Eye On Nature

Have you any Darwinian explanation as to why Willie Wagtails wag their tails? As they do it irrespective of season it is unlikely to have a sexual display purpose. Both sexes seem to do it and it must involve a fair expenditure of energy. A friend suggested it helped their balance when they stop in their run, but there is a certain element of flicking as they run, and besides birds with longer tails don't wag. Any ideas?

Helen Lucy Burke, Finglas Road, Glasnevin, Dublin 11.

Wagtails belong to the same family as the pipits, Motacillidae, and both are essentially terrestrial birds, feeding and running on the ground. Both also, in their various species, wag their tails to varying degrees, with tail-wagging being more pronounced in the wagtails. Some ornithologists suggest that tail-wagging may help to keep feeding flocks together. But, I've been thinking that it might have other uses, such as balance, as both wagtails and pipits have relatively long toes; or, perhaps, for alarming insects to make them move and therefore become more visible.

For the past few years we have a resident cock blackbird in the garden, showing one small white wing feather; but recently we have noticed one and perhaps two each showing two white wing feathers, one on each wing. Is this common, and is there any explanation for what appears to be a hereditary progression?

Henry Deegan, Callow, Foxford, Co Mayo.

Every year, albino or partially albino blackbirds are reported, usually in suburban gardens, and while few, they are not rare. True albinism, total lack of colour in the feathers, irides and soft parts is thought by some experts to be a recessive gene and to be hereditary. They also consider, how- ever, that partially white birds, which usually retain normal colour otherwise, may be suffering from diet deficiency (perhaps too much dependence on the food from bird tables), old age, injury or shock. In partially albino blackbirds, the white area tends to spread as they get older.

I read Evie Anderson's letter of February 27th re the decline of the magpie population in the Kilternan area with interest. It could be that some of her neighbours have a "Larson" trap and are reducing the population. Our magpie population moved on when the nearby tall trees were cut down. The good news is the corresponding increase in the song bird population that follows.

Neil Colin, Dublin 16.

Edited by Michael Viney, who welcomes observations sent to him at Thallabawn, Carrowniskey PO, Westport, Co Mayo. e-mail: viney@anu.ie.

Observations sent by e-mail should be accompanied by postal address as location is sometimes important to identification or behaviour.