Corvids build castles in the sky

Claxton, Norfolk Once the nest building instinct has been unleashed it is remarkable how lavish their designs can be

It is wonderful to walk down the lane on to the marsh and see how, despite April's refrigerated interlude, spring is building still. In some cases, this is literally true, not just the hawthorn hedges, which are fattening up with fresh leaves and blossom, but also the jackdaws, whichjourney back and forth with great gobbets of moss and cattle hair in their beaks. Some are so front-loaded with construction materials that one wonders how they see to navigate.

Corvids are generally great architects, and once the instinct has been unleashed it is remarkable how lavish their designs can be. The standard rook nest is a rough 15cm-deep stick platform, but recently I have come across some where the foundations are in a deeply forked situation. They have gone on until these twisting columns of sticks, which are known as "castles"', are more than a metre tall.