Some bird species, such as the great-crested grebe (pictured), hunt underwater for fish and have red eyes. The red colouring is presumably beneficial to these diving birds, but in what way? If it does provide an advantage, why have other birds with similar habits not evolved red eyes?

Ian McKechnie, Weybridge, Surrey, UK

How is it that birds which lay a large number of eggs are able to have them all hatch on approximately the same day?

The blue-footed booby (pictured) is an extraordinary-looking bird. It has fairly dull plumage but strikingly coloured blue legs and feet. What could be the evolutionary benefit of such a conspicuous feature? Both sexes have blue feet so they don't seem to be for impressing potential mates.

Sam Moore, London, UK

Note:

Except for making sounds

I found the pattern shown in the attached photograph in the snow on my lawn on Christmas Eve.  I assume the two 'arcs' of straight lines were made by a beak, as the lines across the pattern appear to be bird tracks.  The arcs are about 20 cm apart.

The South African highveld gets its summer rain in thundershowers.  The evening following a good shower sees thousands of termites flying off to start new colonies in the soft ground.  This attracts swarms of swallows.  The swallows seem to keep hunting until the termites stop flying.  So how many termites does each swallow then eat?  If they are skilled hunters (which I believe they are), they must be able to catch many more termites than what I would think fits into a swallow's stomach - especially if it wants to keep flying!

A couple of weeks ago I was walking in the local woods when I heard a lovely gentle warbling sound. It turned out that it was coming from a blackbird in a nearby tree, who was singing very quietly without opening its beak. It was definitely this bird making the sound, not another one further away. Do birds rehearse their songs before committing themselves to singing out loud? This song was surely not intended to be heard by other birds at any distance.

I've read about some studies with electrodes in the brains of sleeping zebra-finches which have suggested that they 'dream' of singing, but is this kind of 'closed-beak singing' a known behaviour?

Many birds seem to take long, hopping journeys across grass or other areas by hopping erratically. Is this not very energy-consuming, compared to walking, or flying?

What might they gain by this form of motion?

How is it that birds which lay a large number of eggs are able to have them all hatch on approximately the same day?

Patrick Casement, London, UK

On a beach on the Gower in South Wales recently I saw a seagull fly up from the sand, drop something small from its beak, then dive after it back to the ground, where it then did something with the object (too far away to see exactly), then repeated the procedure. What was it doing?

The sand was wet and quite firm for sand, though obviously not as hard as tarmac or concrete. Could it have been trying to prise a small creature from its shell? If so, is this tool-using behaviour: using gravity and the ground?