Dipper

Overall vulnerability

Feature assessed:

• Dipper (Cinclus cinclus)

Special qualities:

• Internationally important and locally distinctive wildlife and habitats

Feature description:

The dipper is a medium sized dark coloured bird, similar in appearance to a thrush but with a large white patch on its front. It is unique among British passerines for its ability to walk and swim underwater to catch its food. It can be found along streams in the PDNP, especially in the White Peak, where it fishes for invertebrate prey, bobbing its body and cocking its tail. Dipper are a charismatic UK native bird, a pleasure to see along shady PDNP streams, and a valuable indicator of water quality and ecosystem health.

How vulnerable are dippers?

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

The population size in the PDNP is not well known, but national trends show a decline in dipper populations. The largest climate change impacts on dipper will be those that affect their invertebrate prey. Increased water acidity and excess nitrogen will therefore be likely to have the greatest effect. Changes to annual flow cycles will likely also have an impact on dipper populations. The dipper itself is only moderately adaptable, having specific habitat requirements and low dispersal, but could benefit from economic and institutional support. This will mostly be indirect, through initiatives to improve water quality and natural flood management.

Current condition:

Dipper populations are in decline across the UK, with a fluctuating population but an overall downward trend over the last 30 years, especially in England. Trends in the PDNP have appeared generally better than the national average, but recent comprehensive data is not available for this species. Dipper in the PDNP are almost at the eastern edge of their range; they are not currently found east of a line from the Humber estuary to the Isle of Wight. Climate change is thought to be currently benefitting dippers due to increased winter survival. Previously suffering from severe heavy metal pollution of streams, dipper clutch sizes and fledgling success has been steadily increasing in recent years. That the overall UK population is still declining implies less obvious influences are in action on the dipper. Predation may be one factor in the PDNP. The invasive American mink has wiped out the dipper in some areas of Shropshire, and is present here. In areas near housing, domestic predators such as the cat are likely to be a significant factor.

Dipper are highly sensitive to poor water quality, especially in the form of heavy metal pollution and acidity. This is probably due to a reduction in the abundance of their invertebrate prey. The acidity of streams in the PDNP is possibly a significant limiting factor in dipper population recovery, as well as heavy metal pollution from historically contaminated peat. Agrochemical runoff is probably also significant: nitrogen fertilisers, pesticides, and herbicides have the largest effect on the invertebrate prey of the dipper. Inputs from wastewater facilities including pharmaceuticals may also negatively affect freshwater invertebrate populations.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Changes in annual precipitation cycles may affect dipper populations through changes in river flows. High flow can cause rivers to be less suitable for dipper, with foraging opportunity decreased, and prey visibility reduced. Lower summer flows may reduce invertebrate populations and increase pollutant concentration. Ephemeral rivers in the White Peak could also vanish for longer periods, reducing dipper habitat. Dipper breeding and phenology is thought to be primarily controlled by river flows. This reduction in suitability over larger parts of the year is likely to decrease breeding success. Data Certainty: High Flooding and drought may also have a direct effect on adult mortality, but this is less well studied. Data Certainty: Low

Increased atmospheric carbon dioxide may have deleterious effects on dipper populations by increasing stream acidity. Increased atmospheric carbon dioxide will mean more is dissolved into watercourses as carbonic acid. This would decrease the abundance and change the community composition of dipper’s invertebrate prey, causing them to spend more time foraging. Data Certainty: Moderate

Although dipper currently appear to benefit from higher annual average temperatures, this benefit may be cancelled out by declines in invertebrate prey. Modelling has shown that temperature rise could be disastrous for freshwater invertebrate populations, with a potential 21% decline in abundance for every 1⁰C rise in temperature. This would represent a drastic decrease in food availability for dipper, resulting in reduced survival and breeding success. This could offset any gains in dipper populations caused by decreased winter mortality. Dipper may therefore move northwards and upstream if possible. Dipper are on the southeastern edge of their range in the PDNP, so this may result in losses in some areas. Temperature changes may also affect the phenology of some prey species such as the mayfly, resulting in reduced food availability at crucial times of the year. Data Certainty: Moderate

Human behaviour change

Increased water abstraction from rivers in the PDNP during drier summers is likely to further impact river flows. Loss of species that favour faster currents and changes to river channel patterns may reduce dipper populations. Additionally, if flood defences are built to counter high winter flows they may have a similar effect by changing the course of the river. Hard flood defences would also represent a barrier to the movement of dipper prey, and any increase in dredging for flood management could reduce their populations. Data Certainty: High Some smaller streams may also be used for micro-hydroelectric projects to reduce dependence on carbon based power generation, causing channel diversion and modification. Data Certainty: Low

Dipper could benefit from changes in human behaviour as PDNP land use changes. Sheep farming has been shown to affect dipper populations negatively, likely in large part due to sheep dip entering watercourses and killing off invertebrate prey. Increased broadleaved woodland after sheep removal has also been shown to be beneficial. If changes in climate mean stocking densities are lowered, this could cause an increase in dipper numbers in nearby streams. On the other hand, if arable land increases near waterways, then increased sediment, nutrients and agri-chemicals in the water are likely to have negative effects. Hotter summers may also cause an increase in visitor numbers to water bodies in the PDNP, increasing disturbance of the dipper. Data Certainty: Moderate

Nutrient changes or environmental contamination

Warmer conditions increase nitrogen flux in the soil due to higher soil respiration rates, which can be transported by runoff into watercourses. Higher nitrogen availability is likely to increase the frequency of algal blooms, leading to eutrophication. This effect may be compounded by higher water temperatures, as dissolved oxygen capacity reduces. Combined, higher temperatures may lead to larger and more common areas of anoxia within streams, killing off invertebrate prey and thereby reducing suitability for dippers. Data Certainty: Moderate

Higher water temperatures may also decrease the capacity of upland streams to hold dissolved organic carbon and oxygen. Lower ‘brownification’ of water from dissolved carbon improves dipper foraging ability, but lower dissolved carbon and oxygen may impact invertebrate populations. This could make some streams less suitable habitat for dipper as their preferred prey is lost or reduced in abundance. Data Certainty: Moderate Greater runoff from PDNP peatlands could counter this effect to some degree by introducing more peat into the watercourse, acting as a source of carbon that can be dissolved as carbonic acid. Data Certainty: Low

Invasive or other species interactions

Increased annual average temperatures may cause an increase in invasive species in riparian habitats. Non-native species such as Himalayan balsam can crowd out other species on riverbanks, leaving bare ground when they die back in winter. This causes increased erosion and siltation of riparian habitats, as well as changes in water chemistry. These effects may act to reduce the suitability of some habitat for dipper. Data Certainty: Moderate An increase in storm events may magnify this effect by opening up bare ground and increasing disturbance on riverbanks, providing opportunities for invasive species to move in. Data Certainty: Low

Sedimentation or erosion

An increase in the frequency and severity of wildfires could increase erosion material entering the watercourse, especially in peatlands. This would lead to intense events of siltation and changes in dissolved organic carbon, reducing the abundance of freshwater invertebrates and changing community composition. The overall effect would depend on how quickly these systems can recover from these events, but dippers may be affected at least in the short term. Erosion may also be increased generally due to the increased runoff associated with greater winter rainfall and more frequent summer storm events. Siltation would therefore increase in watercourses near agricultural lands and roads, and dissolved organic carbon levels in those near peatlands. Data Certainty: Low

What is the adaptive capacity of dippers?

Overall adaptive capacity rating

Dipper are associated only with riparian habitats within the PDNP, meaning that habitat connectivity is generally only within river systems. Dipper chicks can disperse to other river systems, but generally move less than 10 km from their natal site. Habitat is more fragmented in the WP, with vanishing rivers removing some areas of habitat for part of the year. Data Certainty: Moderate Dipper also have specific habitat requirements, needing high flow variability and areas of deeper water for foraging. Expansion into new habitats is therefore dependent on suitable flow patterns being present, and new flow regimes will be needed to allow dipper populations to move back into some areas where they have been lost. These requirements mean that the dipper is less adaptable to change. Data Certainty: Very High

Some funding is available for dipper conservation, though mostly through conservation of suitable habitat. Works to improve water quality at a catchment level are ongoing in many parts of the PDNP, which will likely benefit dipper populations by increasing invertebrate prey availability. Natural flood management projects would also benefit dipper, as riparian broadleaved woodland and flow variability have been shown to correlate with increased dipper populations. However, the complexity of current environmental land management schemes means that there is a poor incentive for landowners to take them up. Withdrawal from the EU Common Agricultural Policy means that there is now an opportunity to change the way that ecosystem services are valued. Data Certainty: Moderate

Some institutional support is available for dipper conservation. The European Union Water Framework Directive provides a regulatory process for monitoring and improving water quality, but only on main rivers. As dipper usually live on smaller streams, this of value indirectly. Organisations are working within the PDNP to improve water quality and improve watercourse health, benefitting the dipper therefore. Some dipper habitat is protected under Site of Special Scientific Interest (SSSI) designation, providing some protection from degradation and exploitation. The dipper is also an amber listed bird in the UK. Data Certainty: Moderate

Management for dippers is relatively well known, being strongly related to water quality and flow variability. Improving water quality is already a priority in the PDNP, with legacy heavy metal pollution and peat sediment in water courses both undergoing reductions. However, dipper populations are still declining, suggesting that gaps in management knowledge still exist. Data Certainty: Moderate

Key adaptation recommendations for dippers:

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.

• Minimise agricultural inputs, especially slurry, fertilisers and pesticides. Give consideration to good management of waste to improve catchment quality, including effective slurry store management.
• Increased natural flood management measures will benefit dipper. This includes upland woody damming, broadleaf woodland establishment, and natural scrub regeneration.
• Hydroelectric power schemes have the potential to be very harmful to dipper and other riparian species. Natural processes within river systems are key to the adaptive capacity of the system. Developments should only be approved if they interfere minimally with the natural course of the river.
• Dipper should be considered when building structures to regulate flow. Construction should be limited during dipper breeding season.
• Encourage further uptake of environmental land management schemes by farmers within the PDNP.

Improve current condition to increase resilience: Increase structural diversity to improve resilience at a landscape scale

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations focus on increasing the structural diversity of the area or habitat in which the feature is found. This can help to offset the effects of climate change on the feature, as well as to allow it to be in a better position to recover from future climate changes.

• Conifer plantations beside rivers are detrimental to dipper populations. Streamside conifers should be phased out and replaced with native broadleaf wherever possible.
• Improve variation in streams: riffles, rocks, and boulders can create variable flow and deeper sections. This creates better foraging habitat.