EYE ON NATURE

In recent years the bottom of the Portumna swimming pool (where the River Shannon enters Lough Derg) has been carpeted with well-washed milled peat from Bord na Mona bogs. During the swimming season last year I was surprised by the number of freshwater mussels (enclosed shell) underfoot in the milled peat carpet, far more than any previous year. Could this dramatic rise in numbers be due to the enormous kill of bream in the Shannon and Lough Derg last spring?

Eamon Hayes, Portumna, Co Galway.

The shell is that of the swan mussel, Anodonta cygnea, which is commonly found in slow moving waters. A fish kill last spring would not have had any effect on the number of mussels that size - 90 mm long - which would be several years old. Whatever caused the increase happened some time ago. Swan mussels and their cousins the duck mussels Anodonta anatina, are not pearl-bearing like the other, freshwater mussels, the Margaritiferae or pearl mussels.

Christmas cards show robins and holly, and I can honestly say that I have never seen any bird eat a holly berry. These trees remain berried until February when the berries cover the ground.

Catherine Cavendish, Sandymount, Dublin 4.

If your birds are not eating holly berries then they must have an ample supply of other food. Throughout the year, blackbirds and thrushes mainly eat earthworms and also insects. But in autumn they eat fruit and berries such as blackcurrants, haws, rowan and holly. Mistle thrushes will choose a well-berried holly tree and guard it through the winter as their private food supply.