A friend has been trying to photograph water rail at the Great Fen. Not an easy task. Even the RSPB notes that they are difficult to see in breeding plumage. They do also mention that they are highly secretive.
Shockingly, as a non-twitcher (and even non-birdwatcher really) I have seen one. And even photographed it - though finding the image is proving as difficult as the species itself.
I say shockingly as I really can't emphasise enough how it is luck rather than skill in seeing rails. The family Rallidae includes species called the "Inaccessible Island rail" and the "invisible rail". When they aren't being inaccessible or invisible, they are being made extinct. For instance, the Red Rail of Mauritius, described by Peter Mundy in 1638:
"It hath a long, Crooked sharpe pointed bill. Feathered all over, butte on their wings they are soe Few and smalle that they cannot with them raise themselves From the ground. There is a pretty way of taking them with a red cap, but this of ours was taken with a stick. They bee very good Meat, and are also Cloven footed, soe that they can Neyther Fly nor Swymme"
Or the description of the Rodrigues Rail by François Leguat in 1708:
"Our 'gelinotes' [hens] are fat all the year round and of a most delicate taste. Their colour is always of a bright grey, and there is very little difference in plumage between the two sexes. They hide their nests so well that we could not find them out, and consequently did not taste their eggs. They have a red naked area round their eyes, their beaks are straight and pointed, near two and two-fifths inches long, and red also. They cannot fly, their fat makes them too heavy for it. If you offer them anything red, they are so angry they will fly at you to catch it out of your hand, and in the heat of the combat we had an opportunity to take them with ease."
But my favourite is the Ascension Island rail (sometimes called Ascension Crake). All that is known of the species is from Peter Mundy's account and sketch from 1656. Unlike other rails described here, no skins were found, and only a few bones are known. In life, this is the total extent of our knowledge of the species:
"Alsoe halfe a dozen of a strange kind of fowle, much bigger than our Sterlings...colour grey or dappled, white and blacke feathers intermixed, eies red like rubies, wings very imperfitt, such as wherewith they cannot raise themselves from the ground. They were taken running, in which they are exceeding swift, helping themselves a little with their wings...It was more than ordinary dainety meat, relishing like a roasting pigge."
So, with that legacy in the family album, I would be "highly secretive and difficult to see". Wouldn't you?