Scotland’s coasts and inland waters are of particular significance for wintering waterbirds hosting substantial numbers of waders and wildfowl. In an international context Scotland’s extensive non-estuarine coast is important for specialist species such as purple sandpiper and turnstone, and its islands and agricultural lowlands for migratory geese. There are more than 50 sites of international importance for wildfowl and wader species. Many are long distance migrants, breeding in the high Arctic and wintering in Scotland.
Monitoring Scotland’s wintering waterbirds
Each month throughout the winter, volunteers count waterbirds around Scotland’s estuaries, rocky shorelines and inland waterways. These counts are mostly undertaken through the Wetland Bird Survey, with additional targeted counts for geese and swans, and periodic surveys of rocky shore waders. The results are used by Governments and environmental NGOs to provide population estimates, determine trends in numbers and distribution, and identify important sites for waterbirds. Since 1975, trends in 41 species of waterbirds (used here to include wildfowl, waders, cormorant, grebes and coot) occurring in Scotland have been monitored.
Since counts began in the winter of 1975/76:
- Overall waterbird numbers (41 species/populations) decreased by 7%.
- Goose numbers (7 species/populations) increased by 274%.
- Ducks and swans (wildfowl) numbers (16 species) increased by 21%.
- Wader numbers (14 species) have declined to 58% lower than in 1975/76.
Overall waterbird numbers (the combined trend for all 41 species/populations) have decreased by 7%. The individual species trends reveal a range of fortunes for Scotland’s wintering waterbirds. Most waterbirds can be highly mobile and research has shown that some are shifting their distributions in response to environmental change (Pavón‐Jordán, 2019).
Wader numbers peaked around 1997/98. Since then the combined trend for waders has shown a steady decline. Scotland is in an important position within the East Atlantic Flyway (the migration route used by our waders).
Scotland’s rocky shores, host a large number of waders. The species trends used in this indicator include data from the latest non-estuarine wader survey which took place over the winter of 2015/16, and has improved the trend estimates for our waders.
Eleven species declined (oystercatcher, lapwing, golden plover, ringed plover, curlew, bar-tailed godwit, turnstone, knot, dunlin, purple sandpiper and redshank). Their trends show a similar pattern, peaking between 1994/95 to 1998/99 then declining from 2002/03. Two species have increased, black-tailed godwit and grey plover. Wintering numbers of sanderling remained stable.
Reasons for the changes
A recent review on the trends of Arctic birds by Smith et al. 2020 highlighted the scale of the declines for Arctic waders and identified some of the factors. Climate change may be allowing some species to shift their distributions, this may account for some of the declines as birds select wintering areas that are more favourable. However, we lack key knowledge on whether this is actually happening or whether the declines are at the population scale. Climate change effects may result in a northward shift in their Arctic breeding ranges and may be leading to them not being able to find food during the breeding season (climate mismatch). For species where we do have knowledge, such as knot and dunlin, studies have shown that populations can be highly mobile. When there are milder winters across Europe this enables birds to remain on continental wintering sites. For other waders, in particular rocky shore waders such as purple sandpiper and turnstone, the reasons for declines are not well understood. Some studies suggest that poor breeding success is leading to the declines. Collaborative monitoring (across the entire flyway) is essential to help understand and reverse the declines of waders.
For our wintering waders which also breed in Scotland such as curlew, golden plover and oystercatcher, targeted land management has been shown to help. The Working for Waders initiative is taking active steps to reverse the decline in wading birds in Scotland through a range of targeted projects.
Wildfowl numbers have remained relatively stable, peaking around 1993/94. Within the trend, there is marked variation. Eleven species have increased (Mute swan; whooper swan; shelduck; shoveler; gadwall; wigeon; pintail; teal; goldeneye; goosander and little grebe). Six have declined (mallard; pochard; scaup; eider; cormorant and coot). Two were stable (tufted duck and red-breasted merganser).
Reasons for the changes
Many of our wildfowl are migratory, and for some their trends may reflect shifting wintering areas. Such that populations of wigeon and teal are increasing in Scotland with more birds opting to winter around our coasts. In contrast, wintering pochard numbers have declined markedly. Research has started to reveal some of the reasons including changes in water quality, losses in gull colonies (particularly black-headed gull) as pochard may gain fitness benefits from nesting nearby and invasive species such as carp which compete with pochard for food resources in some areas (Fox et al. 2016).
The majority of goose populations have increased. Barnacle geese have seen some of the largest increases, with protective legislation and changes in agricultural management helping to improve their fortunes to the degree that management options are now being explored to help reduce emerging conflicts with crop-growers (McKenzie, 2014). In contrast, Greenland white-fronted goose have declined since the late 1990s. Tthought to be due to factors on the breeding grounds, including high late-spring snowfall and competition with Canada geese that are spreading northwards into Greenland (Fox et al. 2011). On the wintering grounds, many sites have seen local declines of Greenland white-fronted geese, although recent work has shown that some sites are buffered against the overall national trend (e.g. Weegman et al. 2016).
The Wetland Bird Survey operates throughout Scotland. Although most major waterbodies and estuaries are covered by volunteers, there is always a need for new counters. Counts from areas not well monitored (such as North West Scotland and smaller inland waterbodies) are welcome as well. To become a WeBS volunteer contact BTO.
The Wetland Bird Survey (WeBS) monitors wintering waterbirds covering all of the major estuaries throughout the UK. The Wetland Bird Survey (WeBS) is a partnership jointly funded by BTO, RSPB and JNCC, in association with WWT, with fieldwork conducted by volunteers. This is complemented by annual results of the WWT/JNCC/NatureScot Goose and Swan Monitoring Programme and Non-Estuarine Waterbird Surveys undertaken periodically to improve coverage of the coastline outside estuaries. Further information on waterbird trends on protected sites in Scotland can be found online through WeBS Alerts.
Fox, A.D. Caizergues, M.V., Banik, K., et al. 2016. Recent changes in the abundance of Common Pochard Aythya farina breeding in Europe. Wildfowl 66 22-40.
Fox, A.D., Mitchell, C., Weegman, M.D. et al. 2011. Potential factors influencing increasing numbers of Canada geese Branta Canadensis in west Greenland. Wildfowl, 61, 30-44.
McKenzie, R. (Ed.) 2014. Islay Sustainable Goose Management Strategy. NatureScot.
Pavón‐Jordán D, Clausen P, Dagys M, et al. 2019. Habitat‐and species‐mediated short‐and long‐term distributional changes in waterbird abundance linked to variation in European winter weather. Diversity and Distributions. 25(2), 225-39.
Smith, P.A., McKinnon, L., Meltofte, H. et al. 2020. Status and trends of tundra birds across the circumpolar Arctic. Ambio 49, 732–748
Weegman, M.D., Bearhop, S., Fox, A.D. et al. 2016. Integrated population modelling reveals a perceived source to be a cryptic sink. Journal of Animal Ecology, 85, 467-475.