Some recent pictures by Virginia: a Coot skitters across the lake.

Some Common Gulls chase another which has a bit of food, while a party of young Herring Gulls come up from below to join in the fun. Note the very distinctive white 'windows' on the Common Gulls' wingtips, an infallible way of recognising them in the air.

And a Robin perches on a fence. We need to have a picture of a Robin from time to time.

Another bird without whom no day is complete: David Element provided this picture of the female Little Owl near the Albert Memorial ...

... and a Stock Dove, one of the owl's rivals for the hole in the oak tree.

The white Mallard was cruising around the east end of the Serpentine with his mate and the spare drake. Thanks to Ian Young for this picture.

The American Horned Lark is still at Staines Reservoir, and David Element got some video footage of it moving around on the mossy edge while many photographers' shutters click in the background.

The bird used to be called a Shorelark, and here it is on the shore. But restless scientists, not content with naming it Eremophila alpestris, 'the desert lover of the mountains', have now wished a pair of horns on to its head, referring to a very modest crest.

Another picture by Tinúviel from the Los Barruecos nature reserve, a wonderful place. A White Stork and a Grey Heron stand on the shore, while a Green Sandpiper and a Snipe wade in the shallows.

David Element sent me several pictures of birds diving, so let's look at their techniques. The first few pictures are mine, followed by his.

No bird dives as neatly as a grebe. They can flatten their feathers down to a very great extent, which makes them less buoyant and more streamlined. When a Great Crested Grebe does this, it sinks a couple of inches so that its shoulders are under water.

Then it puts its head down, gives a quick slash of its turbine blade toes, and it's under with barely a splash and speeding away like a little torpedo.

Little Grebes can do the same, at staggering speed which makes the action almost impossible to photograph. Their generic name Tachybaptus, 'fast diving', is well deserved.

They reduce their size tremendously before diving, changing from a round ball of fluff into a streamlined projectile. But the only way to show this is with a slow motion video, and I don't have one. When I am on my feet again I will see what I can do in St James's Park or Regent's Park, where Little Grebes are plentiful.

Diving ducks are considerably more buoyant, and must paddle hard to stay down. They have to make a little leap before diving to give them the necessary impetus to submerge. All the following pictures are by David Element. Here is a Tufted Duck ...

... and a Pochard.

Perhaps surprisingly Cormorants, despite their great diving performance, need to jump too.

When a grebe needs to dive particularly deep, it may jump to help it go down. Here is a Little Grebe fishing in deep water.

Update: forgot to say that Duncan Campbell has identified yesterday's mystery hummingbird as a Brown Violetear, Colibri delphinae. He has that wonderful series Handbook of Birds of the World, more accurately known as Fork Lift Truck Book of Birds of the World since so far there have been 19 big thick volumes each weighing 8 to 10 lb. An enviable possession for those whose bookshelves can stand the strain.