Monday, 12 October 2009

The value of weed

After yesterday's excitement there was no sign of either the Long-billed Dowitcher or the Ring-billed Gull today. Even the two Little Stints reported seem to have transformed into two Dunlin and these along with three Green Sandpipers were all the waders I could find on Ibsley Water when I opened up the Tern hide this morning. I did hear that the Great White Egret was seen near the Lapwing hide early on, but flew off as usual.
Even the moth trap provided thin pickings with just the first Yellow-line Quaker of the autumn and the rather fine caddisfly pictured below.
The lakes at Blashford are mostly very clear and water weeds grow very well in them. This is good for birds and water companies as clear water is what they both want. The birds want the weed and the invertebrates that live on it. The two most "important" bird species at Blashford are Coot and Gadwall and both feed on water weeds. At the moment Ibsley Water has huge rafts of floating weed and lots of Coots feeding on it. In places it is so dense that the herons have been standing on it even though the water is three or four metres deep.
We often hear about the problems caused by alien water weeds, clogging canals and generally out competing native species, they are basically viewed as bad news and something to be got rid of. However the Coot and Gadwall at Blashford are almost exclusively eating and alien water weed, one of the Elodea pondweeds often known as "Canadian pond weed". In this case the nationally and internationally important populations need the alien plant. Incidentally the "importance" is defined as a percentage of the population. So for Coot we have over 1% of the UK population and for Gadwall we have over 1% of the W. European population.

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