Oystercatchers are large, noisy shorebirds with striking black and white plumage. They have bright orange-red bills used for prising open or hammering through the shells of molluscs, their main prey. Oystercatchers are found across the UK, both on the coast in winter and inland in summer. However, despite their widespread distribution, oystercatcher numbers in the UK have declined significantly in recent decades. This article will examine the key threats facing oystercatchers today and evaluate which is the most serious risk to the future survival of these charismatic shorebirds.
What are the main threats facing oystercatchers?
Oystercatchers face a number of threats during their breeding and wintering periods. The key dangers can be summarised as:
- Habitat loss
- Disturbance
- Predation
- Pollution
- Extreme weather
- Reduced food availability
These threats may affect oystercatchers directly through increased mortality or reduced breeding success. They can also operate indirectly, by decreasing the quality and extent of suitable feeding and nesting habitat. Let’s examine each of these key dangers in more detail.
Habitat loss
Habitat loss occurs when feeding or breeding areas are physically destroyed, for example through land claim for development, aggregate extraction or construction of coastal defences. Habitat degradation, whereby the quality of areas is reduced, poses an equally serious threat.
In the winter, habitat loss affects oystercatchers reliant on coastal feeding grounds like mussel beds and mudflats. For example, the expansion of commercial mussel aquaculture has eliminated some wild mussel stocks.
During the breeding season, which oystercatchers spend inland, threats include destruction or degradation of nesting habitat through factors like agricultural intensification and drainage of wet grasslands.
Disturbance
Oystercatchers are sensitive to human disturbance, which causes them to stop feeding or abandon nests. Disturbance can come from activities like dog walking, recreational water sports and bait digging.
Coastal disturbance is a particular issue in winter, especially on heavily used beaches. Inland, farm operations and access can disturb breeding birds. One UK study found that disturbed oystercatcher nests were over three times more likely to fail than undisturbed nests.
Predation
Natural predation obviously poses a risk to oystercatchers. However, changes linked to human activities may have increased predation rates.
For example, relatively new predators like American mink have spread through the UK after escaping from fur farms. High corvid numbers benefit from human scraps and may increase egg predation.
Predator control measures can help reduce losses, but may be controversial.
Pollution
Pollution can affect oystercatchers directly through toxins, or indirectly by reducing prey abundance and quality. Oil spills are an obvious threat, especially when oystercatchers congregate in large groups in winter.
Toxic algal blooms linked to fertiliser runoff increasingly affect shellfish populations, potentially reducing food for oystercatchers. Heavy metal and plastic pollution may also impact shorebirds.
Extreme weather
Climate change models predict increases in the frequency and severity of extreme weather. Storm surges can cause direct mortality of coastal oystercatchers, while heavy rain can flood nests inland.
Prolonged cold weather can also reduce survival by making it harder for birds to meet their high energy requirements. Snow cover may restrict access to food.
Reduced food availability
Food shortages seem unlikely to affect oystercatchers, which are adaptable and exploit a wide range of prey. However, some human impacts have reduced populations of favoured foods.
Overfishing has depleted stocks of species like cockles, while pollution and disease have harmed mussel numbers in places. Loss of favourable feeding habitat also restricts access to preferred prey.
Which is the biggest threat to oystercatchers?
All of these dangers have the potential to negatively impact oystercatcher populations. However, habitat loss is arguably the most serious and overarching threat facing these shorebirds today.
Evidence that habitat loss is the primary threat
Several strands of evidence support habitat loss and degradation as the biggest danger:
- Breeding surveys show declines are greatest in areas with most habitat destruction.
- Areas with reduced habitat quality hold lower oystercatcher densities.
- Habitat creation schemes have increased numbers locally.
- Climated change models predict accelerating habitat loss.
In one long-term UK study area, increasing land claim for industry and housing destroyed 20% of saltmarsh feeding grounds over 30 years. Over the same period, the oystercatcher population declined by 48%.
This habitat loss removes essential feeding and breeding sites. But it also exacerbates other threats like disturbance, predation and food shortages by squeezing oystercatchers into smaller sites.
Even if alternative feeding areas exist, the additional competition in these spaces may reduce survival and fitness.
Habitat conservation is vital
Stemming habitat loss is a conservation priority. Protecting remaining high quality areas of intertidal flats, saltmarsh and wet grassland is vital.
Habitat creation schemes can increase the extent of feeding and breeding habitat. For example, managed realignment of seawalls allows saltmarsh regeneration in coastal sites prone to flooding.
Restoring degraded areas, like removing scrub from grasslands, can also enhance habitat quality for oystercatchers. Careful planning of industrial/housing developments helps minimise impacts.
Conclusion
Habitat loss currently appears the most severe threat to oystercatchers across their UK range. Conservation efforts aimed at protecting and expanding habitat are crucial to allow populations to recover from past declines.
Tackling other threats like pollution and disturbance remain important. But stemming habitat loss is key. Unlike factors like weather or predation, habitat conservation is something we can directly control and manage.
Targeted habitat protection and restoration schemes offer real hope that oystercatcher numbers could increase again, retaining these special shorebirds as a familiar sight and sound along our coasts.