Thursday 20 November 2014

A Dutch-ringed Black-Headed Gull turned up on the north shore of the Serpentine. I have not seen this one before. From the fairly dark colour of its legs it looks to be at least two years old. Will report it to the Dutch ringing organisation.

On the other side of the lake, a Grey Heron was landing on a post, with air brakes full on.

You can see from the way the feathers on the upper surface of the wings are ruffling that the airflow has detached from them and become turbulent, so the wings are no longer producing lift -- in aerodynamic language, they are 'stalled'. The heron, an expert at slow flight and precise landing, has judged this moment nicely so that it can drop on to the post, making what a helicopter pilot calls a 'zero-zero landing', reaching zero altitude and zero forward velocity at the same instant.

One of the young Great Crested Grebes at Peter Pan was stretching its wings, which are quite long but narrow, so that they don't produce much lift and the bird has to attain a high forward speed before they will support it in the air. That is why grebes have to make that frantic 50-yard takeoff run, and also why they come down so fast and splashily on the water.

Compare the broad wings of a Red-Crested Pochard, which provide lots of lift and allow it to take off after the shortest of runs.

This is one of the group that are staying on the island at the moment.

A Greylag Goose on the Serpentine had turned upside down during a vigorous washing session.

In the rowan tree on Buck Hill, a Song Thrush ...

... and a Mistle Thrush were eating berries.

You can see the difference in the pattern of their spots, which is the easiest way to tell them apart. Although a Mistle Thrush has a greyer back and paler face than a Song Thrush, and is larger -- the two pictures are about the right size relative to each other -- these differences are not always apparent, especially when you are seeing only one of them.

The stratagem of approaching the Tawny Owls' tree from the other side, so as not to bring a crowd of Jays and Magpies to annoy him, was effective and I found the male enjoying an untroubled doze. There were  lots of noisy Ring-Necked Parakeets in the tree, but these didn't bother him.

The male Little Owl was in the chestnut tree next to his nest tree. The leaves are getting rather thin and he may abandon this place soon.


  1. I saw the Lesser Black Backed at work again today but fortunately this time the kill was much quicker. There was no movement from the pigeon after being submerged and just a little twitching a short while into the eat (not necessarily a sign of consciousness?).

    As before there were a lot of uncertain and unsuccessful sorties into the throng plus much taking off and unsuccessful swooping in. The eventual victim was again grabbed at the edge of the lake. This time the carcase was approached by a couple of other gulls after the Lesser Black Backed had appeared to leave it, but each time it returned and saw them off to have another go at it. The timing also was the same – around 15:00 – and it was still finishing it off forty minutes later. This event was much less harrowing but the sight today of those two little pigeon legs poking out of the water was still affecting. I don’t think I’ll linger in future!

    1. Interesting that the gull seems to have a schedule. I've looked at my pictures of past attacks and they confirm this. I've been going round the lake a bit earlier recently, which may explain why I haven't seen any serious attacks.

    2. Intriguing. The same again today. I walked past around ten past three by which time it had eaten most of its catch. By the way I really appreciated the aerodynamics explanations and illustrations. This blog is a real treat.

    3. Thanks. I was there an hour earlier, while the gull was still stalking menacingly through the crowd of pigeons. It seems to take some time before it can find a good chance.