28 August 2010

Black-headed Gull

Image: Gidzy

As summer comes to its close, the annual influx of gulls gathers pace. By autumn they are everywhere in the district, feeding on pasture and arable and parkland, by and on water of all kinds, and, ever on the lookout for a meal, patrolling the skies above back gardens and industrial sites.

There are five common sorts which visit us here, and the commonest of these is the black-headed gull. This is the smallest and the slenderest of the five, and can be told by its red bill and legs, and the long white triangle on the leading edge of the wings, which have pointed rather than rounded tips.

Despite its name, the black-headed gull’s head is not black. In spring and summer the adult has a chocolate-brown hood, which is moulted in autumn to leave the head pure white except for two dark smudges, the larger one behind the eye and the smaller one just in front of it. The immature bird is more mottled in appearance, but still has the white triangles on the wings and, at all seasons, the smudges on the head.

In grace, buoyancy, and agility of flight the black-headed gull has few equals among our winter birds. During autumn it makes a habit of following the plough, and a hundred or more at a time can be seen swirling like snowflakes against the freshly turned soil. The same sort of prey – wireworms, millipedes, earthworms, and so on – attracts it to football fields and similar grassland; but our local black-headed gulls find their shangri-la on pasture that has just been sprayed with Hydig, the fertilizing sludge produced at Maple Cross sewage works, just south of Rickmansworth.

The sewage works themselves are also an attraction for gulls. In the grounds is a disused gravel pit which, during the 1960s, was filled with solid matter rejected during the purification process. A long black outfall pipe led from the works into the middle of the pit. Some of the outfall consisted of sand, so that the pit slowly became silted up, but it also contained grain, as well as a comprehensive assortment of the things that get dropped or thrown into the lavatory (among them many children’s toys such as rubber Donald Ducks, combs, nailbrushes, pairs of spectacles, and any number of sets of false teeth.)

Among all this detritus the gulls used to gather, picking over the spoils. At irregular intervals there came a distant rumbling in the pipe. At this the gulls’ excitement mounted, and with expectant cries of “kwarr” the flock drew closer to the broad mouth of the pipe, flying up when, with a rush, it disgorged a fresh supply of sludge.

During hard weather this was an important source of food for the gulls in the Colne Valley, and as many as 400 birds could be seen there at once. The dumping has finished now, but the sewage works still draw plenty of gulls. After detailed observation the same individuals can be recognized returning day after day, for some birds have peculiarities such as a deformity of the bill or an odd pattern of plumage. A few of the gulls carry aluminium leg-rings, put there by ornithologists perhaps in other countries.

One ring seen on a living bird bore the number C-17122 or C-1722. From this and a description of the pattern the British Trust for Ornithology were able to say that the ring was of Finnish origin, and in fact many of the black-headed gulls which winter with us breed in the countries round the Baltic Sea, especially Sweden and Denmark.

In Britain the black-headed gull breeds, especially in the north, on saltmarshes and sandhills close to the sea. Yet it is also the most inland of our gulls and nests on marshy islands in lakes and moorland pools far from the coast. In the early 1960s a few pairs even bred at Maple Cross, but the colony was soon abandoned.

It is difficult to imagine today that all gulls, even the black-headed, were once very rare in this area, being seen only when storms at the seaside blew them off course. Their success is attributable directly to man: they have learned to exploit the many opportunities, like the sewage outfall pipe, we have unwittingly put in their way.

The only problem for gulls inland is the need of a safe roost. The first gulls to appear in any numbers in London arrived in the bitterly cold winter of 1894-5, and they roosted then mainly on the Thames at Chiswick Eyot, or at the small Lonsdale Road Reservoirs.

At the turn of the century there was a big increase in reservoir-construction. The huge Staines Reservoir was completed in 1902 and quickly became a major gull roost. The other reservoirs in that part of Middlesex and north Surrey, some even bigger than Staines Reservoir, as well as a chain of reservoirs in the Lea Valley, provided further roosting. Today well in excess of 100,000 gulls roost in the London Area during winter.

When it was filled, in 1955, Hilfield Park Reservoir near Aldenham soon became an important roost, attracting something like 5,000 birds. Many of our local gulls roost there, and at dusk make their flight-lines in that direction. The rest of our birds roost, or did roost, at Staines, and the birds from the Colne Valley can be seen flying south at the end of day. This is where the Maple Cross birds roosted, arriving there 25 minutes after first light, having taken that time to fly, at 40 m.p.h., the distance from Staines.

But now these opportunists have found a way to cut their commuting time. A vast gravel pit, Broadwater, has been dug at Denham, large enough to make a safe roost, and many Staines-bound gulls have adopted it as their own.

A gull roost as it fills is an extraordinary sight. The sheer spectacle of so many birds in one place is not soon forgotten. To see them arriving, each with a different experience of the day’s foraging, is a powerful reminder of the adaptability of living things and the effect that man has had on their world.

As the gulls come in, you tend to forget about their feeding habits and are conscious only of a sense of wonder and beauty. If only all our activities produced a result like that.

(Introduction to these pieces; see all)

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