Wetlands on Orkney – a vital habitat for farmland breeding waders?
The publication of an RSPB-led study describes the importance of wetlands for breeding waders within Orkney’s farmed landscape. In today’s blog, Dr David Douglas, Principal Conservation Scientist, discusses the key findings.
The Orkney archipelago supports important wildlife populations, and this includes its high densities of breeding waders including Curlew, Lapwing, Snipe, Redshank and Oystercatcher.
The Eurasian Curlew, a species of high conservation concern and one of several farmland waders that breeds in high densities on Orkney © Mark Lewis
What gives rise to these high densities?
The absence of foxes, a major predator of wader eggs and chicks, no doubt plays a part. But numerous other known or potential avian and mammalian predators occur on Orkney, so potentially lower predation risk doesn’t explain it all.
Orkney is a predominantly farmed landscape, so the farming system may play a part in supporting high wader densities. Such systems can be referred to as High Nature Value farmland, where farming aims to go hand in hand with the maintenance of nature. Mixed farming systems, where pastoral and arable habitats occur in the same landscape (as in parts of Orkney), often support high nature value.
In these systems, a sensible question to ask is whether the different habitats contribute equally to the maintenance of high nature value. This could identify those habitats most in need of protection. Testing the role of different farmed habitats in supporting breeding waders on Orkney formed the basis of our study.
Survey and results
Orkney is large so we surveyed Sanday, the third largest island. We surveyed all farmland on the island, allocating each field to one of six habitat types (grassland under three management intensities, arable, moor/heath and wetland/marsh) and recording the number of breeding waders present. Analyses tested for variation in breeding densities between habitats.
A typical wetland on Sanday supporting high densities of breeding waders © David Douglas
The results were insightful. Densities in wetland/marsh (hereafter ‘wetland’ – the dampest habitats within the farmed landscape) supported by far the highest densities of total waders and Lapwing, Snipe and Redshank and second highest for Curlew (see graph below).
Densities of breeding waders on Sanday, Orkney, vary between habitats and for total waders and some species are highest in wetlands. Habitat codes: IG = Improved grassland; LIG = Lower intensity improved grassland; UG = Unimproved grassland; AR = Arable; WM = Wetland/Marsh; MH = Moor/Heath.
Grasslands on Sanday, Orkney under differing intensities of agricultural management
Agriculturally improved grassland supported consistently low relative densities across all wader species. ‘Lower intensity’ improved grassland and arable also supported relatively low densities, with only Oystercatcher differing from this pattern, with the highest densities in arable.
Large areas of intensively managed grassland now cover Sanday and are grazed by livestock or cut for silage. The sward lacks species and structural diversity and supports relatively few breeding waders.
Improved grassland which has likely been reseeded with a single grass species © David Douglas
Unimproved grassland, as shown in the image below, supported important densities across most species, with the second highest densities for total waders, Lapwing, Snipe and Redshank, and the third highest densities for Oystercatcher and Curlew.
The greater species and structural diversity in the sward provides better nesting and chick-rearing conditions than improved grassland.
Unimproved grassland on Sanday © David Douglas
Sanday supports over 1400 pairs of waders across seven species, so is clearly important for breeding waders.
Our key finding, that breeding densities of total waders and most species were highest in wetlands, is consistent with previous studies elsewhere. High densities of waders in wetlands could relate to higher invertebrate prey abundance, which is an important correlate of wader breeding success.
Is Orkney a High Nature Value farmed landscape?
Our work indicates that wetlands and unimproved grassland subject to lower management intensity make a disproportionate contribution to supporting high wader densities. Habitats managed through more intensive, mechanized practices, specifically two types of agriculturally improved grassland and arable, supported much lower densities. Worryingly, these latter three habitats comprised 65% of the land area we surveyed.
If these patterns are replicated across Orkney, the most important habitats for waders (wetlands and agriculturally unimproved grassland) are in the minority and may be vulnerable to conversion to more intensively managed land. We suggest that only those habitats managed at lower intensity on Orkney, and not the entire farming system, can be thought of as High Nature Value when it comes to breeding waders.
Whilst continued farming may be required to maintain some habitats in suitable condition for waders, our results show this should be through low-intensity farming.
In the UK and globally, wetlands have undergone widespread drainage and conversion, with agriculture a major cause of this. We recommend the retention of existing wetlands within agricultural landscapes, and the restoration and expansion of larger wetland areas to support targets for habitat and nature restoration. Low-density livestock grazing within wetlands should help maintain diverse swards whilst reducing trampling of nests and chicks.
It is also crucial that unimproved grassland on Orkney, and more widely, is protected from further conversion to more intensively managed farmland, for example, through agri-environment payments at appropriate rates.
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