Friday, 27 July 2007

Has it been a poor breeding season

The question of how our breeding birds have faired is one that I have been asked often of late. The heavy rain and unseasonably low temperatures may have contributed to a poor breeding season and there do seem to be fewer young birds about than usual. Friends who monitor large numbers of nest boxes in different parts of the country have commented on the large number of blue tit and great tit nests that failed, suggesting that one particular band of heavy rain caught them at just the wrong time (heavy rain can wash caterpillars from the canopy and make it very difficult for adults to find sufficient food for their large broods of hungry chicks). Other species that nested slightly later, such as pied flycatcher, seem to have got away with it. This was a pattern also picked up in the southwest by the BBC’s Springwatch team. However, in other parts of the country tits have been reported doing well, so it may just turn out to be a regional problem.

In Norfolk, some of the open nesting species – like blackbird and song thrush – may also have struggled. Regular readers of the EDP will have seen how nesting bitterns and lapwings were washed out by water levels well above average in our reedbeds and wet meadows. While species like bittern are single-brooded and usually only make one nesting attempt, others may get the chance to try again if their first attempt is lost to the weather. Our local blackbird has had at least two unsuccessful attempts this year but has just successfully reared a third brood through to fledging. Mind you, this is more likely to be the result of cat predation, rather than the weather. The blackbirds and tits adopt very different strategies when it comes to breeding. While the blackbird may make several breeding attempts in a season, each with just a few youngsters, the tits adopt an ‘all your eggs in one basket’ approach by looking to rear a large number of chicks in one nesting attempt. This makes sense for the tits, who need to time their nesting attempt to the time of peak caterpillar abundance.

Of course, it will be some time before researchers can make a full and accurate assessment of the 2006 breeding season. Through annual monitoring programmes, like the Nest Record Scheme and Constant Effort ringing, researchers at the British Trust for Ornithology (BTO) will be able to determine the impacts (if any) of the bad weather. They can then compare this information with that gathered in previous years to assess the potential implications for individual populations of our wild birds. So, we need to wait and see what they say.

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