Derek Robertson is a professional wildlife artist, a long-term member of the SOC, and an active ringer with the Tay Ringing Group. His forthcoming joint exhibition with Fiona Clucas at Waterston House runs from 28 February to 14 April 2024 and includes several paintings he has completed of birds in the Tay Reedbeds. As well as working towards a book of his many paintings of the Reedbed’s wildlife, he has been working with his friends in the Tay Ringing Group to study the fascinating range of birds that inhabit the site. Here, Derek describes his research on the migration patterns of the Water Rails that live there. The image on the right is of Derek's Water Rail Studies.
I first visited the Tay Reedbeds with Mike Nicoll nearly 40 years ago and soon became involved in the ringing studies that had begun there in the mid-1960s with folks such as Bob MacMillan, Malcolm Chesney and Bruce Lynch. We often heard Water Rail calling and occasionally one was caught in our mist nets and ringed. The various bird atlases did not seem to recognise this population, so Steve Moyes suggested we develop a call-playback technique to census them in the early 1990s (now adopted as the standard census technique for this and related species). As a result, we recorded over 120 pairs, and Steve and I went on to carry out a radio-tracking project on what was evidently a significant population of these birds. These studies (along with others on Sedge Warbler, Marsh Harrier and, later, Bearded Tit) allowed us to make recommendations on reed cutting and habitat management that were adopted by conservation agencies and land managers such as the RSPB on the Tay and elsewhere.
Water Rail by Derek Robertson; Tay Reedbed scenes showing active management of the site
Our targeted trapping and recapture of rails for the radio tracking project led us to note that there was a changeover of birds and a change in size and age ratio of birds through the seasons, and therefor to suspect that we had birds migrating to and from the site seasonally. However, Water Rail are caught in very small numbers and, together with their preference for hiding in dense vegetation, they generate very few recoveries. Additionally, our recapture and measurements from trapped birds didn’t give us a conclusive picture of what was happening so all we could do was speculate- especially over the one, solitary ringing recovery we generated, which was a juvenile ringed by us in the summer and recovered on Bardsey Island off the coast of Wales the following March.
Derek with one of his Water Rail subjects
The development of lightweight geolocators seemed a promising avenue for research (especially for a species that pushes its way through reeds, so would not be suitable for satellite or other equipment). After a few years of testing trapping protocols and discussions with a team in Norway (who were using the same technology on Water Rail there), I received a small research grant from the SOC, alongside support from local groups, which enabled me to begin fitting geolocators. Birds were caught in self-triggered cage traps baited with tinned cat food (they preferred fish flavour of the cheapest varieties available). Geolocators were deployed in the early spring before chicks had hatched and operating the traps entailed wading along a one-mile track weaving through dense reeds where water could reach nearly waist high. Sometimes the water froze but worse could be still, warm weather in late spring when dense clouds of midges swarmed around me.
Water Rail showing geolocator and metal BTO ring; Water Rail showing colour rings; Water Rail by Derek Robertson
The geolocators do not transmit, so the device has to be recovered in following years to get the data. The between-year re-trap rate for ringed birds without the geolocators was 25% and it was reassuring to find that this was the same rate for the geolocator birds. The data, when downloaded, does not give you a map position; instead, it gives you a precise time and day-length from which location can be determined. Calibration and understanding of all the factors are key and I am extremely grateful to Rob Patchett who has agreed to compile and analyse all the data and co-author the resulting paper with me, for submitting to the SOC’s journal, Scottish Birds. At the time of writing, we are still in the process of producing the paper, but we have discovered that some birds are resident, that others breeding in the Tay Reedbeds spend the winter in South East Ireland (presumably where our recovered ringed bird in Bardsey was returning from), and that some birds spending the winter with us move to Scandinavia to breed. At this stage, it seems that the timing is a regular migration that is not the result of cold-weather events and that the timing is very similar each year. The journey from the Tay to their wintering site in Ireland seems to be just a couple of days.
Young Water Rail
The captures of Water Rail on the Tay regularly comprised over half of the UK annual ringing totals and the data collected has also given us information on laying dates, behaviour and age/sex characteristics. We are very excited to be at the stage of pulling together the findings from our research for publication.
Derek Robertson
January 2024
Acknowledgements
Purchase of geolocators was supported by grants from the Scottish Ornithologists’ Club (Endowment Fund), Fife Ornithological Atlas Group and Tay Ringing Group. Some trapping equipment was loaned by Chris Baker and others gifted by Andre Thiel. Access permission was granted by the Hope and Moulton families, and I would like to acknowledge the kindness of the late David Hope and the late John Moulton. Further permissions were granted by RSPB, with special thanks to Uwe Stoneman and Vicky Turnbull. Members of the Tay Ringing Group assisted at many trapping sessions and invaluable collaboration on Water Rail populations in the reedbeds was given by Steve Moyes. Jez Blackburn and Ron Summers advised on fitting of geolocators and Sven Rislaa and Terje Lislevand gave advice on fitting of geolocators to rails and generous insight of the findings from their own study. Technical advice on geolocators was provided by Migrate Technology Ltd and traps built by John Mawer.
Images © Derek Robertson
