By Will Kelsey
At first glance, the connection between pigs and birds in a woodland might not be obvious. However, a recent study, funded by the Cameron Bespolka Trust and conducted at the Kent Wildlife Trust’s Wilder Blean woodland reserve, reveals how pig rooting can impact the food web that woodland birds depend on.
Three Iron-Age pigs, known as ‘ecosystem engineers’, at Wilder Blean. Photo credit: Will Kelsey.
How Rooting Engineers Woodland Ecosystems
‘Rooting’ occurs when pigs plough through the top layer of soil in search for food. This soil disturbance can lead to greater habitat diversity, which should in theory benefit a range of species, including birds. As a rule of thumb, nature loves diverse, messy habitats! For example, we know that number of nightjars at RSPB Arne tripled after pigs, ponies and cattle were introduced in 1990. And yet, the role of pigs in woodland bird success remains uncertain.
In early 2023, three Iron-Age pigs (pictured above) were released onto Wilder Blean reserve in Kent to scruff up the woodland and in doing so increase biodiversity. This study sought to understand the impact of their rooting on woodland arthropods and birds, including Blean’s nationally significant populations of woodlark (Lullula arborea) and nightjar (Caprimulgus europaeus).
Iron-Age pig rooting at Wilder Blean. The yellow circle shows deep rooting that could become a pond for amphibians, while the red circle marks an uprooted clod of earth that could be the foundation of a future anthill. Photo credit: Will Kelsey.
Key Findings from Wilder Blean
The study revealed that recently rooted areas had a significantly lower arthropod abundance compared to non-rooted areas. This reduction in spiders, woodlice and other ground-dwelling creatures likely stems from the removal of vegetation and exposure of bare soil, which makes these small animals more vulnerable to predation. It may take between 2 to 3 years for these rooted areas to regain their arthropod numbers.
After deploying camera traps at Wilder Blean for 3 weeks, there was no clear evidence of birds actively preferring rooted areas for foraging over non-rooted areas. No woodlark or nightjar were captured on camera, likely due to the short study period.
Wood pigeon foraging in a non-rooted area at Wilder Blean. Photo credit: Will Kelsey.
What Does This Mean for Woodland Birds?
Although there was no clear evidence that birds were using rooted areas preferentially, the decrease in overall arthropod numbers might limit overall food availability for insectivorous birds. Areas are rooted repeatedly and arthropod numbers remain low, this could lead to a long-term decrease in bird numbers at Wilder Blean.
Implications for Wider Conservation
This research underscores the complexity of rewilding projects. Pigs, while useful for creating habitat diversity, need to be managed carefully. If rooting is allowed to occur too frequently in the same areas, it could lead to long-term declines in biodiversity, impacting not only arthropods but the birds and other wildlife that depend on them.
As rewilding efforts like Wilder Blean continue to grow, it is vital to balance disturbance with recovery periods to allow ecosystems to fully benefit from the introduction of ecosystem engineers like Iron-Age pigs.
Note: Will has received funding from our Young Naturalist Fund
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