29/05/2012
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How much does your bird garden weigh?

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Ever wondered how the birds visiting your garden compare with those visiting other gardens elsewhere across the British Isles? If so, you can find out by taking part in the 'Big Garden Weigh-in'. Launching tonight (Thursday 31st May) on BBC Springwatch, the survey is part of a wider piece of research being carried out by the BTO looking at how garden bird communities vary over time and from one place to another. The survey can be accessed via www.bto.org.

Improved foods and feeders, coupled with changes in the wider countryside, mean that gardens are more important for birds than ever before. The types of birds using garden feeding stations have also changed over time, with new species arriving (e.g. Woodpigeon) and old ones being lost (e.g. House Sparrow). The BTO is supplementing its wealth of information on garden birds, which extends back to the late 1960s, with new observations being collected through the 'Big Garden Weigh-in'. Through the survey the BTO is collecting records of 60 familiar garden visitors and then using these to produce a map showing how garden bird communities vary across the British Isles. The map displays the average 'Bird Biomass' (weight of birds), a measure that allows the BTO to look in more depth at the communities of birds using different gardens.

Wood Pigeon
Wood Pigeon, private site, Nottinghamshire (Photo: Darren Chapman)

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Mike Toms, BTO Head of Garden Ecology, commented "Although we are actually collecting information on the numbers of birds seen in gardens during the survey period (something that we will use for other parts of our analysis), we need a sensible measure by which we can compare gardens with different types and sizes of birds visiting. One Woodpigeon will eat considerably more birdfood than one House Sparrow, so it makes sense to use a measure that can best describe this. Bird Biomass provides this measure and participants will be able to see how the biomass of their garden bird community compares with those of others elsewhere. Garden bird communities are changing and we are likely to be supporting more birds now than ever before. Back in 2003, the average garden supported 3.3 kg — more than three bags of sugar — of bird in a typical week and it will be interesting to see how things now compare."

Observers are asked to record the maximum number of individuals of any given species recorded at one point in time and these observations will then be entered through a web-based system, with interactive results pages reporting initial 'live' findings. Other findings will be revealed on Springwatch the following week and, longer term, BTO researchers will produce scientific publications on the topic.

Written by: BTO