I did my monthly bird count on the 16th. There were two Grey herons in a tree on the island, perhaps an incipient
herony. It would be great should they begin breeding loclly. Consulting
recent reviews of the science of lake water quality, shows that poor
quality can be caused by some common bottom-feeding coarse fish: Carp, Tench and Bream,
as well as fish that feed on zooplankton, adding Roach to the list. So,
why am I concerned? Well, the lake attracts fish-eating birds: Grey
herons, Kingfishers, Great-crested grebes, Egrets, Cormorants and Common
terns, all of which are doing well and would do much better, should the
All England and LB Merton heed advice on how to provide them with undisturbed breeding places.
Although the anglers complain that their fish are not doing well, those
birds seem to disagree, they come to the lake because it provides food - those fish! Lake water quality might be at risk from the
wrong kinds of fish. Predatory fish are better, indeed people have tried adding Pike to shallow eutrophic lakes in an attempt to control those other
species. There was a Common tern fishing the lake, but no sign of a nest. As in last summer a sole male Pochard remains on the lake after the departure of the rest. It seems to be a pinioned bird, which begs the question of how it arrived here.
Lake water clarity was good, and big populations of waterfleas were visible, but this is the time of year when the lake can can be overcome by a bloom of blue-green bacteria and there was a worrying amount of Aphanizomenon flos-aquae to be seen. If the nutrient levels of the lake water are low enough, waterweeds can prevail, making for clear water and benefitting wildlife, but if the blue-green dominates the water quality will decline, as has happened all too often in recent years. Let's hope that nutrients locked away in the lake sediment aren't disturbed.
There was vixen with at least four well-grown cubs in Ashen Grove Wood and the adjacent play area, not at all afraid of my presence. The Mute Swans hatched six cygnets this month, counted on the 10th, but the pen was back sitting on the same nest on the 16th, with no sign of the cygnets. Perhaps they were just resting up for a bit, but I fear that brood was lost to foxes, or some other predator. As I arrived at the lake another pair of adult Mute swans was flying off. So, I wonder if there has been a territorial dispute, in which the cygnets were lost? The 50 Canada geese was a count only a little below the long-term average June count of 65. Numbers rise at this time of year when they come for a nice big lake to protect them from predators when they are moulting and flightless. The few Egyptian and Greylag geese had good breeding success, but not enough to bring numbers back up to those of recent years, both were around half of those numbers. Coot numbers remain at their historical high, which is not surprising because there is a good growth of Fennel pondweed for them to eat. There was a Great-crested grebe nest on the lakeside nor far west of the new weir structure. The various pigeon species were feeding on grass seed sown to reinstate areas disturbed by the dam safety works. It's not the best time of year for grass to survive and there were plenty of weeds to be seen as well, so we just might get more wildflowers than intended by mistake!
Most bird species were too busy breeding for the luxury of song, but Blackcaps and Stock doves were singing in Ashen Grove and Horse Close woods and in the eastern railsides. Swift numbers are very variable, so trends are difficult to detect. The long term average number for May and June is 12 birds, but we had none in May and only six in June, suggest that they are indeed decreasing. The fashionable explanation for the decline is loss of nest sites through works on older houses, but this is contradicted by the enormous numbers of nesting boxes that lack breeding swifts. It's probably shortage of food, either here of when they are away on migration in Africa. It will be difficult to establish the cause of the decline, but there is at least as much evidence for maintaining lake water quality so that the swifts can get food when they commute here from their nests.
Water has recently been sent down the new, sinuous channel of the brook in the crazy golf area and it was good to see that the resident Grey wagtails are still to be seen. There was one in the water garden area where the new course of the brook begins. One of the branches of the easternmost Osier on the lakeside promenade has failed at its base, allowing the branch to descend towards the lake water. This tree plot is remarkable because the base of the Osier shelters a young Oak, young Horse chestnut, Hyprid hedge bindweed and a Mugwort. In the long run, allowing the Oak to grow might be good, but the Osier provides excellent habitat, and even better if it dips into the water. The Horse chestnut is not appropriate here and it should go.
Spring flowering was nearly over, but Elders were still in flower. There was much watercress flowering in the brook and a nice Narrow-leaved ragwort in flower on the margin of the stadium.
A sewer that leaves the park beside the lower brook was blocked, leading to a waterfall of raw sewage down into the brook just where it passes the grille to go under the tube embankment. This obviously needs repair, raw sewage not being welcome in a public park, and it is most undesriable also for sending significant pollution down the pipe to the Wandle at Earlsfield.
