Sheep numbers and Welsh Curlew

Blog Jill PThis paper from Ian Johnstone and RSPB colleagues, in the BTO journal Bird Study, provides some interesting evidence as to how the distribution of breeding Curlew in Mynydd Hiraethog (North Wales) relates to habitat. Amongst other things, they conclude that the amount of sheep grazing is critical to the future recovery of the species in this area.

Correlates of Distribution and nesting success in a Welsh upland Eurasian Curlew population by Ian Johnstone, Dave Elliot, Chris Mellenchip & Will Peach. Bird Study https://doi.org/10.1080/00063657.2017.1411466

The bigger picture

old blogsInternationally, the Eurasian Curlew is designated as near-threatened because of the rapid declines in numbers across the species’ range. Irish conservationists are worried that the species may soon disappear as a breeding species and Welsh birds may not be many years behind, if the current population trajectory continues. For more background see this WaderTales blog: Is the Curlew really near-threatened?

While conservation measures such as ‘habitat improvement’ and ‘predator control’ are already being used in specific recovery projects it is still important for scientists to use current evidence to tease apart the factors that may be affecting the distribution and breeding success of Curlews. An earlier WaderTales blog, summarising a paper by Sam Franks and colleagues from BTO and RSPB, concludes that habitat changes and predator impacts have combined to cause declines and lists some of the specific factors involved. Across Great Britain, they found that semi-natural grasslands support the highest densities of Curlew and population declines were highest in areas with more crows and foxes. See this WaderTales blog: Curlews can’t wait for a treatment plan.

The Curlews of Mynydd Hiraethog

H site

Looking down from the moorland of Hiraethog into intensively manged farmland in the valley

Mynnydd Hiraethog is a discrete 150 km2 upland block of high grass and heather moorland with adjacent lower, enclosed and largely agriculturally improved farmland. The area is managed for livestock farming and forestry and nearly half of the moorland was designated as a Site of Special Scientific Interest (SSSI) in 1989 because of the importance of its upland habitats for birds. The mountains of North Wales have long been grazed by sheep, with peak densities occurring in the Hiraethog region in about 1999. Agreements with farmers have reduced stocking levels, in order to enable overgrazed habitats to recover.

This study focuses upon the relationship between habitat variables and Curlew numbers in a landscape containing agriculturally improved farmland and moorland that was partly protected and subject to grazing reductions for nature conservation. Thirty, random 1 km squares, stratified by historical population trend, were surveyed for Curlew density and nesting-success. Habitat-related and predation-related variables such as ground cover, plant communities and crow numbers were collected to test for associations between Curlew distributions and environmental variables.

Blog BelseyCurlew numbers in the study area declined by 29% between 1994 and 2008, which is much lower than the decline of 46% across the whole of Wales in the same period (Breeding Bird Survey). By studying a mix of squares in which Curlew numbers had increased, remained stable and declined, the researchers were able to maximise the power of the tests. As expected from previous studies, densities in the moorland edge were higher than in improved farmland (there’s plenty of detail in the paper). There were fewer Curlews in areas with higher vegetation density, with 78% of pairs in survey squares with below-average ground cover. In dense cover, prey may be harder to detect and access.

By focusing on key plant species that are associated with particular habitat types, the team were able to identify links with Curlew abundance and nesting success. As predicted, they found that breeding abundance was positively related to the presence of mat-grass Nardus stricta, which grows as tussocks and is associated with rough grazing. Nesting success was higher in areas with more cover of deer-grass Trichophorum germanicum, a sedge that is found in bogs and on wet moorland. Blanket mires are known to support populations of surface invertebrates, which are particularly important to chicks.

GT predatedWoodland may provide look-out perches and nesting habitat for avian predators and den-sites for foxes and other studies have shown that waders are less numerous close to woodland, either because of a direct predation effects or because waders avoid areas of perceived danger (as discussed in this WaderTales Blog – Mastering Lapwing Conservation). There was only weak evidence of reduced Curlew abundance in areas with more woodland in the Hiraethog area. Fox and crow control takes place across the whole area (for livestock protection) so there was insufficient variation to look at any effects that predator numbers may have on distribution or breeding success.

What next for Curlews?

On Hiraethog, much of the rough grazing, characterised by Nardus stricta, and mire, characterised by Tricophorum germanicum, is contained within the SSSI, and the RSPB authors affirm that these habitats should continue to receive protection from developments such as agricultural intensification and tree planting.

Curlews preferentially occupy locations within the moorland/farmland edge. Historically there has been concern over impacts on upland breeding waders of high sheep grazing pressure but more recently worries have been expressed over under-grazing of some upland habitats in Wales. In Hiraethog, the fact that fewer breeding Curlews were found in areas of dense vegetation is consistent with under-grazing having potentially contributed to a decline in habitat suitability.

somewhere else

Welsh moorland, with blanket bog in the foreground and a mosaic of grassland in the background

There was a 46% drop in sheep numbers in Hiraethog between 1995 and 2009, according to figures from Natural Resources Wales, in order that priority habitats would recover from historical overgrazing. This reduction in grazing pressure has probably resulted in increased vegetation density and reduced sward suitability for Curlew. Vegetation density was higher inside the SSSI than in comparable habitats outside, particularly for habitats preferred by Curlew such as heath and rough grazing.

The authors recommend that management of the SSSI for Curlew should include increases in livestock grazing of appropriate type and intensity.  These should be targeted at rough grazing and mire, in areas that have a history of Curlew occupation and that have high current vegetation density. It is hoped that modest and localised increases in grazing pressure can reduce vegetation density without negatively impacting on protected habitats. If successful, and implemented in an experimental manner, then similar treatments may well be trialled elsewhere.

The full paper can be accessed here

Correlates of Distribution and nesting success in a Welsh upland Eurasian Curlew population by Ian Johnstone, Dave Elliot, Chris Mellenchip & Will Peach. Bird Study https://doi.org/10.1080/00063657.2017.1411466


 GFA in Iceland

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.

@grahamfappleton

 

 

 

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6 thoughts on “Sheep numbers and Welsh Curlew

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