Changing waterfowl require greater understanding

The latest review of waterbird populations in the UK makes interesting reading. At first glance it suggests contrasting fortunes for many of the species with which we share these islands. The review, jointly published by the BTO, RSPB and JNCC, stems from the efforts of some 3,000 volunteer counters. These volunteers participate in the synchronised monthly counts that take place across our many inland and coastal waterbodies.

While some species reached new ‘highs’ in terms of their population levels, others reached all-time lows. An examination of the ‘winners’ and ‘losers’ reveals that many of the ‘winners’ are introduced species whose naturalised populations continue to expand. These include Egyptian Goose, Mandarin Duck and Barnacle Goose. However, in with these are genuine colonists like Little Egret, a species expanding north on the back of global climate change.

The numbers of some species reflect breeding conditions elsewhere, the UK being a wintering ground with little or no breeding population of its own. A poor breeding season elsewhere may see fewer birds available to make the journey to our shores. The recent downtown in wintering numbers of Bewick’s Swans was once thought to be linked to a contraction eastwards in the wider European wintering range. However, recent research has revealed a decline in the overall population rather than just a shift in distribution. In contrast, our population of wintering Whooper Swans has continued to increase, with most of our visiting Whoopers arriving from Icelandic breeding grounds. The nature of the survey also enables the volunteer counters to gather information on breeding success for some species. In the case of the Whooper Swan, cygnets accounted for 16.8% of the birds present, slightly up on the previous winter.

The estuaries around Britain & Ireland are important wintering sites for many wading birds and these are also surveyed by the volunteers. Again fortunes appear mixed, with some notable increases seen in Avocet (a real conservation success story), Grey Plover and Sanderling. Balanced against this is the apparent news that Ringed Plover and Dunlin have both hit all time lows. Britain has eight sites of international importance for Ringed Plover but, while the decline might seem worrying, news of increasing numbers at sites elsewhere in Europe (notably The Netherlands) suggests that what we are actually seeing is an eastward shift in the core wintering range, perhaps linked to a run of mild winters.

Taken as a whole, this report highlights the need to monitor the changing fortunes of these birds at a much wider spatial scale, since a decline here may not mean that the population is falling, merely that it is now wintering elsewhere. Fortunately, our knowledge of waterbirds is increasing, placing our understanding into a wider context.

Swans on the up

The Fens can seem rather bleak and inhospitable at this time of the year, exposed to a wind that whips in off the North Sea and with an expanse of sky dark with threatening clouds. Yet this unique part of East Anglia attracts huge numbers of wildfowl, counted among which are sizeable numbers of our two migratory swans. Drawn to this area by the combination of secure roost sites and available winter food, whooper and bewick’s swans gather annually on the Ouse Washes, centred around the Wildfowl & Wetlands Trust reserve at Welney.

The bewick’s swans, of which 5,000 or so winter on the Ouse Washes, originate from breeding grounds in western Siberia. These birds migrate west to winter in the Netherlands, Britain and Ireland. Some 50% of those wintering in Britain gather on the Ouse Washes and, during January, the washes may be the most important site for the species anywhere in Europe. Traditionally, the swans would have grazed on aquatic and semi-aquatic plants taken from areas of marsh and flooded pasture. However, since the 1970s there has been a noticeable move onto arable land, with the birds favouring fields with sugar beet, potatoes or autumn sown cereals. The cereals become more important towards the tail end of winter. Each morning the swans leave the safety of open water on which they roosted over night to gather on the arable fields that lie just off the washes.

The larger whooper swans are among the heaviest migratory birds, with adult males averaging around 10kg. The individuals wintering here in East Anglia will, for the most part, have come from the Icelandic breeding population. Those from breeding grounds in Finland and NW Russia winter on the continent but there is a small amount of interchange between the two populations (with an estimated 200 Finish birds wintering here and 600 Icelandic birds wintering on the continent). Like their smaller cousins, the whoopers make good use of the arable land and the area around the Ouse can easily attract 3,500 individuals during the middle of winter. Interestingly, both species of swan arrive in family parties and this has enabled researchers to gain an understanding of their annual breeding success. Young birds with their parents can be readily identified and it is possible to calculate the proportion of youngsters within the wintering herds (groups of swans are called ‘herds’ not ‘flocks’). The most recent figures demonstrate that roughly 1 in 10 swans is a youngster, a figure that has declined over recent years, suggesting a decrease in breeding success. The swans will begin to depart from the middle of the month so it is worth making a trip to Welney to see this winter spectacle.