Research shows climate change is having a significant impact on the UK’s birds

RSPB report says climate change is having an impact on migration patterns, breeding habits, and the distribution of species

Climate change is also thought to be one of the main causes of seabird declines

January 10th 2018

The RSPB has published a report on the state of the UK’s birds which features a particular focus on the impact of climate change. [1] The report was produced jointly by the RSPB, the British Trust for Ornithology, the Wildfowl & Wetlands Trust, and the UK’s statutory bodies for nature conservation in England, Wales, Scotland and Northern Ireland. Much of the data on particular species, showing increases or decreases in bird populations over recent decades, was released by the UK Government last November via the Department for the Environment, Food & Rural Affairs (Defra) and discussed in last month’s article – see ‘Defra releases latest statistics on the UK’s wild bird populations’.

The RSPB report however includes a special feature on the impact of climate change on the UK’s birds, which brings together the results of various research studies. The report summarises recent trends as regards climate change and highlights the ways in which these trends are already having an impact on the UK’s bird populations. Looking ahead, it also discusses the potential impacts of climate change if recent trends continue as predicted, including a number of case studies. It then makes an argument for building ecological resistance to those impacts and presents ways of helping species to adapt. In summary, the report says that climate change will provide some species with opportunities, while others could be threatened with extinction as a breeding bird in the UK.

Climate Change: Recent Trends

The report says that climate change has been assessed as the second-largest driver in the UK of observed changes in wildlife populations, second only to the intensification of agriculture which has been the main cause of wildlife decline. As regards recent trends, the report cites research by the Met Office and evidence from the last climate change risk assessment produced by the Adaptation Sub-Committee of the UK Government’s Committee on Climate Change. The figures show that 8 of the 10 warmest years on record in the UK have occurred since 1990, with average UK temperatures increasing by almost 1°C since the 1980s. Sea surface temperatures have also increased, with 9 of the 10 warmest years for UK seas having occurred since 1989. Heavy rainfall events during winter have contributed to a slight increase in rainfall across the UK, with Scotland’s average rainfall 11% higher in the ten-year period from 2007 to 2016 than in the twenty-year period from 1961 to 1990. UK sea levels rose by 14cm in the last century and the rate is increasing.

These trend are expected to continue. Current projections are for rising temperatures, wetter winters, drier summers, and an increase in the frequency and intensity of extreme weather events, such as heatwaves, droughts, heavy rain and floods. Scientists have forecast that mean summer temperatures could rise by 5°C in many parts of the UK by 2050, while mean winter rainfall could increase by 10% or more, possibly by as much as 50%. In short, we can expect winters to be wetter while summers will be drier and warmer.

The UK’s resident birds have benefited from milder winters

The changes in climate that have already taken place have had a noticeable impact on the UK’s bird populations. The report cites research which shows that trends in temperature and rainfall over the past 30 years have had an impact on the increase or decrease in numbers of specific species, on the distribution of species, and on the timing of natural events such as migration and breeding. The authors state: “Since the early 1990s, birds in the UK, and Europe as a whole, have shown changes in numbers and distribution consistent with a warming climate.”

In last month’s article, we looked in some detail at bird population increases and decreases. To what extent are these changes an effect of climate change? The report says that many resident species have shown long-term increases in abundance which have been linked to increases in winter and spring temperatures, with milder winters boosting the chances of survival. Research cited in the report has found that fluctuations in the population trends of one of the UK’s largest breeding birds, the grey heron, and one of the smallest, the wren, are closely related to annual variations in mean winter temperatures. Another study has found that long periods of cold days with continuous frost reduce wren survival rates, which can be halved by more than 10 consecutive days of frost. [2]

However, the report’s authors go on to say that both the grey heron and the wren have shown increasing trends due to less severe winters. This is not entirely accurate, as Defra’s statistics show that the grey heron has in fact suffered a long-term decline of 17% over a 40-year period (1975 to 2015), whilst the figures produced in the RSPB report show a 5% decline in the long-term and a 17% decline in the short-term. Elsewhere in the report, the great tit, robin, nuthatch, treecreeper and dunnock are also cited as examples of species whose numbers have increased in the long-term due to increases in winter and spring temperatures. This is not entirely accurate either as Defra’s statistics, reproduced in the RSPB report, show long-term declines for the treecreeper and dunnock. [3]

The wren, great tit, robin and nuthatch do however show long-term increases, together with a number of other resident species which appear to be benefiting from milder winters. [4] These increases vary across the UK. The report says: “Country-specific trends for great tits and wrens show that increases have been greatest in Northern Ireland, followed by Scotland, with no significant difference between England and Wales. These patterns are likely to be caused by overall population increases and improving climatic conditions in the north and west.” The report says a number of summer migrants are also faring better in Scotland compared to the rest of the UK, such as the willow warbler, tree pipit, house martin and cuckoo – the cuckoo has seen a 33% increase in Scotland in the 1995 to 2015 period but has declined elsewhere in the UK.

“Go forth and multiply”

As well as regional variations in species increases, research has shown that the overall distributions of bird populations have changed, with climate change being the most likely cause. In short, species have expanded their territories northwards and westwards, and also to higher altitudes where suitable habitats can be found. A comparison of population distributions over a twenty-year period, comparing a bird atlas of 1991 with a bird atlas of 2011, shows an average shift of about 13km to the north and west for some species more generally found in the south, including the goldfinch and the nuthatch, and also summer migrants such as the chiffchaff and blackcap. The report says “both blackcaps and chiffchaffs are expanding their breeding range northwards and into higher altitudes as the climatic conditions become more favourable.” Milder winters in the UK and in Europe have helped to boost their chances of survival, and the report says that increasing numbers of both species now stay in the UK for the winter, though the report also says that other drivers (such as the availability of food and habitat) may also be playing a part in these changes.

Previously scarce species have expanded their range

Changes in distribution have been noted not only for common and widespread species, residents and visitors alike, but for some species that used to be scarce in the UK, such as the Cetti’s warbler, which takes its name from the eighteenth-century Italian zoologist Francesco Cetti. The RSPB says that the Cetti’s warbler bred initially in Kent in 1972, and its preferred habitat is damp areas close to wetlands. The Cetti’s warbler colonised the south-east of the UK in the 1970s, but the report says that the Cetti’s warbler has subsequently expanded its range and now has the core of its distribution in the south-west. Although its numbers were dramatically reduced by the cold winters of 2009/2010 and 2010/2011, the species has since recovered and it continues to increase in numbers and expand its range. The report says that “the arrival and subsequent population expansion of Cetti’s warblers breeding in the UK since 1973 is seen as an example of the northward shift in distribution of some species as a result of climate change.”

The report includes a case study of the Dartford warbler, which used to be the UK’s only resident warbler and was found only in small numbers in the south of England. The authors say that the Dartford warbler is vulnerable to severe winter weather, and its numbers in the UK “may have declined to a low of 11 pairs in 1963 following two very cold winters.” Milder winters have subsequently produced a population increase, with research recording more than 2,500 pairs in 2006. Milder winters are also thought to be the cause of a wider distribution. The Dartford warbler has expanded its range by moving into suitable habitat at higher altitudes and by spreading into more northerly areas including Derbyshire and Suffolk, compared to its southern base in Dorset and Hampshire. Like the Cetti’s warbler however, its numbers have fluctuated due to its vulnerability to cold winters. The report says that the UK’s population of Dartford warblers could become increasingly important in a European context as its numbers are declining severely in France and Spain, and much of its territory in southern Europe may become unsuitable given the projected impact of climate change.

Changes in distribution are having an impact on bird communities

Some of the UK’s birds are generally more prevalent in the south (such as the two warblers mentioned above), while some are generally more prevalent in the north of the UK. Thus some species have a northern margin to their range while some have a southern margin. With this northward expansion and rising numbers, does this mean that some species are now generally more widespread, or are they simply moving further north and leaving their former territories behind?

The research cited in the report suggests that what is happening is in fact a northern shift, but the loss of territory on the southern margin is happening at a slower rate than the gain of territory in the north, which has resulted in a more widespread distribution. The report says that for a number of resident species, “expansion at the northern edges of their ranges, where suitability is increasing, has been more rapid than the rate of loss at the southern range margins, where suitability is declining.” This has produced an overall expansion of the ranges of some species at a rate in excess of 1km per year. One piece of research has found that “southerly-distributed species, resident species and habitat generalists are increasing relative to northern or upland species, long-distance migrants and habitat specialists,” while another study has found that, across Europe, “warm-associated species are becoming more common relative to cold-associated species”. Looking ahead to the future impact of climate change, research suggests that “there are more southern species with potential for northward expansion in the UK than there are northern species predicted to contract, and observations suggest this is already happening.”

These changes in distribution have led to changes in the composition of bird communities, with research showing that bird communities are becoming more similar to each other. The regional variations in populations trends, and the timing of important events such as breeding and migration, have also led to these changes in the composition of bird communities. The report says that this can affect species interactions, “such as predator-prey relationships and competition,” which in turn can drive further population change.

Research has also investigated the potential impact of climate change on the UK’s rare breeding birds, with the trend for a northern shift in distribution meaning that some rare species could disappear completely. The report says that these birds often occur at the edge of their breeding ranges: “Species currently only found to the south of the UK are projected to shift north and east, and to higher elevations as the climate there becomes more suitable. Conversely, those birds which have their southern, ‘trailing’ range edge within the UK are likely to decline as that edge moves north, or even moves out of the UK altogether.” Because of the impact of climate change, the report says most of these species have been assessed as having a high potential for extinction as a breeding bird in the UK, “as the projected shifts in suitable climatic conditions mean that the UK will become less suitable.” In the case of the purple sandpiper, whimbrel, dotterel, common scoter, capercaillie, Arctic skua and Slavonian grebe, “the effect is likely to be more detrimental as their UK populations are already in decline.”

The early bird catches the worm?

Climate change is not only having an impact on the numbers and the locations of the UK’s birds, but is also having an impact on the timing of natural events such as migration and breeding. The report cites research which has found that a number of common migrants are now arriving in the UK earlier than they used to, and also laying eggs earlier, “with the result that swallows, for example, are arriving in the UK 15 days earlier and breeding 11 days earlier than they did in the 1960s.” Some species are also delaying their departure, including blackcaps, chiffchaffs and garden warblers, which means that some migratory species are now staying longer in the UK as a result of their earlier arrival and later departure. The report says that sand martins and whitethroats, for instance, now spend around two weeks longer in the UK than in the 1960s, while garden warblers spend four weeks longer.

Research has found that “species that have extended their stay in the UK show more positive trends in abundance over the period studied (1960 to 2010), compared to species that have not altered their timing of migration, for example cuckoos and turtle doves.” However, the report also says that “timings vary annually in relation to spring temperatures and conditions on migration.” For instance, surveys published by the British Trust for Ornithology found that blackcaps and chiffchaffs bred significantly later in 2016 than they have in recent years, which is thought to be the result of lower April temperatures.

The report says that the great tit is one of a number of species, “including swallows, chiffchaffs and willow warblers,” that now breed earlier compared to the past, with great tits now laying their eggs on average 11 days earlier than they did in 1968. With these advances in egg-laying however, there is the potential for a mismatch between the timings of the peak food demands of breeding birds and peak food availability, as the timings of events vary between birds, plants and insects. Research has found that “across a wide range of species of plants and insects, timing has advanced on average by about four days for a 1°C increase in temperature, compared to birds which have advanced by an average of two days.”

Food availability and breeding success: Winners and losers?

Is this mismatch having an impact on breeding success? The report says that the mismatch between breeding and food availability has been studied in detail only for a few species, and has not been directly linked to reductions in breeding success or large-scale population decline in the UK. The authors say that changes in the abundance of insect prey populations may be more important.

However, one study has concluded that the impact of climate change on bird populations is most severe for long-distance migrants because of this mismatch during the breeding season, leading to a potential reduction in breeding success and subsequent population decline, as in the case of the pied flycatcher in the Netherlands. Another study suggests that climate change may explain the decline of the UK’s ring ouzels, as “long-distance migrants may suffer negative consequences from warmer, drier conditions during the spring and summer potentially influencing food availability and abundance”. The report says that the tree pipit (another long-distance migrant) may also be vulnerable to changes in the timing of insect availability. This negative outlook for long-distance migrants is counterbalanced however by the research mentioned above, which has found that migrants who stay longer in the UK are more successful at breeding.

Warmer and drier conditions during spring and summer may have negative consequences for some bird species, but these conditions can also have positive consequences for others. The report says that warmer temperatures during the breeding season have been shown to have a positive effect on breeding success for a range of species:

“For example, birds that feed insects to their young, such as great tits and chaffinches, have improved productivity in warm, dry springs, probably mediated by increased prey abundance and good foraging conditions. Further evidence comes from numerous studies which show positive effects of temperature on chick growth and productivity in waders and other ground-nesting species with mobile young (for example, golden plover, common sandpiper and corncrake).”

Despite these positive effects however, all three species (golden plover, common sandpiper and corncrake) have declined in the long term, along with several of the UK’s breeding waders and farmland birds. [5]

The impact of extreme weather

As mentioned above, research has shown that trends in temperature and rainfall over the past 30 years have had an impact on bird population fluctuations. The RSPB report says that “changes to patterns of rainfall and temperature can have diverse effects on a population’s breeding success.” Can we conclude therefore that it is climate change that is causing a bird population to rise or fall? This is a challenge for researchers, as the report states:

“Identifying whether observed changes are caused by climate change remains a challenge, and the subject of a range of studies, analyses and modelling approaches. Conversely, there remains much to understand about the importance of extreme weather events in driving population change, and the impact of increasing severity and frequency of such events on species survival and breeding success.”

Current projections on climate change predict an increase in the frequency and intensity of extreme weather events, as mentioned above. These projections also predict milder and wetter winters, and warmer and drier summers. In the last decade however, the UK has experienced extreme weather events at various times throughout the year, which means that winters can also be extremely cold (such as the long cold spell of 2010/2011), while spring and summer can also be extremely wet. The RSPB report says that “over the last decade, wetter June weather has become more frequent, in line with expected climate change.” This can have an impact on the breeding success of the UK’s birds.

For instance, the Met Office reported that the spring of 2012 was the wettest April to June period on record. Grahame Madge, a press officer for the RSPB and also the Met Office, said this was having an impact on ground-nesting waders. “Flooding at several key sites has seen hundreds of wader nests washed out,” he said, “including 600 at the RSPB’s Ouse Washes reserve in Cambridgeshire.” [6] A report by the British Trust for Ornithology on the 2011 Breeding Bird Survey suggested that unfavourable weather conditions was exacerbating the long-term decline of the UK’s breeding waders, such as the lapwing and curlew. [7]

On the other hand, a period of drought can also have an impact on the breeding success of the UK’s waders. The RSPB report says that the drying of soils on their breeding grounds, “which is already a problem due to the drainage of lowland meadows and upland bogs, may be exacerbated by climate change. Wetter areas are important sources of insects which breeding waders, such as curlews and golden plovers, feed to their young.” The report includes a case study of the golden plover, whose numbers were down by 20% in 2015 compared to 1970. The authors of the study warn that golden plover populations could decline further as warmer, drier summers and periods of drought have an impact on cranefly populations, which are essential food in the breeding season. The report states:

“Golden plovers breeding in the UK uplands are among the most southerly populations in their global range. Golden plovers rely on cranefly larvae (also known as leatherjackets) for food, which are highly sensitive to drought, and high temperatures in August reduce the abundance of craneflies the following year. This means that climate change could limit the birds’ food supply, reducing chick survival and overall breeding success.”

The report says that, overall, golden plovers have been assessed as having a high risk of climate-related decline. A study of golden plover populations in the Peak District has concluded that improvements in winter survival are likely to be outweighed by the reductions in breeding success as cranefly populations decline. As for the curlew, its population is projected to fall by 50% over the period 1997 to 2080 under a medium climate change scenario. And, as mentioned above, other waders that breed in upland areas, such as dotterels, purple sandpipers and whimbrels, are considered to be at a high risk of extinction as a breeding bird in the UK due to habitat changes and reduced food availability.

However, the report says that habitat management could help upland birds such as the golden plover to be more resilient to climate change. It cites research on how to maintain peatland ecosystems in a changing climate:

“Throughout the 20th century, many UK upland peatlands were drained to improve agriculture, but this exacerbates cranefly declines and has further impacts on ecosystem functioning. Experimental examination of three drained peatlands has shown that blocking drains as part of restoration programmes leads to wetter peat and higher cranefly abundances. Blocking drainage ditches therefore provides more food for golden plovers in drained peatlands, aiding populations in a climate that is changing to drier summers.”

Another study has found that “re-wetting” peatlands can achieve similar benefits for ecosystems, which include not only an increase in cranefly abundances, but also improvements in water quality and carbon storage together with reductions in flood risk. The RSPB report says that such benefits are already being realised through landscape-scale restoration projects; for instance, the Sustainable Catchment Management Programme, which is a partnership between United Utilities, the RSPB, local farmers, “and a wide range of other stakeholders.” The programme was designed to ensure the sustainable environmental management of 20,000 hectares of a water catchment area owned by United Utilities and situated in the Peak District and the Forest of Bowland. [8] Other studies have identified further actions that would help golden plovers. These land management measures, not related to climate change, include “the legal control of generalist predators, the removal of conifer plantations in inappropriate areas, the re-profiling of forest edges around protected areas, and the provision of suitable feeding conditions through vegetation management.”

As a further example of the impact of temperature and rainfall, the report cites research on the Slavonian grebe. In this case, it is rainfall rather than drought that is known to cause problems. A study has found that “Slavonian grebes in Scotland had higher breeding success when temperatures were higher during chick rearing, but periods of particularly heavy rainfall during the breeding season led to smaller populations.” Another study concludes that the breeding success of some raptors and grouse species can also be very sensitive to rainfall during chick rearing. The report says that cold and wet weather conditions over a number of breeding seasons may be a factor in the decline of the hen harrier population, which is on the brink of extinction as a breeding bird in the UK. However, a national survey of the hen harrier in 2016 identified the main factor limiting its numbers as “the illegal killing of birds associated with driven grouse moor management in northern England and parts of mainland Scotland.”

The report also cites a national survey of the capercaillie carried out in 2015/2016. The authors say that the breeding success of the capercaillie is “known to be adversely affected by high rainfall in June when the chicks hatch, and by delayed warming in spring. Understanding how rainfall affects breeding success, and how patterns of rainfall might change in the future, will be important in assessing the vulnerability of the population to climate change and the relative importance of other drivers.”

Climate change and seabird decline

As we have seen, changes in the timing of migration and breeding, as well as changes in distribution, have been linked to rising temperatures, and indicate how the UK’s birds are changing their habits in response to a changing climate. The RSPB report says that, as the climate changes, the ability to adapt to a changing environment will be essential in enabling bird populations to persist. However, it points out that the ability to adapt varies between species. This is apparent in the case of the UK’s seabird populations, with some coping better than others.

Three seabird species have suffered a marked decline since the beginning of the seabird index in 1986: Arctic skua by 80%, black-legged kittiwake by 62%, and the European shag by 48%. [9] These declines, and those of other seabirds, are partly the result of reduced breeding success, which has been associated with warming seas and changes to food abundance and availability. During the breeding season, kittiwakes and shags are heavily reliant on sandeels, and declines in sandeel abundance are thought to be having an impact on their productivity. Declines in sandeels may also be a factor in the decline of the Arctic skua. The report says that the overall decline of the UK’s breeding seabirds is a particular cause for concern, with climate change being a major contributory factor:

“Climate change is considered to be one of the primary causes of seabird declines, through indirect effects via changes in prey availability and abundance, and through direct effects such as increased mortality from the increasing frequency and intensity of extreme weather events. These processes will interact with current drivers such as unsustainable fisheries, pollutants, marine renewables and disease. Overall negative relationships between temperature and the productivity of seabirds have been shown for kittiwakes, fulmars and puffins, as well as common, Arctic and little terns.”

The report includes a case study of the UK’s kittiwake population, which has declined as a result of “both falling breeding success and adult survival.” Kittiwakes tend to feed off the sea surface, and research has shown that their reliance on sandeels during the breeding season means that they could be affected in two ways: firstly, through a reduction in the availability of sandeels caused by industrial fishing in the North Sea; and secondly, through changing ocean conditions caused by rising sea temperatures. [10] Pulling together research on this subject, the report explains:

“Rising sea surface temperature has changed the plankton community on which sandeels rely. In addition, rising temperature is also changing the process of stratification – the relationship between sea temperature and salinity, which creates density differences between deep and shallow waters. Earlier or stronger stratification can ultimately reduce food availability for kittiwakes and the species’ breeding success has been found to be lower in areas where this has occurred. Based on these relationships, projections for the late twenty-first century suggest that the breeding success of the 11 northern UK colonies studied could fall by up to 43%.”

The decline of the shag population has also been linked to reduced breeding success and the availability of sandeels, but the report also says changes in weather patterns may be having an impact as a shag’s plumage is only partially waterproof, “perhaps making them more susceptible to mortality during prolonged periods of wet and windy weather.” The report states:

“Stormy weather may also lead to shag starvation through reduced foraging success, probably due to increased water turbidity. Such weather patterns are predicted to increase with climate change. Severe events in the winters of 1993/94, 2004/05 and 2012/13 caused large numbers of birds to die (known as a “wreck”) and affected the population considerably. Breeding numbers were not fully recovered following the wreck of 1993/94 when the storms of 2004/05 hit and no recovery was apparent before 2012/13. The population was at its lowest yet recorded in 2013, and by 2015 had only improved marginally.”

In our article on the wild bird statistics released by Defra, we reported that five of the thirteen species in the seabird index have increased since the beginning of the index in 1986: razorbill by 58%; common guillemot by 57%; Arctic tern by 39%; sandwich tern by 5%; and great black-backed gull by 7%. The black-headed gull population (included in the ‘other’ index) has also increased by 16%. Figures produced in the RSPB report from the Seabird Monitoring Programme include figures for the gannet and the great skua, which also show a long-term increase in the 1986 to 2015 period, and figures for the roseate tern, which show a long-term decline but a short-term increase (2015 compared to 2000). [11] This raises the question: why are several seabird species in decline in the UK, while a number of other species show long-term increases?

The report says the reason for these long-term increases is that these species are more flexible in their food sources, foraging strategy, and breeding habits, “which may be allowing these species to thrive while others are failing”:

“A trait that many of these species share is a lack of specialisation in their preferred food types. When sandeel abundance is low, guillemots can switch from their preferred sandeel diet to sprat, young gadids (species in the cod family), pipefish or even squid when feeding chicks. Both black-headed gulls and gannets have a varied diet, with the former feeding on multiple species of crustaceans and molluscs, and the latter on varying species and sizes of fish. As these species are increasing when more specialised feeders are in decline, it appears that being flexible with food may mitigate the effects of climate change.

However, the report says that fulmars appear to be an exception to this apparent pattern. Although fulmars “have long foraging ranges and are not particularly specialised in their feeding habits,” the species has seen a long-term decline in numbers since 1986 (a fall of 22% according to Defra’s statistics, and 33% according to the RSPB’s figures). [12] The report says that, although correlations have been observed between North Atlantic climate variation and both fulmar adult survival and breeding success, the specific driver for this decline is unclear.

Looking ahead, the report says that habitat suitability for seabirds around the UK is projected to shift northward over the next century, and the distribution of species may shift with changing conditions. In the case of the Arctic skua, models of the likely impact of climate change predict that this bird could become extinct in the UK by 2100.

Climate change and the UK’s wintering waterbirds

According to Defra’s statistics, the number of waterbirds that migrate to the UK for the winter has seen a 92% increase overall when 2014/15 figures are compared to 1975/76, as we reported in our last article. However, this increase peaked in the late 1990s and has subsequently declined. The UK’s wintering waterbird populations can be impacted by several factors, which include breeding success or failure in the countries where they breed, the availability of suitable habitat in the UK, and changes in migratory patterns, “at least some of which are known to have been affected by climatic changes.” [13]

The RSPB report says that climate change is already having an impact on the abundance and distribution of the UK’s wintering waterbirds, with projections indicating that temperature and habitat changes could have a significant impact on numbers in the future. The report highlights two main reasons for the decline: firstly, reduced productivity in the breeding season may be limiting the numbers of some winter migrants; and secondly, milder winters on the continent mean that fewer birds need to migrate to the UK to avoid colder conditions. On the first, research on the future impact of climate change predicts that the breeding ranges of Arctic and sub-Arctic species that winter in the UK could be reduced by 50% by the end of the century, which may cause further declines due to reduced productivity.

Wintering Waterbirds: Changes in migratory patterns and distribution

However, the RSPB report says that in many cases the decline of the UK’s wintering waterbirds is explained by changes in distribution, linked to milder winters across the Continent, and particularly evident in the reduced use of sites along the UK’s east coast. The report cites research that has demonstrated a north-eastward shift in the range of some wintering waterbirds in north-west Europe, including the UK, associated with the trend for milder winters. For instance, a study of grey plovers and curlews wintering in north-west Europe has shown that their distribution had shifted nearly 120km to the north-east in the two decades between 1981 and 2000. On the other hand, the RSPB report says that in severe cold winters, such as the winter of 2010/11, the numbers of bar-tailed godwits visiting the UK were higher than in the mid-2000s, “probably because they were escaping cold conditions in north-west Europe.”

The importance of habitat for the UK’s resident and wintering waders

Wintering waterbirds receive a certain amount of protection across the UK through a wide range of sites that are designated as Special Protection Areas: “Special Protection Areas are strictly protected sites classified in accordance with Article 4 of the EC Birds Directive, which came into force in April 1979. They are classified for rare and vulnerable birds (as listed in Annex I of the Directive), and for regularly occurring migratory species.” [14] These protected areas span the length of the UK and include a wide range of locations frequented by wintering waterbirds, such as the Dee estuary, the Northumberland coast, the North Norfolk coast, the Humber estuary, the Mersey estuary, Portsmouth harbour, Morecambe Bay, a number of lochs in Scotland, and the Isles of Scilly. [15]

The RSPB report says it is likely that most of these areas will continue to support internationally important numbers of wintering waterbirds, despite changes in the distribution and abundance of populations due to climate change. It highlights the importance of these protected areas during particularly cold winters (such as the winters of 2009/10 and 2010/11), “when the trend for wintering further east was reversed, and numbers on UK sites were much higher.” The report also notes that many of the species that have recently colonised the UK, “or which appear to be on the verge of doing so,” are associated with wetlands, with most of these species first becoming established in these protected areas. The list of these colonists include night herons, cattle egrets, great white egrets, black-winged stilts, spoonbills and little bitterns, though the numbers of breeding pairs may be no more than a single figure. [16]

As well as wetlands, the RSPB report also highlights the importance of the non-estuarine coast for some species of waders wintering in the UK. For instance, the Northumberland coast is visited by purple sandpipers and turnstones who migrate from north-east Canada for the winter. The report says the majority of purple sandpipers, turnstones, ringed plovers and sanderlings present in midwinter are to be found on these non-estuarine coastal areas, and the species using these areas are “considered vulnerable to the impact of climate change and changes to invertebrate communities” (i.e. changes to the availability of food such as shellfish). For example, figures from the Breeding Bird Survey show a 23% decline in the resident oystercatcher population during the 1995 to 2015 period. Trends for wintering waterbirds produced by the British Trust for Ornithology also show declines in the oystercatcher population, both over a 25-year period (a 26% fall from 1989/90 to 2014/15) and over a 10-year period (a 15% fall from 2004/2005 to 2014/15). In terms of numbers, the oystercatcher is still second in the top ten of waterbird populations according to the Wetland Bird Survey, but internationally the oystercatcher is considered to be Near Threatened on the IUCN Global Red List. [17] The report says that “the sustainable management of shellfish fisheries and habitat protection is considered vital for the future conservation of this species.”

Trends for wintering waterbirds produced by the British Trust for Ornithology also show long-term and short-term declines in the numbers of ringed plover, turnstone, and purple sandpiper wintering in the UK. The RSPB report says that the possible explanations include shifts in distribution, as noted above, and declines in breeding productivity, both of which could be related to climate change. Local environmental factors, such as changing sewage treatment and disposal practices, may also play a role.

“Building ecological resistance”: Helping the UK’s breeding waders

To help species to be more resilient to the impact of climate change, both current and potential, the RSPB report advocates building ecological resistance. Building ecological resistance is one of the objectives in the UK Government’s National Adaptation Programme (see below) and encompasses various land management measures, such as the creation of new habitat and the restoration and sustainable management of existing habitat. The report says that land managers across the UK have been developing a range of such actions, “from coastal realignment to increasing micro-climate heterogeneity.” These schemes are aided by a growing body of research that has investigated various ways of helping species to cope with climate change. We have already seen how research has identified ways of helping golden plovers and other waders that breed in upland areas, including measures to offset the drying out of peatland areas that will help to increase the abundance of cranefly populations. The report also describes ways of helping lowland breeding waders during the breeding season:

“Lowland breeding waders such as lapwings, redshanks and black-tailed godwits require shallow pools and moist soil for foraging. Current measures to increase water availability in the face of lower rainfall and higher temperatures include storing water for the breeding season, and maintaining wet features by digging shallow channels. Conversely, for black-tailed godwits, existing breeding habitat in the UK is only found in wet meadows used for floodwater storage; in years with high levels of rain they have lower breeding success. To safeguard the population from increased flood risk, additional unflooded grassland is being created for those occasions when adjacent washlands are flooded.”

New wetlands for potential colonists and current species

Research on climate change adaptation has also investigated ways of helping the UK’s potential colonists. As mentioned above, many of the species that have colonised the UK in recent times are associated with wetlands. One study has said that many of these colonists require large areas of this type of habitat, and has suggested that large areas of new wetland will be required to encourage further colonisation. Coastal realignment schemes such as the Wallasea Island Wild Coast Project, described as “the largest coastal wetland to be constructed in the UK,” are cited as examples of what is required:

“The re-establishment of breeding by spoonbills, great white egrets and little bitterns in the UK has all occurred at large wetland expanses. However, there are very few large wetlands capable of supporting large breeding colonies of such waterbirds. Wetland habitat creation to benefit current species as well as potential colonists would therefore be best focused on providing a small number of very large wetland complexes in the vicinity of existing habitats.”

The RSPB report explains how a coastal realignment scheme can help our current species as well as potential colonists:

“Little terns and common terns nesting on low-lying coastal islands require sites to be raised using shingle as the sea level rises and sites become more vulnerable to storms. In managed realignment areas new nesting islands can be created. Island nesting sites are important because in many nesting areas, breeding success is reduced by high levels of disturbance and impacts of ground predators.”

Wallasea Island is situated in Essex, a few miles from Southend, and it is here in the south-east of England where most of the potential colonists from the Continent will first arrive, according to the research on climate change adaptation. However, the south-east of England is likely to experience “greater warming, more reduced rainfall, and the greatest level of human pressure.” Consequently, “future management of wetlands needs to take into account increased climate-related drying and increasing human demand for water in the region.” [18]

Heathland restoration

In addition to schemes that will help waterbirds, wetland birds and coastal species, residents and colonists alike, adaptation schemes have also been developed to help the UK’s heathland species, such as the Dartford warbler and the nightjar. The report says that these birds are characteristic species of lowland heathlands, and that “restoration and re-creation of these scarce and fragmented habitats to the north of the core area for these species will aid northward expansion.” Heathland restoration involves optimising the level of grazing, cutting and/or burning to maintain structure and condition, and managing fire risk, “which is projected to increase with warming temperatures and reduced rainfall.” The report also stresses the importance of protected areas for the Dartford warbler, which have been key to its expansion as 74% of the expanded population were located in protected areas.

A “National Adaptation Programme”

Protected areas have not only been key to the expansion of the Dartford warbler, but have also been important for the UK’s wintering waterbirds and recent colonists, as mentioned above. The RSPB report says that “protected areas are going to be a vital part of responding to climate change, enabling conservation management as a priority.” It also stresses the importance of wildlife corridors: “Connectivity between protected areas by increasing habitat availability in the wider countryside will also be an important factor in facilitating the movement of species under climate change.”

In July 2013, the UK Government published a National Adaptation Programme which set out “what government, businesses and society are doing to become more climate ready.” [19] With regard to action on the natural environment, the programme specifies four overarching objectives:

• “Building ecological resilience to the impacts of climate change: To build the resilience of wildlife, habitats and ecosystems (terrestrial, freshwater, marine and coastal) to climate change, to put our natural environment in the strongest possible position to meet the challenges and changes ahead.”
• “Preparing for and accommodating inevitable change: To take action to help wildlife, habitats and ecosystems accommodate and smoothly make the transition through inevitable change.”
• “Valuing the wider adaptation benefits the natural environment can deliver: To promote and gain widespread uptake in other sectors of adaptation measures that benefit, or do not adversely affect, the natural environment.”
• “Improving the evidence base: To improve the evidence base to enhance the knowledge and understanding of decision makers, land managers and others of the impacts of climate change on the natural environment and how best we can influence adaptation or accommodate change.”

The first two objectives stress the importance of protected areas and connectivity, while the fourth stresses the need for monitoring and research. On the third, the RSPB report cites the examples of coastal realignment and catchment management, both of which provide wider benefits:

“Climate change has impacts on people as well as wildlife and the way society adapts to the threats it faces may have positive or negative impacts for birds and other species. One of the clearest examples is where hard sea defences designed to reduce coastal flooding may prevent natural readjustment of the shoreline and lead to a loss of coastal habitats. By allowing natural processes to create new habitats through managed realignment, we can have more natural solutions to flooding which will have multiple benefits: reducing the risks of flooding to people, creating extensive wetlands, as well as carbon capture in the intertidal habitats created. Other examples include upland catchment management for wildlife and water, trees in shaded open spaces for people in urban environments, and re-naturalising river systems to reduce flow rates and retain flood waters.”

The National Adaptation Programme is due to be updated this year, and this week the UK Government will also be publishing its 25-year plan for the natural environment. The intention to produce such a plan was first announced in October 2015 when it responded to a set of recommendations from the Natural Capital Committee [20]. It will be interesting to see how the Government’s plan deals with the current and projected impact of climate change on the natural environment, and conservationists will be hoping that this long-anticipated document is worth the wait.

Acknowledgement

Photograph: Jubilee Marsh, near Southend, Essex: View east at low tide to Breach Two, the River Roach and Foulness, taken 8th October 2017 © Copyright John Myers and licensed for reuse under this Creative Commons Licence. Jubilee Marsh forms part of the Wallasea Island Wild Coast Project, which the RSPB says is a landmark conservation and engineering scheme and the largest of its type in Europe:

“The Wallasea Island Wild Coast Project is in the middle of transforming this island into a magical landscape of marshland, lagoons, ditches and sea. More than 3m tonnes of earth was brought by boat from the tunnels and shafts created by the Crossrail scheme in London. This allowed us to raise the land above sea level and place the soil in way that created a new 115ha intertidal area of saltmarsh, islands and mudflats (known as Jubilee Marsh).”

The saline lagoons are managed using sluices to control water levels with the aim of creating a variety of depths of water to suit different species. The RSPB says Jubilee Marsh needs minimal management “as the tide comes in and out bringing with it sediment, seeds and other bits of plants plus the invertebrates and fish which the birds then feed on.” Sea water entered the marsh for the first time in July 2015. See the RSPB website at: https://www.rspb.org.uk/reserves-and-events/reserves-a-z/wallasea-island-wild-coast-project.

Notes

[1] Hayhow DB, Ausden MA, Bradbury RB, Burnell D, Copeland AI, Crick HQP, Eaton MA, Frost T, Grice PV, Hall C, Harris SJ, Morecroft MD, Noble DG, Pearce-Higgins JW, Watts O, and Williams JM. The state of the UK’s birds 2017 (SUKB 2017). Published by the SUKB Partnership, Sandy, Bedfordshire. Retrieved as a PDF document from https://www.rspb.org.uk/globalassets/downloads/documents/conservation-science/sukb-2017—web-version.pdf. The SUKB Partnership consist of the Royal Society for the Protection of Birds (RSPB), the British Trust for Ornithology (BTO), the Wildfowl & Wetlands Trust (WWT), the Department of Agriculture, Environment and Rural Affairs (Northern Ireland) (DAERA), the Joint Nature Conservation Committee (JNCC), Natural England (NE), Natural Resources Wales (NRW), and Scottish Natural Heritage (SNH).

[2] For details of the studies cited in the report, see the references in [1].

[3] This is clearly an error as the figures for the treecreeper and the dunnock that are tabled in the RSPB report are exactly the same as those produced by Defra. In the case of the grey heron however, the RSPB report says that the data comes from the Heronies Census (1982 to 2015), and it is unclear what periods are covered in the long-term or the short-term. There is an overall agreement however that the grey heron population is in decline. It is important to note that there are several discrepancies between the figures produced by Defra and those reproduced in the RSPB report, most notably in the figures for seabirds (see Note 10 below). There are three explanations for why these figures should diverge, apart from the most obvious one of an error in the calculations or the transcription. Firstly, the periods covered in the calculations. Defra’s figures for the most part cover the periods from 1970 to 2015 (the long-term comparison) and from 2010 to 2015 (the short-term comparison). The figures produced in the RSPB report however cover a range of periods, including not only those used in the Defra report but also longer periods for some short-term calculations (1995 to 2015 for instance). As increases and decreases are calculated from a baseline, this means that whilst a species might show a long-term increase over the last 45 years, for instance, it might also show a long-term decline if calculated over the most recent 20-year period. Secondly, the surveys used for the calculations can also produce different results. Defra’s report combines a number of survey results to give a composite figure, whilst the RSPB report tends to use the most representative surveys for particular categories. Thirdly, the use of a “smoothed index” and an “unsmoothed index” in the calculations. The former is intended to compensate for peaks and troughs in seasonal variations, such as an extremely cold winter, whereas the latter can produce a slightly different result when these are not taken into account. For the most part however, the figures in the RSPB report and those presented in our analysis of Defra’s figures both use the smoothed index.

[4] Defra’s statistics include figures for 130 species of common birds, defined as species with populations of at least 500 breeding pairs that are native to (and breed in) the UK. The species that have increased in the long term include the long-tailed tit, blue tit, coal tit, bearded tit, chaffinch, pied wagtail, stonechat, Dartford warbler, Cetti’s warbler, woodlark, siskin, great spotted woodpecker, green woodpecker, jay, sparrowhawk, raven, buzzard, red kite, peregrine falcon, carrion crow, hooded crow, magpie, jackdaw, wood pigeon, stock dove, collared dove, red grouse, goldfinch, cirl bunting, oystercatcher, mallard, coot, tufted duck, pochard, teal, goosander, red-breasted merganser, gadwall, greylag goose, mute swan, black-headed gull, great black-backed gull, razorbill and common guillemot, and some summer migrants including the blackcap, chiffchaff, redstart, lesser whtethroat, reed warbler, swallow, sand martin, Arctic tern, sandwich tern, and avocet. See last month’s article ‘Defra releases latest statistics on the UK’s wild bird populations’ for the details.

[5] For the details, see the ENA article above [4].

[6] See: ‘Lapwings hit new low; further declines in breeding waders revealed’, British Trust for Ornithology, July 2012. Retrieved from: https://www.bto.org/news-events/press-releases/lapwings-hit-new-low-further-declines-breeding-waders-revealed.

[7] Ibid: see [6].

[8] See ‘A chance for the new Environment Secretary, Michael Gove, to “listen and learn”‘, Martin Harper, RSPB, June 2017. Retrieved from: http://www.rspb.org.uk/community/ourwork/b/martinharper/archive/2017/06/14/a-chance-for-the-new-environment-secretary-michael-gove-to-listen-and-learn.aspx.
Martin Harper says that thirteen years ago the RSPB “made the case that Ofwat should change the rules that governed water company investment in catchments.” The partnership involved in the Sustainable Catchment Management Programme “developed a new approach to managing the land which complied with the Habitats Regulations, enhanced biodiversity and improved the quality of the water abstracted for drinking, as well as providing an enhanced source of income for tenant farmers. As the approach has broadened and been taken up by other water companies, we have seen huge benefits as restoration of habitat has led to increased species populations and improved water quality.”

[9] These figures are taken from Defra’s statistics. See last month’s article ‘Defra releases latest statistics on the UK’s wild bird populations’ for more details on the UK’s seabird populations.

[10] Sandeels are commercially fished by Denmark under the terms of the Common Fisheries Policy. Recent research led by the RSPB has shown a correlation between the breeding success of kittiwakes on the Yorkshire coast and the abundance of sandeels at Dogger Bank. See: ‘Protecting our Seabirds in Post-Brexit Waters’, Euan Dunn, RSPB, 14 June 2016. Retrieved from: http://www.rspb.org.uk/community/ourwork/b/martinharper/archive/2017/06/14/protecting-our-seabirds-in-post-brexit-waters.aspx. The research paper ‘Kittiwake breeding success in the southern North Sea correlates with prior sandeel fishing mortality’ was published in Aquatic Conservation: Marine and Freshwater Ecosystems in June 2017 and is available at http://onlinelibrary.wiley.com/doi/10.1002/aqc.2780/full.

[11] It is important to note that percentage increases are relative and say nothing about actual numbers. This means that if an increase is calculated from a low base, a high percentage rise does not necessarily equate to a large population. This is the case with the roseate tern. The RSPB says that the roseate tern is one of our rarest seabirds “whose severe, long-lasting and well documented decline make it a Red List species.” The current estimate of its UK population is 111 pairs, according to the RSPB website. The report says: “&hellip species which are exhibiting rapid population increases may be coming back from extremely low numbers. For example, roseate terns increased 229% between 2000 and 2015, but this was calculated from 56 apparently occupied nests in the last census (Seabird Monitoring Programme 2000) to 113 in 2015, and numbers are still well below the 950 pairs observed between 1969 and 1970.” Defra’s statistics, showing data for species with at least 500 breeding pairs, exclude figures for the roseate tern, gannet and great skua, whilst the figures reported by the RSPB exclude figures for the herring gull. It is also important to note that figures produced by the RSPB from the Seabird Monitoring Programme differ widely from those produced by Defra from the same source and virtually the same period – 1986 to 2014 (Defra) and 1986 to 2015 (RSPB). Consequently, the possible explanations for divergences do not seem to apply here (see Note 3). As an example, both sets of figures agree that the numbers of razorbill, guillemot, Arctic tern, and black-headed gull have all increased in the long term, but they disagree over the percentages. In contrast, Defra’s figures show a long-term increase of 7% for the great black-backed gull but the RSPB’s figures show a 1% decline; and Defra’s figures show a long-term decline of 7% for the cormorant but the RSPB figures show a 4% increase. Given that statistics are used as part of the evidence base for determining conservation priorities, it would be useful if not vitally important to see some consistency in these figures.

[12] On the divergence in statistics, see [11].

[13] Wild Bird Populations in the UK, 1970-2016, Biodiversity Statistics Team, Department for Environment, Food and Rural Affairs, 23/11/2017. Available as a PDF document from: https://www.gov.uk/government/statistics/wild-bird-populations-in-the-uk.

[14] The quote comes from the Joint Nature Conservation Committee (JNCC). See the JNCC website at: http://jncc.defra.gov.uk/page-162.

[15] A full list is available from the JNCC website: see [14].

[16] The report also says that, in recent years, “purple herons have bred in Kent, a pair of glossy ibises have built a nest in Lincolnshire, and male white-spotted bluethroats have held territory,” while other potential colonists, described as “great rarities in the UK”, include zitting cisticolas, short-toed eagles and short-toed treecreepers. Other rare visitors include the two pairs of bee-eaters which were spotted nesting alongside sand martins in a quarry in Cumbria in the summer of 2015. A similar number had also nested successfully in previous years in the Isle of Wight and in County Durham. See: ‘Rare bee-eater birds found nesting in Cumbrian quarry,’ BBC News, 31 July 2015. Retrieved from: http://www.bbc.co.uk/news/uk-england-cumbria-33732567.

[17] The IUCN (International Union for Conservation of Nature) uses a range of categories to assess the status of a species with regard to its population and the priorities for conservation. These are: 1. Extinct; 2. Extinct in the wild; 3. Critically Endangered; 4. Endangered; 5. Vulnerable; 6. Near Threatened; 7. Least Concern; 8. Data deficient; and 9. Not evaluated. Defra’s statistics show little change in the number of oystercatchers wintering in the UK, together with a long-term increase in the number of oystercatchers resident in the UK. However, this long-term increase covers a forty-year period from 1975 to 2015, whereas the RSPB figures cover shorter and more recent periods. (See Note 3 on explanations of divergences.)

[18] The Environment Agency produced a report in 2011 on future water availability (‘The case for change: Current and future water availability,’ Report: GEHO1111BVEP-E-E), while Defra produced a climate change risk assessment for the water sector in 2012. The RSPB report summarises the outcome of these assessments: “Overall reductions in water availability, particularly in the south-east, are expected to be exacerbated by increased demand for water for agriculture, industry and services.”

[19] See ‘The National Adaptation Programme: Making the country resilient to a changing climate’, UK Government policy paper, July 2013. Available as a PDF document from: https://www.gov.uk/government/publications/adapting-to-climate-change-national-adaptation-programme”.

[20] See the ENA UK article ‘Defra responds to recommendations of the Natural Capital Committee’. In fact, the plan is expected to be published tomorrow (11th January).

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