started using them. EURING (the European Union for Bird Ringing) coordinators for large and small gulls work with ringers to avoid duplication of codes, and put observers of ringed gulls in contact with the ringers. Similarly, ringers of other large species, such as Greater Flamingo Phoenicopterus ruber and Spoonbill Platalea leucorodia, have transferred to using coded rings. In addition, Dirk Raes has created a website (www.cr-birding.org) where colour-ringing schemes are listed, together with contact addresses for the ringers, allowing observers to find out who ringed the birds they have seen. This has worked extremely well, and there is now a network of observers throughout much of Europe who are in close contact with the various ringers in different countries. So why are some large waders still being marked with multiple colour rings? Here I report on my experiences in a detailed study of colour-ringed Curlew Numenius arquata on the Severn Estuary, south of Lydney, in Gloucestershire. The study aimed to provide information on both survival and turnover. A total of 165 birds were trapped in cannon nets on Wibdon Warth (ST5796) from 2010 to 2013. Each bird was marked with a combination of five colour rings and a BTO metal ring. The ringers felt that combinations would be easier to read than engraved rings, as the birds were expected to be quite distant from observers. This scheme was agreed with the International Wader Study Group (IWSG), which coordinates the colourmarking of waders on behalf of EURING. For each bird a yellow ring was placed over a white on the left tarsus, to identify the scheme, with a single colour ring on the left tibia, and two on the right tibia, to identify the individual. A metal ring was put on the right tarsus (Figure 1a). Although the IWSG agreed the type of rings fitted, they will not have been able to take into consideration whether the rings were appropriate for the species in the location where it was trapped. They would not have determined whether the rings were easy to identify, but just taken into account that there was no duplication, and the possibility of confusion with other schemes. It soon became clear that birdwatchers were having difficulty in identifying the colour-ringed birds. An extreme example is shown in Figure 1b. The bird was marked with yellow over white on the left tarsus, blue on the left tibia, red over red on the right tibia, and metal on the right tarsus. It was subsequently seen on its breeding grounds, and its rings were described as red on the left leg, and green over yellow on the right. Fortunately the observer took a picture that was of sufficient quality for the bird to be identified. In reporting the bird he had difficulty in distinguishing the bird’s left from its right, and made no distinction between the tarsi and tibiae. The two red rings, placed one on top of the other, appeared as one, and the blue ring was mistaken for green. The white ring on the tarsus, below the yellow, was not noticed, as the bird was standing in short grass. In view of the errors in reading combinations, the recorders on the Severn are now reluctant to accept sightings from inexperienced observers, unless they are accompanied by pictures. In an analysis using data collected on colour-marked birds on the Tees, reports from members of the general public were excluded, as they were considered to be unreliable (Bearhop et al