EYE ON NATURE

"I was surprised to read (Eye, November 18th) that the presence of undeveloped tadpoles in a pond in winter was an unusual phenomenon, as this appears to be an annual occurrence in our small pond. I don't suppose the large tadpoles I observe each winter are the same creatures from one year to another.

Measuring approximately 10-12 mm in body length with a tail of similar proportions, these creatures have passed the smooth, black, rounded stage of younger tadpoles, and instead possess a more angular body of greyish colour. I have seen one feeding one a younger tadpole in early summer.

Peter McIlwaine, Manor Kilbride, Co Wicklow.

Your greyish creatures are not tadpoles but the larvae of the great diving beetle (Dytiscus marginalis) which is ferociously carnivorous in both adult and larval stage. Both will attack and eat creatures larger than themselves, and tadpoles are their staple diet in late spring and summer. The larval stage of the great diving beetle can last up to one year.

Recently I have noticed coming to feed in our garden a male house sparrow with either a deformed lower beak or a pea-sized growth under his beak. He has difficulty getting meal and peanuts off a hard surface and turns his head sideways and horizontally (as rooks do) to pick them up. Nevertheless he is plump though his tail looks a bit bedraggled.

Are deformities rare in birds? We are led to believe that nature selects out imperfections.

Mary McKeogh, Kilkenny.

Usually, deformities leave birds more vulnerable to predators or starvation. In the case of your sparrow, his difficulty could mean that he takes more time to pick up food and so his alertness to danger is sidetracked for longer than normal during feeding, leaving him exposed to predators.