• Overwintering distributions of many coastal waders have shifted in recent decades. From a UK perspective this initially meant that many species developed more easterly and northerly distributions. Latterly, numbers of some species appear to be increasing further east in Europe and falling on the east coast of Britain as the general eastward shift continues.
• These changes in distribution appear to be driven by waders taking advantage of new opportunities to over-winter on sites offering better feeding conditions closer to their Arctic and sub-Arctic breeding ranges rather than being negative impacts.
• In the future, however, these newly developed distributions may make populations more susceptible to the intermittent severe weather events to which they are particularly vulnerable.
• Similar distribution changes are probably occurring in wildfowl although the evidence is less robust.
• The effects of climate change on the mainly Arctic and sub-Arctic breeding grounds of waterbirds over-wintering in the UK can be expected to be detrimental. Main impacts are likely to be loss of habitat, a northwards shift in suitable habitat resulting in increase migration costs and increased predation pressure. These impacts may outweigh the benefits of milder weather on the wintering grounds.
• There is little evidence as to how the impacts of climate change on the prey base of over-wintering waterbirds is affecting their numbers.
• Our own efforts to mitigate climate change including improved sea-defences and the renewable energy industry and its supporting infrastructure may also have adverse affects on these birds through loss of habitat, disturbance, displacement and possible direct mortality.

What is already happening: Low

Aside from the observed changes in over-winter distribution of waders and possibly wildfowl there is little direct evidence for the effects of climate change on waterbirds.  Waterbirds face a host of pressure, including amongst others those arising from developments in estuarine habitats, increased disturbance from recreation, shellfisheries and changes in water quality. It is therefore difficult to ascribe changes we monitor in populations to any one factor. Furthermore, assessing the impacts of climate change as it affects these species on their Arctic and sub-Arctic breeding grounds is hampered by the scarcity of basic monitoring let alone focused scientific research.

What could happen: Low

Waterbirds are generally highly mobile and adaptable species. Many species over-wintering in the UK also over-winter in southern Europe and Africa where they inhabit a variety of habitats and feed on a wide range of prey. It is therefore difficult to predict how these species will adapt to climate change on the wintering grounds. It is even more difficult to predict how they may respond on their breeding grounds as there is such a paucity of baseline data.

The top priority knowledge gaps that need to be addressed in the short term to provide better advice to be given to policy makers are:

1. Most research focused on the effects of climate change on waterbirds has been derived from programmes that monitor over-wintering populations, something that we in the UK do especially well. However, the waterbirds that the UK hosts breed largely in Arctic and sub-Arctic regions where there is a paucity of monitoring. However, changes in annual productivity and predation pressure on the breeding grounds may outweigh any changes occurring on the wintering grounds. There is a general consensus amongst scientists that monitoring on the breeding grounds is a priority for the conservation of many of these species.
2. Some long-distance migrants, rely on stop-over areas to refuel before continuing their journies. However, many of these areas are in remote or poorly monitored parts of the flyways and our knowledge of pressures on these areas and number of birds passing through them is scant.
3. To understand changes in waterbird populations in response to climate change it is necessary to develop integrated population models that include annual productivity, adult and juvenile survival and to explore how these are affected by climate change.

Waterbirds are popular with the general public and attract a high level of eco-tourism. Changes in numbers and distributions of these species could affect this relationship.

Many waterbirds are important predators of intertidal invertebrates. In some cases they are seen as competitors with the shellfish industry. Changes in distribution could result in new conflicts. The corollary of this is that waterbirds foraging on intertidal areas occupy a central position in nutrient flow and maintaining the ecological balance. Consequently, changes in numbers in either direction may affect the ecological balance in perhaps unforeseen ways.

Austin, G. (2010) Waterbirds in MCCIP Annual Report Card 2010-11, MCCIP Science Review, 7pp. www.mccip.org.uk/arc