The House Martins nesting on the embassies in Knightsbridge are gradually returning to the French Embassy. This was always their preferred building of the two, because its cornice faces the setting sun and the masonry stores heat to keep the nests warm at night. But three years ago, when the building was redecorated, their nests were destroyed, and they moved to the Kuwaiti Embassy opposite. They have been reluctant to abandon their laboriously built nests on this side, but this year for the first time I saw more birds visiting the French building, and it is clear that they have rebuilt their nests here from scratch. Here a House Martin flies up to one of the downward-facing stucco roses on which they have put their new nests. The upper side of the petal makes a good supporting shelf, and the square recess around the flower forms a convenient and cosy shelter.

The following picture was not taken in the park -- I took it yesterday in Gloucestershire. It shows how House Martins attach their mud nests to a vertical wall.

First the bird lands and sticks its beak into a patch of mud of a suitably sticky consistency, picking it up rather like a bricklayer with a trowel full of mortar. It flies up to the wall and clings to it, then pushes the lump of mud into a small hole or irregularity in the masonry, which will hold the mud in place when it is dry. Once they have made enough of these attachment points they can extend the mud outwards to make one of their cup-shaped nests. It is a lot or work for a small bird, and you can see why having a ready-made plaster moulding appeals to them.

After these quite attractive photographs, here are two pictures which are neither beautiful nor of birds, but I think they have a certain interest.

This one shows the wire basket of twigs that interests the Great Crested Grebes so much. A school of small fish about two and a half inches long has momentarily quit the safety of the inside of the basket and is streaming across the surface.

The fish might be roach, but it is hard to tell -- can any reader help? The shot was taken at an angle, so refraction has flattened them considerably.

And this picture shows a Blue Tit's hygienic arrangements. I was feeding some birds when the tit arrived holding this object, hung it over a twig, and came down to pick up a pine nut from my hand.

It is a faecal sac produced by one of the nestlings, a convenient arrangement that avoids fouling the nest. The excreta are enclosed in a membrane. I don't know why the tit carried it some way from the nest and hung it up, but this may help to conceal the location of the nest from predators.