The birdwatchers at Cley provide daily observations of the colour-ringed Black-tailed Godwits that turn up on the site, revealing some fascinating stories and contributing massively to migration research.
This blog was originally written for the Norfolk Wildlife Trust’s magazine, Tern.
No two visits to Cley are the same; the birds change with the seasons and even from day to day. If there are 200 Black-tailed Godwits in front of Daukes hide on Tuesday and only 100 on Thursday does that mean that half have moved on – or did all of the earlier birds leave, to be replaced by a new selection? The fact that several individuals wear colour-rings enables regular godwit observers, such as David and Pat Wileman and Mark Golley, to help provide some answers.
The highest Cley counts of Black-tailed Godwits now occur in the autumn, when birds can be found feeding or roosting on the scrapes and lagoons, pulling worms from the wet meadows or picking up grain from nearby stubble feeds. Many colour-ringed birds have only been seen once but others become old favourites, like ‘orange/green – orange/green-flag’. Until 2015 he spent the late summer weeks at Cley moulting out of his red summer plumage (see series of three pictures below). As autumn turned to winter, he flew onwards to the Tagus Estuary in Portugal, where he was first ringed in 2007 by José Alves, one of a team investigating migration at the Universities of East Anglia, Iceland and Aveiro (Portugal).
Another well-watched bird is ‘lime – yellow/black//white’. She was first caught on the Wash in September 2002 and has spent every March/April at Cley or Stiffkey. She has been seen in Ireland in mid-winter and nests in northern Iceland. This bird was already an adult when ringed 12 years ago so her exact age is unknown. The current record for Icelandic Black-tailed Godwits is 25 years but colour-ringing is likely to show that they can live even longer.
Cley is just one observation point across the whole of the Icelandic Black-tailed Godwit’s range. Jenny Gill, who leads the godwit research at UEA, is working with colleagues in Iceland, Portugal, France, Spain, Ireland and across the UK to understand migration patterns and their consequences for survival and breeding success. Every reported set of colour-rings is important, even if the same bird was seen in the same spot yesterday. It may not be there tomorrow, in which case today’s record has helped to pinpoint the departure date. Visitors at Cley can send their sightings to David at email@example.com , write them in the hide log book or contact Jenny at firstname.lastname@example.org
Whilst the vast majority of Cley Black-tailed Godwits are of the Icelandic race, a few birds from the small population of birds that breed in the Ouse and Nene Washes also pass through in the autumn. Later they will join thousands of birds from continental Europe, wintering in Iberia and west Africa. The Icelandic colour-ringed birds are providing fascinating insights into the migratory movements of that subspecies, the numbers of which have risen at the same time as the numbers of the continental subspecies have declined. Icelandic birds winter all around western Europe; Cley birds have been seen in France, Portugal, Spain and Ireland, as well as around much of the UK.
Colour-ring sightings have helped to reveal a huge amount about Black-tailed Godwits. Amongst many other findings:
Rates of population increase were greater on estuaries with low initial numbers, and Black-tailed Godwits on these sites had lower prey-intake rates, lower survival rates and arrived later in Iceland than those on sites with stable populations. The Buffer effect and large-scale population regulation in migratory birds. JA Gill, K Norris, TG Gunnarsson, PW Atkinson & WJ Sutherland. Nature 412, 436-438 (26 July 2001).
We know that birds from the same pair have nothing to do with each other outside the breeding season, even wintering in different countries, but that they need to arrive on territory within a day or two of each other if there is not to be a divorce. Pair Bonds: Arrival synchrony in migratory shorebirds. TG Gunnarsson, JA Gill, T Sigurbjörnsson & WJ Sutherland. Nature 431, 646 (7 October 2004).
We have learnt that spring migration is getting earlier, driven by new recruits getting back to Iceland earlier than older birds. Why is timing of migration advancing when individuals are not?
Cley is a great place to see godwits at really close quarters, as are a number of other nature reserves around the country. Reports of colour-ringed birds provide an important element of ongoing migration research. Please contact Jenny Gill at email@example.com and you will receive a life-history of your bird, either from Jenny or from one of her collaborators.
WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research. Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.