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Nestboxes in Little Wittenham Nature Reserve |
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Just over 120 nest boxes for tit species are sited in the more secluded areas of the wood, and in nearby areas. These have been built up gradually over 16 years, reaching 120 in 1997. They supply the lack of natural holes, and have been taken up by not only blue and great tits but nuthatch, treecreeper, coal tit and in the last few years marsh tit (a Red-listed Bird of Conservation Concern since 2002).
They are monitored regularly in the late spring and the fledglings ringed if possible. In the autumn the boxes are cleaned out and the final results for each box noted, such as second nests, dead fledglings, or ideally empty, trodden nests. Each visit is recorded using a special computer program supplied by the British Trust for Ornithology, and the results submitted to them online at the end of the year.
The information is collated by the BTO with many others from all over the country in their Nest Record Scheme, where it is used for various research programs; the BTO refer to the scheme as 'a vital barometer of the health of the UK's breeding birds'.
Birds hatched in these boxes are frequently retrapped in the wood, and it has been proved that some of them return to the boxes themselves to breed. They form about 75% of the blue and great tit population in the wood immediately after fledging; this proportion falls to about 35% in the early spring when the youngsters have spread out and mingled with the neighbouring birds. Something like 1 in 8 of the nestlings are retrapped over their lifetime, which may be up to 6 or 7 years.
The proportion of boxes used has gradually increased as small siting improvements have been made; the majority are now on oak trees as these have been found to provide more food and hence larger and more successful broods. Over the last three years two-thirds of the wooden boxes have been replaced gradually by modern woodcrete ones, which provide better weather-proofing and some degree of protection from predators.
Generally 80 or more boxes are occupied and 70 or so are successful; 83 were used in 2005 and of these 71 were successful.
The occupancy of nestboxes varies from year to year and from species to species; in 2002 many of the new boxes had smaller entrance holes which allowed in only blue tits so this tipped the balance in their favour - in subsequent years more larger-holed boxes have been installed to allow more choice for great tits.
The table below summarises the nest box activities over the last 8 years.
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This page last updated 10th February 2006 by E M Gill