As I write this the bulk of the nesting season is over. The Trust is involved in checking and maintaining over 300 small nest boxes. In doing so we record and input data to the British Trust of Ornithology, or BTO. We have records for the Trust for the last 4 years, so have an idea of a successful season and the ones which are less so.
The camera box at the Trust was occupied by Great Tits, this was a success, however other boxes have had reduced clutches and in the case of numerous Blue Tit nests there has been dead chicks, abandoned nests, part built nests, and unhatched eggs.
Why has this happened? Generally Blue Tits time their nesting and feeding of their chicks with the emergence of caterpillars. Long term studies have shown that blue tit populations grew more in years when moth numbers were higher, indicating that the abundance of moth caterpillars impacts blue tit breeding success. Among the moth species linked to blue tit success was the winter moth, which emerges early in spring and is known to be a key food source. Weather is a main factor, cold wet weather can limit that emergence.
For further information https://www.bto.org/understanding-birds/articles/blue-tit-diary
All our boxes are checked and any birds that are ringed are BTO permit holders, allowing them to record data. Birds such as Goldfinches are seed eaters, and feed their young on seed, so even in poor insect years finches can do well on garden feeders.
On a positive note it is always a great sight to see a successful fledging like the Great Tit below. However, even this successful nest box you can see in the a dead chick remains!
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