On West Sedgemoor we have one of the few growing populations of breeding curlew on lowland wet grassland in the UK. In 2017, RSPB Somerset started looking more closely into why this is in order to inform our land management for curlew and to maybe get an insight into why other lowland populations are failing.
West Sedgemoor in spring and early summer is a wonderful place, full of the sounds and smells of traditional hay meadows and pasture, including displaying curlew with their array of bubbling calls and conspicuous aerial displays. Adults are really feisty birds in spring and defend their territories vigorously against buzzards, grey herons and carrion crows which venture into their airspace. Their territory fields are often full of bright yellow marsh marigold, the deep purple of southern marsh orchids, with the gentle pink of frogbit flowers in adjacent ditches. West Sedgemoor is a great place for many breeding birds at this time, including snipe and redshank, reed buntings and large numbers of yellow wagtails, an important summer visitor to the Levels.
From late April onwards we spent many hours locating curlew nests on the north side of the moor, weighing and measuring each egg to get an estimate of when they would hatch. This was done so we could return to the nest just as the chicks hatched in order to attach radio tags to them. This was done so we could follow them as they explored the grasslands and see where they fed and whether they survived to become independent from their parents. Finding curlew nests is time consuming and requires a lot of fieldcraft. We reckon it took on average 8-9 hours to locate each nest – curlew are very, very careful in how they approach a nest, and may spend 30 minutes or more pottering about before they settle - there’s no point in being well-camouflaged if you give the nest location away to an observant carrion crow!
Photo 1: A typical curlew nest of four eggs on West Sedgemoor 2017 by Richard Archer
In all, we located nine nests, including one which was a re-lay by a pair that had been predated. We also found a curlew family from another nest site which we hadn’t previously located. 70% of our curlew nests were predated between April and June, which is quite a high rate of loss; however we think that three pairs on the north side probably produced one or more chicks to the stage where they could fly (fledge), and with up to five pairs on the south side of the moor, it seems likely that the 15 or so pairs on the whole moor produced eight young (at a conservative estimate): it is very difficult to be absolutely sure once young birds have fledged (unless you are fortunate enough to locate them in a silage field). This suggests that our curlews produced over half a chick per pair this year - probably enough to explain why the population is growing, although it wouldn’t take much of a reduction in the number of fledged chicks for this population to be in trouble. We therefore need to continue the work to get a longer run of data before we can feel confident that productivity really is good enough to maintain the West Sedgemoor population.
Interestingly, all our nine nests were located in species-rich hay meadows, and the chicks we managed to radio tag spent most of their time in these same fields, where there is lots of invertebrate food (such as grasshoppers and spiders) and the grassland is dense enough to provide cover for the chicks to hide in, but not too dense to make it difficult to move about. Because water levels in the adjacent ditches are held quite high at this time of year, the grassland soils remain damp, encouraging invertebrate abundance and making it easier for adults and sometimes the chicks to probe the soil for food, although the chicks, with their shorter bills mainly take food from the soil surface and from vegetation. Up to the time of fledging, none of the nest or chick fields had been cut for hay – something which would result in a lot of chick deaths. The RSPB on West Sedgemoor works with its tenant farmers to delay hay cutting until after mid-July, and this seems to be of critical importance to the attraction of the site for curlew.
Photo 2: Curlew chick hiding in the long grass, West Sedgemoor 2017 by Richard Archer
2017 was a good year for breeding cranes on West Sedgemoor, which produced fledged chicks for the first time. This success is probably linked with the work we have done to reduce fox predation. We are thinking about whether we could extend some of these measures to the north side of the site in 2018 to help reduce curlew nest predation. In the meantime, we will continue to manage our species-rich hay meadows in the traditional way, work with our tenant farmers to delay hay cutting until our young curlew have fledged, and holding field water levels high enough to keep soils damp.
Photo 3: Taking weight and wing / bill / leg measurements of a 26 day old curlew chick, West Sedgemoor 2017 by Richard Archer
Part of the 2017 study was done through my sabbatical, and we managed to attract a Masters student from Leeds University (Leah Kelly). We also had the support of a great ringing team, led by Alison Morgan as our chief ringer and radio tagger, aided by Rich Hearn from Wildfowel and Wetlands Trust (WWT) and Ed Drewitt who provided invaluable support in the early stages of radio tagging. Jen Smart, Kirsty Brannan, Tony Cross, Harry Paget-Wilkes and the West Sedgemoor reserves team were also critical to getting this project off the ground. Our neighboring farmers on West Sedgemoor were also very helpful and allowed us to venture into their fields to look for nests. Watch this space for an update on the 2018 breeding season next autumn.
Great conservation work by the RSPB.
Delaying hay cutting is obviously a very important factor in curlew fledging success. It will also be important to ensure the results of this investigation are made available to all other reserves and as many farmers as possible so that the curlew decline can be reversed.
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