Blog by Sean Jellesmark, PhD Candidate at University College of London and the Zoological Society of London, in collaboration with the RSPB.
In this blog, I discuss the article “A counterfactual approach to measure the impact of wet grassland conservation on UK breeding bird populations” which has recently been published in Conservation Biology.
The article shows how data from national monitoring schemes, such as the BTO/JNCC/RSPB Breeding Bird Survey, can be combined with breeding bird counts from RSPB reserves to understand the impact those reserves have on target species. The methodology is then used to evaluate the impact of lowland wet grassland reserves on breeding populations across five different wetland bird species.
Considerable efforts have been invested into protecting wetlands and the special species that breed and depend upon them. Wading bird species that use wetlands as breeding habitat, such as Lapwing and Redshank, have shown dramatic declines across most of the UK.
Lowland wet grassland created on ex-arable land at RSPB Frampton Marsh in Lincolnshire. Photo by Malcolm Ausden
To mitigate these declines, the RSPB has created, restored and managed lowland wet grasslands for many years. These reserves are managed to benefit breeding waders primarily by grazing and cutting vegetation, managing water levels and reducing predation pressure. Understanding how effective these methods are at increasing populations of breeding birds is a key task for conservation scientists.
However, and perhaps surprisingly, such assessments are rare and rarely performed on a national scale simply because setting up experiments and monitoring across such a large scale is impractical and too resource hungry, thus requiring funds that are much needed elsewhere.
The impact of wetland reserves
The study used ‘counterfactuals’ to evaluate the impact of RSPB wetland reserves on breeding populations of the reserve priority species Lapwing, Redshank, Curlew and Snipe, as well as on Yellow Wagtail, which has not been a priority species on RSPB reserves. Counterfactual evaluations work by creating a ‘counterfactual’ that is similar to the ‘treatment’ group in all respects, except that the ‘counterfactual’ group have not received the ‘treatment’.
In this study, the ‘treatment’ was the conservation action on reserves designed to benefit the target species. Specifically, the counterfactual meant creating a single population trend for each species, representing how the populations would have developed in the absence of wetland reserves. The counterfactual groups were created from the Breeding Bird Survey data by selecting matching observations from the same species, same mean altitude as the reserves and comparable habitat types.
Snipe is one of the species that have benefitted from wetland reserves © Andy Hay (rspb-images.com)
The study found that wetland reserves benefitted breeding populations of Lapwing, Redshank, Snipe and Curlew but was not able to identify any effect for Yellow Wagtail (see Figure). Out of the four wader species that benefitted from wetland reserves, Redshank populations increased the most relative to their counterfactual while Curlew benefitted the least.
There are a few possible explanations to why the study did not show a positive effect of conservation for Yellow Wagtail. It is the only long-distance migrant among the study species meaning that changes on its wintering grounds affect the breeding population different than the other study species. Furthermore, limiting livestock grazing in the spring to reduce trampling of waders’ nests could have a negative effect on Yellow Wagtail. This is because they often feed in association with livestock.
Breeding trends from 1994 - 2018 for the five target species inside reserves (solid line) and the benchmark counterfactual trends (dashed line). The shaded area shows the standard error.
The findings of this study demonstrate that wetland conservation on nature reserves works for the target species and underpins the great value of national monitoring programs, such as the Breeding Bird Survey. Demonstrations of this kind are rare and show that conservation works! However, reserves alone will not solve the biodiversity crisis. Breeding conditions for birds and other wildlife across the wider countryside must improve in order to turn the decline around and bring populations back.
Finally, in ongoing work with RSPB, I plan to explore in more detail which of the different management actions used on reserves most influence bird numbers and population recovery. In this way, I hope to be able to improve the efficacy of those actions.
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