August & September 20

I did my August standard bird walk in mid-month. I was interested to see if there was any ill effect of the blue-green bacteria, first noted in the lake at the very beginning of August. The bacteria were still very much in evidence, with the lake water quite murky. Well, there was no sign. The 70 coots were a record number for August and the 140 Canada geese the second-highest August count. The greylags were as high as in any previous August. Only the 45 Egyptian geese might suggest an easing back of numbers. Perhaps the trapping and killing of these on the golf course is having an effect? The pair of mute swans and their surviving seven cygnets were healthy. The long-term increase in moorhen numbers seems to be continuing, as the count of 20 birds was twice the previous highest August count. Long-tailed tits don't breed in the public park and even the winter flocks are only occasional there, so it was good to see an unseasonably large flock of 5 in Ashen Grove Wood. Gypsywort is often seen growing in the crevices of the sheet piling on the lakeside, but there was also some water mint seen there for the first time.

My September bird walk was on he 11th. Coot numbers remained high, with 125 the second highest count over the last 35 years. As all too often these days, I found no greenfinches. The graph shows the huge decline of this species. The national monitoring dates the onset of trichomonosis disease to 2006, but my counts suggest that the population declined around 2001 and rallied at 2006 only to decline again around 2014. There's no sign of any recovery as yet. The blue-green bacteria were still evident and the water murky.

In a reply to a query from the Friends of Wimbledon Park, the golf club claims that there are record numbers of Canada and Egyptian geese in the park this year. My monitoring statistics show that this is not the case. The average count of Egyptians rose to a peak in 2018 and has come down somewhat since. Peak counts might give concern, but in every year between 2014 and 2018 these have been higher than in this and last year. Canada goose numbers have increased in recent years, but the long view shows that they did not achieve the peak numbers that occurred in 1989, 1990, 2008 & 2009. The club assert that the cull of these two species is justified further by the nutrients and pathogens that they transport to the lake when they return from feeding on grassland to rest up on the water. Here the agument may have some weight, although it's true that the greylag geese, coots, moorhens and gulls do precisely the same but are not covered by the same general licence to cull and, apparently are not being culled. The statement by the club is odd in citing the carbon content of faeces as a nutrient, wheras the science tells us that the nutrients of concern are nitrogen and phosporous (very likely nitrogen in our lake). The movement of geese from terrestrial feeding places to the lake will import nutrients, but the consequent link to water quality is overstated for two reasons. First, is that Janet Kear established in 1963 that the throughput of food is such that much of what is consumed terrestrially is also deposited terrestrially. Second, is that Robert Unkless in 2006 showed that imported nutrients are sequestered rapidly in the sediment of a lake and so do not pollute the water. The faeces of all birds can contain pathogens and there's no doubt that these two species of goose will contribute to the pathogen load in the water, as will greylags, mute swans, ducks, coots, grebes and gulls. So, a pathogenic risk will remain even if the numbers of these two goose species are controlled effectively. The golf club alludes to the risk to their ground maintenance staff from pathogens in faeces deposited terrestrially that are disturbed as the course is managed. There is certainly a theoretical risk of this, and it's unpleasant, but it's strange that there is no such concern expressed for the public park where large numbers of geese feed on the great field every morning. Why does the London Borough of Merton not control the geese to prevent a pathogenic risk on the great field I wonder? I'm sympathetic to the golf course users and managers when faced with a nuisance and unknown risk, but I observe that goose numbers are still high despite the ongoing cull and that the public might expect that killing wild birds is not undertaken lightly.