On final approach

Look carefully and you will see a sand martin hurtling along, on its final approach to its nesting burrow. 

Sand martins Riparia riparia are summer visitors from Africa and nest in small colonies. They usually fly over water hunting flying invertebrates which they catch on the wing. Their eggs are laid in burrows dug into river banks and firm sandy outcrops. Here you can see their burrows in the face of an ancient quarried kame, a mound of sand, gravel and till left behind by a retreating glacier.

On my way back from the martin colony I passed through a small conifer plantation where the local herons nest,  high above the ground in the crowns of the trees. The young are now hatched and the remnants of the egg shells have fallen to the ground to lie among the pine cones. The extra photograph shows one of the egg remains. they are a beautiful sky blue colour. Why should this be so, what evolutionary pressures have led to blue eggs? Does the colour have a function, conveying some advantage to the bird? The simplest questions are often the hardest to answer.