Blog by Sean Jellesmark, an Inspire4nature PhD student at University College of London and the Zoological Society of London, working in collaboration with the RSPB.
Across Europe, wader populations (order Charadriiformes) are declining at alarming rates. Due to climate change, intertidal habitats have been lost and rainfall patterns are changing. In the broader countryside, densities of generalist predators appear to have increased thus affecting nest survival; and agricultural developments, such as drainage and changes in grazing regimes, have reduced the quality and area of wet grassland suitable for breeding habitat.
Redshank numbers are falling nationally in the UK and breeding birds are increasingly dependent on nature reserves and other protected sites © RSPB-images
In response, the RSPB has created, restored and managed wetlands for target species including breeding waders. Conservation actions inside reserves include converting former arable land into grassland, adding structures that allow control of water levels beneficial to breeding waders and other measures that aim to increase nest survival.
A previous study showed that this type of reserve management positively impacts breeding numbers for species such as lapwing. The figure below is from the earlier study and shows that RSPB nature reserves have maintained breeding wader populations more effectively than the wider countryside between 1994 and 2018.
So, the evidence suggests that these reserves are effective which leads us to the next question – why is that the case and how exactly are breeding waders being affected? We address these questions in the new article “The effect of conservation interventions on the abundance of breeding waders within nature reserves in the United Kingdom” has just been published in the journal IBIS.
We set out to tease apart what drives successful wetland management by collating the best available information about each reserve, its management history and local weather information in combination with modern statistical techniques.
Not surprisingly, we find that the size of a reserve plays an important role for the number of breeding birds; bigger is better. We also find that older reserves support higher numbers of breeding pairs and the initial increase in breeding numbers is higher on former arable land than on former dry grassland, simply because dry grassland can already provide breeding habitat, albeit not optimal.
Fencing out ground predators is also important, but lethal predator control alone does not seem to influence breeding numbers in this dataset. These findings support previous work and our understanding of how to manage for breeding waders on RSPB reserves.
The new results also demonstrate the difficulty of conserving lowland wet grassland-breeding waders in landscapes that usually only support small areas of good quality wader breeding habitat surrounded by land that might support high densities of generalist predators, some of which have increased during the study period.
An example of lowland wet grassland in good condition for breeding waders, with a mixture of shallow, water-filled pools and rills that will gradually dry out in May and early June and provide feeding habitat for adult and young lapwings and redshank © RSPB-images
We know that the effectiveness of predator control can vary greatly depending on site-specific factors that we were not able to take account of in this study. The RSPB’s own system of annual reporting that reviews the effectiveness of management carried out on each of its sites has also identified situations where predator control has not benefitted waders. This has resulted in the development and installation of predator-exclusion fences at these sites to exclude ground predators, such as foxes.
An example of a predator-exclusion fence used to prevent ground predators from accessing an area used by nesting waders © RSPB-images
Indeed, our study demonstrated the success of this fencing at increasing numbers of breeding lapwings and redshank, with the benefits of fencing then further increased by fox control outside of fenced areas. Note however that it is often impractical to fence the entire area of lowland wet grassland at many sites.
Understanding what works in conservation is a challenging task
Over the last 20 years, conservationists have become increasingly aware of the importance of evaluating whether conservation actions work and better understanding why. Financial resources are limited, so it makes sense to identify which actions have the greatest impact. However, doing so, as we set out to do in this paper, comes with many challenges and practical constraints.
A lapwing in breeding plumage, one of the iconic target species for conservation on lowland wet grassland in the UK. The national population has declined strongly and it is increasingly dependent on nature reserves to provide nesting sites © RSPB-images
Conservation actions operate in the real world and there can be numerous reasons for change in for example nesting success, survival and population sizes of birds. To disentangle the effect of conservation action accurately requires a good understanding of what to measure and a lot of high-quality data.
One recurring challenge is the lack of precise and representative data. Often the information is site specific, which means that we don’t know if a conservation action successful at one location would be equally successful at another.
Additionally, limited resources mean that detailed records of conservation actions are often not readily accessible and sometimes do not exist. Instead, evaluations are often performed using opportunistic data, prone to bias reflecting how data was collected and exactly what was collected, which in turn reduces our confidence in the results.
We argue that standardizing how data is collected and considering what information is required to evaluate a given conservation action early on, will lead to better understanding and conservation outcomes in the long run.
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