Swallow

Overall vulnerability

Feature assessed:

• Swallow (Hirundo rustica)

Special qualities:

• Internationally important and locally distinctive wildlife and habitats

Feature description:

Swallows are common summer migrants to the PDNP and the rest of the UK. Overwintering in Africa, swallows return to the UK to breed in spring and early summer. Agile flyers, they take insects on the wing and can be confused with other summer visitors, including related martins and the unrelated swift. However, with a good view swallows are easily distinguished by their characteristic red throat patch and long forked tail. Common birds on farmland, they are mostly found on meadows and pasture in the PDNP, and can often be found nesting in the eaves of nearby buildings. While they are still common in the UK, they have suffered losses in some parts of the country. As a charismatic farmland bird associated with summer, they are a favourite of many around the PDNP.

How vulnerable are swallows?

Swallows in the PDNP have been rated ‘moderate’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, but with a reasonable current condition and a high adaptive capacity.

PDNP swallow populations appear to be faring well despite some recent losses. Drier conditions restricting nest building are likely to be leading stressors on future swallow populations. Changes to their wintering grounds may also have strong effects that are more difficult to address. Despite their low conservation priority and restricted funding and support, swallows have shown themselves to be very adaptable birds, already showing some adaptation to climate change.

Current condition:

Swallows are common across the UK, with the population showing a slight increase since the 1990s. However, this trend varies by area. In the PDNP, swallow populations peaked around 2014 and have declined since, but are still higher than they were in the 1990s. Swallows may already be responding to climate change in their phenology, with migration dates advancing by 15 days and breeding by 11 days across the UK since the 1960s.

Swallows suffer from parasites such as mites and lice, especially in those individuals with low immune responses. Parasite infection reduces tail length, and so longer tailed males and their offspring tend to be more resistant to parasites. Swallows have few natural predators, but some birds of prey such as hobbies and sparrowhawks are able to take them on the wing. Swallows are strongly linked to human development, with older buildings providing many of their nesting sites, and agricultural land providing most of their current habitat. They are therefore strongly linked to changes in human land use. Fewer available open spaces in newer buildings and loss of some older buildings have reduced nesting opportunities. The type of agricultural land is also important: Pastureland is better habitat than arable, and cow pasture is better than sheep. As such, the move towards sheep farming in the UK has probably been detrimental to swallows. Pesticide use on agricultural land is also thought to have played a large role in swallow decline. Worming agents and antibiotics in livestock are a particular problem as they reduce larvae populations in dung, thereby lowering flying insect abundance and reducing food availability for swallows significantly.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Drier conditions during summer are likely to have a detrimental effect on swallow nesting. Loss of some drinking resources, especially in the White Peak where surface water is already rare, would increase swallow dehydration and hyperthermia. Drier ground conditions could also mean fewer areas of soft ground and mud required to build nests. This may result in smaller nests of lower quality, leading to reduced clutch sizes and egg and nestling losses from fallen nests. Data Certainty: High

An increase in extreme and unpredictable weather events may reduce swallow survival and breeding success. Swallows require fair weather conditions as their insect prey will not fly in adverse weather. Late cold snaps and snowfall during or just after swallow arrival will likely have the greatest effect, as swallow condition is already poor from migration. More frequent and severe summer storm events could cause reduced survival, as both swallows and their prey are unlikely to fly. Similarly, extended summer drought periods would reduce insect prey populations and therefore swallows. Data Certainty: Moderate

Sea level rise may have a detrimental effect on PDNP swallows on migration. Swallows gather to roost in UK wetlands before migrating south. Sea level rise is likely to remove some of this habitat and reduce the suitability of that remaining through saltification and increased competition. The loss of these habitats and their associated food supply would result in poorer swallow condition before migration, causing greater migration mortality. Data Certainty: Low

Higher temperatures earlier in the year will continue to advance swallow migration dates. Swallows have already begun to adjust to their migration dates more than other migrants do, and so may adjust well to future changes. As leaf bud burst and insect population maximums are advancing with climate change, any phenological mismatch will likely be minimal, especially compared to other less flexible migrants. More time in the UK would also allow more swallow broods in one year and a greater time between broods, potentially increasing breeding success. However, male and female arrival dates are already beginning to diverge, with males arriving a week earlier than females. This may limit the ability of swallows to advance their nesting date, as the females appear to be less adaptable in migration timings. Data Certainty: High

Increased average annual temperatures may have positive effects for swallows. Warm conditions will likely mean reduced thermoregulatory costs for both adults and nestlings, increasing survival. Nest sites are also more likely to be outdoors, meaning swallows could become less dependent on buildings and other man-made sites. Warmer conditions during the breeding season may increase the flight activity of their insect prey, resulting in greater food availability. This is particularly important as female swallows form eggs from their daily diet rather than fat reserves. Therefore, food availability has a direct link to clutch size and egg quality. However, this effect could be reversed, as drier conditions may eventually result in reduced insect populations. Higher temperatures also result in increased insect flight agility, potentially increasing the difficulty of swallow foraging. This may lead to adaptation in the form of shorter tail length, as has been seen in Spanish swallow populations. Data Certainty: Moderate

Other indirect climate change impacts

Changes to their African wintering grounds pose a significant threat. Altered precipitation patterns are likely to have the largest effect, as swallow winter survival is strongly correlated with high rainfall on wintering grounds. Predicted rainfall change is variable across the wintering grounds and so swallow populations may be affected differentially. Those birds that migrate overland are more likely to be negatively affected, as drought is more likely inland. Desertification could also create a barrier to migration as the Sahara and Kalahari expand. Those that take a coastal route will probably be better off. As some wintering grounds become less suitable, the competition at those remaining will also increase. An increase in frequency and severity of storms would also be damaging to swallows, especially during migration. Overall, it is likely that swallow migration fitness will be reduced, increasing migration fatalities and reducing breeding success. Data Certainty: High

Invasive or other species interactions

Increased average annual temperatures and drier conditions may result in greater parasite and disease prevalence. Swallows often carry parasites with few effects, but are more susceptible when in poor condition. Parasite and disease spread is increased during migration, when swallows travel in large, close groups. As swallows may already be stressed by changing conditions and extreme weather events, increased parasite load may exacerbate their poor condition and cause increased mortality. Data Certainty: Moderate

Nutrient changes or environmental contamination

Increased annual average temperatures may lead to increased agricultural pest populations. Pesticide usage may increase to counter this effect, particularly on new arable land. This would lead to a subsequent reduction in insect prey availability for swallows foraging on agricultural land. Swallows would therefore spend more time foraging and be in poorer condition. Pesticides may also bio-accumulate in swallows, causing a direct reduction in condition and breeding success. Data Certainty: Moderate

Human behaviour change

Hotter drier summers may result in changes to agricultural practices in the PDNP. As most PDNP swallow habitat is pastureland, these changes could be damaging to swallow populations. Abandonment of some drier sites could be detrimental as scrub and woodland is poor swallow habitat. Loss of hay meadows to pasture or abandonment or conversion to arable could also reduce swallow populations, as meadow insect populations are higher than most agricultural land. Data Certainty: Moderate

What is the adaptive capacity of swallows?

Overall adaptive capacity rating

Swallows have few barriers to movement and dispersal. A highly aerial species, they are able to travel large distances and so can easily disperse and colonise new areas. This is evidenced by their large range throughout the UK and further south in Europe. The PDNP is well within swallow climatic envelope with much suitable habitat, and so swallows are unlikely to move out of the PDNP boundary. Data Certainty: High

Swallows are a very adaptable bird. Their large population and ability to breed several times a year allows a good capacity to recover from bad conditions in the previous year. Swallows feed on a variety of aerial insects as well as some terrestrial, and so can adapt to some changes in prey abundance by utilising other prey species. Swallows have already shown adaptive ability in their response to climate change, with Spanish populations exhibiting reduced tail length and UK populations advancing in migration and egg laying date. Data Certainty: High

Some funding is available for swallow conservation, but this is limited as they are not a conservation priority. Swallow populations may benefit from environmental land management schemes on pastureland, as insect populations increase with better management. Data Certainty: Moderate

Some institutional support exists for swallows. Some swallow habitat will be protected by Site of Special Scientific Interest (SSSI) designation in the PNDP, but swallows are not a cited feature of these. Swallow nests have legal protection when active under the Wildlife and Countryside Act. As they are a green listed species in the UK, swallows are seen as low conservation priority. Data Certainty: High

Swallows are generally well researched worldwide as a migratory species with a large range. Extensive monitoring of UK migration patterns is ongoing and will enable management decisions to be well informed. Data Certainty: Moderate

Key adaptation recommendations for swallows:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Reduced pesticide input to livestock on pastureland. This would increase populations of swallows and other birds, as well as associated soil health benefits.
• Transition lowland pasture in the White Peak from sheep to suckler cattle, to improve insect populations.
• Ensure planning decisions leave some swallow nesting space in buildings by allowing access. Platforms with bags to catch droppings can be built. Only a small access hole is required.
• Increase potential for swallow nests in new and restored buildings, with particular consideration for agricultural buildings.
• A whole range approach, with partnership with organisations in their African wintering grounds would be needed to maximise swallow adaptive capacity.
• Encourage further uptake of environmental land management schemes by farmers within the PDNP.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Better knowledge and monitoring of PDNP swallow populations would help understand whether they are declining, and where action is needed.
• A review of planning applications where swallows have been a considering factor would increase understanding of where action has been done or is needed.