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A tale of two waterbirds


Gadwall

Moorhen

Counters

 

Counting waterbirds on a monthly basis can be a bit of a slog at times. For a start, it takes several hours to get around all the lakes in Wanstead Park, let alone those on Wanstead Flats. The weather may be cold and wet, the paths muddy and sometimes not very much has changed since the previous month. Counting gulls on Wanstead Flats is particularly frustrating, regularly producing the classic situation where – close to the end of logging a large loafing roost of Common Gulls, 583, 584, 585 … a dog charges through the middle and disperses the lot. Right, where was I? 1, 2, 3, 4 …

Despite this, the numbers produced provide useful information for the British Trust for Ornithology (BTO), helping them to evaluate which species are faring well and which are in trouble. Locally, we have a team of tireless counters, so during the winter months not only Wanstead Park and Wanstead Flats but Eagle Pond (Snaresbrook) and Hollow Pond (Whipps Cross) are covered. We also now have an almost complete record for the months of autumn, winter and early spring stretching back to January 2009. That makes it possible to look at trends and, maybe, draw some conclusions. Combined counts for Wanstead Park, Wanstead Flats and Eagle Pond can be compared now over seven WeBS counts. Systematic counting has only recently restarted at Hollow Pond, so a comparison cannot be made including that site. Browsing through the figures, trends for two birds jumped out at me: those for Gadwall and for Moorhen. Figures for the recent WeBS count produced record January numbers for both species.

The ‘Gadwall army’

The main concentration of Gadwall in our area is on Alexandra Lake and the lakes of Wanstead Park, all waters where there is plentiful weed for these ducks to eat. Numbers at Eagle Pond rarely exceed single figures. The rate of increase was slow and irregular in the first years of the sequence: 40 in January 2009, 24 in January 2010, 101 in January 2011 and 88 in January 2012. During these years, the peak counts were respectively 111, 86, 137 – and this is where things really start to lift off – 200+ in December 2012. Since then, the rise of the ‘Gadwall army’ (as former Wren newsletter editor Steve Swaby has dubbed it) has been seemingly inexorable, with 363 in December 2013 and 459 in December 2014. The 422 counted in January 2015 was the highest-ever January count, and the biggest count on a WeBS day.

Gadwall was a pretty rare bird in London not that long ago. According to Andrew Self (The Birds of London, 2014), the average wintering population in London was only about 100 in 1970. Wanstead Bird Reports from the late 70s and early 80s mark it out as a local rarity. However, by the end of the century the London winter population was around 2,500, and Self describes an average of 600 in the Lea Valley in recent years. The peak count (at the time of publication of his book) he lists was 453 at Cheshunt GP in December 1989. A larger share of London’s birds is now wintering in Wanstead, but there is no obvious reason why. Clearly there is a plentiful supply of weed on which the birds can feed, and maybe the growth of weed in our lakes has made it easier for these attractive dabbling ducks to feed by upending. Whether other factors are involved – such as an increase in the continental populations from where most of our birds originate, or problems with the food supply at locations where they previously wintered – is not clear. One thing is certain, we should enjoy the phenomenon while it lasts because like pretty much everything in nature, numbers go down as well as up. Cutting of the weed in The Basin later this year may well impact on the numbers that lake can support next winter.

Moorhen success

Another success story, though much less dramatic, concerns Moorhens. Again, January WeBS figures for the years 2009-2015 show a consistent increase: 20, 21, 35, 44, 2013 figure lost by a careless recorder!, 66 and 80. And maximum counts for those years were as follows: 47, 56, 35, 65, figure unavailable, and 78 in 2014. Judging by the number of juvenile Moorhens seen on our lakes in recent autumns, I believe this increase can be put down to local breeding success. The species nests in emergent vegetation, where they are better protected than Coots’ nests, which are exposed stick islands, easy pickings for Lesser Black-backed Gulls. With the highest-ever January WeBS count for the species this year, I reckon we could be in for another bumper breeding season.

Tim Harris 19/1/2015

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January 20th, 2015

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