Red-breasted Flycatcher (Tony Broome)
WeBS and Waders
I originally wrote this article without having read 'Declines in midwinter counts of waders roosting on the Dee Estuary' by J.R. Mitchell, M.E. Moser and J.S. Kirby published in Bird Study in 1988, I hadn't realised how closely much of my article follows the same ground as theirs. Now having read their excellent and detailed paper I hope the authors forgive me in publishing the following less detailed account, if only to bring it up to date with recent data. I have handled the data slightly differently as they used peak counts December to February whereas I have used average counts November to February - with much the same conclusions. I have also gone in to some detail about the effect of tide heights on where the birds roosts, a topic they didn't cover. So here is my article, slightly amended from the original:
The Wetland Bird Survey (WeBS), originally called the Birds of Estuaries Enquiry (BoEE), is now in its 38th year. I always find looking back through the old data fascinating; seeing how numbers change over the years and wondering why. Changes can be due to variations in populations as a whole, perhaps due to a series of successful (or unsuccessful) breeding seasons. Others are clearly local and I thought I would highlight two species where large local changes in numbers have taken place on the Dee Estuary and North Wirral coast, how numbers of these same species have varied on the nearby Alt Estuary and why the two are linked.
A snowy day on Little Eye with
Knot numbers like they used to be pre 1980 (©
Note that Dee WeBS counts shown below include birds both in the Dee Estuary itself and along the North Wirral coast. WeBS high tide counts take place once a month with the majority on the highest, i.e. spring tides. Counts for the winters of 1977/78, 1978/79, 1992/93 and 1993/94 have been omitted from the graphs due to incomplete coverage on the Dee for the former two winters and on the Alt for the latter two winters. To make it easier to compare like with like I have taken the average high tide counts for each winter, November to February, rather than just single peak counts. Low tide counts, on the other hand, are one off counts. WeBS counts detailed below are all birds counted at the high tide roosts unless it is specifically stated that they are low tide counts.
Was this reversal in fortune just a coincidence? Apparently not as it is evident from the data and observations of flock movements at the time that birds which were roosting on the Dee (mainly at West Kirby and Hoylake) started to roost on the Alt Estuary. However, it is not clear why the reversal was so sudden given the fact, well documented, that a large amount of disturbance had been going on for well over 10 years. Nevertheless, for whatever reason, both Bar-tailed Godwits and Knot largely deserted Dee Estuary roost sites (at least on spring tides) in the winter of 1980/81, the same winter that numbers shot up on the Alt. May be there was a combination of a large amount of disturbance together with some very high tides which covered the sand banks at West Kirby and Hoylake (there were high spring tides on count days on three out of the four winter months of 80/81).
Bar-tailed Godwits on north
Wirral Shore Feb 2007, left to right - winter plumage, breeding plumage
and just showing first signs of turning from winter to breeding plumage (© Richard Steel)
But Bar-tailed Godwits hadn't left the Dee altogether.
The orange line on the graph shows some typical low tide counts, i.e. counts
of birds using the Dee Estuary area (or to be more correct, the North Wirral
coast) for feeding. The last five points on the graph are of particular
interest as numbers increase and decrease in sequence with numbers on the
Alt roost site**, which is very strong evidence that the birds which feed on
the North Wirral coast at low tide are the same ones that roost on the Alt
at high tide. Mitchell et al state that in the period 1979 to 1986 birds
were clearly observed flying to and from the Alt over high tide. This isn't
the whole story, however - although fairly unusual these days, quite large
numbers of Bar-tailed Godwits do still sometimes roost in the Dee area, but
usually only on neap to medium tides when much larger areas of sand banks
are available for roosting on. For example 4,700 were recorded on a high
tide in Jan 2002 at Hoylake, in the same year 1,900 were at West Kirby on
Dec 23rd and on a neap tide on Nov 20th 2006 1,500 spent high tide on
Wallasey Shore. Apart from these occasional flocks birds have shown little
sign of returning to their old roost sites, even though there has been a big
reduction in disturbance. For example the max high tide WeBS count for the
Dee Estuary for the winter of 2004/05 was only 132.
So taking these 1960s counts at face value it is ironic that the year the BoEE started we had a collapse in numbers. Even more ironic, perhaps, is that the numbers the Knot collapsed to - an average of around 30,000 through the winter - we would now only be too pleased to have this number with averages at high tide roost counts presently only around the 10,000 mark.
From the figures in the 1960s Bird Reports and the data in the above graph we have to conclude that there have been two collapses in numbers of Knot on the Dee Estuary, the first in 1970/71 and the second in 1980/81. Perhaps another dip into a Cheshire Bird Report will help to explain what was going on, this time 1969: "For some years past the huge numbers of Knot in the Dee estuary have taken to 'Flying Out' the peak of the very high tides. Formerly they roosted on the Hilbre islands or even on local golf courses when the sea covered the shore, now, no doubt due to human disturbance, the birds circle to a great height over the estuary and glide down to suitable places as they become uncovered" - no wonder the birds ended up using the much less disturbed Alt for a roost! But, as with the Bar-tailed Godwits, it is not clear why the switchover to the Alt was so sudden.
Since the collapse in 1980/81 on the Dee Estuary average roost counts have stabilised at around 10,000. That numbers haven't decreased any further is partly due to the Dee Estuary Voluntary Wardens as without them West Kirby shore would have become unusable as a roost - credit here to RSPB and Nature Conservancy (now Natural England) for helping to set up the Voluntary Wardening scheme. Also the accretion of West Hoyle Bank and adjacent beach at Hoylake has helped establish the roost site there, currently the most important roost for Knot on the Dee. Indeed, the proportion of the total Knot flock (Alt and Dee) now roosting on the Dee since 1990 has been, on average, just under 50%, whereas from 1985 to 1988 it was only about 25%, a big improvement. Despite virtually no disturbance now on Little Eye and Middle Hilbre the Knot haven't returned to these former huge roost sites. On the Alt large numbers occurred for just five years before coming down to an average of around 10,000, as on the Dee. This down turn in numbers is likely to be due to a series of mild winters which have kept Knot further east on North Sea coasts, rather than for any local cause.
Low tide counts on the Dee Estuary and North Wirral Shore are consistently higher than high tide counts, two typical examples are shown on the graph. This is because a portion of these feeding flocks, counted at low tide, fly over to the Alt Estuary to roost and are therefore 'lost' as far as Dee high tide WeBS is concerned. But unlike for Bar-tailed Godwits we still consistently get relatively good numbers roosting on the Dee, and sometimes large flocks as in Dec 1989 when 44,715 were recorded and in Dec 2001 the count of 52,792 is still the highest count since BoEE/WeBS started. The difference, of course, between now and the 1960s and 1970s is that then high numbers were present all winter, not just on a single count day.
With birds roosting on both the Dee and the Alt, how do they choose where to go? A look at WeBS data versus tide heights show that the tide height plays a large part in the Knot's choice of roost site, as the graph below demonstrates very nicely. As shown on the map above the nearest roost sites to the main feeding areas at Dawpool Bank and Mockbeggar Wharf are West Kirby and Hoylake, and birds roost here when the tide doesn't cover the sand banks, i.e. at medium tides. But when these roosts sites are covered by the tide they fly over to the Alt. The graph shows the correlation between tide height and numbers at the Dee and Alt roost sites for the winter of 2004/05. On the Alt, the higher the tide is the higher the count is, the reverse is true for the Dee.
The table below further demonstrates this point for some previous winters:
On the 9.2m and 8.6m tides a good amount of roosting area would have been available at Hoylake and West Kirby, whereas the Spring tide in February 2004 would have completely covered the sand banks and therefore the birds flew to the Alt. But just to demonstrate that this is a trend, rather than a rule - on the WeBS count of February 2002 there were 44,012 Knot on the Alt Estuary and just 141 on the Dee, on a high tide of only 8.6m!
Sources of information for this article:
Voluntary Wardens wanted for Gronant Little Tern Colony
Gronant is a wonderful place to spend a few hours in the summer with the constant activity of the Little Tern colony, some great sea-watching, skylarks and meadow pipits singing over head and wildflowers covering the sand dunes. 2007 will be the 32nd year that there has been wardening here, and as can be seen from the graph below the Little Terns continue to increase in numbers despite the best attentions of the foxes, crows and kestrels; great credit must go to all those wardens doing a great job over those 32 years.
Wardening will be starting in May and usually ends early August. If you want to help out as a voluntary warden, or just want to come along to see what it is all about, contact Adrian Hibbert at Denbighshire Countryside Services, email: email@example.com, tel no. 01745 356197.
April Bird News
The third bird was a Red-breasted Flycatcher, the sixth record for Wirral. These breed in Eastern Europe and winter in western Asia, so another one which has overshot it's normal range. It was caught and ringed on Hilbre on the 23rd.
Migration during the first half of the month was relatively quiet with persistent north to north-west winds holding the birds back, but then the wind switched round to the south and east and the birds started pouring in. As you can see from the table below we had an early cuckoo, this is a species which has become quite scarce in our region and for the past few years we haven't seen or heard any until the end of April or early May. The table shows the dates the first bird of a selection of species were seen.
As well as the Black Kite described above there were also a couple of Red Kites over this month. A total of seven Ospreys was an excellent count but there were no reports of Marsh Harriers (just two possibles?). A female Montague's Harrier flew over Moreton on the 21st.
Avocets are back at Inner Marsh Farm with a max of 10 on the 14th. Up to nine Spotted Redshanks were at Inner Marsh Farm all month, turning in to summer plumage these birds are always good to look at. The first Little Terns were back at Gronant on the 22nd and the first common Terns back at Shotton the following day. Off shore there have been the usual Gannets (150 on 28th) and also a couple of Arctic Skua and a Great Skua. We had a good passage of Little Gulls with 174 on the 8th and 217 on the 11th, both counts off Hilbre.
What to expect in May
Although easing off in terms of volume there will still be plenty of migration this month. One or two Ospreys and Marsh Harriers will still be on their way north, as will those waders who have wintered far to the south. I'm always awestruck by these waders knowing just how far they are travelling with Sanderling, for example, wintering in South Africa and breeding in the Artic. Travelling even further are the Arctic Terns coming up from Antarctica, some of these pass through the country inland and may turn up at sites like Inner Marsh Farm as well as out to sea.
May is often very good for rarities with some birds overshooting their more normal range whilst on migration. In the past three years in May we have seen Montague's Harrier, Pectoral Sandpiper, Laughing Gull, Bonaparte's Gull, Temminck's Stint, Wryneck and Red-backed Shrike. Sea watching can be very good especially during fresh west winds. As well as the more normal Gannets, Scoters and Manx Shearwaters we can get Black-throated diver, Black-necked Grebe, Slavonian Grebe, Black Tern and Roseate Tern.
Many thanks go to Mark Turner, Glyn Roberts, David Esther, David Haigh, Ian Fleming, Neil McLaren, Peter Newman, Paul Roberts, Dorothy Jebb, Stephen Ainsworth, James Armstrong, Chris Wilding, Norman Hallas, Tanny Robinson, Iain Douglas, Dave Rigden, Geoff Robinson, Gill Jakeman, Pete Button, Tina Stokes, Phil Woollen, Steve Hassell, Damian Waters, Steve Edwards, Jason Stannage, Stephen Downing, Stuart Taylor, Steve Menzie, Steve Oakes, Brian Roberts, David Harrington, Dave Edwards, Allan Conlin, Mike Hart, Dave Wild, Colin Schofield, Steve Round, Steve Williams, Chris Butterworth, Jane Turner, Charles Farnell, Richard Steel, Paul Shenton, Paul Rowlands, Leon Castell, Chris Moore, Matt Thomas, Nick Bullen, James Smith, Mark O'Sullivan, Paul Roberts, Geoff Watkin, John Fisher, John Blades, Nigel Troup, Ron Graves, Paul Gutteridge, Steve Renshaw, Jeremy Bradshaw, Ian Emmitt, Karen Foulkes, Tony Twemlow, Dave Kenyon, Chris Davies, Jeff Stephens, the Dee Estuary Voluntary Wardens and the Hilbre Bird Observatory for their sightings during April. All sightings are gratefully received.
Highest Spring Tides
see Tides page.
Forthcoming Events (organised by the
Wirral Ranger Service,
Flintshire Countryside Service and/or the RSPB):
Thursday 3rd May, Evening Sunset Walk to
Sunday 6th May, Dawn Chorus on the Dales. 4.30am
Sunday 6th May 2pm. Birdwatching for Beginners
at Greenfield Valley.
Monday 7th May Bank Holiday,
Wepre Spring Walk, 2pm - 4pm.
Sunday 20th May, A Gentle Stroll around
Heswall Beacons, 11am - 12 noon.
Wednesday 30th May, Our Feathered Friends at
Wepre Park, 1pm - 3.30pm.
Wednesday 6th June, Evening Sunset Walk to
Thursday 7th June. Night Owl Watch, 8.30pm -
NOTE: Many of these forthcoming events are extracted from the 'Birdwatchers Diary 2007', which covers both the Dee and Mersey regions. Hard copies available from the visitor centre at Thurstaston, Wirral Country Park 0151 648 4371.
All material in this newsletter, and indeed the whole web site, has been written by myself, Richard Smith, unless specified.
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