A group of householders here, none more than 500 yds apart, have found dead greenfinches. We have all had great numbers of them feeding from our nuts. What is causing this mortality, and why greenfinches and no other birds?
Helen Lamb, Clara, Co Offaly.
This mortality among greenfinches tends to occur in March and April, and is caused by bacterial infection, most likely Salmonella typhimurium, (which is not the same as the human type), or possibly E.coli. The infection is passed on where large numbers of birds congregate, such as at feeders. Greenfinches and siskins seem to be more susceptible than tits. Normal household hygiene should be applied - bird tables should be cleaned regularly, the sites of feeders changed, and hands washed before refilling them.
I was recently surprised to see a dunnock repeatedly picking up a thumbnail-size piece of crust and banging it on the ground to break off crumbs which it then ate as they broke away. Surely, whilst feeding on the ground, their normal habit is to scurry around busily picking up minute particles of food, barely visible to the human eye? Kathleen Gaughan, Bishop's Nympton, North Devon.
Dunnocks usually feed on insects picked up off the ground, but when insects are scarce they eat seeds and the crumbs from bird feeders. This is behaviour I have not come across previously; thrushes break snail shells in the same way.
On the evening of April 12, between hail storms, I spotted my first house martin of this year - a single bird near Kerry Airport. From previous years it seems a little earlier. What is the usual arrival date? Niall Wallace, Dublin. Your Kerry house martin was just on time. They start arriving in this country in April and latecomers arrive in May.
Edited by Michael Viney, who welcomes observations sent to him at Thallabawn, Carrowniskey PO, Westport, Co Mayo. e-mail: viney@anu.ie. Emails should include postal address.