How much does your bird garden weigh?

01 May 2012 | No. 2012-15

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 British Trust for Ornithology (BTO) looking at how garden bird communities vary over time and from one place to another. The survey can be accessed via

The types of birds using garden feeding
stations have also changed over time.

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.

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.”

He continued “Garden bird communities are changing and we are likely to be supporting more birds now that 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.  

Notes for Editors

  1. Add all the UK’s gardens together and you end up with an area about the size of Suffolk.

    Gardens are the main contributors to urban biodiversity.

    90% of the UK’s population lives within urbanised landscapes and gardens provide opportunities for people to connect with nature.

    62% of the House Sparrow population, 54% of the Starling population, 38% of the Greenfinch population and 33% of the Blackbird population breed within urbanised landscapes.

    A Woodpigeon weighing 400g is four times the weight of a 100g Blackbird, 40 times the weight of a 10g Blue Tit and 80 times the weight of a 5g Goldcrest. While a Woodpigeon will need between 50 and 80g of food per day, a Goldcrest will need some 4.5g of food per day. When faced with food scattered on the ground a Woodpigeon can peck at a rate of between 70 and 103 pecks per minute.

    You can access live results from the survey at:
  2. The BTO is the UK’s leading bird research organisation. Over thirty thousand birdwatchers contribute to the BTO’s surveys. They collect information that forms the basis of conservation action in the UK. The BTO maintains a staff of 100 at its offices in Norfolk, Stirling and Bangor, who analyse and publicise the results of project work. The BTO’s investigations are funded by government, industry and conservation organisations.

Contact Details

Mike Toms
(BTO Head of Garden Ecology)
Office: 01842 750050
Email: gbw [at]

Paul Stancliffe
(BTO Press Officer)
Office: 01842 750050
Mobile: 07585 440910 (anytime)
Email: press [at]

Tim Harrison
(BTO Garden BirdWatch Development Officer)
Office: 01842 750050
(9am - 5.30pm)
Email: gbw [at]

Images are available for use alongside this News Release.
Please contact images [at] quoting reference 2012-15

The BTO has an ISDN line available for radio interviews. Please contact us to book an interview. Office: 01842 750050

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