The RSPB's Curlew Trial Management Project saw the testing of conservation interventions between 2016 and 2019, and now scientists from the charity have reported the results in a new paper published in the Journal for Nature Conservation.
Eurasian Curlew is widely recognised as a high conservation priority in UK, where up to a quarter of the world's population breeds, meaning its status here has a significant bearing on the prospects for the species globally.
Long-term declines are thought to be the result of intensive agriculture and forestry, with predation of eggs and young driving poor breeding success. The Curlew Trial Management Project sought to test whether these problems could be fixed across large areas through habitat management and legal control of foxes and corvids.
Six landscape areas across the UK had both a trial site and a 'reference' site (where no curlew-related interventions took place). All sites measured up at around 10 sq km, contained suitable curlew habitat, included farmland and RSPB reserves, and were surveyed in the baseline year of 2015, before any management started on the trial sites.
Predator control doesn't seem to be an easy fix in Eurasian Curlew conservation, but birds took well to areas with managed habitat (Paul Bateson).
Throughout the trial period, detailed information on each site's curlew population, predator abundance and habitat condition were recorded. This was key in assessing whether the habitat improvements, including reducing taller vegetation, and control of foxes, Carrion Crows and Hooded Crows worked to boost curlew numbers.
Since the end of the trial period, RSPB scientists have been distilling the data and the results have significant implications for the conservation of Eurasian Curlew in the UK.
It was found that reducing vegetation density worked in that managed areas were well used by curlews during the breeding season. However, the habitat work combined with predator control did not lead to increased curlew productivity at trial sites, though it did benefit Northern Lapwing and possibly Common Snipe to a lesser extent.
Although foxes declined by 25% per year at trial sites, compared to 7% per year at reference sites, the researchers said that the differences were not statistically significant and could be related to complex factors at individual sites, such as woodland cover and gamebird abundance. The same applies to crows, which declined by 20% per year at trial sites and 10% at locations with no targeted management.
It is possible that additional years of study might have picked up an increase in curlew productivity, as these large waders do not breed until they are two or three years old, but research in the field was cut short by the COVID-19 pandemic.
While the scientists could not draw firm conclusions on the effect of predator control from the trial, they pointed to evidence gathered on grouse moors that breeding waders benefit from it. However, control on grouse moors is undertaken on an intensive basis year-round at sites with little woodland for predators to seek refuge in.
The RSPB pointed out that the cost of predator control sufficient to aid the recovery of curlew would be huge, while such measures may receive widespread opposition on ethical grounds and would not have a guaranteed outcome.
The RSPB suggested a better solution to the predator problem than high-cost lethal control could be addressing aspects of agriculture, forestry and road infrastructure that favour generalist predators such as crows and foxes, and addressing the lack of apex predators that would offer natural control.
Fencing off nests in Northern Ireland and Wales through the EU-funded Curlew LIFE project is showing some promise in terms of boosting curlew breeding success, but further research into the potential drivers of high predator abundance, and how to reduce its impact, must be a priority, says the RSPB.
Douglas, D J T, Tománková, I, & 8 others. 2023. Varying response of breeding waders to experimental manipulation of their habitat and predators. Journal for Nature Conservation (2023): 126353. DOI: https://doi.org/10.1016/j.jnc.2023.126353