Dee Estuary Birding

"Sanderlings are only normally found at the tide edge on sandy shores, for this is the little bird that follows each wave in and out like a clockwork toy, picking small shrimps from the water. At low water they sometimes feed on tiny molluscs and at high tide they may search along the strand line of seaweed for sandhoppers and small flies."
Birds in Cheshire and Wirral (Atlas) (Ref1).

These are the first two sentences in the Sanderling description in that landmark publication (The Cheshire and Wirral Atlas) and, as it was as good as anything I could write, I decided just to quote it!

It was Allan Conlin's count 0f 1,475 Sanderlings at Hoylake in November, the highest there since 2013, which got me thinking about this small wader. Other than a general impression that numbers have recently been increasing here, I realised I didn't really know a great deal about them. So this article brings the current status of Sanderlings locally up to date as well as summarising the work which has been ongoing internationally, particularly over the past 20 years, to try and better understand their movements along the East Atlantic Flyway.

Dee Estuary and North Wirral

As far as Sanderlings on the Dee Estuary are concerned, the year can be split into three - autumn migration (July to September), over-wintering (October to March) and spring migration (April to June). Historically, numbers spending the winter here were much lower than the large migrating flocks. Hedley Bell (Ref 2), writing in the early 1960s, said that counts in winter were never more than 50 and often considerably less. Regular counts started in 1970 (mainly Webs [Wetland Bird Survey] but also ad hoc counts started to be regularly reported in the Bird Reports) and these winter counts show a definite, if somewhat irregular, trend upwards - as the graph below shows:

There was a time when the Dee Estuary, together with Morecambe Bay, had the highest counts in the country during the migration periods. These migrating flocks reached peak numbers in the year of 1973/74 when 15,000 were recorded in both the autumn and the following spring with Gronant holding the biggest numbers. Similar numbers were recorded in Morecambe Bay at a time when the whole of the Wash held less than 2,000. The table shows the maximum counts during each migration period for each decade as reported in the Bird Reports.

The numbers of Sanderlings counted migrating through our area differs wildly from year to year, particularly in spring. The drop off in numbers in the 1980s was actually greater than is apparent in the above table with only nine years between 1981 and 2000 when the max spring count was greater than 100. More recently, these spring counts have become more regular and since 2012 the max count has always been greater than 100, and the latest figures show a five year average of 355 for max spring counts. Although there was a similar drop off in autumn counts during the 1980s numbers have usually been both higher and more regular than in spring. Flocks can pass through quickly, though, and 1983 was an interesting example and I quote from the 1983 Cheshire Bird Report "An extermely high count was received of 5000 at Red Rocks on Aug 9th; the observer had recorded 400 the previous day". More recently the five year average was 424 for max autumn counts (2019 to 2023).

The monthly distribution shown above (2020 not included because of lockdown) shows that numbers peak in winter as recorded by WeBS. These once a month WeBS counts probably underestimate numbers during migration as there will be a high turnover of birds and larger flocks may only be present for a day or two before moving on.  For example, in April 2023 a good sized flock of 420 were at Hoylake on the 18th, but only 140 were present two days later for the WeBS count.

Liverpool Bay

The Liverpool Bay estuaries are on the north-west edge of the Sanderlings' non-breeding range and lie directly on their migration route to Iceland and onwards to Greenland - they are thus vitally important stop-over sites for them to feed up before crossing the Atlantic, and for their return after breeding. Their relatively mild martime climate also means they are important as a mid-winter refuge during freezing weather on the European continent.

The Ribble has thousands of Sanderlings present during migration and the monthly distribution is almost the opposite of that on the Dee, although the Ribble winter minimum in December is still higher than our mid-winter maximum! For Sanderlings it seems that the vast stretches of sand on the Ribble estuary is particularly attractive to them. The highest count in recent years was 8,000 in August 2015. Intiguingly, the monthly distributions for the mud loving Knots and Dunlins also show peaks in spring and autumn on the Ribble, and in winter on the Dee estuary (Ref 3), so I'm not quite sure what it is about the Ribble that is so attractive to migrating waders.

The stretch of coast between Ainsdale in the north and Seaforth in the south, including Formby and Crosby shores, (WeBS rather misleadingly call this large area the 'Alt Estuary') is another important area for migrating Sanderlings although the contrast between the migrating periods and winter is far less pronounced. For example, in 2022 numbers peaked in August with 1515 whereas in 2023 they peaked in December with 988. Colour ringing shows there is much interchange of birds between this stretch of coast and the north Wirral coast and it seems likely that there is an over-wintering flock which uses the whole area to feed and roost in.

Morecambe Bay holds the record for the second ever highest WeBS count of Sanderlings in the UK. This was in May 1974 when 15,200 were counted. There were several other five-figure counts in the early 1970s then, for unknown reasons, numbers just crashed and for 1975/76 the maximum count was only 65! Numbers remained very low and the next count greater than 1,000 wasn't until May 1986 when there were just over 4,000. Probably there were problems with counter coverage during the migration periods, although tens of thousands of Dunlins, Knots and Oystercathers were being counted in winter over those same years. Whatever happened numbers never recovered and for the 24 years between 1986 and 2010 max counts were above 1,000 only 10 times. Over the past five years the highest count was 2,953 in May 2019, but the most remarkable figure was the max count in 2022/23 when 885 Sanderlings were counted in June 2023. Obviously very late migrants feeding up before flying to the high Arctic to breed - maybe they had come all the way from South Africa.

UK Status

In the UK Sanderlings have been increasing since the start of WeBS in 1970, with the five year average currently about double it was back in 1974/75.

Numbers in the UK peak in August and then decline to about half that through the winter. The spring peak is vary variable but usually only slightly higher than winter counts. The winter population is around 20,000 (Ref 4) which includes an estimate of birds found on the coast away from estuaries and therefore not covered by WeBS. Of our regular wintering estuarine birds Sanderlings have the smallest population, compare that 20,000 with the estimates for Dunlin, 340,000, and for Knot, 260,000.

Currently the Wash has the biggest numbers in the UK, and there was a massive 17,374 Sanderlings counted there in August 2019, the five year average (2022/23) on the Wash is 10,720. The second most important site is the Ribble estuary followed by the Alt estuary, Morecambe Bay, Thames estuary and Carmarthen Bay, with the Dee estuary in seventh place.

Migration

I've mentioned migration several times already in this article, but where exactly are our Sanderlings migrating to and migrating from?

If you'd asked that question a few years ago you would have got some very vague answers like "It's assumed that......", "We think that.....", "...not fully understood...", ...information is not yet available...", "the origins and movements of the different populations are still not clear....". Perceived wisdom had it that the birds breeding in Greenland passed through the UK and spent the winter in West Africa whereas our wintering population were all birds that breed in Siberia and Svalbard. In addition the Sanderlings which winter as far south as South Africa where also thought to be part of the Siberian breeding population, and the Greenland birds didn't go beyond west Africa. Sanderlings also breed in north-east Canada and it was just not known whether any of these crossed the Atlantic with the Greenland birds or all headed south towards South America. The situation is complicated with waves of Sanderlings coming through - some flying straight through the UK after feeding up, some stop to moult and then fly on whilst others stay several weeks before moving on, and then we have the over-wintering birds.

To try and clarify all this Jeroen Reneerkens set up a Sanderling colour-ringing scheme in 2006, with birds to be initially ringed in Greenland, Iceland, the Netherlands, Mauritania and Ghana. Covering such a large area with a large number of birds to ring, this was a big undertaking. Jeroen had to organise ringing teams in different countries together with all the different coloured rings, and equipment for catching the birds, plus ensuing that all the paperwork was carried out properly. Then he had to rely on people to observe and report the colour-ringed birds - people like you and me, citizen science in action - and lastly find the resources and people to subsequently analyse and write up the results (Refs 5 and 6). On the Dee estuary we've been only too pleased to help the recording of these birds and in my database we have 76 records of 25 colour-ringed Sanderling, these included birds which were ringed in all the countries mentioned above. I know many more colour-ringed Sanderling have been recorded elsewhere in Liverpool Bay, especially along the Sefton coast.

This work continues but we can now say that the birds that breed in Greenland distribute themselves all the way from Scotland to southern Africa. Many stay in north-west Europe for the winter with many also in West Africa, but some end up all the way in southern Africa. The south-west of Iceland has been confirmed as a major staging area. Colour ringing has shown that at least some birds which breed in north-east Canada join the Greenland birds in Europe and Africa (Ref 6).

However, the birds that breed in Siberia remain something of a mystery. We know some certainly use the East Atlantic Flyway but exactly where and in what proportion remains unknown, but the indication is that numbers are relatively small. There has been some interesting observations on the eastern end of the Wadden Sea in Denmark of Sanderlings heading north in spring. They noted that the Sanderlings flew either WNW/NW or ENE/NE, with no intermediate directions observed. The proportion heading easterly towards Siberia was 14%, significant but obviously a lot lower than the 86% heading towards Iceland/Greenland (Ref 7). Remember this is the eastern end of the Waddensea where, presumably, any Siberian breeding Sanderling will concentrate.

So Jeroen, and everyone else involved in his project, still has plenty of work to do.

References and Other Sources of Information

For the Dee Estuary I have used the data in the Cheshire and Wirral Bird Reports (1964 to present day), Clwyd/North-east Wales Bird Reports (1972 to present day), Wetland Bird Survey counts and records from sightings published on this website (www.deeestuary.co.uk). For the Ribble Estuary, Alt Estuary and Morecambe Bay I have used data published in the Lancashire Bird Reports (2018 to 2023), and also Wetland Bird Survey counts.

As well as the books referenced below numerous on-line articles have been read, mostly (co-)authored by Jeroen Reneerkens. I have referenced the most important ones below but I would recommend going to Google Scholar and searching for 'Sanderling migration' to get a more comprehensive list.

References

1. David Norman (editor), Birds in Cheshire and Wirral (Breeding and Wintering Atlas), Liverpool Univerity Press, 2008.

2. T. Hedley Bell, The birds of Cheshire, 1962.

3. Richard Smith, NW Estuaries - Knot and Dunlin, Dee Estuary Birding July 2010 Newsletter.

4. Population estimates of wintering waterbirds in Great Britain, March 2019, British Birds Vol. 112.

5. Jeroen Reneerkens & Edward Koomson, Migration routes of Sanderling: insights after a year of colour-ringing, Global Flyway Network: progress report for 2007.

6. Jeroen Reneerkens, Demographic monitoring along the East-Atlantic Flyway: a case study on Sanderling using international citizen science, East Atlantic Flyway Assessment 2020, Wetlands International/BirdLife International.

7. Kim Fisher & Hans Meltofte, Departure directions of Sanderlings and 'tundra' Common Ringed Plovers from the northernmost Danish Wadden Sea in spring, Wader Study 122(1), 2015.

Richard Smith