Search for cause of blue tit's death (From Gazette Series)

Search for cause of blue tit's death

I HAVE been using a webcam to follow the fortunes of a family of blue tits that had chosen to nest in a box on my house.

All had been going very well. Seven eggs were laid and incubation began on May 10. Five then hatched on May 22, followed by two on May 23. The parents were attentive and brought in plenty of food. I could see three nestlings begging for food at 16.51 on May 23, but 24 minutes later the parents looked bewildered when there was no interest in the latest offering.

Later in the evening, I checked the nest and found all nestlings dead or dying. The following day all were dead and I removed them from the nest box. There were no signs of injury or disease.

Their death is a mystery. There had been no obvious outside interference, the nest box was dry and it had not been unduly hot or cold. A starling had looked into the nest box early on May 23 but couldn't reach far enough to do any damage. The parents had been bringing in food and the five that had hatched on May 22 were a similar size and all had put on weight.

I contacted the RSPB. They said that blue tits were having a poor season because earlier cold weather had reduced the potential food supply. However, the parents had been bringing food. If food had been short, the stronger nestlings would have taken the bulk of the food leading, perhaps, to the death of the weaker ones.

The only plausible explanation I have is that the parents had collected caterpillars contaminated with pesticides; the nestlings would have been far more sensitive to pesticides than their parents. Have readers any other explanation or experience of similar problems with blue tits or great tits this year?

Dr Clive Mowforth 13 Jubilee Road, Kingshill, Dursley